Scott, It may be technically possible, but there will be issues:
(1) The tail of the distant repeater will prevent you from breaking into a net or conversation, except at moments when the repeater is allowed to drop by other users. If the repeater encodes a CTCSS tone only when there is a valid user on the input, you can use CTCSS-decode to solve that problem. The VHF radio monitoring the repeater's output will release the UHF transmitter when the user on the input unkeys, allowing you to break in before the tail drops. (2) Transmitter duty cycle. If the repeater stays busy, you could overheat the transmitter in the UHF mobile. (3) Legal ID and control. The UHF transmitter in your vehicle will not be identifying with your callsign, which is required. If the vehicle is not close enough that you could reach it quickly, you cannot consider it to be under "local control," and would need to configure it like any other repeater in this regard. I use a dual-band handheld, so I can receive the VHF repeater directly, and use the mobile only to repeat my QRP outbound UHF signal at full power/good antenna on the VHF repeater's input. I set my Alinco dual-band mobile to repeat only UHF-to-VHF, not bidirectional. That way, my periodic ID on UHF also goes out on VHF. The Alinco has extremely clean, flat audio on repeat, and nobody on the VHF repeater can tell I'm being repeated in. I never get more than a minute from my vehicle at a dead run, (comparable, I suppose, to the time it would take to run to a traditional repeater control point in your home if you were caught in the porcelain lounge,) so I consider it to be under local control. I use CTCSS on an out-of-the-way UHF link, and have never had an issue with interference or unauthorized use during a public safety event, etc. Some mobiles with crossband repeat capability (like my Alinco DR570T) require creativity in locking out bidirectional operation. Others have built-in programmable ID-ers to satisfy the need for ID on the UHF return. And many of the early ones simply built in the bidirectional function with no provision for ID, Part-97-be-damned. You'll have a world of choices rolling your own. If you could get the UHF side of the mobile repeater to be full duplex, it would be easy and slick - use a minimal repeater controller and flat-pack mobile duplexer, and just set it up like any other low-power UHF repeater with a VHF remote base. With a simplex UHF radio, you'd want to time any automatic ID to fire only when the distant repeater was being relayed, so you wouldn't be locked out of your own link receiver when it came your turn in the conversation. 73, Paul, AE4KR ----- Original Message ----- From: turboelesjuan To: Repeater-Builder@yahoogroups.com Sent: Tuesday, June 30, 2009 1:42 PM Subject: [Repeater-Builder] GM300 Crossband Ham repeater Bi-Directional A little background on what I'm trying to accomplish here; I'm a member of a Ham radio club but do not live in the city the club's repeater resides in. Due to the distance away I'm unable to access the repeater with a handheld radio without the use of a large external antenna and thats what I'd like to change. Installed in my vehicle is a Yaesu FT-8800 mobile that has ability to perform crossband repeat option. Example: A: 145.170MHz (-600khz offset) B: 438.500MHz simplex. I have a UHF Radio that I can set to 438.500MHz simplex to walk around my house and both TALK and RECEIVE traffic to and from the repeater. Basically the radio in my car has the ability to transmit and receive on BOTH frequencies. Heres my question: Is there a controller I can build which has the ability to control TWO Motorola GM300 mobiles w/16pin connectors the same way? Use each radio as a transceiver for bi-directional traffic? I already have both of the GM300 radios and they didn't cost 400$, which my 8800 Did. I want something perm. installed at my house so I can use a small UHF handheld on low power anywhere around my area to chat. Is this possible? Thanks!! -Scott
