[Linrad] Progress

[Dave Sublette <arrl.net; k4to@xxxxxxxxxxxxxxxx>]

I have added 10 dB of amplification to the direct input of the SDR-14 
for a total of 25 dB now. When I disconnect the 144 mhz signal from the 
input to the SDR-14, the main spectrum base line now drops 20 dB, I 
believe this tells me that I have enough gain ahead of the SDR-14 to 
have proper operation.

I experimented with RCF shift and found that a value of 4 gives a base 
line of +20 dB in the main spectrum display. If I read everything 
correctly, I believe this is the desired level.

The sensitivity of the LINRAD now appears to be very close to the same 
as the K2 receiver that I use to copy by ear. I can see signals on the 
waterfall as weak as I can hear them in the K2.


However, the audio demod from the baseband through the speaker is at 
least 10 dB less sensitive than the K2. In other words, I can copy 
signals on the K2 by ear and can see them, but they are not audible in 
the speaker of the computer, nor is there a visual indication in the 
baseband window. I am sure that the BFO tuning is identical on both 
because on stronger signals, the CW tone is the same. I use about 450 hz.

I think maybe this is due to not having a narrow enough filter setup in 
the LINRAD parameters. I am still struggling to understand all of the 
various FFT's and multiplying factors.


But, progress is progress and I am pleased to have gotten this far.

73,

Dave, K4TO


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