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Re: [TowerTalk] 160 RX antenna

Subject: Re: [TowerTalk] 160 RX antenna
From: "Dan Zimmerman N3OX" <>
Date: Sun, 30 Dec 2007 21:43:23 -0500
List-post: <>
>It drops the nose from S9...+10 down to S3 and you hear all the europeans in
>the middle of Toronto with no problem.

I've been using a flag RX antenna at my house in the suburbs of DC
here and have had pretty good luck with it on 160m and 80m.

It has a reasonable directive pattern but I don't think that's why it's so good.

My vertical has S9+ manmade noise 24/7.  From what I can tell, a lot
of it might be coupled into the somewhat minimal ground system by the
bonding of the shack single point ground to the utility ground.

Some other noise is coupled into the ground system after being picked
up by the vertical.

With the flag, I've taken great care to isolate it from the ground
because I know common mode pickup can totally destroy such a low gain
antenna's utility. The transformer is an isolated winding type on a
binocular core as described in Low Band DXing, and I added a *second*
1:1 isolation transformer near the base of the mast the flag is on,
and yesterday I added a several thousands-of-ohms choke on that
feedline back near the shack.  The whole time I was trying to reduce
the noise I heard on an AM portable radio with it's ferrite stick
antenna coupling to the magnetic field around the coax feeding the
flag.  The new choke helped quite a bit and it seemed to help the
noise level on the flag as well.

Every single coax feedline in my backyard is absolutely full of junk
from some source as heard on the AM portable, but now the flag's
feedline is almost free of it.

I think a small receiving loop like that, especially if it's coupled
to the feedline with a smaller coupling loop, should really reject
common mode noise being conducted from the house.

I think in a residential/urban environment, anything you can do to
keep your receiving antennas from picking up ANY ***conducted noise***
is critical, and I think it may be 90% of why I find the flag useful.
It also has plenty front-to-rear which does help with the occasional
neighborhood noise like the loud one that was thankfully off the back
to the Europe path last night...

Anyway, long story short, think about what noise might be conducted
from your house to your antennas on your feedlines, think about what
noise might be conducted from OTHER ANTENNAS and their feedlines to
your sensitive antennas, and you'll have a good shot at reducing your
noise level tremendously.

In my case, a really noisy utility ground (hot with regular line noise
and also, it seems, consumer electronics) desperately needs to be
decoupled from the sensitive RX antennas.


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