Crossband Repeating is a process where a Ham transmits one signal on one band (typically UHF), and it is received by another radio with a better antenna/power installation, and re-transmitted (typically on VHF) to another radio system, or a repeater. Everyday examples of cross-band repeaters are repeater receive sites that hear the input signals on 2m and retransmit those signals on a frequency higher than 220 MHz.
When is it a good time to crossband repeat? Anytime that you are using an HT, and cannot be heard into the repeater system, or when you are working an extended event, and do not want to exhaust your HT's batteries. With two crossband repeaters, it is also possible to also build a temporary portable repeater.
The radios that I used for this example are Alinco dualband VHF/UHF mobiles, and Alinco dualband VHF/UHF HT's. Other equipment may be used, but important things to look for are: tone squelch, split sides, split tones, remote control, and crossband capable. Not all dualband radios support crossband operation. If possible, ask for a demonstration before purchase, as some radios claim to support it, but require someone holding the microphone over the radio's speaker. For the purpose of this article, I assume you wish to crossband into a 2m repeater. By adjusting the settings, you may crossband into 440 or other frequencies. It all depends on your equipment.
NEVER CROSSBAND REPEAT TWO REPEATERS TOGETHER!! By doing so, you run the risk of a signal loop, causing both repeaters to remain up, and rendering the systems useless. Repeaters tend to have squelch tails on them, and that tail will key up the other repeater that will cause a tail that will key up the first repeater, and so forth!
What is tone squelch? Tone Squelch, sometimes called Tone Decode, is a setting on a radio that will prevent the frequency from opening unless a proper PL tone is received on the audio signal. Repeaters, such as the 145.13, require a PL tone in order to use the repeater. The hardware on the repeater has a tone squelch set for 127.3. Because your crossband repeater will be a temporary part of the repeater system, you need to protect the repeater by investing in a tone squelch. Otherwise, any random noise (static crunches, intermod) will enter your system, and cause headaches for other users on the system. Tone Squelch is strongly urged.
What about remote control? Some crossband mobiles, such as the Alinco 610, or the "cool blue" Kenwood support limited remote control of the radios. This is handy for remotely shutting off your crossband repeater with your HT. Be aware though, that the commands should not be transmitted through the "live" side of your station, as those tones will also be sent to the repeater. In order to effectively use remote control, you need to transmit "backwards". I will explain more later as we discuss the types of crossband repeating.
What are split sides? I refer to radios as "split sides" (some call it split frequencies) if they are dual band radios (mobile or HT) that can transmit on VHF and receive on UHF (or vice-versa) on the same "side" of the radio. For example, a typical radio has a frequency on the left side, and another frequency on the right side. Some radios will allow you to program a VHF frequency on one side, and create a split so that the same side can transmit in the other band. For example, I can with my Alinco program 145.13 receive and 445.175 TX on the left side, and the right side may be programmed to 443.80 RX / 448.80 TX. Split sides really increase the power of your transceiver.
What are split tones? Some radios allow you to set a transmitting PL tone of X, and a tone squelch of Y. For example, my Alinco can transmit a PL tone of 127.3, but be configured for a different tone squelch of 100.0 I have found that some radios that support split tones will not do them during crossband repeating. Be sure to test.
Any other concerns? Yes. Be sure to have a larger battery for the mobile radio, as it may be utilized greatly during your session. Also make sure it is properly cooled, so it does not overheat. Also, some radios may not allow transmitting from 2m to 440. I think I heard about one of Kenwood's models not working properly as illustrated below.
Types of Crossbanding
There are two types of crossbanding- half duplex and full duplex. Full duplex means that the crossband repeater manages both "sides" of the conversation through to the repeater, whereas half duplex means that only your "side" of the conversation is re-transmitted.
The easiest setup for crossband repeating is half duplex. Consider the diagram below:
Using half duplex, the HT is set to transmit on a private UHF simplex frequency to the mobile radio. The mobile receives the signal, and re-transmits it into the repeater. When the HT is done transmitting, the mobile radio falls quiet, and the HT hears other people directly on the repeater.
How to setup this scenario:
* Setup your HT to transmit on UHF (let's say 446.00) Do not use that frequency... find your own! Set the PL tone of the UHF to something besides 127.3... let's pick 100.0
* Setup your HT to receive on 145.13. If your HT supports crossband transmitting on the same "side", such as my Alinco DJ-G5, use the same side as the UHF setting, and remember to set the proper split.
* Setup your mobile radio to transmit on 144.53 (the input of MAARS), and transmit a tone of 127.3 Do not, in this case, program in 145.13 with a (-) offset. You want the 144.53 simplex in the radio. If your radio supports split tones (Alinco does), set the tone squelch on VHF to something different, say 100.0. Not all radios can do this, but setting a different tone squelch will prevent others from backfeeding your system.
* Setup your mobile radio to receive on UHF simplex (our example, 446.00) and if possible, setup the tone squelch to our sample 100.0 This will prevent other UHF signals without that tone from using your mobile without your permission.
