Topband: Comments on High Performance RX Antennas for a Small Lot (Webinar)

[James Wolf]

It seems as though if data were taken as to categorize the (average or
typical) noise temperature with the angle of intensity of atmospheric noise
that this could be utilized as part of the RDF equation.
For instance, if at 20 degrees, the noise temperature was 5 dB higher than
at 80 degrees, then we might have a *more* accurate measure of comparison of
performance increase. Take the data every 5 degrees for city, urban, and
rural areas and the user can determine which RDF model to use.

My experience like K9LA and others, is that some antennas that should work
better by the numbers, just don't.

Jim - KR9U



-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of
donovanf at starpower.net
Sent: Friday, March 04, 2016 12:04 PM
To: Topband at contesting.com
Subject: Re: Topband: Comments on High Performance RX Antennas for a Small
Lot (Webinar)

Hi Tim, 


While RDF is helpful, nothing substitutes for devoting the effort to analyze
the detailed antenna pattern. RDF is especially useful in quiet rural areas
with very few homes and power lines and within several miles of our antenna,
but its insufficient for most of us. 



Very few of us live in an extremely quiet local RFI environment any more,
especially now that just one RFI generating electrical or electronic device
in a single home within a mile (or more) can suddenly ruin our previously
quiet RFI environment. Life was much easier when we only had to worry about
power line RFI. 


RFI caused by a high efficiency heating and air conditioning system in a
home a mile from my QTH caused me to install the 8-circle W8JI receiving
arrays at W3LPL to provide a much narrower main beam than I could achieve
with Beverage antennas. The 8-circle often provides a tremendous improvement
compared to my 580 foot Beverages which I still have and use. I don't have
adequate space for longer Beverages or arrays of phased Beverages. 


Most of us care more about narrowing the beamwidth of the main beam at
elevation angles below about 30 degrees while also inimizing RFI arriving at
all azimuths outside the main beam at low angles. RDF doesn't do that for
us, it optimizes over the entire hemisphere, often at the expense of better
RFI rejection at low angles. 


Better RFI rejection usually results in a different optimization than RDF
alone can provide. RDF provides a good starting point, but it doesn't
provide the complete answer for most of us. 


73
Frank
W3LPL 

----- Original Message -----

From: "Tim Shoppa" <tshoppa at gmail.com>
To: "Richard (Rick) Karlquist" <richard at karlquist.com>
Cc: Topband at contesting.com
Sent: Friday, March 4, 2016 2:59:34 PM
Subject: Re: Topband: Comments on High Performance RX Antennas for a Small
Lot (Webinar) 

The RDF seems to be the best we have at the moment, for taking a
3-dimensional pattern and turning it into a single number. Of course the
details of the 3-dimensional pattern are lost. 

In addition to the quantitative RDF or S/N numbers, the qualitative change
in pattern as you move up the RDF is remarkable. We go from 

* no directivity
* a null in back with not much differentiation between forward and side
* increasing side rejection
* near-complete side rejection
* increasing rejection of directions near forward but not quite forward 

The 8-circle is mind-blowing. 

Tim N3QE 

On Fri, Mar 4, 2016 at 12:37 AM, Richard (Rick) Karlquist <
richard at karlquist.com> wrote: 

> In this webinar, it was asserted (without explanation) that for every 
> 1 dB increase in RDF, you get 1.5 to 2.0 dB improvement in S/N ratio. 
> I've never heard that before and don't even see how it makes sense. 
> Actually, I don't even know how you can make generalizations like that 
> unless you are describing a theoretical QTH with uniform isotropic 
> noise. I'd like to believe this is true.
> Can someone educate me as to why I should believe this? 
> 
> Rick N6RK
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