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Antenna Systems Information (antennas, feedlines, duplexers, circulators, isolators, calculators, etc.) Compiled from a multitude of sources and donations by Mike Morris WA6ILQ (callsign) at repeater-builder dot com |
Note that the contents of this page, like most here at www.repeater-
builder.com, are totally dependent on donations of information.
If you have something to share please consider writing it up and sending it in.
If you have relevant data sheets, class handouts or any other information that we do not have here, please consider scanning them and emailing us the scans.
If you don't have access to a scanner we can arrange to get
documents scanned and made into a PDF for download.
Please email Mike WA6ILQ at (callsign) //at// repeater-builder //dot// com for details.
| Jump to: | System Engineering Antennas and Towers Connectors, Coax and Shielding Cavities and Duplexers |
| Combiners Isolators and Circulators Calculators Mobile Antennas |
Just in case you are trying to locate some documentation...
Phelps-Dodge (also known as PD) was bought by Celwave (year?), which was bought by Radio Frequency Systems (aka RFS) (year?) whose web site is at http://www.rfsworld.com/RFSGlobal. If you are looking for other web pages containing information on a specific antenna - for example some repeater group whose web page mentions a Phelps-Dodge PD-458 in passing - you may have to check under all three company names. For example, under Google, you would type (less the square brackets): [ "Phelps Dodge" OR Celwave OR "Radio Frequency Systems" OR "RFS" 458 ]. Note that the OR parameter in a Google search must be in ALL CAPS.
Antenna Specialists was sold to PCTel (year?) - and their corporate web site is at http://www.antenna.com, and the product web site is at http://www.antenna.com/products.html. The 2-way mobile product model number lookup page is at http://www.antenna.com/lm_cat/index.html.
I was told recently that PCTel bought both Maxrad and Antennex (but I don't know the dates)
DB Products was bought by Andrew, but they didn't want everything. The leftovers (including duplexers) are now sold by a company called dbSpectra, located in Lewisville, Texas (the web site is at http://www.dbspectra.com). From their web site: "...in December of 2004, dbSpectra signed a licensing agreement with Andrew Corporation to manufacture and sell the Legacy Decibel Products site management equipment such as filters, duplexers, combiners, tower top amplifiers and more. These products had been outsourced and dbSpectra successfully brought them back and have since hired many of the personnel involved in the design and manufacture of these excellent products."
In March of 2006 the Laird Group of England (AKA LairdTech) purchased Antenex for about $20.5 million, and then in Febuary of 2007 bought Cushcraft for about $90 million.
And about month later Andrew purchased the English manufacturer Precision Antennas for about $36 million.
In December of 2007 Andrew was bought by CommScope for US$2.6 Billion.
In many cases you will find that manufacturers web sites have theoretical information that is applicable to all... i.e. the theory articles on Manufacturer "X" products applies to Manufacturer "Y" and to "Z". Sometimes researching other manufacturers web sites can save you a lot of money... for example, if Manufacturer "X" claims that a crystal filter will solve your desense problem. Then you go to "Y"s web site and there you discover that, yes, a crystal filter can be used in the receiver feedline to notch out a local signal, or to pass your signal. What the Manufacturer "X" web site didn't tell you, and the Manufacturer "Y " or "Z" web site did, is that in your specific case it may not work. Unless you were familiar with crystal filters you would not know that the insertion loss can be as high as 12db, which in many cases makes a crystal filter on a repeater receiver unusable.... the signal level budget just isn't there (i.e. while adding the crystal filter would kill the interfering signal, it also reduced your receiving range to 1/2 of what it was, or maybe even less). So do your homework and learn all you can about the theory behind the hardware before you hand over your money.
| System Engineering A system's coverage area is primarily determined by how well it receives stations in the field, not by how much transmitter power it has. Both the receiver and the transmitter depend on antennas - and both it and the feedline are usually the most critical components in any amateur radio station, be it a home station, a mobile, a repeater, a remote base or a point-to-point link. Perversely they are usually are the most difficult to install, maintain, or troubleshoot - and usually during extreme climate conditions like in freezing temperatures and / or high winds. If you are installing a repeater that will be used in any type of emergency services situations it does not make any sense to go "cheap" on the antenna system. Creative (legal) aquisition of good quality equipment, yes. Low or poor quality equipment, no... that decision will always come back and haunt you. Simply put, a good antenna will hear and talk better than a poor antenna and for a lot longer. If you go with quality hardware and proper installation the first time you won't have to do it over (like my dad used to say about both hand and power tools: "buying quality only hurts once"). A good Phelps-Dodge, DB Products or Sinclair antenna connected to 7/8 inch Heliax feedline (you can use 1/2 inch on 6m or 10m) will last over 20 years of seriously hostile winters. How many Comets or Diamonds or replacement lengths of RG-series feedline will you buy and install in the same 20 years ? A preamp can help some systems, but realize that preamps are all about the internal noise figure (NF) of the preamp and the amount of gain it provides. The lower the NF, the weaker the signal that will be heard. Regarding gain, most modern preamps have gain on the order of 14-18dB in a single stage. That's enough to take a signal that's barely above the noise floor and make it very usable on a decent receiver. But don't attempt to use a preamp to make up for a long, lossy feedline - once you've lost the signal all the preamp does is amplify what's left (the noisy signal). Likewise don't attempt to use a preamp to make up for a poor receiver - fix or replace the receiver. There are ways to put a preamp up at the antenna (but only if it is a receive-only antenna). Many sites use shared "community receive" antennas that feed a preamp/multicoupler panel - at one site I visit semi-regularly there is a single UHF (406-512 MHz) Sinclair antenna that feeds all of the UHF system receivers (over 35 of them). On the transmit side, never forget that SWR is not the only measure of antenna performance. A low SWR only means that the transmitter is "seeing" a reasonably non-reactive load. That is, it looks like a 50 ohm resistor (a dummy load). The SWR tells you nothing about what is really important, the antenna efficiency, the antenna noise level, its pattern (gain) and decoupling of the RF from the feedline. And don't forget that the feedline loss runs both directions and can dramatically affect the SWR reading !! Your transmitter sends power up the feedline (let's say it's 100 watts), and some gets lost going up (let's say that it's 20% and 80w gets