[hpsdr] Penelope sound quality

[Jarl Risum]

Tokio,

Out of curiosity I took some measurements on my HPSDR setup to get an idea
of the S/N from my (TAPR) Penelope. You should have similar values in your
setup when using a low-noise mike amplifier.

At 500 mW out from Penelope I measured approx. 58 dB S/N when using a 1 kHz
tone from an external audio generator as compared to the noise level when
the generator was removed. Test frequency: 3,7 MHz. The signal was observed
on a Spectrum Analyzer with a 30 Hz analyzer bandwith.
In my setup I use the K5TFD 22 aug 2009 PSDR, Ozy FX2 2009 05 24, Ozy:16,
Mercury:27, Penelope: 12,  Initozy11.bat set to 0x14 and mike gain set to
15.

I have to add that I am very impressed with both the receiver and
transmitter-performance of this HPSDR setup. With the internal two tone test
I measure an IMD below 75 dBc at full output from Penelope (@3,7 MHz). After
Penelope I use a fixed attenuator of 22 dB before amplifying the TX signal
to 100W in a PA/LPF "borrowed" from an IC-756. Even after this rather old
bipolar amplifier I get an IMD of approx. - 40 dBc which I still think is a
remarkable figure at this power level and 13 V DC feed.

Any chance that you have RF into your audio circuit ? I use plenty of
ferrite on all small signal cables.

73's from OZ9MO / Jarl
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