[Premium-Rx] Fw: Farady Shielding

[Michael O'Beirne]

Hi you knowledgeable gentlemen,

Building an RF tight room or a Faraday cage seems to me to be a waste of
time unless you are doing sensitive receiver testing.  Any decent
professional receiver will already be well screened.  Even old sets such as
the Racal RA17 and ITT-Mackay 3010 are a mass of heavy solid diecastings and
the power input and the HT and LT feeds are well filtered.  Adding a decent
external power filter and good RF earthing are obviously sensible but surely
most of the QRM around is inevitably going to be picked up from the aerial
itself and fed in to the receiver unless you are at a professional site with
the aerial farm some distance away from QRM sources.  At a city site,
however, you simply cannot avoid the QRM unless you own the whole
district!!!

I suspect that many embassies use auto-tuned loop aerials on the roof
because these have good immunity to man-made QRM as well as being compact.
I have seen a beauty on the roof of an Arab military mission building in
London.

More difficult in some cases is when you are operating several receivers at
the same site.  There you have potential problems of LO radiation
interferening with other receivers.  The ancient HRO was a prolific leaker
of its LO.  Here in UK the third harmonic could cause TV QRM when the old
Band 1 TV was in use (around 45MHz).  The Collins TCS receiver was another
source of LO radiation, in fact sufficiantly bad that the Royal Navy's regs
required the set to be switched off during periods of radio silence.  The
Eddystone 880 was specifically designed in the 1950s for microscopic LO
radiation - down to about 5 microvolts - almost certainly for a government
contract, and as you know, the LO radiation is inevitably one of the
receiver specs nowdays.

73s
Michael
G8MOB
> 73s
> Michael
> G8MOB
> ----- Original Message -----
> From: "Steve Stutman" <steve at oceanrobots.net>
> To: "Michael O'Beirne" <michaelob at tiscali.co.uk>
> Sent: Friday, January 07, 2005 12:03 AM
> Subject: MagLoops
>
>
> > Hi Michael,
> >
> > Would be interested in John's data.
> >
> > Building some magloops now. Interested in any related info.
> >
> > Thanks,
> > Steve
> >
>