Topband: 8 circle: DXE vs Hi-Z

[Tom W8JI]

> 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
> log...

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