there). The lightning-damaged antenna reflects some power back down (let's say it's 10%, or 8 watts). The 8 watts comes back down, and 20% gets lost, and you see 6.4 watts on the Bird wattmeter. So you see 100 going up and 6.4 coming back, and you think the SWR is a lot better than it really is at the antenna. Look at this web page on the topic: Power Antenna Manufacturing Inc. SWR Calculator (an off-site link). It removes the "masking effect" of the feedline loss. And before you sign a site agreement, pay your money, and go to the trouble of installing a system, measure the noise floor on your frequency at the site. Just borrow an appropriate already-installed antenna for fifteen minutes (with permission) and make the measurement (i.e. if you are installing a VHF system use a VHF antenna). If site A has a 0.8uv noise floor (due to the broadcast and paging systems there) and site B has a 0.1uv noise floor take a guess as to which site will hear better (and I have seen sites that have noise floors that are above 2.0 uv on the frequency of interest). You may chose to install a UHF system at a particular site if the noise floor on VHF is intolerable (or vice versa). And with repeaters it all depends on how well you hear (see the article on measuring effective sensitivity below). Given the limits of antenna power rating, feedline and local geography, increasing the talk range is easy - how much amplifier, duplexer and antenna can you afford? In most repeaters the duplexer provides a certain amount of isolation between the receiver and the transmitter (some systems, like those that use two antennas, or even two sites, don't use duplexers). If the amount of isolation, however it is acquired, is greater than what is required (the excess is sometimes referred to as "headroom"), then the system design is adequate for the job (see the article Some thoughts on Repeater Receiver-to-Transmitter Isolation below). That situation is fine until they decide to add a preamp to help out the handheld users. Then they discover that the amount of isolation isn't enough. They forgot that you need (at least) the same amount of extra isolation ("headroom") as the amount of gain the preamp provides, since it raises the apparent noise floor as well as the signal of interest. In most cases you will have to fight with desense when you add a preamp (a top-quality preamp like an AngleLinear will help). Always have enough extra headroom in your duplexer to handle any of a couple of situations: First, the site owner adds additional repeaters to the site, or second, that you want to add a preamp later on. If the duplexer is your primary provider of receiver-to-transmitter isolation do not scrimp on the duplexer. Next to a good antenna and feedline the duplexer is the most critical part of a good repeater system. Long ago I gave up on four-cavity duplexers (two cavities on each side) on VHF/2m, 222 MHz and UHF, I use the six cavity pass/reject type exclusively. Duplexer tuning is very, very critical. A return loss bridge is nice, a spectrum analyzer with a tracking generator is the second choice. It is possible to tune one without a spectrum analyzer, but an analyzer is the best way and the only good way to tell if it is tuned correctly. And don't tune the duplexer on the ground, then transport it to the site over a bumpy four-wheel-drive road, and expect it to be as precisely tuned when you get there. Always have the test gear with you at the site to verify final tuning after mounting it in the system rack. |
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Getting the most from your repeater system By Kevin Custer W3KKC |
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Recommended Coax and Connectors for the iDEN Enhanced Base Transceiver System Motorola Engineering wrote this three page discussion of cable and connector types with regard to combining, intermodulation, and other RF performace factors. They concluded that LMR-nnn and LMR-nnnn series cable is specifically NOT recommended in any radio site RF environments, especially duplex environments. While iDEN is a 900 MHz system the physics are the same at 28 MHz through 1296 MHz. Well worth reading. |
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HELIAX Coaxial Cable for Low Intermodulation Generation Andrew Engineering wrote this one page writeup on why foil-braid cable causes intermod. Despite the fact that you'd expect that conclusion from the makers of Heliax there's a lot less sales pitch and a lot more engineering presented than you'd think. Worth reading. |
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Where exactly is your repeater? And are you really sure? Read this before you file any paperwork and help out your local coordination folks, and prevent an FCC or FAA citation. Donated by Eric Lemmon WB6FLY |
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MIL-STD-188-124B "Grounding, Bonding, and
Shielding for Common Long Haul/Tactical Communication Systems including Ground Based Communications-Electronics Facilities and Equipments" 3.8mb
PDF file dated 01-Feb-92 This is the newer military handbook on grounding, and is a quicker read at about 40 pages, however it says on the second page of the forward that "This Standard is further implemented by MIL-HDBK-419", listed below. This handbook is approved for public release and distribution is unlimited. |
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MIL-HDBK-419A "Grounding, Bonding, and
Shielding for Electronic Equipments and Facilities" 9.6mb PDF file dated 29-DEC-1987 This is the big military handbook on grounding. It is large, in two volumes totaling about 812 pages. Volume one is 396 pages of theory, volume two is 394 pages of practice. This download is the complete 2 volume set in one PDF file, and volume 2 starts on page 419 of the file. This book covers grounding for safety, lightning, nuclear blast and most everything else. A very good read and a real eye opener. This handbook is approved for public release and distribution is unlimited. At one point (Feb 1999), the hardcopy (including postage) was FREE if you ordered it from: Commanding Officer Naval Publication and Forms Center 5801 Taylor Avenue Philladelphia PA 19120 |
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MIL-STD-464 "Department of Defense Interface Standard Electromagnetic Environmental Effects Requirements for Systems" 1.17mb PDF file dated 18-Mar-97 "This standard establishes electromagnetic environmental effects (E3) requirements and verification criteria for airborne, sea, space, and ground systems, including associated ordnance." This handbook is approved for public release and distribution is unlimited. Why, you might ask, is this one on a web page that covers antenna systems? Well, "electromagnetic environmental effects" includes lightning. And lightning can have seriously negative effects on antenna systems (and the radios they are connected to). |
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RF Communications - A Non
Technical Approach By Decibel Products Corp. Many years ago Decibel Products (a major RF hardware manufacturer) published a series of informative pamphlets on systems engineering topics. The earliest seems to be 1964. The topics included Base Station Antennas, Combiners, Selective Cavities, Duplexers, RF Transmission Lines and Lightning. All five pamphlets were recently combined into a single PDF document titled "RF Communications - A Non-Technical Approach". DB made it available on their web site at http://www.decibelproducts.com/collateral/aboutrfcommunications.pdf. This document should be required reading for anyone wanting to learn about antenna systems. (thanks to Duane Hall KA8GVH for the pointer) |
