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Re: Topband: 8 circle: DXE vs Hi-Z

To: "Don Moman VE6JY" <>, "Topband@Contesting. Com" <>
Subject: Re: Topband: 8 circle: DXE vs Hi-Z
From: "Tom W8JI" <>
Reply-to: Tom W8JI <>
Date: Sun, 21 Dec 2014 14:16:10 -0500
List-post: <">>
The HI-Z was erected quite aways from anything else which involved
bushwhacking and clearing the entire circle, trenching almost 1200 feet of
feedline etc so there was a lot of  sweat work done on that project.  But
on 160 and 80 where I have the tx antennas to use as a comparison, the
specialized rx stuff just doesn't hear the weaker stuff. And it's not that
I have a pristine "can hear a pin drop low noise qth", esp on 160 - plenty
of flare stack ingitors plus the usual powerline and smps junk.  It's
especially frustrating to hear all the glowing success stories of these rx
arrays and how they make the dx just jump out of the noise and into your

The proper test is, during the quietest time, to replace the antenna system elements with loads of the same impedance and see if the noise floor drops significantly. If the noise does not drop significantly (at least 8-10 dB), you will lose weak signals.

Another test that *sometimes* works on lower bands is to measure and observe the noise floor from midday to night. If you observe a significant noise increase in the "hissing" background noise, your site and antennas are limited by propagated noise. This does not work with local or power line noise dominated systems.

The difference here between day and night on quiet winter nights is about 20 dB or more on 40 meters, and sometimes almost the same on 160. If the ionosphere is sucking up signals, the increase can be less. That noise level is different for different directions.

That ratio tells me what sidelobe levels are acceptable. I can have antennas with higher directivity that work consistently worse because side lobes don't adequately attenuate noise from unwanted directions.

I'm sure the ideal case for a station looking out over the cold ocean without thunderstorms is much different than the case of a system looking out over thousands of miles of noise generators. My NE direction, because the path is over densely populated land for several hundred miles, is noticeably noisier with background "hiss" than the more easterly paths or southeast paths that reach the ocean in a few hundred miles.

I don't necessarily assign the same pattern priorities (like side lobe levels) to NE as I do other directions. NW here is actually pretty quiet because population is so low on that path, which means I have to be fussier about different things.

I'm sure this is the case for everyone, and why we can't really use calculated RDF (directivity) for everything. It was just intended as a better guideline than other things being used, not as a perfect answer.

73 Tom
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