At 07:16 12/04/00 +0000, you wrote:
All at G3WSC/P.
Nice signal yesterday early evening. Very strong but you had key clicks
on the LF side of the signal on 136 khz covering a total of 250 hz. I
expect the switched mode class D amplifier is the problem with such a
high tower plus at least 1w erp.
G3WSC was 9+10dB at my location, I had no problems copying a DL, who was
only 529, calling at about 400Hz down while G3WSC was transmitting. The
'magic' of this might be the use of a attenuator between antenna and RX,
adjusting attenuation until the weak station is just readable. This avoids
a lot of IM in your RX.
At about 350km from G3WSC I could not notice any clicks, so their signal
seemed OK to me.
He does not have any key clicks, because his signal is generated as
sine wave, then a valve amplifier and pi filtered output.
Key clicks are not caused by non-linearities of an amplifier but by the way
the signal 'rises' and 'falls' when keyed. So it does not matter if your PA
is class A,B,C,D,E or whatever. Also low-pass filtering will not affect
these 'clicks', although it is essential to reduce the harmonic contents of
the signal (but that is another story).
Further the class of an amplifier is independent of the 'active element'
used, one can make a perfect class A amp with bipolar transistors or FETs
and a class C or D with valves.
To the G3WSC/p gang : great job and very interesting. With this big antenna
(and known efficiency) it is possible to generate a rather exact ERP,
interesting to know what signal 1 Watt ERP produces.
BTW : the WSC signal was about 5dB down on the 7S6 signal some time ago, so
considering the difference in distance the Swedish guys must have been
running an ERP in the 100W range.
73, Rik ON7YD
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