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TX-RX Tech Aid #77001 Some very useful charts and procedures. Worth printing and adding to your tech notebook. By TX-RX Corp. |
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Help!! My repeater seems deaf By Kevin K. Custer W3KKC |
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Is a 3 DB change in power really worth it? The answer is "It Depends" By Neil Johnson WBØEMU If you are in charge of maintaining a repeater system, or building a new one, then this is worth reading. |
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Some thoughts on Repeater Receiver-to-Transmitter Isolation By Mike Morris WA6ILQ |
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Guidelines for mounting antennas on towers A scan of a guidelines page covering tower-to-antenna distances - donated by Skipp |
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ANTPLOT - A Side-Tower Mounted Antenna Pattern
Prediction Program This is a Zip file of both version 5.3 and of
version 5.4 of the DOS program originally provided by Antenna Specialists. It's
noted as being "Program No. 3 of the Antenna Specialists RF TOOLS Series". Also
called "tplot" for some reason. Donated by A. Nony Mous Does anyone have Program #1, #2 and any others? |
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High power amplifiers and duplex radio Tubes vs. Transistors, By Kevin Custer W3KKC Short version: at high power levels tubes win. |
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Is this connector any good? An article on the perils of cheap connectors by Jeff DePolo WN3A |
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EMR Corp. Technical Papers Index An index of downloadable PDF papers on Isolators, Duplexer retuning, Ferrite and Hybrid Combiners, Multicouplers, Preselectors, Bandpass and Pass-Notch Cavity Resonators. |
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Using Preamps with repeaters... and why sometimes you wouldn't want to... by Mark Malm NØFAZ and Kevin K. Custer W3KKC |
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The Effects of Trees on Slant Propagation Paths By Vogel & Hagn This is an academic paper that will be of special interest to UHF, 900 & 1200 MHz system owners. |
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Best Practices Guide By Motorola Inc. This is a write up on solving interference problems at 800 MHz and oriented towards Public Safety communications, but it's worth reading by any repeater owner or builder. |
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Interference Technical Appendix By Motorola Inc. This is intended to be an add-on to the "Best Practices Guide" above. Also very worth reading. |
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Calculating Your Radio Horizon By A. Nony Mous |
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Radio Mobile Coverage
prediction software by Roger Coudé VE2DBE A bit of a learning
curve, but darn good stuff (offsite link) A Yahoo group supporting it is at http://groups.yahoo.com/group/Radio_Mobile_Deluxe If anybody wants to put together a "Getting Started" article, we'll make room for it here. |
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The calcualtors, especially Dale Bickels HAAT, Coordinate and Distance calculators are useful. Scroll down to the Calculators section for them. |
Combiners
A Combiner is a system of cavities and optionally isolators (or cavities and optionally circulators paired with external loads) that allows multiple transmitters to share one transmitting antenna, but at a cost. Some combiner systems can cost you from 50% to 75% of your transmit power... i.e. that 100 watt repeater transmitter that gave you N miles radius coverage on a stand-alone antenna may only have the performace of a 50 watt or 25 watt system once the combiner is in line. Also don't forget that the antenna the combiner is feeding has a finite power limit. Some are rated at 200 watts, and by the time you combine 5 transmitters, each with 100 watts out, through a 3db loss combiner, that's still 250 watts that's going up the hose to the antenna, and (poof) goes the antenna (and the combiner needs a dummy load that can handle 250w continuous duty, and good ventillation). Note that systems that use combiners usually have a separate receiving antenna that is multicoupled to each receiver.
Additional detail for this introductary paragraph, and additional articles / publications on this topic are welcome. One useful article would be how to pick the frequencies that can be combined onto a single antenna.
About Combiners By DB Products, copyrighted 1975.
From the preface: "This booklet has been written for the many people engaged in two-way radio communications who are NOT radio engineers. A non-technical presentation of a rather complex subject has been attempted in an effort to bring about a better understanding of combiners used in two-way radio systems."
Tuning
Procedure for Two-Transmitter Combiners DB4351, DB4381, DB4352, DB4382,
DB4384
Two page
64kb PDF describing the tuneup of a unit that is essentially two
isolators, two low pass filters, a hybrid coupler and a dummy load.
Tuning Instructions for
the DB4350 and DB4360 Low Loss Combiners 8kb A one-page
PDF file.
Tuning
Instructions for the DB4379 Low Loss Combiner 9kb A
one-page PDF file describing a unit for up to 8 transmitters.
Isolators and Circulators
Comments below are compiled and summarized from several postings on the
repeater-builder yahoogroup.
A circulator is a magnetic ferrite three-port device that acts like a one-way-valve for RF energy, and the third port usually has a dummy load attached. A isolator is just a circulator with a built-in or bolted-on load (usually fairly low in power handling capability) so as long as you stay within the power handling limits of the load all comments below on isolators also apply to circulators and vice
versa. Isolators and circulators are physically fragile devices - and for this reason you
NEVER want to pay full price for any isolator or circulator that has a dent (or other damage) in
the housing that could have been created by dropping it. If you plan on using your own
dummy load on a new circulator, you should send that dummy load with the circulator to the vendor
so that the circulator can be properly tuned. Due to the variation in impedance and return
loss between individual dummy loads (even if outwardly identical), it is never a good idea to change
the load(s) after an isolator is properly tuned. Hint: put a stripe of nail polish across the
connectors of the isolator and the load, and use an obnoxious color (like fluorescent pink,
bright orange or purple). If anybody swaps the loads (or even borrows it and replaces it) then it will be obvious.
If you see a "4-port circulator" advertised it's probably a dual stage circulator with two devices in one box with the output of the first fed into the input of the second, and two dummy load ports. Triple circulators also exist, and in fact were a factory option on the Motorola MSF5000 stations.
