The biggest challenge to owning and operating a GMRS repeater is installing it, and keeping it operating. Last month we talked about installing your repeater in a commercial site, so this month, we look at the correct ways to do some normal repeater setup tasks on the repeater installed at home.

The most important link in the repeater system is the antenna. We discussed choosing the best antennas for repeaters in a previous article. Assuming you have already chosen the antenna you are going to use, now we need to discuss installation.

Antenna height is the single most determining factor of range. Since UHF (GMRS is UHF) operates using the line-of-site rule, the transmitting and receiving antennas need to ‘see’ each other. For the best coverage and range, you need to mount the repeater antenna as high as possible to clear obstructions including buildings, foliage and terrain.

For smaller base station antennas, the popular telescoping TV antenna masts are a smart choice. They are inexpensive and easy to install. Radio Shack and your local hardware store are good sources for the masts, guy wire, and hardware for your installation.

A telescoping mast is installed by first mounting the base and the guy anchors to the structure you are installing the mast on, usually the roof of your home. Guy anchors should be installed at angles toward the mast, and there should be four. Viewed from above, the guy wires should come off the mast at angles to make as near to a perfect ‘+’ as possible.

First, attach four lengths of guy wire to the guy ring at the top of the bottom section of mast, and erect the mast. With a helper holding the mast upright, attach the guy wires to the anchor points and secure. Use a level to ensure the mast is straight. Tighten and tension the guy wires in place. Next install four lengths of guy wire to the next section up and extend it fully. Attach the guy wire ends to the guy anchors, but do not pull tight, leave some slack. Lower the section and do the same for the next section above it, letting the guy wires hang slack when the sections are retracted. Keep doing this until you have the entire mast up, with all the guy wires attached, but only the bottom level tight.

With the mast collapsed, mount your antenna on the top section and attach the cable. For runs up to 60 feet, use a minimum of LMR-400 cable, and for longer runs up to 120 feet, use ½-inch Heliax. If your antenna cable run exceeds 120 feet, use a minimum of 7/8-inch Heliax. Support the cable every 5 feet or less by taping or clamping it to the mast as you extend the sections.

Once the mast is fully extended with the antenna and cable mounted securely, tighten and tension the guy wires at the anchor points. Check the mast again visually to make sure it is straight and adjust guy wire tension as necessary.

Run the coax cable to the area where the repeater will be located inside your home. Be sure not to kink the cable, or make any sharp bends. That can ruin you whole day, not to mention your cable. Where the cable enters through the wall, seal around it with a household all-weather sealant or the popular ‘foam in a can’.

The next part of the repeater installation is tuning the duplexer. We discussed duplexer types and duplexer function here before, and if you need a refresher course, check the past columns for more info.

To tune a pass, or pass/reject duplexer, you need a professional service monitor with a tracking generator to do it properly. There is NO substitute.

Procedure is, you connect one side (let’s say the transmit side) of the duplexer and tune the pass cavities until the pass waveforms overlap each other exactly on the center frequency line (let’s say 462.600 MHz). Then, if you have a pass/reject duplexer, you change the center frequency of the sweep to the reject frequency and tune the notches to overlap exactly on center (in this case, 467.600 MHz). The other side is done the same way, but reverse the frequencies.

You can tune a notch only duplexer without a full blown service monitor, but it won't be perfect, just close enough. Use a signal generator to inject signal on the transmit frequency of 462.600 MHz (example) into the antenna port of the duplexer. Use a signal strength meter to receive signal in the receiver port. Install a 50-ohm load on the empty transmitter port. Tune the notches for minimum indication on the received signal meter. Do the same on the other half of the duplexer for the transmitter side, except tune using the receiver frequency of 467.600 MHz.

Better yet: order your duplexer already tuned to your frequency pair! Duplexer tuning is a step more easily handled by your local commercial two-way radio shop anyway. They do this stuff almost every day. Ho-hum…

Jumper cables from the duplexer to your transmitter and receiver should be of the double shielded variety like LMR-400, LMR-240 or ¼-inch Heliax or Superflex. Connect the duplexer to the radios using the shortest cables possible to minimize loss and possible transmitter/receiver interference from cable leakage.

Most home located GMRS repeaters I have seen work amazingly well. A home-located repeater I experimented with once was located in the center of town with the antenna 60 feet above ground on a TV mast. The rock-solid coverage of the repeater was over 15 miles! Portable coverage was extraordinarily solid out to about 15 miles. A good mobile could easily use the repeater in a town 20 miles away.

Locating the repeater equipment itself inside the home can be a challenge itself. You need to be able to access it for maintenance, it needs a good supply of cool air, and it needs to be out of the way.

If you have a desk full of other radio gear, such as a ham radio operation, keep the repeater away from the other gear to minimize the possibility of interference amongst them. Otherwise, an unused room or out of the way corner would be best.

Do not install the repeater equipment in the garage. The summer heat, winter cold, dirt and moisture will all work together to shorten the equipment life. Closets do not offer enough air circulation unless there is a vent from a central cooling unit going to it. Kitchens are out of the question! A den or guest room would be a better choice. Besides, what a great conversation piece!

In the trenches, or on a hilltop, good engineering practice is just as important to building a reliable repeater system. Just because your repeater is in a convenient location like your home, you don't want to have to tinker with it all the time to keep it working! Home located repeaters still offer exciting performance without the expense of commercial site rent.

Next month, test equipment every GMRS repeater owner should have, and can afford.

Gummers^(TM) is a trade mark of Paul Shinn