* Place the mobile in crossband repeat. Check the power levels to ensure they are at minimal levels.
Now, when you key up your HT, it will transmit on UHF to the mobile. The mobile, hearing the proper signal, and the proper tone, will open, and re-transmit the signal on 144.53 with a PL of 127.3
Notes: There are two concerns with this setup. The first is that unless you have a dual squelch on the mobile radio, any other stations talking near your mobile radio will be able to backfeed the link, transmitting back to your HT on UHF. You can get around this by creating a different offset on the crossbanding radio. Program a different frequency, such as 144.38 or something, and then when the mobile transmitter keys, make sure it ends up on 144.53. If you don't want to change the default offset, you could program in 143.93, and program a positive offset, so that a keyup will be +.6, placing you on the proper 144.53 frequency. The second concern is that your HT will repeat what you are saying on the VHF side as you talk into the UHF side (remember, when you are talking, so is the repeater, so the HT should hear the repeater too). This can be fixed on some radios by muting the sub-band (the band not transmitting); others, like my Alinco DJ-G5, allow for crossband transmit, so I only use one "side" of the radio for all this. If in doubt, you might end up turning the volume up and down on the VHF side while you are transmitting.
Also, use minimal power on the crossbanding mobile. That will save your battery life and keep the heat down.
With this setup, it is easy to transmit remote-control commands if you can use split PL tones. If your setup allows for this, program in 144.53 with your non-127.3 PL tone, and remote control your mobile radio. If you cannot use split PL tones, meaning your system is 127.3 toned on all frequencies, your commands may be heard by the repeater, and we request that you manually control your crossband repeater.
Full duplex crossband repeating is more difficult to setup, but it does work. If your particular situation allows for half duplex, I strongly suggest that you proceed with that setup. Full duplex places many more demands on your crossband repeater, because it will be working almost 100 percent of the time. Remember, it re-transmits all of the data on the repeater, too! Only use this scenario if your HT is in a location that cannot hear the repeater directly, such as in your basement during severe weather.
Consider the following diagram:
Using full duplex, the HT transmits to the Mobile radio on a private UHF simplex frequency, such as our sample 446.00. It transmits your private PL tone. The mobile radio receives the UHF signal, and it re-transmits on VHF, making the automatic switch to 144.53 PL 127.3 that is sent to the repeater. When the HT is done, the mobile radio switches back to 145.13 (and hopefully, you have a tone squelch of 127.3). When the repeater transmits, the mobile radio hears it, and sends a signal back to the HT on UHF, with the proper private tone (100.0).
How to configure for this scenario:
* Program your HT to transmit and receive on one UHF simplex frequency, with a private PL tone. Let's use 100.0 again.
* Program your mobile radio to transmit and receive your UHF simplex frequency, with your private PL tone (100.0) enabled. Program the VHF side of the radio to receive on 145.13 with a PL decode of 127.3, and transmit with the normal (-) offset and tone of 127.3
* If your mobile radio features a time-out timer, consider enabling it for 10 – 20 minutes, with a rest period (some call it penalty) of 2 minutes, so that your radio has a chance to recover. The time out timer will also let you get a command transmission in if you have remote control functionality.
* Place the mobile radio in crossband repeat mode. Check the power levels to make sure they are at minimal levels.
Notes: This scenario utilizes your mobile crossband repeater for 100 percent of the time. It is transmitting when your HT is using the system, and it is transmitting when the repeater is operational. This means that you need a lot of battery power, and a lot of cooling. Keep that radio cool! If it does not come with a fan, install one! You can burn out a radio in this configuration! Also note that if you wish to remote control this system with your HT, you can do it if you transmit on 145.13 PL 127.3 SIMPLEX , and your HT is stronger than the repeater. Again, this is a minor violation of the FCC rules, but that is your decision. Also note that when the repeater is transmitting, your HT will not be heard by the crossbanding mobile because the UHF side of the radio is transmitting, and cannot "hear" your HT. You will need to wait for the repeater's carrier signal to drop completely before your HT can transmit.
Other Ideas Involving Crossbanding
With crossbanding technologies, you can do other things:
* Build a temporary VHF or UHF repeater. Using two crossbanding mobiles, setup the first one with the VHF output of the repeater (let's say 147.00 simplex) and a UHF frequency (let's choose 446.00 simplex). Setup the other radio with the standard input of the repeater (with 147.00 as the output, we should program 147.60) and the corresponding UHF frequency (446.00 simplex). Choose proper PL encode and decode protection. Move the mobiles into position where they are needed, and give the radio with the input (147.60) a higher location, and give the radio with the output (147.00) more TX power. Use gain antennas. When a HT keys up this repeater, it will talk to the radio on 147.60. That signal will be crossband repeated over UHF to the other crossbanding radio, where it will be re-transmitted on 147.00, just like a traditional repeater signal would be. If you need to make the reverse (a UHF input, and link over VHF), then just reverse the setup. A VHF linking system is technically illegal, however.