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900 MHz Frequencies to Avoid When You Set Up Your New Repeater
Compiled by Mike Morris WA6ILQ from several sources
900 MHz is a "new band" for a lot of folks, and many are unaware that amateur radio is a secondary allocation in that spectrum. This status requires hams to put up with interference from both licensed and unlicensed users... from equipment designed by engineers that care about their product, and from those that are out to get the very last penny of profit... The systems you will find include wireless data networks, point-to-point links, automatic vehicle locator systems and cordless telephones just to mention a few. The data network info we have is towards the bottom of this page, however cordless phones are more prevalent. Here are the cordless phone frequencies that are known... if anyone has any more, please let us know so this list can be updated.
Since many cordless phone models are based on the same RF synthesizer chip design you will find that other models in the same manufacturers product line may share the same channel frequencies as the ones listed below. And many "manufacturers" are just re-labelers and buy their circuit boards from the original manufacturer, and put their own plastic box and name on them. So that new cordless phone you bought at Wal-Mart, Circuit City, Best Buy or mail order may actually use the same synthesizer chipset (and therefore the same frequency list) as a GE, Panasonic or V-Tech.
The Motorola GTX radios (both handheld and mobile) are very popular "starter" radios for 900 MHz repeater users. Unfortunately the GTX has a design flaw that precludes the reverse burst function of the PL encoder from ever working properly, and since it's in the radios CPU firmware (which is a masked programmed chip, therefore not upgradeable) it's not fixable... see the GTX page for more info on this. Due to the popularity of the GTX (it goes on amateur 900 MHz with no hardware mods, and is relatively inexpensive) and the existence of this unfixable tone squelch design flaw many systems run DPL on the repeater input exclusively. DPL code 411 seems to be the "open repeater" DPL code in several areas.
Using DPL on 900 is not a negative since almost all user radios on 900 MHz
are ex-commercial radios (GTX, Spectra, Johnson 8640 and 8655, Kenwood 431, 481, 931,
941, and 981 are the most popular). Every single radio has every tone and DPL in
it from the factory, so having a DPL system input does not exclude anyone.
For more info on the GTX and the ultra-simple "mod", see the Motorola page. For more info on the Johnson and Kenwood 900 MHz radios see those pages.
And when you program your 900 MHz mobile or handheld, here are a few additional frequencies to include:
Note 1: In many areas the grunge on 900 MHz has made subaudible tone almost a requirement to maintain sanity... there are very, very few carrier squelch systems. Due to the grunge, 900 MHz is unusual in that many areas have a "default" tone, even on simplex. 100Hz and 151.4Hz are common, but check with your local coordinator to see what tone you should encode on your local simplex channels. And if your coordinator is not 900 MHz "savvy" he may not know that the locals are running a tone on simplex... Personally, I'd have 927.5 MHz in my mobile twice, one with 100.0 and one with 151.4, and put both in the scan list.
Note 2: In Southern California (and in some other areas) the 902.700 / 927.700 pair is the 900 MHz "Test Pair", or Shared Non-Protected frequency. Nationally, the SNP frequency / frequencies (in any band) are utilized to minimize the "paper repeater" problem - those repeaters that exist nowhere except on paper in the coordinators file cabinet. In areas that have adopted this technique all new repeater owners are expected to build their systems on an SNP frequency. Once the coordinator (or his agent) can "kerchunk" your box he knows that you are for real, that you really have an operational repeater and then he allocates a "real" repeater pair. Since most of the 900 MHz repeaters are synthesized there is next to no cost involved in moving from the test pair to the final pair (other than retuning the duplexer, and many "garage repeaters" use two antennas).
Important note for Colorado, New Mexico, Texas and Wyoming: FCC Rules restrict operation on the 900 MHz band to certain frequencies, which may require some simplex and repeater users to choose alternate or non-standard frequencies. The applicable sub-part of §97.303g has been reproduced below:
(1) In the States of Colorado and Wyoming, bounded by the area of latitude 39° N. to 42° N. and longitude 103° W. to 108° W., an amateur station may transmit in the 902 MHz to 928 MHz band only on the frequency segments 902.0-902.4, 902.6-904.3, 904.7-925.3, 925.7-927.3, and 927.7-928.0 MHz. This band is allocated on a secondary basis to the amateur service subject to not causing harmful interference to, and not receiving any interference protection from, the operation of industrial, scientific and medical devices, automatic vehicle monitoring systems, or Government stations authorized in this band.
(2) No amateur station shall transmit from those portions of the States of Texas and New Mexico bounded on the south by latitude 31° 41' N, on the north by latitude 34° 30' N, on the east by longitude 104° 11' W, and on the west by longitude 107° 30' W.
Note that almost all 900 MHz repeaters listen between 902 and 903 MHz, and transmit between 927 and 928 MHz. All the simplex channels are in the 927 area since most receivers will not go down to 902. There are point-to-point links on 900 MHz and different coordination groups have different policies on where to put them. The Southern California 900 MHz band plan is here. It was put together with the co-operation and assistance of the commercial (i.e. primary) users of that spectrum.
