[hpsdr] Penelope Performance Measurements_3

[hartfuss]

Hi all,
last night I continued my performance tests with Penelope, trying to 
determine the carrier and sideband suppressions. As before in the IMD 
measurements I used the Rohde&Schwarz "ESPI" type analyzer and 
additional 20 dB of attenuation in between the DUT and the spectrum 
analyzer.
Penelope was driven by the PowerSDR internal two-tone signal to 500 mW 
PEP output at 3.7 MHz LSB. I was unable to see besides the IMD products 
any other lines in the USB even with averaging for a few minutes. I am 
concluding that sideband suppression is better than about -95 dB which 
corresponds to the analyzer's noise level under the conditions described.
The residual carrier, however, can still be resolved with this test 
equipment. It is down -90 dB referred to 500 mW PEP.
The residual carrier amplitude is within 1-2 dB independent of drive 
level, which means at 20 dB smaller output level it has almost the same 
amplitude and suppression is then "only" -70 dB.

I repeated also IMD3 measurements at 3.7 MHz and measured IMD3 as 
function of output power.
At 20 dBm (100 mW) in each of the tones (400 mW PEP), IMD3 power is 
about -72 dB down, monotonically decreasing further, approaching the 
noise level of the spectrum analyzer by reducing the output power in 
each tone to 13 dBm (20 mW), corresponding to 80 mW PEP.
At this level IMD3 is -83 dB down compared to one of the two tones
(-89 dB /PEP).

Qualitative modulation tests comparing the "sound quality" under 
otherwise the same conditions of audio processing (AT4040 microphone, 
dbx preamp and dbx EQ) of the SSB signal with 50 to 3650 Hz ESSB 
transmit profile when going with the Mic input
1. directly to Penelope
2. via Janus
3. using the Flex-5000
gave no audible difference. Audio quality was excellent in all cases.

Great development!
Thanks, Hans, DL2MDQ.