Remote Base / Cross Band Repeater / Cross Band Link All of these terms mean the same thing! This feature must be built into the radio at the factory! There are no add on kits! Mostly mobile radios mainly have this feature, it varies from model to model, some do some don't. This feature allows the radio to receive a signal on one band and simultaneously transmit the voice out on the other band. Normally these are 2M and 70CM (440 MHz), however radios with other band choices do exist, and would work fine as long as the handheld bands matched the mobile bands. I will mainly talk about using a Remote Base with a 2M/70CM mobile and utilizing a dual band 2M/70CM handheld. This is the most common and preferred situation. WARNING! Until you are familiar with how to do this, this do not attempt to use a mobile for both an up link and a downlink to a repeater, this is all too common problem on the airwaves. Because if you do <> you will get the signal through your remote base up to the repeater, then the repeater comes up, and when you un-key your HT, the repeater continues to transmit. Your mobile will then flip bands, hear the repeater, lock on to it and it will be transmitting on the link frequency back to you, and will continue to do so until the repeater drops. In the meantime you are locked out of the system. This is known as the "Crossband Trap", don't fall into it. If you have ever head people on the air tell someone to let the repeater drop before they are able to call back, you now know they are stuck "IN THE CROSSBAND TRAP". In a busy situation the repeater may Never Drop, thus you will not be able to transmit back through your mobile, and now you are stuck!! So now that you have read about the "CrossBand Trap" which is the Wrong Way to do it, there are other ways. Here are some options. I am going to start out with some requirements. You should have: 1. Have a real 2m / 440 Dualband Handheld, one which could receive on one band and by just pressing the PTT automatically transmit on the other, from a stored memory location would be fine. 2. Have a 2M / 440 Mobile, with the Remote Base Feature built in at the factory, mounted in a vehicle, with power and antenna/s. (All frequencies in your Remote Base will be simplex frequencies and none will use a + or - offset shift - this is Very Important.) 3. You must know how to program your handheld. 4. You must know how to program your mobile and how to activate and de-activate the Remote Base Feature. 5. For the "Link" frequencies I prefer are "Splinter" or "four digit" frequencies, to avoid interference to any existing system. You probably will have to activate your 12.5 KHz step in the radios to get them. So here we go, using the ARPSC 145.370/144.770 repeater and 449.6125 as examples: *NOTE: 446.000 is the National Calling Frequency and is Not an unused frequency! BEWARE: Some frequencies which seem to be un-used may be system links. Everything you say on your handheld may be broadcast over a large area on another system! For 99.44% of the time you will just need an uplink assist only for your handheld to reach the repeater, as you can normally receive the repeater directly on your handheld. ----------------------------------------------------------------------------- UPLINK ASSIST ONLY 1. Pick an unused UHF frequency, such as 449.6125 2. Program your handheld with 145.370- and 449.6126 Simplex. 3. Program your Remote Base with 144.770 Simplex and 449.6125 Simplex in each side, and activate the Remote Base. (All frequencies in your Remote Base will be simplex frequencies and none will use a + or - offset shift - this is Very Important.) You are good-to-go. To access the repeater directly, transmit on and receive on the 2M side as normal. Once you cannot get the repeater directly, but can still hear it, and you are in range of your car, which is in range of the repeater, with it's more power and better antenna system, transmit low power on 449.6125 Your car will hear this and will relay your voice out on 144.770, which happens to be the input of the 145.370- repeater, your message will make it. After transmitting listen on the 2M side for any traffic. NOTE: You are not locked out, you can transmit to the repeater at any time through your Remote Base, as you "have full break-in capability". ----------------------------------------------------------------------- Just in case you cannot hear or hit the repeater with your HT, but your car can. ----------------------------------------------------------------------- PHANTOM REPEATER OR FULL DUPLEX REMOTE BASE For this you will need Two Remote Base Radios, one for the Uplink Assist and another one for the Downlink Assist. 1. For convenience pick an UHF repeater pair un-used in you location. I chose 444.6125/449.6125. 2. Program the Remote Base Uplink just as in 3. above: Program your mobile with 144.770 Simplex and 449.6125 Simplex in each side, and activate the Remote Base. (All frequencies in your Remote Base will be simplex frequencies and none will use a + or - offset shift - this is Very Important.) 3. Program the Remote Base Downlink with 145.370 Simplex and 444.6125 in each side and activate the Remote Base. (All frequencies in your Remote Base will be simplex frequencies and none will use a + or - offset shift - this is Very Important.) 4. Program your handheld with 145.370- and 444.6125+. a. To access the repeater directly, transmit on and receive on the 2M side as normal. b. Once you cannot get the repeater directly, but can still hear it, and you are in range of your car, which is in range of the repeater, with it's more power and better antenna system, transmit low power on 449.6125 Your car will hear this and will relay your voice out on 144.770, which happens to be the input of the 145.370- repeater, your message will make it. After transmitting listen on the 2M side for any traffic. c. So far IDENTICAL TO THE UPLINK ASSIST d. Once you cannot hear the repeater on the 2M side of your handheld, switch to the UHF side, listen and transmit there only. You should hear any 2m repeater traffic on the UHF side of your handheld, this is being received in your car as 145.370 and is being relayed to you directly on UHF on 444.6125, complete with all ID and all other repeater messages. e. To transmit back just transmit on UHF on your handheld, it will switch to 449.6125, the Remote Base Uplink in your car will hear this and the car will transmit on 144.770 which is the input to the 145.370 repeater, and you will be heard on 2M. NOTE: You still have "full break-in capability". --------------------------------------------------------------------------------- I fully recommend using CTCSS (PL's) to guard against interference. Do not use 88.5, which is a default PL for many radios, 100.0, which is too easy to remember, and 123.0, which is the PL which all repeaters in Cincinnati are supposed to be using. Some are transmitting a PL only, not required on the input. BTW your Remote Base may pass a PL through, but it will not re-generate a PL while in the Remote Base Mode. Many amateur radios will allow a PL to pass through, you have to test yours. This is a non-standard function, which means it might or might not work. Most commercial radios will not pass through a PL, as they are designed to receive a PL from a mobile station, identify it, filter it out of the audio, as they pass 300-3000 Hz only and cause a more stable PL to be transmitted from another board. Most amateur radios only have one PL board which can do receive or transmit, not both at the same time. For information on how to provide a uplink assist which is "invisible to the operator" say for the people working at the scene of an emergency back to the EOC, just like I did at Fernald a few years ago. They noticed that sometimes they were falling out of the repeater, but the EOC heard them anyhow. They did not find out just how their signal was getting to the EOC until after the exercise was over. Or for more information on remote basing - contact us at MONIX. http://www.monix.net 021121