Using 900Mhz Maxtrac D37-B2 for simplex.

[ns0w]

Me and some of my ham buddies are trying to convert a number of D37-B2 Maxtracs for simplex use. We have replaced the filters and have the VCO's open. After some experimentation around 907Mhz it seems that both RX and TX happens on the left VCO - which I suppose is due to the fact that B2's does not have talkaround. I cannot have Rx and TX on the same frequency on one VCO with a 20Mhz tuning span and 39.150 IF - right? The only solution that I can think of would be to use the right VCO for TX. Although I am working above 902.5, the radio still uses the left VFO for TX. I was thinking of initializing the radio as a B3 model which has talkaround or force the right VCO for TX with the pin-shift by installing the 27K resistor between J6/8 pin 4 and 14. Will this work and which is the best way to go or should I just sell this to a repeater builder and get a GTX -

[rocketman]

I have messed with the D37's and B27's. personally, I would initialize the radio as a B3 so that the radio does the talkaround or simplex instead of adding additional stuff. In case you want to also use it for repeater use, forcing the radio to the right VCO will take that option away.
Dave

[ns0w]

Thanks for response and suggestions. We have the radios working on simplex where we want them. It seems it was using the right VCO for TX all the time - I was confused by the VCO test point (seems that you use the same test point for both the VCO's) and also by the fact that the voltage on pin 14 on J6 on the RF board sits at 3.8V all the time (RX and TX). Somewhere in the conversion instructions here on Batlabs I saw something that it should go to logic "1" (> 5v) on TX when using the right VCO. This does not happen from what I can see on the D37-B2 radios we worked on. I still have not located a 900Mhz service manual - but there is hope. Well, we have the process down and have successfully repeated it on 6 radios.