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November 27th 06, 01:36 AM posted to rec.radio.shortwave

Bret Ludwig Bret Ludwig is offline

Bret Ludwig is offline

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First recorded activity by RadioBanter: Nov 2006

Posts: 55

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IMD observations

wrote:
I have been doing some experiments this weekend and found that the
smaller
MiniCircuits 9:1 and 1:1 transformers are, when used in "high" RF
fields, very
prone to distortion.

I wasn't at home so I couldn't use my standard pests on 770 and 1240,
but I was
within a mile of a single MW station and found that with antenna
lengths longer
then 50' I found the 2nd and 3rd harmonics to be very strong. Going to
a larger
home made 9:1 and 1:1 did not have these issues. I suspect that with 2
or more
signals the mix products would be very excessive.

Don't you have a generator?

I have been intrigued every since I added my ground ring back in 2005
and found
I had spurs where none existed before. Given that 770 and 1240 had the
S-meter
on my R2000's pegged should have set me thinking. It took a while. Not
only did
the MC transformers add to the problems, the input transformer in the
R2000 is
before the attenuator and also produced mix products. And my trusty MC
ZFXC-2-1
hybird coupler, power divider, power combiner, will under these
conditions produce
a very small 2nd harmonic and at home I could just detect the 770+1240
product.
Again a home made splitter, based on Bryants design, did not have this.
Smaller
is not always better.

I suspect, but haven't verified, the issue is core saturation.

Leason learned?
Antennas should be as long as needed and no longer.
The less RF noise you have, the longer the antenna you can use.

One word: attenuators.

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