[600MRG] Receiver bandwidth for WSPR

[Brian Pease]

I have AGC on because it is fast and seems to make no difference with 
WSPR.  The atmospheric noise experiment is running now.  I averaged ~10 
spots for each result.  At 400Hz BW I got -20.4dB avg followed by 3100Hz 
BW with -20.25dB avg followed by 400Hz BW with -20.0dB.  This shows that 
the s/n is virtually the same for both bandwidths in real-world conditions.
My receiver has a 20Hz bandwidth which I will try next, but as it is 
only 1/10 of the WSPR band, I predict bogus results unless the software 
is really clever.
On 3/21/2014 12:58 PM, Edward R Cole wrote:
> Just for comparison, my 80m noise floor using 2.8 KHz bw with K3 
> connected to inverted-V is running S3-4.  There are times it reaches S5.
>
> This is how WSPR and JT65 provide their super sensitivity.  They run 
> FSK with a maximum shift of about 180 Hz and use DSP filters to detect 
> the tones with under 10-Hz RBW.  SNR improvement by reducing bw from 
> 2.5 KHz to 10-Hz is 24 dB.
>
> Reduction of bw from 2.6 KHz to 400-Hz is exactly = 10Log(0.4/2.6) = 
> 8.1 dB
> Probably your s-meter lies! ;-)  Did you disable your AGC for this 
> measurement?
>
> But no doubt narrowing bw helps reject noise.  Best SNR will result 
> when Rx bw is same as signal bw.
>
> At 07:44 AM 3/21/2014, Kenneth G. Gordon wrote:
>> On 21 Mar 2014 at 9:50, jrusgrove at comcast.net wrote:
>>
>> > I don't know how Joe
>> > is making the calculation but I can tell you that bandwidth size 
>> does matter.
>>
>> Most definitely true. Even in the very simple, and MOST annoying, 
>> case I am
>> experiencing here: on 80 meters, my constant noise level at the 
>> moment is
>> 20db over S-9 when my receiver is in the "SSB bandwidth", about 2.6 Khz.
>>
>> When I drop the bandwidth to around 400 Hz, the noise level drops to 
>> S-7, a
>> difference of almost 40 DB.
>>
>> So, yes, bandwidth can make a HUGE difference in S/N ratio.
>>
>> Ken W7EKB
>>
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>
> 73, Ed - KL7UW
> http://www.kl7uw.com
>     "Kits made by KL7UW"
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>
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