One characteristic of isolators / circulators is that they generate harmonics. This property is inherent to the device and cannot be "tuned out". For this reason, an isolator is always followed by a bandpass or low pass filter in any application where good engineering practice is followed. This same situation is why folks say that isolators cause intermod. They do, but when installed properly, the pass cavity kills off any harmonics (which precludes the intermod from ever being created). NEVER, EVER have an isolator looking directly into an antenna !
Example: Years ago I heard about a 52.525 MHz remote base (on a UHF repeater) that had a circulator and no pass cavity on the 6m transmitter. At the same site was a 420.200 MHz RX that was one end of a point-to-point link. So? you ask... Well, the 8th harmonic of 52.525 MHz is dead on 420.200 MHz. Whenever the remote base transmitted it trashed 105.05 MHz in the FM band, 157.575 MHz, and since 5 KHz deviation at 52 MHz is 40 KHz at 420 MHz it trashed 420.175 MHz, 420.200 MHz and 420.025 MHz... Ooops.
When you rent space at a 2-way site and are handed the contract terms do not be surprised to see the requirement of an "intermod panel" on each transmitter. This "panel" consists of either (a) an isolator followed by a pass cavity, or (b) a circulator, an external dummy load, and a pass cavity. Many radio communications equipment manufacturers make isolators and circulators: Andrew, Connecticut Microwave, EMR, Celwave, Decibel Products, MECA, REC-USA, Raditek, Telewave, TX-RX, and many more. Contact suppliers such as TESSCO or Talley for prices and availability (and make sure you are sitting down when you ask the price). Contact information is on the suppliers index page at this web site, or you can use Google.
IMPORTANT: The frequency "range" shown on the spec sheet for an isolator / circulator is not the field tuning range of the device, it is in reality an indicator of the manufacturer's capability to build a device to any one particular frequency. For example, once an isolator / circulator is made for a particular high band frequency, it can only be tuned about two to three percent either side of that frequency (figure 2 to 3 MHz at 2M / high band) and retain optimum performance. Once outside of that "window" (which is 4 to 6 MHz wide at 2M / high band), it will cost between $200 and $300 (about 1/3 of the new price) to have an isolator / circulator remanufactured from (for example) a 165 MHz frequency to your specific 146 MHz frequency (or from a commercial UHF frequency to your 440 MHz frequency) because it involves a considerable amount of precision bench work using RF test equipment, special mechanical tools and professional skills that very few shops or people have: copper or bronze vises (nonmagnetic) to position and clamp the isolator "just right" and nonmagnetic tools to do the actual assembly or repair, plus a network analyzer to get the RF performance "just right". Besides, having your unit rebuilt by a person who does it 8 hours a day, and every day guarantees that it is done right the first time, it comes with a factory guarantee and lands in your hand already precision tuned on your frequency with a warranty and some nice proof-of-performance plots. And it is much cheaper than buying a new device ! Be forewarned: Once you open an isolator or circulator housing the manufacturer may refuse to perform the rework - it's way too easy to crack a magnet or something and then all you have is an expensive precision doorstop or paperweight... (and I've seen a damaged low band isolator being used as a doorstop).
Remember that an isolator / circulator is a MAGNETIC device, and don't mount it on a steel rack panel... you WILL detune it... use aluminum panels only, using brass screws and aluminum standoffs if you need standoffs (or use a block of wood). I'm only mentioning it because I forgot when I was cleaning up a cabinet - the UHF circulator was floating in the breeze, supported by the 7/8 inch heliax jumpers, so I rearranged things and mounted it to the same panel as the UHF pass cavity... then the system transmitter performance dropped like a rock. A group member that lived in the fringe area of the system (he had a 6-element beam on his tower fixed pointed at the repeater) reported that the system went from its normal 90% quieting at his site to 1/3 quieting. It was only after I measured the SWR between the isolator and the transmitter did I realize that the isolator was detuned... I switched the mounting back to "in the breeze" and the system performance went back to normal... The temporary mounting the following day was a piece of 1x6 inch pine shelving mounted to the rack rails with drywall screws through the holes in the rail into the wood. The permanent fix a couple of weeks later was relocating the pass cavity and the isolator to an aluminum panel and using brass screws to mount the isolator to the panel. The pass cavity didn't care, I used regular screws for that.
If you are going to make any adjustments to an isolator / circulator do it with low power - 2 to 5 watts, maybe 10 watts max, and EACH port must be terminated with a 50 ohm load. You don't want any off-resonance circulating currents or voltages during tuneup... at high levels they could demagnetize (or change the permanent fields of) the internal magnets and damage the isolator. Also when tuning, in an ideal environment you would have available another (already tuned) isolator to put between the transmitter and the isolator being tuned to make sure the unit under adjustment sees a consistent 50 ohm source... in other words, the first one isolates the transmitter from the one being adjusted...
If circulators and isolators are a new topic to you, I suggest that you read the first three articles below, especially the one by William F. Lieske. Yes, there is some repeated material between the articles, but if you're new to yhe topic, it won't hurt. When you have multiple people writing on the same topic some repetition is inevitable.
What's a circulator? a.k.a. Properties of
a Ferromagnetic Circulator By Kevin Custer W3KKC
The Care and Feeding of the R.F. Isolator
a 14kb PDF by William F. Lieske, Sr. Founder, EMR Corporation
An Elementary Introduction to Ferrite Isolators, Circulators and RF Loads a 1mb PDF file A TX-RX Corp. "Seminar Series" writeup - 14 pages.
Field
Tuning Instructions for Dual Junction Tunable Isolators a
one-page 21kb PDF file by Decibel Products
Generic single-section isolator tuning
instructions from EMR a 26kb PDF file donated by Eric Lemmon
WB6FLY
Generic dual-section isolator tuning
instructions from EMR a 55kb PDF file donated by Eric Lemmon
WB6FLY
Sinclair's instructions on tuning
isolators Donated by Eric Lemmon WB6FLY
Microwave
Associates 7R011 Isolator Tuning Instructions Donated by Micheal Salem N5MS
Good for
125 watts, with 0.9 db insertion loss typical with 1.3 db max. The isolation
can be as high as 60 db with 50 db typical.
Data
sheet on the DB 4318H-2C High Band Single Channel filter and isolator
A
two-page PDF file describing a Decibel Products 164 - 168.5 MHz dual isolator
but the directions apply to similar units. The drawing is in error, it does not
show the termaline on the output port.
