18 February 2018

Cross-Band Repeat

The more I use it, the more I like it.

Several months ago I bought an Icom ID-5100, both for its D-STAR capabilities but also for its cross-band repeat feature. I had never run a cross band repeater before (UHF in, simultaneous VHF out) but found myself bumping up against several scenarios where it looked like it might be a useful tool.

The basic concept behind cross-band repeat. A signal on one band (UHF or VHF) comes in
and is simultaneously re-transmitted on the opposite band

The first was a charity bike ride event where I was the only communicator at a large but isolated rest stop at the turn-around point on the ride route. I needed to roam around the rest area, checking on bike riders and coordinating with ride officials, but the repeater we were working through was too far away to hit reliably with a 5 watt HT. In this situation I ran a 50 watt VHF transceiver connected to a tripod mounted j-pole antenna and was able to hit the distant repeater with no problem, but this setup tied me to the fixed radio setup. In this case a cross-band repeater would have allowed me to roam the rest stop at will with just a low powered HT set to a UHF simplex frequency, hit the on-site cross-band repeater with ease and get my signal out on VHF at 50 watts.

The second scenario involves my local neighborhood. I live in a fairly hilly subdivision and when I walk my dogs there are several 'dead spots' on my waking route where I can not reliably hit our local 2-meter repeater with a 5 watt HT. By running a cross-band repeater at my QTH I can reliably hit the local repeater with only 1/2 watt on UHF using my HT.

The last scenario is similar to the first, but involved needing to run a simplex VHF net in support of a recent charity 5k trail run. The course covers a small area and the trails fold back on each other, but the terrain is rough and in many spots blocks signals from getting to the local repeaters. We decided to run this event using a simplex frequency, but because of the terrain masking challenges I needed to increase the odds that the communicators at the checkpoints could reach net control with 100% reliability. I also needed to be able to roam the race operations area to coordinate issues. This was the perfect scenario for a cross-band repeater setup. At a high point near the race operations site I set up a mast-mounted j-pole antenna and ran the coax into my truck to the ID-5100 set up to cross-band repeat the VHF simplex frequency we were using.

Icom ID-5100 set up as a cross-band repeater. The radio is sitting in the
back seat of my truck, powered by a 33 amp hour golf cart battery

A j-pole antenna (an Arrow open stub j-pole) provided the elevation needed
to ensure communicators with simple HTs could reach net control. The cross-band
repeater setup re-transmitted their signal on a simplex UHF frequency that the net
control HTs were set to, allowing us to freely roam the race operations site while still
maintaining contact with all communicators

This set-up worked great. In fact, better than I expected. The ID-5100 is a no-brainer when it comes to running a cross band repeater setup. Icom did a great job of incorporating the feature in the firmware, and the touch screen interface makes it easy to select the mode with just a few finger pokes. My overall repeater setup is fairly simple, but it can be done even cheaper and simpler, yet still be just as effective. The ID-5100 is one of the more expensive dual-band mobiles, but all of the 'big three' amateur radio manufacturers offer less expensive mobile rigs with cross-band repeat capability. For almost $200 less than what I paid for the ID-5100 you can pick up the very highly regarded Kenwood TM-V71A, connect it to an inexpensive twin-lead j-pole antenna and achieve the same results. All you need on the HT side is an inexpensive UHF transceiver - even a $40 Baofeng dual band radio will work nicely.

As I use cross-band repeat more and more, more and more use cases pop up. For example, fishing with fellow ham radio operators on remote streams in north Georgia, well out of range of cell towers and local ham radio repeaters. By setting up a cross-band repeater in my truck (with a roof mounted antenna) we can work the stream in opposite directions from the truck but still maintain reliable communications.

I love it. Things like this bring out the geek in me and keep me off the streets at night 😄

W8BYH out

1 comment:

  1. Hello, having just picked up a 5100, I was curious if you were able to solve the issue of needing to identify the repeater every 10 minutes?

    Thanks and 73,

    -Bob (KO4CLV)