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LF: Re: Re: Carriers, remote RX, antenna

To: [email protected]
Subject: LF: Re: Re: Carriers, remote RX, antenna
From: [email protected]
Date: Sun, 26 Aug 2001 08:38:04 EDT
Reply-to: [email protected]
Sender: <[email protected]>
Hi Larry, Bob, and the group,

Thanks Larry for the info about your remote RX. It is very helpful for me to
hear someone else is using such a system with such good success. The main
problem here is that the club station DF0WD is not private property, it is
located on a public soccer field which is visited by hundreds of very curious
people. Close to this location are some fields and small woods, where the
remote RX could be installed ("close" meaning a few hundred meters). I
thought about building a small unit which could be camouflaged as a milk-can
or similar.
For several reasons, it's impossible to use optical fibre cable for the
remote RX.
The suggested SAW filter for 433 MHz seems to be an alternative for building
a simple and low-power TX. I have a very small ultra-low-power transmitters
for 70cm here (used to control lamps etc), but it seems to use On/Off-keying
for the digital modulation. The oscillator uses an SAW filter and -as it
seems- cannot be frequency modulated. Using phase modulation at 433MHz will
certainly not work because the modulation index would be too low for a good
SNR. Any suggestions  ?

To Bob, ZL2CA:
> Several ZL amateurs, including myself, have had quite good results in
> minimising LF QRM by using an active whip antenna sited somewhat
> away from houses (and their mains wiring).  Attention needs to be paid
> to RF isolation of the power supply for the antenna, and using balance
> RF transmission lines, otherwise the mains QRM can still get to the
> antenna via the shack and feeder.  5 metres or so separation of an active
> whip from house wiring can greatly reduce the mains-conducted QRM,
> but is still good for receiving wanted DX signals.
Thanks for this info as well. I have never tried an active whip antenna,
because I thought the QRM mainly travelled via E-field; so I favoured a
loop-type antenna with the benefit of nulling out at least one of my enemies
I have used several kinds of RX isolation, the best was a large ring core
covered with foam tape before winding the primary and secondary coils to keep
the capacitance as low as possible. Both coils were separated from each other
as far as possible, but the remaining capacitive coupling was still too high.
(I checked this using battery power and disconnecting the mains  supply
outside the clubhouse).
BUT - I didn't use a balanced line from the RX loop to the RX, just 50 Ohms
coax with two isolation transformers as described above on both ends of the
cable. What kind of balanced RF lines do you use Bob ? Is it shielded with
two center conductors or is it unshielded like the old "240 Ohm" cable ?

Kind regards, and thanks for all info.
 Wolf DL4YHF.
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