The receiver gets RX_IN from Q508 in the upper middle of the final page of the schematics (page 5).
Q508 is where the transmitter is blocked from the receiver, though there will still be
a very strong signal on RX_IN when transmitting.??
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The receiver is on page 4, RX_IN goes into IC408 which steers the signal into the appropriate band pass filter,
IC402 selects the output from the appropriate band pass filter and has the received signal coming out on pin 9.
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So your SDR receiver could grab RX_IN, or it could try grabbing IC408 pin 9 and get it after all the local
AM broadcast band stations and (most of) the other amateur bands have been filtered out.?
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A buffer is a good idea, driving coax to your SDR receiver.
Mostly because you don't want a bare wire picking up other crud from the SMPS's and such.
No buffer would probably work fine, an extra 50 ohm coax load on RX_IN would drop the received signal
for the QMX by maybe 3dB, or half an S unit.
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You might want to use the "RX" signal on page 5 to desense your SDR receiver somehow,
perhaps by clamping the output of your new buffer when "RX" is logic low (0v).
"RX" goes low when transmitting, logic high (3v) when receiving.
Seeing some of the transmitted signal on the SDR could be a good thing,
it will tell you exactly what the receiver is tuned to.
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Your SDR receiver will inevitably see a very strong signal from CLK1 and CLK2 going into IC403
a few KHz away (12 KHz?) from the received signal.? Since they are at the same frequency?
but 90 degrees out of phase, they will be seen as a single signal.
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Using a cheap RTL-SDR type receiver for your panadapter might be sufficient.
If it works well, I'd expect such a solution to be very popular with QMX users.
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Jerry, KE7ER
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On Fri, Feb 21, 2025 at 07:15 AM, <410733@...> wrote:
Let's summarize my requirement: I'd like to have a second independent SDR-Receiver while QMX is in RX. I am very used to that feature and I don't want to miss that when working with the QMX. I will share my experience (solution?) here, I thing that might be interesting for other users, too.
