"Sal M. Onella" wrote in message
news:J9adg.27540$QP4.14620@fed1read12...

"Steve N." wrote in message
...


snip

Another concern (though I have no experience with roofs, just autos) is
the
intermitent contact (as opposed to a rectifying junction, as Richard
points
out) that is possible. If there are joints that can make and break, say
in
the wind, you may have noise generated. Chain-link fences would be
susceptable to this as well. Wether or not it produces noise in your
receiver, I would think, is rather unlikely, unless you were somewhere
near
a broadcast station or another ham for reasons described next.

It's mostly a problem if you are running two or more rigs at the same
time. Your 2M packet rig could interfere with your 2M ragchew.

Yes, the "offending" transmitter needs to be in close proximity so that

1- the offending junction(s) are sufficiently illuminated by it to produce
strong enough sidebands to be a problem in the offended receiver.
2- The offended receiver has to be close enough to be offended by the levels
involved.

The Navy, for whom I work, bonds (or isolates) everything ...
Every spark, no matter how small, is an RF generator.

It isn't necessarily a spark, in fact probably infrequently sparks unless
you're dealing with higher power. It goes like this.

Both sides of the offending junction are picking up RF. They are
conductors, so there are RF currents flowing. When there are RF currents
flowing you have radiation. As the junction opens and closes, the RF
currents change. When the junction is making contact, current can flow -
when disconnected, current can not flow (pretty much; let's not get into the
capacitance thing). The changes in current with a noisy contact will mimic
the "noise" of that contact. The radiation will therefore mimic that noise
also. That noisy radiation will sum with the original, desired radiation.
This, in effect, modulates the radiated signal after it leaves the
transmitter. If it is sufficiently high level and the receiver able to pick
it up, you have a problem..

Chains
are awful. We hate chains.

Perhaps you know, but during the Apollo space shots, there were NASA ship at
sea which had really high power HF transmitters. They would interfere with
the radars. It turned out that the deck chains were the offenders. Whether
or not there were sparks, it shows just how wide band the noise can be.

Gee... What's the resonant frequency for a deck chain link?

73, Steve, K9DCI (USN, but never on a real ship untill after I got out)