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Re: LF: AF-filters and CW versus SlowCW

To: [email protected]
Subject: Re: LF: AF-filters and CW versus SlowCW
From: "Mike Dennison" <[email protected]>
Date: Thu, 1 Apr 1999 14:51:23 +0100
In-reply-to: <[email protected]>
Organization: Radio Society of Great Britain
Priority: normal
Reply-to: [email protected]
Sender: <[email protected]>
>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


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