Cavities, Duplexers, Theory, and More
The purpose of a duplexer is to allow the simultaneous operation of a receiver
and a transmitter on the same antenna... but saying "duplexer" is like saying
"car". They come in various types, makes, models, and performance levels. Some
are notch-only, others are notch-pass. There are 3-cavity, 4-cavity, 5-cavity,
and there are 6-cavity models (more cavities give a higher level of receiver-to-transmitter
isolation, but at a cost of insertion loss). In general, the higher the RF level
at a site (i.e. how many other systems there are, and the power levels involved), the more
cavities you need. If you run a split site system at a leow RF level site you
may not need a duplexer. And depending on circumstances even a single site
system can be built with no duplexer at all.
A duplexer is made up of a number of cavities and critical length cables, each of which adds to the total transmit-to-recieve isolation provided by the assembly. If you're just starting out, I suggest that you read the first eight articles below, expecially those by Jacques Audet VE2AZX, John Portune W6NBC and by William F. Lieske. Yes, there is some repeated material between the articles, but if you're new to duplexers, it won't hurt. When you have multiple people writing on the same topic some repetition is inevitable. The 8 articles collectively will give you a basic education on duplexers.
Note that duplexers are initially tuned and the ports labeled at the factory. A duplexer is built with a "higher" side and a "lower" side, and the loops and inter-cavity cabling are selected for those frequencies. The application a ham has may conflict with the original port labels. Most commercial repeaters (definitely in UHF, usually on VHF) receive on the higher frequency and transmit on the lower frequency, whereas amateur repeaters can swing either way. So look at the original label and note if the receive side is the higher of the two frequencies, or if the transmit side is... and keep the high / low relationship the same as you retune it. You may end up using the original receive side as your transmit side. Personally, I remove the factory "Receiver" and "Transmitter" labels and replace them with my own permanent labels reading "Higher Side" and "Lower Side", then I add temporary "Receiver" and "Transmitter" labels for each application. This is expecially true on GMRS (+ offset) and on amateur UHF (- offset in southern California and many other areas).
The cable length between the cavities in a duplexer is very critical, and the actual length of any one cable is dependent on both cable velocity factor and frequency. On a UHF duplexer the optimum length is different between the receive and transmit side. And the lengths of the cables between the duplexer ports and the antenna "T" are also critical and frequency dependent. Many duplexers are wider in frequency than their harnesses - for example if you move a VHF duplexer from 150-174 MHz to 2 meters you will have to aquire a new cable kit, or lengthen the old one. Hams that are moving a 470 MHz duplexer will have the same problem.
Double-shielded silver-plated coax is the best thing to use to connect duplexers. For example, RG-214 has two silver-plated braids and a silver-plated inner conductor for maximum noise rejection. Avoid coax types that have disimilar metals rubbing against each other such as LMR-(any 3-digit or 4-digit number) or Belden 9913, both of which use an aluminum foil shield rubbing against a copper braid. Many amateurs have purchased LMR-400 or similar cable, installed it, and it works fine (for a while). They just rave about how good it is. Then anything from 9 months to 5 years later they find themselves taking it down as the cable itself causes "duplex noise" (see the article titled "Help!! I have a crackling noise in my repeater" by Kevin Custer W3KKC in the Antennas section on this page). The expensive LMR cable gets reused somewhere else. RG-142 and RG-400, both a smaller version of RG-214 but sharing the same construction, can also be used (but see the article on this page titled "Double Shielded Coax Cable, The differences between RG-142 and RG-400, and why you DON'T want to use RG-142..." by Eric Lemmon WB6FLY). My personal preference is to use nothing but Heliax and Superflex on the antenna side of the duplexer, and nothing but Superflex and RG-400 on the radio side. Yes, it's expensive, but only once. It's going to last a long, long, long time, and it's one less thing to worry about.
The cable length between the end cavity and the receiver or transmitter is NOT supposed to be critical, and if it is on your system then you have an impedance problem in the receiver or transmitter. The proper way to tune a cavity or a duplexer is to use 6db or 10db 50 ohm pads between the test equipment and the cavity or endmost duplexer can, as that ensures that pad "masks" any non-50-ohm-impedance in your test equipment and ensures that the duplexer is tuned to 50 ohms. The attached feedline is 50 ohms, and the receiver or transmitter is SUPPOSED to be 50 ohms. If it is not, the most common way to "fix" the problem is to use a "magic" length cable - but the right way is to fix the radio so it is 50 ohms. Some radios can't be fixed easily (but a Z-Matcher helps), so a good way is documented here: Cabling lengths between the Duplexer and Radio Set.
A note on small mobile duplexers from Eric Lemmon WB6FLY:
(Most "mobile duplexers" are notch-only, and are sometimes called notchplexers)
Most UHF mobile notch-only "flatpack" duplexers will work fine below 50 watts
at a 5 MHz split- but their performance rapidly deteriorates when operated
outside of their stated band limits. For example, a commercial-band mobile
duplexer that was manufactured to operate in the 450-470 MHz band will
likely perform poorly in the 440-450 MHz Amateur band. Although such a
duplexer may SEEM to be working in the Ham 70 cm band, it may have excessive
insertion loss that the owner may not realize. That's because the internal
coupling loops are set at the factory during manufacture and not readily
adjustable by the owner.
I once tried to use a commercial-band mobile duplexer on 70 cm in a portable
repeater, and was disappointed in its performance- especially receive
sensitivity. I then ordered a new Celwave duplexer of the same model, but
factory-tuned for my Amateur pair. What a difference! Once the new
duplexer was installed, the range of the portable repeater was significantly
improved, with no other changes.
