willbartlett
Member
Hi All.
So, I picked up a couple uhf-lo P25 7100 system radios at Dayton last year. I' ve been able to move them to to 440-450 with minor tweaks to the VCO coils accessable under the stickers on the top of both the tx and rx vco. In RX, the radio gets progressively more deaf as you go higher in frequency, but not more than 3db down from nominal expected sensitivity vs. my EFJ5100. I'll pull the RX BPF assembly and revork it later.
The RX vco seem unconditionally stable up to 450, but I'm having an issue with the TX vco.
first off the radio seems to be a bit low in frequency in TX, 600hz with one radio and 800hz with the second.
The transmitter will come on upon PTT, and will stay on for approximately 20-30 seconds, at which time the transmit LED will go out and RF carrier dissappears. If you press the PTT immediately, the radio will do nothing. No Synth unlock, no error, simply nothing. Waiting 3-5 seconds will result in the radio transmitting again, but for no more than a couple seconds before dropping TX again.
The lack of error message is very odd. I would expect a synth unlock.
I'm tempted to depop the VCO ( I can handle that) and test it off the board to see if it's an issue, but is there more going on in the antenna switch/Low pass assembly?
I know that there is some TX power feedback going on there, but it doesn't look as though it goes any farther than PA power control. I'd expect to see a carrier at significantly reduced power bleeding through the PA even if it went into some sort of shutdown mode, but it looks like the TX is shutting down completely. is the power sense handed back to the controller, or is it a small closed loop independent of the rest of the radio?
I know this is fairly advanced stuff, but I'm real curious about this kind of stiff.
Will
So, I picked up a couple uhf-lo P25 7100 system radios at Dayton last year. I' ve been able to move them to to 440-450 with minor tweaks to the VCO coils accessable under the stickers on the top of both the tx and rx vco. In RX, the radio gets progressively more deaf as you go higher in frequency, but not more than 3db down from nominal expected sensitivity vs. my EFJ5100. I'll pull the RX BPF assembly and revork it later.
The RX vco seem unconditionally stable up to 450, but I'm having an issue with the TX vco.
first off the radio seems to be a bit low in frequency in TX, 600hz with one radio and 800hz with the second.
The transmitter will come on upon PTT, and will stay on for approximately 20-30 seconds, at which time the transmit LED will go out and RF carrier dissappears. If you press the PTT immediately, the radio will do nothing. No Synth unlock, no error, simply nothing. Waiting 3-5 seconds will result in the radio transmitting again, but for no more than a couple seconds before dropping TX again.
The lack of error message is very odd. I would expect a synth unlock.
I'm tempted to depop the VCO ( I can handle that) and test it off the board to see if it's an issue, but is there more going on in the antenna switch/Low pass assembly?
I know that there is some TX power feedback going on there, but it doesn't look as though it goes any farther than PA power control. I'd expect to see a carrier at significantly reduced power bleeding through the PA even if it went into some sort of shutdown mode, but it looks like the TX is shutting down completely. is the power sense handed back to the controller, or is it a small closed loop independent of the rest of the radio?
I know this is fairly advanced stuff, but I'm real curious about this kind of stiff.
Will
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