[hpsdr] Penelope Performance Measurements_2

[hartfuss]

Phil,
refering to your Penelope performance tests I was wondering  why my IMD3 
measurements conducted at 3.7 MHz are much better than those you 
reported for 14.2 MHz.  The TI OPA2674 data sheet (page 14, figure 10) 
shows a significant frequency dependence of the 2-tone 3rd order 
spurious level of this amplifier used in the final stage of Penelope.
To verfify this dependency I repeated my measurements at a PEP level of 
about 300 mW and KD5TFD's latest SVN, using the PowerSDR build-in 2-tone 
test generator. The measurements were done using the R&S ESPI spectrum 
analyzer and 20 dB of attenuation in front. The dB values given refer 
the D3 level to one of the two test tones (not PEP).
Below are the results listed for D3 only, however, beyond 7 MHz D5, D7 
etc are clearly visible and are becoming stronger with frequency. I 
include the level of the higher intermodulation products obtained at 
28.5 MHz.

1.8 MHz: -74 dB
3.7 MHz: -72 dB
7.05 MHz: -65 dB
14.2 MHz: -58 dB
21.25 MHz: -52 dB
28.5 MHz: D3: -48 dB, D5: -58 dB, D7: -64 dB, D9: 69 dB;

With greetings and my best regards, Hans, DL2MDQ.



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