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
|
