[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Linrad Gain and Noise Floor
- Subject: Linrad Gain and Noise Floor
- From: VK2KU <clearmail.com.au; vk2ku@xxxxxxxxxxxxxxxx>
- Date: Fri, 28 Dec 2007 20:37:55 -0800 (PST)
I am shifting this to another thread since we have moved way off the
>If you make a graph of noise floor level as measured
>by Linrad vs gain you will find a straight line with
>a knee where the noise floor goes to zero.
>The knee is soft, it ranges over something like 20 dB.
>The statement that your noise floor should increase
>by 15 dB is valid only if it already is above the knee.
>Otherwise it has to increase by at least 15 dB above
>the level you would get by extrapolating the straight line
>below the knee. Use the RCF output shift to set gain in
>6dB steps and check the noise floor you get.
>Easiest if you change par_sdr14 with a text editor and
I tried this today both with the preamp power on and off,
though I think you intended it to be off.
Within the limited accuracy of my measurements, each change of 1 in
the RCF Shift gives a 6dB change in the Linrad Noise Floor.
With preamp off, noise floor runs from 39 to -2 as RCF Shift runs from
0 to 7.
With preamp on, noise floor runs from 54 to 13 as RCF Shift runs from
0 to 7.
The whole noise floor is Red when the noise floor is 54, regardless of
the setting of the 2 selective limiters, presumably because of my
value of 4000 for Selective Limiter Max Level.
No evidence there of any knee, so presumably I am above it.
However I did notice a "funny" in the main spectrum scale when I used
the arrows on the right to move the spectrum up to show below 0 on the
Instead of nice scale increments in fives, in one case I got a scale
24, 19, 14, 9, 4, -0, -5, -10
and in another slightly different scale position:
35, 30, 25, 20, 14, 9, 4, -0, -5.
Sorry to keep finding these little things!
Oh, Linrad version is 2.39.
You received this message because you are subscribed to the Google Groups "Linrad" group.
To post to this group, send email to linrad@xxxxxxxxxxxxxxxx
To unsubscribe from this group, send email to linrad-unsubscribe@xxxxxxxxxxxxxxxx
For more options, visit this group at http://groups.google.com/group/linrad