The connections don't have to be diodes at all to cause trouble. Although
that is one possibility, there's another effect.

The fence will have RF current induced in the conductors - posts, rails and
links. These currents can come from any transmitter. After all, it is just
like any other antenna, except that it isn't connected to a receiver. Any
and all conductors that exist are picking up RF currents just like the ones
we call antennas. There's nothing special about those conductors we call
antennas (in this regard). It is why the Yagi works.
Where two conductors touch, you may or may not have current through the
joint depending upon the RF field. As these conductors make and break
contact, lets say in the wind, the current through these connections will
also most certainly change. This changes the current in the conductors and
since these currents cause some small amount of radiation, the resulting
radiated field will change also. Because your antenna is near to these
unintended elements and can pick up a significant amount of signal from
them, two effects can result.

1- When you receive, this can cause noise in your receiver. What kind of
noise? The easiest to understand would be if you have a local radio or TV
station. The currents caused by this station can be rather high and
therefore significant. Becuase the field in close proximity to this "dirty"
antenna is changing in a noisy manner (described above), due to the bad
connections, the signal as seen from this transmitter is also dirty, or
noisy. It looks just like modulation, noise modulation extending, in the
two sidebands, away from the carrier. To a receiver this looks just like
noise modulation on the transmitter.
The bandwidth of this kind of noise can be rather startling. A 10 MHz
transmitter can have noise easily extending up into the GHz region. If the
field from the transmitter is strong enough, the noise can cover what you
are trying to recieve. I had to troubleshoot this problem at 150 MHz once.
This can be duplicated by listening slightly off channel of a signel. A
2M repeater will do. Just go 5 or 10 KHz. If you are very close, you may
be able to tune further off. Now just take any two conductors of a few
inches or more in size and rub them together within a few inches / feet of
you receving antenna. I call this "the screwdriver effect" because I first
saw it when a screwdriver was drawn across a chassis & I heard noise.

2- On transmitting, you have the same situation, except YOU are the close
transmitter and your signal can have this noise modulation. I lied. Its
the same effect.

On calm days, perhaps you'll be ok.... perhaps even on windy days. RF is
fickle.

On the Program Apollo ocean ships used for monitoring communications around
the globe and spacecraft recovery, chain used on parts of the deck railings
was found to be the source of noise which modulated the multi-Kw HF
transmitters resulting in degraded Radar performance! I think it initially
made the radar useless.

--
Steve N, K,9;d, c. i My email has no u's.




"Crazy George" wrote in message
...
All the individual "loose" connections at the joints are notorious for
creating intermod. It may or may not be a
problem in your case. For receiving, you may hear numerous broadcast
station harmonics and intermod combinations. When
transmitting, your signal will likely be "dirty" and you may get BCI and
TVI complaints, even though your transmitter is
clean. Sort of like putting a thousand diodes in the antenna.

--
Crazy George
Remove N O and S P A M imbedded in return address
"Jack Twilley" wrote in message
...
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My yard is adjacent to a large park. The park's border with yards
like mine consists of a chain link fence that's in excess of one
thousand feet in length. The vegetation is such that I could run a
long wire about a foot over the top of the fence for a large part of
that thousand feet. Would the chain link fence cause negative
interactions? Would this be a receive-only antenna and not any good
for transmitting? I'd connect it to the random wire lug on my MFJ
Versa Tuner II to match it to my Kenwood tube rig.

Thoughts? Comments? Suggestions?

Jack.
(I'm going to try it regardless for receiving, but what should I
expect?)
- --
Jack Twilley
jmt at twilley dot org
http colon slash slash www dot twilley dot org slash tilde jmt slash
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