Miss Mosquita - a new girl in town

Since last weekend a new QRP transceiver joined my shack V1 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.


The transceiver works pretty well, but the sidetone was far too low - about 400Hz - even for an OM like me to deep. 100pF Sidetone.

Some measurements on the oscillators revealed the problem. RX Mixer Q4 4.915.742Hz - TX Mixer Q5 4.915.365Hz --> Delta 377Hz

After changing C11 on the RX mixer from 100pF to 47pF the sidetone is now about 650Hz - same as on the other transceivers in my shack: 56pF Sidetone. The change in the passband can also be seen.

100pF 100pF Noise 47pF 56pF Noise

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 :-/

V2 1 V2 2


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

19 03 2017 08 44 03

I ran a spectrum scan on my Mosquita to check for harmonics on the output signal.

The measurement was done using an Siglent SSA3021X and the FA power attenuator.

Peak   Frequency   Comment
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