audio filtering & muting


From: Bruce Robertson (
Date: Sat Jun 18 1994 - 09:54:44 EDT

I'm almost ready to assemble my 30m vxo/rx with only a few outstanding issues.
Firstly, I have to decide whether or not to include the 5 watt power amp.
This is complicated by the fact that I can't measure the power out of the
2N3866 before the power amp with any accuracy. If it's putting out 1 - 1.25
watts, do you think that's enough for a first time qrp rig on this band?
This reminds me, I rewound a transformer and found that this increased current
into the rig, but didn't make my wattmeter/dummy load jump nearly at all.
I suspect the wattmeter is very non-linear, however. Question: is any increase
in current (& warming up of the 2N3866) likely to signify an increase in
rf power out?
Secondly, while the Sudden receiver (an NE602 and LM386 special) is working
fine, I'm a bit worried about the wide audio freq. response. (Practically
DC to dog-whistle.) A filter built around a '741 seems easy enough, but
given that the rx tuning is separate from the tx, can I get by without it?
Finally, in testing the tx & rx near each other, I found that the rx
naturally produces a whopping sig. when I xmit. Is there a simple audio
muting circuit I could apply to the LM386 or the possible 741 audio
filter before it?
Thanks & 72, VE3UWL
Bruce G. Robertson internet:
Dept of Classics Satius est enim otiosum esse quam nihil agere.
University of Toronto It's more fun to relax than it is to do nothing
                       at all. Pliny _Ep_ 1.9.8

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