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By Peter Policani, K7PP

I know that many of those amateurs who have used community radio sites have had some kind of difficulty from time to time. It's hard to know what to do or who is at fault or who to talk to about an interference problem. A big problem can be lack of test equipment.

    • How does one know if their transmitter is clean?.
    • How does one know if the other guys equipment is clean?
    • For that matter, how do you tune up a duplexer or a receiver with out a good signal generator?
    • If you don't know someone with the proper test equipment, do you install at the site anyway and take your chances?

Many hams do. They may feel the public service they are providing is worth the risk. Worse case is a general damage to the integrity of amateurs operating on community sites.

At the risk of rambling, I will give you some examples.

A site where I operate a two meter repeater came under some terrible interference from an unknown source. It was even wiping out the studio to transmitter link receivers for the FM stations at that location. The first transmitter they checked was mine. It was clean. The concept among site owners is that an amateur is just that. An amateur. I hope that we can change that concept. There are many dedicated hams out there who could provide a wonderful service to the community with their repeaters but are denied site access because of a concept shared by many site owners. They are put off by impossible site rental fees or in some cases are told they are not welcome. It's happened to me many times.

I would propose that the WWARA technical committee be made available to do repeater site walk thru's and inspect the amateur installation. As I mentioned in my last article, a certificate or notation could be stamped on the coordination showing the amateur meeting all of the appropriate site standards for a professional installation. The technical committee might have access to test equipment to check the operation to verify its integrity. The sign off of the inspection could be done by a volunteer with a Commercial license.

I feel that when the site owners see that we really care, our ability to obtain decent sites will improve.

I know what you might be thinking. What are all these site standards anyway? The following is a list taken from engineering standards required of a Washington site owner but are currently used as a standard for many community sites. Some of the standards might surprise you. I am including only those rules that would apply to amateur radio frequencies. Some of the standards apply to commercial frequencies only and were not included but do exist. I am not worried about talking any of you into using any of these site standards. As time goes on, you will find them something you will have to do to obtain or stay on a community site. If you are serious about providing a system that will benefit your friends and other amateurs, you will want to learn more.

Site owners have found that the number of paying customers they can put on their site is in direct proportion to those who can co-exist with each other. As many owners find their troubles curable as a direct result of implementing these standards, many will make a change or operate their sites at a loss.

Communications site standards derived from those set down by the

Western Washington Cooperative Interference Committee.

Equipment not permitted on community sites without express permission of the site owner;

  • A. Any RF transmitting equipment without an FCC type acceptance.
  • B. Add on power amplifiers.
  • C. Digital//Analog hybriding in exiters, unless type accepted.
  • D. Equipment which does not conform to FCC rules and regulations.
  • E. Non continuous duty rated transmitters used in continues duty.
  • F. Transmitter circuits without harmonic filters.
  • G. Change in operating frequency without site coordination with Lessor. (Remote bases)
  • H. Equipment not designed for high density site applications.
  • I. Ferrite devices looking directly into an antenna. (notch-notch duplexers or no cavities at all).
  • J. Nickel plated connectors.
  • K. Cascaded receiver multicoupler/preamps without proper preselection bandpass filters and attenuators to prevent multicoupler/preamp and receivers front end overload.

Required Radio Frequency Interference Protective Devices.

  • A. Transmitters in the 25 to 54 MHz range shall have isolation of at least 20 dB followed by a lowpass filter or cavity providing a minimum of 30 dB attenuation removed 1.0 MHz from the operating frequency.
  • B. Transmitters in the 130 to 225 MHz range shall have at least 50 dB of isolation followed by a lowpass filter and bandpass cavity with a minimum of 25 dB attenuation 1 MHz from the operating frequency.
  • C. Transmitters in the 400 to 470 MHz range shall have at least 50 dB of isolation with a minimum of 15 dB of attenuation 1 MHz removed from the operating frequency.
  • D. Transmitters in the 806 to 960 MHz range shall have at least 50 dB of isolation followed by a lowpass filter and band pass cavity with a minimum of 15 dB of attenuation 1 MHz removed from the operating frequency.

Also it should be emphasized that the above specifications are minimum requirements. Additional protective devices may be required based upon evaluation of the following information.

Theoretical TX mixes, particularly second and third order Antenna location and type Combiner/multicoupler configurations Transmitter specifications. Receiver specifications Historical problems Transmitter to transmitter isolation Transmitter to antenna isolation Transmitter to receiver isolation Calculated level of IM products Transmitter output power Transmitter Effective Radiated Power Spectrum analyzer measurements VSWR measurements Existing cavity selectivity Any other equipment, signal, measurement or specification to protect the integrity of other Licensees radio frequency or signal.

Antenna or mounts

  • A. Mounted only on approved side arms or other specified mount. All inverted antennas must be designed by the manufacturer for inverted mounting.
  • B. All mounting hardware hot-dip galvanized or stainless steel.
  • C. Tagged with weatherproof labels showing manufacturer, model, freq range and owner.
  • D. Connections to be taped with vulcanizing rubber tape and covered with strech vinyl tape (Scotch 33 or equiv) and Scotchkote electrical coating applied to tapered areas (included booted jumper cables) E. Must meet manufacturers VSWR specifications.
  • F. Antennas with corroded elements must be replaced within 30 days of notification.
  • G. Must be DC grounded type or have proper lightning protection such as a Polyphaser arrester or equiv.
  • H. Unless otherwise authorized, all antennas must be encased in fiberglass radomes.
  • I. Mounting pipes must be cut such that they do not extend above the antenna mounting sleeve.
  • J. Any corroded hardware must be replaced.


  • A. Must be teflon filled "N" type including chassis/bulkhead connectors. UHF connectors are to be used only when no other type of connector is available on the equipment.
  • B. Must be properly fabricated if field installed
  • C. Must be taped and Scotchkoted at least four inches onto the jacket if exposed to weather.
  • D. Male pins must be proper length.
  • E. Female contacts may not be sprung.
  • F. Connectors must be plier tight as opposed to hand tight.
  • G. Must be silver plated or brass.


  • A. No RF preamps permitted in front end unless authorized by lessor.
  • B. All shields must be installed.
  • C. Must use helical front ends.
  • D. Must meet manufacturers specifications, particularly with regard to bandwidth, discriminator swing and symmetry, and spurious responses.
  • E. Crystal filters/preselectors/cavities will be installed in receive systems as required.
  • F. All repeater tone squelch circuitry must use tone and carrier detect (and squelch logic).


  • A. Must meet original manufacturers specifications.
  • B. All shields must be installed.
  • C. Must be tagged with Licensee's name, equipment model number, serial, and operating frequencies.
  • D. Must have visual indication of transmitter operation.
  • E. All low level, pre-driver and driver stages must be shielded.
  • F. Output power may not exceed 330 watts unless authorized by Licensor.


  • A. Must meet manufacturer's specifications.
  • B. Must be tuned using manufacturers approved procedures.
  • C. Must provide a minimum of 55 dB transmitter to transmitter isolation.


  • A. All cabinets must be bonded together and must be grounded to the building ground system.
  • B. All doors must be on and closed.
  • C. All non-original holes larger than one inch will be covered with copper screen or sold metal plates.


All stations will be licensed and a copy of that license, modification or renewal application shall be secured to the equipment and a copy sent to the site manager.

Pete Policani, K7PP

Have fun On-Line !