Topband: 4SQ vs. 8 circle rcv

[John Kaufmann]

Based on the RDF metric, which is a very useful way of comparing antennas,
the differences between the "best" arrays is not that great--maybe 1 to 2
dB.  I have used Beverages and a number of different receiving arrays, and
found that in practice it is very hard to discern 1 dB RDF differences
between antennas.  So yes, in a sense, there is not a huge difference
between the published numbers for the 4 square and 8 circle.

However, there are other things to consider here.  When the RDF gets large,
say more than 12-13 dB, the beamwidths get very narrow.  This means that the
angular footprint over which the high RDF is actually realized is quite
small.  Once you are outside the "sweet spot", performance falls off pretty
sharply.  Unless you can somehow rotate the beam footprint in fine steps,
like a rotary Yagi, you will have gaps where the large RDF actually doesn't
help you and you may do worse than with a lower RDF antenna with a wider
beam footprint.

The other point is that RDF is a good predictor of receiving performance
only to the extent that external atmospheric noise is more or less uniformly
distributed over the entire receiving hemisphere of solid angles.  When
noise is stronger in one particular direction, then RDF is less accurate at
predicting performance.  When you beam in a direction of high noise, you
just pick up more noise and you won't see the theoretical advantage of RDF.
I observe this every morning when I beam SW, where the ambient noise level
jumps up typically 5-6 dB  compared to other directions.

73, John W1FV

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Mike
Waters
Sent: Wednesday, January 13, 2016 9:56 AM
To: Bill Hider
Cc: topband
Subject: Re: Topband: 4SQ vs. 8 circle rcv

According to what I read there, there is little difference between the two.
That seems odd. Was some information left out, or did I read the wrong .pptx
file?

73, Mike
www.w0btu.com