Hi Hugh they can create horrendous RFI if you are not careful. The ones used
for TV distibution "may" be better......the good ones are notched at the
amateur bands and being for digital levels dont use AGC.
Alan
G3NYK (who moonlights on the EMC committee)
----- Original Message -----
From: "LineOne" <[email protected]>
To: <[email protected]>
Sent: Tuesday, October 11, 2016 8:38 PM
Subject: LF: Audio link
To avoid having laptop running in the shack, which occasionally produces
some QRM, I can send received audio from the shack to a desktop computer
in the house on a twisted telephone pair. This works but any wire
connection between shack and this desktop introduces some spurious signals
on 136khz even if I use an audio isolating transformer.
I bought a cheap digital baby alarm, disconnected the microphone and
padded down the input to the sender's microphone pads including a
potentiometer to adjust the input. Audio seems to reach the house OK but I
think the automatic gain control in the sender has a strange effect with
some sort of attack time allowing the start of, say, an Opera signal to be
seen but not the whole of a pulse. The background noise does come up
slightly between signals also. Nevertheless I can hear the audio normally
and did send a decent Opera report for G3XDV this evening. WSPR doesn't
seem to decode at all but I will persevere tonight before abandoning the
project. Has anyone else tried these baby alarms nad managed to overcome
the agc?
My next attempt is likely to be a 36kHz PWM laser link which will take
some time to build.
73, Hugh, M0DSZ
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