It could also be possible that the transistor might be short, permanently operating the said relay.
On Sun, Jun 24, 2018 at 10:14 AM, Jerry Gaffke via Groups.Io
<jgaffke@...> wrote:
If K1 welded up inside such that there was no path from pin 12 to pin 14 when the coil was not energized,
then the receiver would not get RF from the antenna and be deaf.
K3 does most of the antenna T/R switching, during receive it passes signals from the antenna over to K1.
During receive, K1 is not energized and pins 12 and 14 are connected, sending RF up into the 30mhz LPF at L1,2,3,4
During transmit, there will be some capacitve coupling between K3 pin 12 and K3 pin 14 even though those contacts are open.
So during transmit, K1 shorts pin 12 to ground to avoid feedback from antenna back into Q90 creating an oscillator.
Jerry
On Sat, Jun 23, 2018 at 07:48 pm, Joel Caulkins wrote:
The receiver would not work until I changed the relay. I was wondering about that myself, why would the absence of TX voltage cause the receiver not to work unless a RX voltage was missing also. I checked all that I saw on the schematic and they were all there. Don¡¯t know.
