Hi! Fred.
When you are next in the UK let me know and you can attack my
installation!!!!
Yes, on Bill Bells' recommendation after walk around tests with hand held RT
set with the engine running I've a considerable improvement by painting out
the cowl with a nickle based paint but the problem still with my radio is
that the bloody auto squelch control is being activated on the same receive
frequency as most air traffic control frequencies and takes the required
messages out with the trash. Viz:- if I "pull to test" the auto squelch
control is dumped and I can "read" receive messages from afar but after a
while the other trash gets very tiresome and inclined to drive me
skitsu!!!!(Not the best of attitudes to be in when flying?). I have had the
stupid thing back to "authorised installers" who claimed it is set "to the
book" and would only slightly adjust it at my insistance so where to now?
(there is no squelch regulate facility either you have it or you don't !)
regards
Bob Harrison G-PTAG
PS Alfred Buess do you understand all this now ?!!!!!!
-----Original Message-----
From: forum-owner@europaclub.org.uk
Subject: Re: Bundling of coax cables
Hi, Bob --
If yer referrin' to ignition noise, that's radio freq interference
(RFI), which don't care about no steenkin' _electrical_ grounds! If
we look at a marker beacon "sled" antenna, it's grounded one end, with
the antenna tap clamped at a proper point along it's length.
Aumiminum is nonmagnetic, but that's the magnetic part of EMI -
aluminum foil is used as a coax shield for better RFI shielding verses
EMI, where braid is better. If one metalizes the firewall only, to
block ignition noise, it will be only partially effective, since the
RFI merely bends around the "plate," which in free space can even
reradiate the RF. If have read where it's thus effective to also
metalize the inside of a fiberglass cowling with a conductive paint,
enclosing all in a box.
Separate grounds for electrical items isolate the ground from noise in
a "main" ground cable that's carrying everybody else's contributed
noise. The only items of concern I believe are mic and headphone
audio due to their signal/noise ratio issues, where one might shield
both the hot and ground wires. Either in separate shielded wires, or
twisted 2-conductor pair inside of a shield, with shield grounded only
one end in both cases (at box in panel).
Another possible trouble spot are sensor wires for instrumentation -
another candidate for shields. Yesterday I opened up the little sensor
module for an automotive temp gauge, to modify it for the Rotax
sensors. It's design to deal with stray pickup stinks (for A/C use),
and 1 lousy millivolt is good for a 1/8" of needle error!
[Experimenting with cool gauges - only 2" round, 270-degree linear
needle sweep, orange backlighting through only the white parts of the
dial].
Best,
Fred F.
Bob Harrison wrote:
>
> Hi! Alfred
> Not being a "pro" with this "wire bound water" called electricity !!!!! I
> wasn't going to reply
> especially since you have had a good responce, however I'll repeat what I
> said to another enquiry recently on this forum. If I had my "time over
> again" I would ensure that I have a completely separate system for
> "grounding" every concievable item back to the engine or battery direct
and
> so ensure that the "negative" part of all the power supply circuits are
> completely separated from the "grounding" circuit with their own circuit
> systems.
> Someone would have done me a favour to explain there are two types of
return
> ........ !!!!!!
> Also remember that aluminium has no capacity to shield magnetism ,like if
> you put a sheet of metal across the rear of the bulkhead it needs to be
thin
> gauge stainless, or you'll need to buy 5 litres (minimum order) of Nickle
> Based paint at about 200 a go !!!!
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