From: "Mike Dennison" <mike.dennison@rsgb.org.uk>
Organization: Radio Society of Great Britain
To: rsgb_lf_group@blacksheep.org
Date: Thu, 1 Apr 1999 14:51:23 +0100
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Subject: Re: LF: AF-filters and CW versus SlowCW
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In-reply-to: <37033EDB.63B6BC32@phonakcom.ch>
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> >From HB9ASB, JN36pt
> 
> Today I've made some comparisons of different Audio-filter settings and
> CW against Slow CW. All test were made blind and under real band-noise
> conditions with the main receiving antenna (low noise, no QRN) and a
> QRP-TX with a separate antenna. Here the main results (RX Harris RF590):
> 
> 1. Good audio filters with BW from 10 to 50Hz may give a 6dB advantage
> above the receiver without Audio-filter (250Hz IF). A 150Hz passive
> LC-filter was somewhere in between.
> 
> 2. There is no big difference between different BW in the range from 10
> to 50Hz. Although I got the impression that 10Hz was already to small
> and 20Hz the optimum in my case (Timewave DSP599zx)
> 
> 3. Slow CW with the Spectrogram (3sec dots) gives an advantage of about
> 10dB above aural CW with narrow audio filtering.
> 
> 4. I can confirm the optimal settings of Spectrogram found by Marco,
> IK1ODO
> 
> 5. There is no clear advantage of using longer dot-periods (e.g. 10s). 
> 
> 
> These findings differ from theoretical values but it proves how good our
> ear-brain detector works.


This is most interesting. I note that Toni agrees with Marco's 
assumption that there is no benefit using longer dots - I presume 
that the averaging control was altered to the optimum for each of 
these measurements, to perhaps 15 for 3s dots and 50 for 10s.

My experience on-air is that static bursts are very much reduced 
(or even eliminated) when setting the averaging control to a higher 
value. It would seem reasonable, then, for 10s dots to work better 
under noisy conditions than 3s.

Any comments?


Mike