The LO leakage of LP-PANs after serial number 200 is about -120dBm. Earlier serial numbers had a bit more leakage, but this is easily fixed by changing the value of C40 to 0.001uF. -120dBm is overkill for LP-PAN's intended purpose, but connecting LP-PAN directly to a receiver (P3) tuned to the LO frequency changes things a bit.
I have run some tests to simulate this situation. First, I connected an LP-PAN directly to a receiver tuned to the LP-PAN LO frequency (8.209MHz for most units, 8.215MHz for the first couple runs). I verified that the leakage was in the -120dBm range by comparing the received signal to my calibrated HP signal generator. Then, I connected the second receiver, LP-PAN and K3 together using a 3dB hybrid splitter . This is reportedly what the P3 uses to split the K3 IF signal.
I could detect nothing on the second receiver at the LP-PAN LO frequency. This makes sense since the hybrid splitter has an isolation spec of -25dB between output ports, which should provide an LP-PAN signal of about -145dBm at the receiver input.
If you make the change to C40 and if the hybrid in the P3 is working as mine does, you should see nothing from the LP-PAN. I repeated the test using a couple different LP-PANs, and I also tried a couple different models of Mini-Circuits splitters. The results were consistent.
BTW, the LP-PAN preamp kit adds another 15-20dB of LO isolation, and lowers the LP-PAN NF to 7dB to help offset the additional loss of the splitter in the P3.
73,
Larry N8LP
VE3NFK wrote
Yes, Alan
an LP-Pan
and yes that is where the spike comes from...
I checked Brett's suggestion that the in/out might be backwards.. but it is fine.
So - now I need to find out how to stop the leakage.
73
John VE3NFK
Locked
