On Sat, 27 Apr 2013 12:44:40 -0500, Fred wrote:
I put up a horizontal loop on my lot in town. I needed to reduce the
noise coming from my neighbours and local industry. I had been using a
75 meter dipole. I was enduring an S7 noise level with my dipole. I used
450 ohm window line from one corner of my loop as the feed point to the
corner of my home where it transitioned to LM400 coax from a 4:1 balun.
I then had 25 feet of this coax coming in through metal siding to my
amplifier. This scheme reduced my noise level to S3-4. This felt like a
very nice accomplishment. My friends on 75 meters locally here all
reported a higher signal level from my transmitter. This was unexpected.
I was just trying to deal with the high noise level in my receiver.

I used the loop this way for about two years. Next an antenna guru who
lived about 80 miles away finally talked me into changing to an open
wire feed line with of course air dialectric instead of plastic. This
further reduced my noise level. I have no idea why. He did not either,
he just knew it worked for him. At this point I am at a normal noise
level of S2.

I was pretty happy with this. Then a retired engineer in Iowa who owned
the same rig as myself, an Icom 751A said that I could improve noise
rejection and increase receiver gain by paralleling all the dual gate
mosfets in my IF strip with the latest type of high gain Mosfet from
Philips in Germany. The number was BF988. I was reluctant to do this
because I am 70 years old and do not have the best vision or steadiness
of hand. I finally dove in and did it. As he predicted, my receiver gain
jumped up and 75 meter stations within about 300 miles from me were
pegging my S meter. I was immediately afraid of losing this meter and
was sure it would never be able to be replaced. I turned down the
internal RF gain pot so that those stations no longer banged my meter
against the peg.

Now my S meter noise level during the day without lightning is 0. Some
days it bounces up to 1.

I am so glad I bit the bullet and put in those new transistors. This low
noise level makes ham radio so much more enjoyable. I am able to copy
mobiles on 75 that I just could not hear before.

The other benefit from the loop antenna with the air dialectric feed
line is that by dumb luck it made 20, 15, and 10 meters a very good
match with no tuner. I have a solid state amplifier and now jumping
around these bands chasing DX is really fun.

Just one hams journey trying to reduce received noise. A nice part of
this story is that there is very little monetary investment in a wire
loop antenna.

Michael

MNI TNX, OM!!
We need more first-person reporting like this in r.r.a.a.

73 ES GUD DX
JONESY W3DHJ
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
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