Other people report no problems with moving flatpacks to 440 MHz or even 420 MHz.
| DUPLEXERS - An Introductory Tutorial by Jack Daniel KD6YVL (offsite link) This is a nice writeup that should be titled "Duplexers 101". Well worth reading. |
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| Theory and Testing of Duplexers by Jacques Audet VE2AZX This is a large (60 pages) technical writeup that should be titled "Duplexers 102". Again, well worth reading. |
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| Technical Duplexer Page with good theory and explanations, and some homebrew construction notes. By John Portune W6NBC | |
| Understanding, Maintaining & Re-Tuning Antenna Duplexers 145kb PDF By William F. Lieske, Sr., Founder, EMR Corporation A good basic theory writeup, including the differences between Band Pass and Band Reject. The original copy at the EMR web site |
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| Combating Spurious Output And Overloading With Cavity Filters 1.2mb PDF by TX-RX Corp. A "Seminar Series" writeup that covers the theory behind cavity filters - mandatory reading for those unfamiliar with them. |
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| Coaxial Resonators, Applied theory and practice, with photos by Mike Pinfold, ZL1BTB | |
| Interference Control Through The Use Of Cavity Filters And Ferrite Isolators 900kb PDF by TX-RX Corp. | |
| Technical Notes on Duplexer Problems and Remedies 1mb PDF By TX-RX Corp. | |
| A Guide to Duplexer Specifications over 130 different models, by Paul Kelley N1BUG (Contributions to the list are very welcome) | |
| Tuning and Adjusting Vari-Notch-Duplexers 185kb PDF by TX-RX Corp. A "Seminar Series" writeup that covers the theory behind cavity filters and isolators. |
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| T-Pass Expandable Cavity Muticoupler System 500kb PDF by TX-RX Corp. A "Seminar Series" writeup that covers the various type of cavity-based multicouplers and the T-Pass design. |
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| The Hybrid Ring Duplexer A comprehensive explanation of the Hybrid Ring, by Kevin Custer W3KKC | |
| Six Meter Heliax Duplexer
Design by Jim Poll, WB5WPA (off-site link) Here's one implementation of the above design by Oscar KF6YB (off-site link) Here's another implementation of the above design by Mike Perryman K5JMP (off-site link) Six Meter Heliax Receive Filter Construction and Testing article based on the above designs, by Robert Meister WA1MIK and David Malicki N1OFJ. Note that this is NOT a full duplexer; just the receive half. |
|
| Using open stubs to notch interference By Nico PAØNHC
(offsite link) An excellent article on reducing paging transmitter (and others) interference into 2m repeaters. Note that common European usage is that a comma is used where Westerners use a period to mark decimals, for example 144.550 MHz is written as 144,550 MHz so readers used to the period will have to do some mental "translation". In this article Nico has used a mix of both forms so it can be a little confusing on the first read. |
|
| GE Datafile Bulletin 10002-1,
A 25-250 MC Quarter Wave Stub Filter General Electric produced several useful DataFile Bulletins (the ones we have are available for free download from the GE LBI page at this web site). This one is a 400KB PDF file, and is subtitled: "Even though General Electric Two Way Radio Transmitters well exceed FCC requirements for spurious radiation, the 60-80-db sprious attenuation provided may, in a few situations, be insufficicient to provent interference. This bulletin describes the construction of a filter, useful for supressing spurious radiation at one specific frequency...." |
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| Someone say 6 meter duplexer? A comprehensive conversion of a lowband pass cavity to BpBr by Jeff DePolo WN3A... | |
| How do I tune this notch duplexer? by Kevin Custer W3KKC | |
| A Homemade Duplexer for 2-Meter Repeaters by John Bilodeau, W1GAN (from the July 1972 QST magazine) Note: In the 30-plus years since this article was written, the spring-contact based BNC has fallen out of favor. Type N connectors are much preferred over BNC connectors as they depend on a silver-to-silver screw compression contact, plus they can handle more power. You must use double shielded coax in the harness. RG-55 is mentioned in the article, I'd use RG-400 and compensate on the inter-cavity lengths. If anybody has built this unit with better connectors and modern cable, and would like to update this article please let me know. |
|
| Tests of the DCI VHF and UHF 4-pole
bandpass filters by Robert W. Meister WA1MIK These filters definitely do the job, meeting or exceeding manufacturer's specs. They cover the entire 144-148 and 440-450 MHz bands and have sharp cutoffs. If you need more filtering, they also sell 6, 8, and 10-pole filters with attenuations over 80dB. These handle 200 watts and can be used at repeater sites. |
| Celwave Click here for Celwave antennas | ||
| Celwave model 696, 696SR (UHF), 896 or 896SR (800-960 MHz) Duplexer 86Kb PDF file Donated by Allan Crites WA9ZZU, scanned by Eric Lemmon WB6FLY | ||
| Celwave Duplexer Cable Harness Lengths (oriented for printing) 44Kb PDF file Donated by A. Nony Mous | ||
| Decibel Products Click here for DB antennas
Same drawing sized to be printed on 11x17 paper Both donated by Chris Nicholson N9LLO A two-page PDF file describing wide-spaced (3 MHz and 5 MHz) duplexers that are not of much use to hams, but would be to public safety and disaster services folks. Here's a photo of the internals of a 4072 housing. I have a DB-4062, which is the 6 cavity version of the 4060. It was old when I placed it in service in 1997 but worked OK. Over the years it just slowly deteriorated until it became essentially unusable. Finally I took the thing apart to investigate, and was able to restore it to excellent function after 15-20 hours of work. I created a web page that covered my experience...
Motorola Phelps-Dodge
Sinclair Labs
Wacom At some point Wacom was bought by Remec, and
in November of 2001 was sold to TX-RX.
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Antennas and Towers
Repeater owners have favorite antennas - some prefer colinear antennas ("fiberglass sticks"), others prefer dipole arrays. Personally I prefer grounded dipole arrays. Colinear antenas are more prone to duplex noise (see the "crackling" article below), dipole arrays can have phasing harness degredation. Picture four loop dipoles side mounted on a steel mast. Suddenly one day you notice that the coverage has gone to hell. When you check the antenna with a SWR bridge you discover that you still have a 1:1 SWR. Phasing is the key concept here. The RF is fed to the dipoles by means of a cable harness of critical-length coaxial lines that accomplish both the phasing of the dipoles and RF power division. The VERTICAL pattern of the antenna is determined partly by the RF phase relationship between the dipoles. When the antenna is new, the phase relationships are perfect. As the antenna ages, moisture can infiltrate the coax and connectors. Coax dielectric can begin to deteriorate. This will slowly cause the vertical pattern (and gain) of the antenna to change. A perfect SWR does you no good when your RF power is going straight up in the air or straight down into the ground! So if you use a dipole array then you want to be an annoying perfectionist about the phasing harness.
