The Cross Band Repeater THE PROBLEM AND POSSIBLE SOLUTIONS (originally written for the Link, 3/200) The recent collapse of the Broadway radio tower triggered the following message from Charles E. Scharlau (NZ0I): "We were going to use the Broadway repeater as a back-up for communications during the Scholastic Orienteering Championships March 23-24. Now it looks like we're going to have to make 2-meter simplex work through more than a mile of forest." Let's think about this. This is not such an outlandish disaster scenario. An "emergency site", maybe a mile square, and no repeaters available. In a real disaster, the repeaters might not survive or be temporarily out of commission. Or you might want to reserve the repeater for communications over a larger distance. Simplex will work, especially if the terrain is forgiving. However, you may have to use higher power on your HT. Now how long will the battery last? However, there are other solutions. In a previous article for the LINK (a couple of years ago), I related an experiment where we used two linked cross-band mobile rigs, separated by 1/4 mile or so, to duplicate the full function of a repeater. That worked well enough but it ties up more resources than are absolutely necessary. A single mobile rig with cross-band capability is all it takes, if participants know how to program their HT and the HT has certain capabilities. (Below I have the setup instructions for 3 different Yaesu HT models. Maybe someone else can fill in with instructions for other models). The basic one-rig-solution is to set up the mobile rig with receive set to one band (e.g. 2 m) and transmit to the other (70 cm) and to put it into cross-band mode. Then everyone listens on 70 cm, but talks to the group on 2 m. ISSUES There are two major questions: 1. What does the mobile rig (repeater) buy you over using simplex? and 2. How do you make this mode easy to use? Having a repeater (the cross-banding mobile rig) has several advantages. You can put some real effort into finding a good location. If there's an elevated site that you can drive to, then that's obviously good. You might even have the time and resources to set up a good antenna, although most mobile rig antennas are already much superior to an HT's rubber duck. For example, you might hoist a j-pole antenna into a tree. It also makes it easier for each participant to insure that he/she is reachable at all times. With a repeater, all each person has to check is that they can communicate well with the repeater. You don't have to worry about your "connection" to everyone else. Finally, if you do a good job in setting up the repeater, it is likely that you can communicate well with minimal power from your HT. This both saves your batteries and keeps your HT cool. SETTING UP YOUR EQUIPMENT The trickiest part is making your HT easy to use in this mode. It obviously requires a dual band HT. But for ease of use, it requires more than that. Some of the older and/or more expensive HT's are true dual banders in that they effectively contain two radios that can work more-or-less simultaneously. For these, you can listen on one band and have it set up to transmit on the other. Thus, the setup is almost trivial. However, many dual banders these days consist of a single radio that can easily work on either band, but not truly simultaneously. For many of these you can program them to work as follows: You are listening on one band, but when you push the PTT, they switch to a frequency on the other band. This is ideal for use with this cross-band repeater . I have access to and have used several models of Yaesu HT's to accomplish this: FT50, VX-1, and VX-5. None of these are true dual-banders in that they can't handle two band simultaneously. Each allows you to set up memory so that if I retrieve that channel, it shows the receive frequency on one band. When I push the PTT switch, it automatically goes to the transmit frequency on the other band. SPECIFIC EXAMPLE On my HT, I want to listen on the 70 cm band. Let's choose the simplex frequency (from the SERA band plan) of 446.100 MHz. I want to transmit on the 2 m band. For this example we'll go with 147.555 MHz. That means our mobile rig should be set up to listen on 147.555 MHz and transmit on 446.100 MHz. It should then be put into cross-band mode. For those rigs supporting one-way cross-band, this is what you should use. (If you have only two-way cross-band, like my Standard 5900, you should probably have it set to require a tone to receive on 446.100 MHz so that if there are stray transmissions on that frequency, we won't have it repeating in the opposite direction and locking out the repeater for that period.) OK. Now you (and everyone else participating) needs to set up your HT. On my VX-1, I would first set up a memory channel, say channel 50, as though I were operating on 446.1 MHz simplex. That is: A. Set and store the Receive Frequency (in channel 50) 1. Set to the 70cm band. 2. In VFO mode, enter the frequency, 446.100 MHz. 3. Make sure it is set for simplex. 4. (If you want to use tones, set them now). 5. Save this in the memory: For the VX-1 that means hold the function key for a second; set the memory number to 50; tap the function key again (within 5 seconds). B. Set and store the Transmit Frequency (in channel 50) 1. Set to the 2 m band. 2. In VFO mode, enter the frequency, 147.555 MHz. 3. Using the special procedure below, save the transmit frequency in the same memory channel: Hold the function key for a second; set the memory channel number to 50; WHILE HOLDING THE PTT BUTTON, tap the function key again (within 5 seconds). Now I'm ready to go. If I use channel 50, I'm listening for traffic from the cross-band (mobile-rig) repeater on 446.1. When I push the PTT, I automatically transmit on 147.555 which is the input to the cross-band repeater. The setup procedures described for the VX-1 are essentially the same for the VX-5 and the FT-50. What differs, in detail, is how you enter the frequency, how you set the modes. Also, in contrast to the VX-1, you don't have to set things up by bands. VHF and UHF frequencies can be entered at any time. [11/2006: these comments also hold for VX-2, VX-6, and VX-7.] If you have a true dual-band HT with two independent radios, you don't have to go to this much trouble. Just set up one side to listen on 446.1. Set up your other side to transmit on 147.555. As long as your receive is muted while you are transmitting, then there shouldn't be any (feedback) problems. ^ o cross-band | | repeat | ~ ~ ~ > 446.100 ~ ~ ~ > ~ ~ ~ ~ > | ^ | HT mobile rig v < ~ ~ ~ < ~ ~ ~ 145.555 < ~ ~ ~ | [O] | -----+---+-- | | --------- | *--------------+---------------* (r| 446.100 || |(o) receive transmit (o)| |x| 145.555 || | -------------------------- | | --------- | | | 145.555 446.100 | | | ( ) O | | -------------------------- | \ / |o[ ][ ][ ][ ][ ][ ][ ]o| | [][][][] | *------------------------------* | [][][][] | | [][][][] | | [][][][] | *----------* Dee, KU4GC