rf pa stage query

Discussion in 'Wireless & RF Design' started by Damo666, May 20, 2010.

  1. Damo666

    Thread Starter Member

    Aug 25, 2009
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    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.
     
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    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.
     
  3. Damo666

    Thread Starter Member

    Aug 25, 2009
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    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.
     
  4. Damo666

    Thread Starter Member

    Aug 25, 2009
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    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.
     
    Last edited by a moderator: May 23, 2010
  5. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    Can you post the make and model numbr of the radio?
     
  6. Damo666

    Thread Starter Member

    Aug 25, 2009
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    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.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    Not if that schematic carries a copyright.
     
  8. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    Hi Damian, I got your message but can't reply. Can you try again & include your email address?
     
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