Message-ID: <96A364FD96384B12A5C11912AFBFE844@gnat>
From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <57FD3F9F.80409@lineone.net>
Date: Tue, 11 Oct 2016 22:09:04 +0100
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Subject: LF: Re: Audio link
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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" <dhchurch@lineone.net>
To: <rsgb_lf_group@blacksheep.org>
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
>