Since last weekend a new QRP transceiver joined my shack I bought her used from a German HAM via the QRPFORUM community. The transceiver is one of the older projects from the DL-QRP-AG but still a neat little transceiver. It is still offered in kit-form from QRP-Project in Berlin.
Some measurements on the oscillators revealed the problem. RX Mixer Q4 4.915.742Hz - TX Mixer Q5 4.915.365Hz --> Delta 377Hz
I replaced the standard 207° potentiometer with a precision 10-turn version. For this I had to replace the case with a slightly larger one - only 3mm where missing :-/
Rereading this article I discovered, that this precision potentiometer must be about 37 years old! It was a present during my SWL days from my long passed away friend and elmer, Rainer Kiess DB7SS - r.i.p.
Spectrum analysis of transmitter signal
I ran a spectrum scan on my Mosquita to check for harmonics on the output signal.
|1||7.053||Main carrier. Abt. 37dBm what is 5W|
|2||14.056||1st harmonic. Abt. 37dBc below carrier. Too less. I must check this.|
|3||21.060||2nd harmonic. Abt. 58dBc below carrier. This is fine.|
|4, 5||Spurios. Abt. 60dBc below carrier. Also fine.|
|6||2.101||VFO signal. Abt. 62dBc below carrier|
|7||9.102||Carrier+VFO. Abt. 64dBc below carrier|