And as said above, don't go cheap on the antenna or feedline. You can have the best sounding repeater on the planet, but it's both worthless and useless if the users can't get into it or hear it because you used a Ringo Ranger and RG-213-type feedline (don't laugh, I've seen it).
| Radio Antenna Engineering By Edmund A. Laport This is a 1952 textbook and the original copyright has expired. The PDF file is 38.5 Mb. At the time, Mr. Laport was the Chief Engineer of RCA International Division. While the book is oriented towards antennas up to 30 MHz, the Preface is worth reading (4 pages) as theory doesn't depend that much on wavelength. The Introduction (11 pages) has some math, but it's also very interesting. | |
| The W1GHZ Online Microwave Antenna Book By Paul Wade W1GHZ (ex N1BWT) An excellent text, and worth reading. (offsite link) | |
| Antenna Design for
Omnidirectional Repeater Coverage By James Ruxlow N9SN What do you do when you need omni coverage, and you have to side mount the antenna to a triangular tower that is over fifteen feet on each face? The Western Illinois ARC figured it out. And their solution works well. |
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| Precipitation Static and Duplex Radio... The Phenomena and the Cure! Rain and snow clouds contain more than rain and snow By Kevin Custer W3KKC. | |
| Help!! I have a crackling noise in my repeater Why it's there and how to cure it... By Kevin Custer W3KKC. | |
| Vertical and Horizontal antenna separation charts Provided by Kevin Custer W3KKC. | |
| 440 MHz Folded Dipole Repeater Antenna (222kb PDF file) This is a two page PDF file of the classic 73 Magazine construction article by Chuck Kelsey WB2EDV - Yes, you can build yourself a DB-224 folded dipole array. | |
| Information on a Cycloid Dipole (also known as circular polarization) antennas By the WA7X crew (offsite link) | |
| "Calculating Downtilt" by Scala Division of Kathrein Corp (Technical Bulletin #112) 39kb PDF | |
| Omni-Directional Gain Vertical Collinear Construction Project By Mike Collis WA6SVT Yes, you too can build a Stationmaster - for any frequency from 2 meters to 1.3 GHz |
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| Build A 9 dB, 70cm, Collinear Antenna From Coax By Michael Martell N1HFX (offsite link) Yes, you can build a decent home base station antenna from RG-58 coax. |
|
| Cheap Yagi Antennas for VHF/UHF By Kent Britain, WA5VJB for the Clear Lake Amateur Radio Club of Houston, Texas. This article describes a easy-to-build inexpensive yagi (beam) antenna that can be built for 2m, 220, 440, 900 or 1296 MHz. |
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| A Copper Cactus Dual-Band J-Pole Antenna Project By Tony Petersen N7QVC | |
| Fiberglass Antenna Painting Procedure by Celwave Corp., provided by Mike Dees N3EZD See the next article as well. | |
| Some Notes on Fiberglass Antenna Painting Comments from several folks that accompany the above article. | |
| Retuning a Stationmaster type antenna By Jim Barbour WD8CHL | |
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How to look up a tower location Lists all FCC registered towers - broadcast, cellular, everything... (offsite link - to the Berkana server) |
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Tower lookup page at the FCC web site (offsite link - to the FCC server) |
| The Rohn Towers 2004
Catalog 38 Mb PDF file This was sent in anonymously and it's a big download. |
| Advanced Electronic Applications / AEA | ||
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For information on AEA antennas including the Isopole please see the AEA page. | |
| Celwave | ||
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A detailed drawing by Skipp of the Celwave-built Motorola TDE6090A welded yagi beam antenna 69KB PDF file This is a two page PDF, the first page is Skipp's measurements, the second is the Celwave drawing. There is enough information here that anyone with a welder could make their own very strong winter-ice-proof welded 10db gain yagi antenna. Note that the element length measurements shown in the diagram are for 420 MHz frequencies. | |
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| Motorola | ||
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The 1964 manual for the TAD1000-series
coaxial VHF antennas donated by Skipp Description,
Installation, Assembly, Parts. 150KB PDF file Covers the models TAD1001x, TAD1002x, TAD1003x, TAD1004x, TAD6071x, TAD6072x, TAD6073x, TAD6074x (where "x" is an "A" or a "B"). |
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VHF unity-gain antenna model information
and specifications for the TAD1010-series antennas donated by
Skip 255KB PDF file More info on the 1001, 1002, 1003 and 1004 models listed above, plus info on the TAD1012x, TAD1013x, TAD1014x, TAD1021x, TAD1022x, TAD1023x and TAD1024x series (where "x" is an "A" or a "B"). |
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VHF 3dB-gain antenna model information
and specifications for the TDD602x-series antennas donated by
Skip 240KB PDF file Covers the models TAD6021A, TAD6022A, TAD6023A and TAD6024A units. |
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VHF 5.5dB-gain antenna model information
and specifications for the Motorola branded Stationmaster style antennas donated
by Skip 268KB PDF file This sheet covers the models TDD6071A, TDD6072A, TDD6073A, TDD6074A, TDD6075A, TDD6081A, TDD6082A, TDD6083A, TDD6084A, TDD6085A, TDD6090A, and TDD6100A. |
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| Connectors, Coax and Shielding The feedline and the connectors can make or break a system. If you stick to Heliax, Superflex and RG-400 for cable, and silver plated connectors you will minimize your problems. |
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| WA2ISE's chart of the specs of common coax cables By Robert Casey WA2ISE | |
| Another chart of the specs of common coax cables (offsite link) Courtesy of Coastel Cable Tools of Syracuse, New York | |
| More specifications (bend radius, velocity factor, loss) of common coaxial cable types By A Nony Mous | |
| Yet another chart of cable specifications of common coaxial cable types By TX-RX Corporation | |
| Double Shielded Coax Cable The differences between RG-142 and RG-400, and why you DON'T want to use RG-142... by Eric Lemmon WB6FLY | |
| Shielding Effectiveness.... A 268kb PDF Document by Andrew Corp. covering the types and parameters of shielded cables. Original copy is here. | |
| Installing PL-259 connectors on FSJ1-50A 1/4" Superflex Heliax a photo article by Tony King W4ZT. | |
| MIL-SPEC for RG214 dated 1986
328 KB PDF courtesy of Eric Lemmon WB6FLY RG-214 is the good double-shielded coax that has the stranded center conductor and the solid polyethelene core. Each strand is individually silver plated. Both shields are made from 34ga silver plated copper wire. The inner shield exceeds 95% coverage and the outer shield equals or exceeds 98% coverage. |
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| MIL-SPEC for RG214 dated 1991
courtesy of Eric Lemmon WB6FLY This is the new RG-214 that meets the requirement of the vertical flame test. It has the aluminum coated polyester tape layer between the outer braid and the outer jacket. |
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| Amendment 1 to MIL-SPEC C-17/75F for RG214 and RG365 dated 1998 courtesy of Eric Lemmon WB6FLY This is simply an administrative update. |
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| Calculators (dBm / voltage, intermod, fade margin, etc.) | |
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| Converting between dbm and millivolts or
microvolts A no-math graphical calculator it's
only a xerox copy of the metal rim of a attenuator wheel from a Measurements Corp.
