RadioBanter - IMD observations

Bret Ludwig wrote:
..

Don't you have a generator?

Yes, but I hadn't expected to run into power levels high enough
to cause this in the "real world".

One word: attenuators.

Yep, got to love them.

The only thing was I didn't realize what was happening.
I had used variations of the
http://www.members.aol.com/WA1ION/nrants.pdf
for several years with no problems. It was only after making
substantial improvements
to my ground system that the RF levels got high enough to be an issue.

In the R2000 the attenuator is after the input matching transformer.

I have a nice selection of attenuators, but I didn't see the need.

I had three sources of IMD.
The MC 9:1 at the antenna coax interface.
The MC power divider.
The input transformer on the R2000.

Attenuators after the MC 9:1 would have only dealt with 2 sources.

Keep in mind the signals where pegging the R2000 S-meter. Pegged the
R8B and 7030+, drove the PCR1000 completly nuts wioth a 40Db PAD,
but I didn't think to check them before making serious changes to the
antenna system.

I broke the leads on one of the small MC 9:1 so I cracked it open to
see
how large the ferrite core was. Tiny, very tiny. ~1/16 of an inch.
Unless
space is so tight that you simply can't afford the slight size increase
home
wound cores present, I can't see any reason to use the micro sized MC
devices. For 99.99% they are fine. But for those who live too close to
a couple of MW stations, they can produce odd results. The IP2 was
not killer, but it was enough, S2, to cover any signal on
770+1240=2010
and 1240-770=470. I never noticed any IM on any HF frequencies, but
then I wasn't really looking.

And I suspect that any one source of IMD might be minor enough to
not be an issue. I just lucked out, the perfect storm effect.

My post was meant to be a cautionary tale about what to be aware of.
I really think that had I not added an additional ~50' to make up for
the ~3dB
loss the MC power divider produced, I wouldn't have ever noticed
anything.
IMD prodcucts that are buired in the noise aren't much of an issue.

Since signal and noise increases with antenna length, it stands to
reason
that at some point the noise will become an issue. And off frequency
signals
became noise for me. There were 2 simple solutions, either use a home
made
9:1 and power divider, or to use 2 seperate HF wire antennas. I use one
R2000
as a time source, I keep it tuned to WWV and record it in the left
channel, with
the target HF signal in the right. In an attempt to keep our home from
looking
like an NSA montoring post, and to avoid (false) TVI complaints I try
to leep
my antennas in a very low profile. While I am a ham, extra class, and
have
a nice transceiver, It sits on the shelf and I would have to errect an
antenna
to use that rig. But I had some TVI complaints that were only resovled
when
the complainer moved away. He saw my antennas and knew I was the
source.

Low profile means low conflict.

My car used to look like a FCC monitoring vehcial. One night while
comming back
from eastern Kentucky a car pulled up close behind us. I was mildly
freaked when
I heard a cop on the scanner run my plates with the comment "he has
too many
antennas to not be up to something." Nothing came of it, but it did
encourage me
to adopt a much lower profile.

Terry