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- Subject: [Linrad] Progress
- From: Dave Sublette <arrl.net; k4to@xxxxxxxxxxxxxxxx>
- Date: Tue, 14 Apr 2009 14:51:11 -0400
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.
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