Message-ID: <38F422C1.A543FFD1@netscapeonline.co.uk>
Date: Wed, 12 Apr 2000 07:16:17 +0000
From: "g3kev" <g3kev@netscapeonline.co.uk>
Organization: Netscape Online member
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To: "rsgb" <rsgb_lf_group@blacksheep.org>
Subject: LF: G3WSC/P acty
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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. If you intend using more power out as
you suggest then more rf filtering is essential plus using an amplifier
in linear mode or use a valve linear amplifier, otherwise you will
render the band inoperative for others
Dave MM0ALM was also on the band yesterday at the same time and his
signal is marginally stronger than you and he is further away from
me.  He does not have any key clicks, because his signal is generated as
sine wave, then a valve amplifier and pi filtered output.
Square wave generators/dividers and class D/E amplifiers are fine for
small antennas and low erp but NOT SUITABLE for larger antennas and high
power. An abundance of LPF and BP filters might help to clean up the
signal. 
With my antenna system I use 3 cascaded 5 pole LPF FILTERS to overcome
this problem when using a class D mosfet amplifier. Design data is
available in the ARRL h/book using T-200 cores, and other alternatives. 
Good luck with the experiment but keep the signal clean so avoid
swamping others on the band, and check your harmonics especially odd
order, you might get a surprise at the intensity and surface wave
propogation of these harmonics on these low frequencies. 
de G3KEV