Scroll down for wireless internet
Superscript numbers reference notes at the bottom of the table.
|Transmit Frequencies 1||Manufacturer
|905.600||925.500||V-Tech Tropez DX900||01|
|905.700||925.600||V-Tech Tropez DX900||02|
|905.800||925.700||V-Tech Tropez DX900||03|
|905.900||925.800||V-Tech Tropez DX900||04|
|906.000||925.900||V-Tech Tropez DX900||05|
|906.100||926.000||V-Tech Tropez DX900||06|
|906.200||926.100||V-Tech Tropez DX900||07|
|906.300||926.200||V-Tech Tropez DX900||08|
|906.400||926.300||V-Tech Tropez DX900||09|
|906.500||926.400||V-Tech Tropez DX900||10|
|906.600||926.500||V-Tech Tropez DX900||11|
|906.700||926.600||V-Tech Tropez DX900||12|
|906.800||926.700||V-Tech Tropez DX900||13|
|906.900||926.800||V-Tech Tropez DX900||14|
|907.000||926.900||V-Tech Tropez DX900||15|
|907.100||927.000||V-Tech Tropez DX900||16|
|907.200||927.100||V-Tech Tropez DX900||17|
|907.300||927.200||V-Tech Tropez DX900||18|
|907.400||927.300||V-Tech Tropez DX900||19|
|907.500||927.400||V-Tech Tropez DX900||20|
|923.700||925.900||GE model 26938GE1-C||01|
|923.800||925.950||GE model 26938GE1-C||02|
|923.800||926.000||GE model 26938GE1-C||03|
|923.850||926.050||GE model 26938GE1-C||04|
|923.900||926.100||GE model 26938GE1-C||05|
|923.950||926.150||GE model 26938GE1-C||06|
|924.000||926.200||GE model 26938GE1-C||07|
|924.050||926.250||GE model 26938GE1-C||08|
|924.100||926.400||GE model 26938GE1-C||09|
|924.150||926.350||GE model 26938GE1-C||10|
|924.200||926.400||GE model 26938GE1-C||11|
|924.250||926.450||GE model 26938GE1-C||12|
|924.300||926.500||GE model 26938GE1-C||13|
|924.350||926.550||GE model 26938GE1-C||14|
|924.400||926.600||GE model 26938GE1-C||15|
|924.450||926.650||GE model 26938GE1-C||16|
|924.500||926.700||GE model 26938GE1-C||17|
|924.550||926.750||GE model 26938GE1-C||18|
|924.600||926.800||GE model 26938GE1-C||19|
|924.650||926.850||GE model 26938GE1-C||20|
|924.700||926.900||GE model 26938GE1-C||21|
|924.750||926.950||GE model 26938GE1-C||22|
|924.800||927.000||GE model 26938GE1-C||23|
|924.850||927.050||GE model 26938GE1-C||24|
|924.900||927.100||GE model 26938GE1-C||25|
|924.950||927.150||GE model 26938GE1-C||26|
|925.000||927.200||GE model 26938GE1-C||27|
|925.050||927.250||GE model 26938GE1-C||28|
|925.100||927.300||GE model 26938GE1-C||29|
|925.150||927.350||GE model 26938GE1-C||30|
|925.200||927.400||GE model 26938GE1-C||31|
|925.250||927.450||GE model 26938GE1-C||32|
|925.300||927.500||GE model 26938GE1-C||33|
|925.350||927.550||GE model 26938GE1-C||34|
|925.400||927.600||GE model 26938GE1-C||35|
|925.450||927.650||GE model 26938GE1-C||36|
|925.500||927.700||GE model 26938GE1-C||37|
|925.550||927.750||GE model 26938GE1-C||38|
|925.600||927.800||GE model 26938GE1-C||39|
|925.650||927.850||GE model 26938GE1-C||40|
Table Note 1: When a frequency range is specified (like 902.0-905.0) it's a "spread
spectrum" phone. This is not true military type spread-spectrum, it's just a conventional
FM radio with multi-megahertz deviation. The modulation may be analog or digital.
Table Note 2: No channel number indicates a single channel phone.
Some ADT Alarm systems use 927.1375 MHz as a sensor-to-base link.
Unlicensed 900 MHz internet traffic is among the largest 900 ham band spectrum polluters and there is very little that can be done. The user transmitters can run as high as 700mw and stay legal, and there are amplifiers (illegal ones) that can raise that to several watts. One manufacturer of these systems uses this channel plan:
The Motorola "Canopy" system uses a different channel plan.
From the manual: ("AP" refers to a "Access Point")
The Canopy 900 MHz modules provide 3 non-overlapping channels within the allocated 900 MHz spectrum. Channels are 8 MHz wide, and can be set with RF Frequency Carrier (center of the channel) at 906, 907, 911, 915, 919, 923, or 924 MHz. For normal operation, it is recommended that the operator use:
(this channel trashes 902-910 MHz, which includes the repeater inputs)
- 906 MHz for north and south facing APs
915 MHz for northeast and southwest facing APs911-919 MHz 924 MHz for southeast and northwest facing APs920-928 MHz This suggested channel plan takes advantage of the spectrum available to provide 9 MHz between channel centers, 1 MHz greater than the minimum 8 MHz channel size, for additional channel separation.
