Hi guys. I've got myself an obsolete ex police radio from circa 1980 and retuned the transmit oscillator and multiplier stages via the trimmer caps to work on 433mhz. The radio originally worked between 450-470mhz recieve/transmit and the final pa stages aren't tuneable. It originally gave out approx 400mw of rf, but i've managed to get approx 150mw from it. My question is this: the final pa transistor gets quite hot. I test the transistor heat my using my top lip. The transistor isn't too hot to touch though. Will i be causing any harm to the output stages by running it slightly out of the designed frequency band, or will it be just fine? Also - will my final output transistor last in your opinion? For your information, the final transistor is a 40965 made by rca and it's operating in class c mode. Thanks in advance for any help. Regards, Damian.

 

When I've done similar mods in the past, I've changed or piggy-backed capacitors in the tuned power stages and sometimes antenna filter to improve operation in the ham band.

Increasing the cap values by about 10% should put you in the ballpark and give considerably better output.

 

Thanks for the reply Robert. Unfortunately - i can't gain access to the pa components as they're all modules that are difficult to access. Based on this fact, do you think i can cause any harm to the final stages by running them out of band. The original transmit frequency was around 465mhz and i'm txing at 433mhz. Thanks again. Damian.

 

Forgot to mention: i can send a schematic of this thing if it helps. It's all transistorised and uses no ic's, so should be a doddle for the experts out there. Regards. Damian.

 

Can you post the make and model numbr of the radio?

 

Hi Robert. The radio is a Burndept BE470 as used by the UK police circa 1980. There are a few images on the net, but no info. I have a schematic here that i could upload to an host but it's 14MB. Am i allowed to do that on this forum? Regards. Damian.

 

Not if that schematic carries a copyright.

 

Hi Damian, I got your message but can't reply. Can you try again & include your email address?