Hello,
I took back an old board coming from an IRReceiver and used it with
the software.
The interface is made of 2x AD831 with their output directly connected
to the sound card input (the internal amp of the 831 is wired for a
gain of 3)
The local oscillator is an AD9854 without any filter or amp at its
outputs. The drive level required for the 831 is -10dBm.
My first comments :
1- The noise level of my sound card at 48kHz is -130dB (read on the
display
2 - the calibration sound card was impossible until I put a 47k pot in
one of the 2 outputs, the amplitude control had a very small effect
before that.
The calibration was made at 10 100 kHz with a 10 110kHz LO.
Tha amplitude control was put at midscale and the pot was adjusted to
get a minimum (not very deep at this time).
Then the amplitude cursor and the phase were adjusted alternatively to
get a solid -70dB suppresion of the image.
The audio gain (control panel) is very low (close to zero)
3- The audio is nice despite the high level of noise on the bands this
morning
4 - The overall sensivity depends on the noise level and had been
measured at -130dBm with my HP generator (MDS) which is very good in
SSB band pass (2700 Hz)
The signal remains perfectly visible on the display and "seems more
visible than readible"
At -130dBm from my generator, the signal level on the display is -110dB
5- The noise increases severely close to the carrier. This is due to
the DDS phase noise I suppose.
The noise level at 0 is around -90dB on the display, so I choose a
20kHz offset to be in the best conditions
5- The denoiser is very useful but quite desorienting...,it really
cleans the noise from audio and listening is more easy.
However, there is a significant loss of audio level when it is IN and
the global S/N remains about the same. The audio gain (control panel)
has to be increase merely to recover the same audio level in the
loudspeakers.
6- Side band inversion is OK
7- Band pass :
The reduction of the band pass (ie CW mode) does not appear very
attractive, the audio sounds rough and the improvement is not obvious
in my opinion.
7- S-Meter
I suppose its calibration depens on the frontend but also depends on
the audio gain (control panel)
This is the chart I plotted, denoiser OFF :
S1 = -87 dBm
S2 = -76 dBm
S3 = -67 dBm
S4 = -60 dBm
S5 = -54 dBm
S6 = -47 dBm
S7 = -40 dBm
S8 = -33 dBm
S9 = -26 dBm
"S10" = -20dBm
All comments are welcome.
Best regards
Gérard/F6EHJ
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