Model 80 RF Signal Generator... but it's very handy. Courtesy of Ray Von
Neumann K6PUW I suggest that you print this out and tape it to the front panel of your signal generator that is calibrated in uV and mV only. Once you realize how dbM numbers work you will find yourself referring to it on a regular basis. |
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| Converting between dbm and millivolts or microvolts A no-math tabular calculator (a lookup table). The above xerox of the attenuator scale is easier to use. | |
| dBm to Microvolts Conversion Chart By IFR Corp. The above xerox of the attenuator scale is easier to use. | |
| An online intermod calculator from AudioTechnica Note that this is oriented to wireless microphones, but since it handles up to 30 frequencies it is very handy. (offsite link). | |
| Another downloadable intermod calculator This one is shareware written by KE6QH. | |
| This downloadable calculator program figures intercept points and device intermod levels This one is is from Kessler Systems Inc. (offsite link) | |
| This online calculator program from TCS Consultants, Inc. saves the site description to a 'cookie' file on your computer. (offsite link) | |
| Online fade margin calculator program from TCS Consultants, Inc. This is neat! (offsite link) | |
| FCC HAAT (Height Above Average Terrain) Calculator (offsite link to the FCC web site) | |
| FCC Coordinate
Calculation Program (offsite link to the FCC web site) This is a useful calcualtor for point-to-point links... "This program will calculate the end coordinates, in degrees, minutes and seconds, given an initial set of coordinates, a bearing or azimuth (referenced to True North or 0 degrees), and a distance...." |
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| FCC
Coordinate Conversion Program (offsite link to the FCC web site) "This utility permits the user to convert latitude and longitude between decimal degrees and degrees, minutes, and seconds. For convenience, a link is included to the National Geodetic Survey's NADCON program, which allows conversions between the NAD83 / WGS84 coordinate system and the older NAD27 coordinate system. NAD27 coordinates are presently used for broadcast authorizations and applications." |
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| FCC
Distance Calculation Program (offsite
link to the FCC web site) "This program will calculate the distance and azimuth (referenced to True North) between two sets of coordinates on the earth." The last four calculators above are courtesy of Dale Bickel of the USA Federal Communications Commission. The FCC also has a number of "Conversions" calculators including FM Channel to Frequency, FM Frequency to Channel, TV Channel to Frequency Band, Feet to/from Meters, Miles to/from Kilometers, dBu to/from mV/m, kW to/from dBk, Relative Field, Transmission Line Efficiency, and more. |
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| An old DB Products DOS program that calculates down-tilt for antennas 128kb ZIP file | |
| An old DB Products DOS program that plots some antenna patterns 383kb ZIP file | |
| An old DB Products DOS program that gives you some insight
into the effects of side-mounting vertical antennas 134kb ZIP file
The above three programs were supplied by Dave Gartner WD6AXM. |
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Mobile Antennas
Hints: (1) Don't use solid center conductor coax on a mobile antenna (especailly on something that moves). (2) Punch-mounts are 20 times better than clamp-on-the-edge-of-the-trunk-lid mounts and 50 times better than magnetic mounts. If you have to use a mag mount use a 1/2 wave antenna intended for zero-ground-plane installations (like motorcycles).
| Base and mobile antenna cutting chart from Larsen Antennas a 668kb PDF file from the Larsen web site, specifically the Technical Reference page. | |
| Low band radios that cover a wide frequency range (like the GE Delta, GE Rangr, Motorola Syntor X or Syntor X-9000 which covers 28-54 MHz in one range) have a problem: the antenna bandwidth is much narrower than the radio is. Motorola came up with a solution: a "Diplex Antenna Matching" kit that allowed two differently cut low band whip antennas on one radio (i.e. one could be on 36 MHz and the other on 43 MHz), and done in a way that prevented them from interfering with each other. The two antennas can be cut to any two low band frequencies. Here is the documentation on the kit (Motorola manual part number 68-80100W86, a 1.9mb PDF), which contains three pages of info - enough to duplicate it yourself. | |
| The KØBG web site (link to another web site) Alan Applegate KØBG lives in Roswell, New Mexico and has created a very good reference web site for mobile amateur radio operators. I was pointed to it by a police department radio tech. While the site is mostly oriented to HF mobile, there is a lot of information that is relevant to VHF operation as well. Just look at the index along the left edge. |
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| W8KI's page on Inductors and Loading Coil Current (Mobile and Loaded Antennas) (link to another web site) Charles Rouch has a good web page on loading coils and how they work. It's HF oriented but the math is the same. |
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| Urgent Communications Mobile Radio Installation Notes (link to another web site) Urgent Communications is a two-way radio industry publication, and their web site has some notes on mobile radio installations. |
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This web page created and first posted 14-Oct-2004.
Layout and hand coded HTML © Copyright 1995 and date of last update by Mike Morris WA6ILQ
This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.