Re: LPF-Control PCB TX Logic at U3 & U7
¿ªÔÆÌåÓý
Oliver,? I was having some kind of feedback/oscillation problems a couple of weeks ago and traced it back to the T/R switch also.? The relays and associated parts all checked out but, when I removed the 3-"0" ohm resistors that were there in place of?the Low
Pass Filter (160M) and inserted the parts for the LPF the problem stopped.? I wanted to go back and remove the filter parts and place just two "0" ohm parts at c14-c16 and a single cap at c-15 but never did.? Wondering if the oscillation problem boards have
the "0" ohm resistors and not the LPF filter in place.? Maybe, I will try it later just thought I would mention what I had, when you suggested a possible feedback issue.
Rick, KN4AIE
?
From: [email protected] <[email protected]> on behalf of Oliver KI3P via groups.io <oliver@...>
Sent: Saturday, March 22, 2025 1:40 PM To: [email protected] <[email protected]> Subject: Re: [SoftwareControlledHamRadio] LPF-Control PCB TX Logic at U3 & U7 ?
The situation I think we might have is that both TX_BPF_SEL and RX_BPF_SEL are HIGH during SSB transmit. This lets a little bit of the transmitted signal leak through the TR switch back into the amplifier input through the BPF selection
stage, like this:
?
?
These two lines are controller by GPIO register bank A:
?
?
This register is set by the function call ; the code there looks correct and unchanged. Scanning the code, it all appears to be correct. Some judiciously placed statements like this will confirm:
Debug("Set LPF GPA state: "+String(LPF_GPA_state,DEC));
?
The fix that I implemented (major change to radio layout) to cure the short that caused the burning smell has created a display freeze issue, so I'm not able to test this myself right now.
?
?
?
?
?
|