With 8 MHz wide channels that means that the 906 MHz assignment reaches down to 902 MHz. If you have a Canopy system in your area you could request the system manager to use 907 instead of 906. The Canopy system management software allows the center frequencies to be assigned on a 1 MHz increment.
emails from others with comments on this page...
... from Greg KJ6KO, the operator of the NC9RS system in the San Francisco bay area
The list is HUGE!
Here's some info I have dug up...
Wireless power meters or "Smart Meters" are a new addition to 900 and are spread spectrum channel hopping. The meters themselves are not a big nuisance, but when you have a hilltop looking down on thousands of them, they can be. There are two major manufacturers of them and one (Silver Spring Networks) completely avoids 927-928, but has three 100 kHz wide channels between 902-903, all above 902.300. You can get a TON of info on these by simply looking at the FCCID on the front of the meter and looking it up on the FCC's web page. All manuals, specs, channels bandwidth etc is all listed there! The FCC's "new and improved" website is still a little difficult to use, but contains a wealth of information on 900 Part-15 equipment!
RFID Tag Readers are a real nuisence! They can operate anywhere in the band, but luckily, they are frequency steerable by the user and I have had success simply asking them to move if they end up on a repeater input channel.
Most of the WISP operators have a pretty good "guard band" near the band edges and we have found that 902.0125-902.200 is usually pretty clean for repeater inputs. I have a couple repeaters that coexist on the same hilltop with them with minimal to no interference. I run 902.0125 in Sacramento and with a N6CA preamp and 0.17uV sensitivity at the antenna port, I can take the machine out of PL and it will never break squelch! The exception is the Motorola Canopy! These things spew trash 2 MHz out of the band within 100' of a transmitting unit! I had to get the FCC involved with one operator that refused to move frequency and have a specan shot of the noise floor between 901-902 being raised 20 dB by a Canopy 100' away and behind it's antenna! The FCC tech that went to the site confirmed this and the matter was solved after that. They entered a few keystrokes and moved up to 915. No problems now.
There is also a ton of licensed stuff that usually ends up in the middle of the band where we are not bothered by it, unless you are running a 12MHz split. These are usually automated bridge toll machines, vehicle tracking systems etc.
There are also clear channels between 902.2 and 902.9 for inputs, but you have to hunt for them. There are gaps between the "hopping channels" on most Part-15 equipment, but without the spec sheet, it's hard to determine.
Cordless phones and baby monitors are random and usually have changeable channels, so although a nuisance, they can be dealt with.
Remember, although we are secondary to ISM (FCC Part-18) I have never actually heard a Part-18 device on 900 and no one can claim they are Part-18 if it is being used for any type of communications! An ISP tried that with me already! As for ALL Part-15 equipment, we, as licensed amateurs, have priority! Period! The FCC made that clear to me over the phone and has been helpful with me so far with those who "abuse" their Part-15 privelages. The main rule for ALL part-15 equipment states, "This device must not cause harmful interference and must accept any interference even if it results in undesireable operation". Pretty much says it all!
Hunting down an interference source can be challenging in a big city with the tons of stuff out there, but recently, I found out that the "Smart Meters" seem to be causing a lot of havoc with the other Part-15 users and many are vacating the band! My big interference generators have been RFID tag readers, usually sounds like a "buzzing" similar to a TV sync buzz, and the Motorola Canopy. All taken care of and in the case of the RFID tag readers, very cooperative and once we explained what portion of the band we use, they were happy to move to another portion of the band. I like it when solutions are easy and friendly like that!
So, basically, there are no "frequencies to avoid", but there are clear ones we as amateurs can use without interference or at least be tolerable interference.
Right now we are hunting something entirely new that is swallowing up all the 900 repeaters outputs in the San Francisco Bay Area between about 926.7 and 927.4! It is a series of timed 100ms pulses repeating every 1 sec changing in amplitude and it is way too powerful to be Part-15. There were two "experimental" licenses granted in the SF Bay in the last 4 months, so we are looking into that and I plan a DF search within the next couple weeks! Not sure what kind of priority we have over experimental license stuff if that is what it is! I guess we'll find out! Several repeaters located below 927.3 already moved to the top of the band due to the interference from this thing. We have resorted to "unusual splits" to get away from the trash. All the repeaters n the NC9RS system use 902.0125 for the input and different PL's and output frequencies. Most also have a standard 25 MHz split (Maxtrac RX in SCAN mode) for the few with radios that won't do odd splits like some Kenwoods and Johnson radios, but the interference on the standard split inputs gets very bad sometimes.
Hope this helps!
73 de Greg KJ6KO
The author can be contacted at: his-callsign // at // repeater-builder // dot // com.
This page originally posted on 30-Dec-2006
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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.