Hi Paul,
I've been working on a similar project so I'd like to share some ideas with
you. First off, you are probably already aware that when you get up into
the 12 dB RDF range the patterns generally start getting narrow enough to
warrant 8 fixed directional coverage as opposed to 4 so as to avoid the 4-6
dB nulls at the 45 degree overlaps. To my knowledge... the DXE Circle 8
array operates as a broad-side, end-fire array, and not 2 sets of staggered
4-squares. The BSEF array can produce about 13.5 dB RDF (impressive for
its size) when optimized for a single band, which is generally about 1.5 dB
better than an optimized receive-only 4-square at about 12 dB RDF, and about
2 dB better than a TX 4-square. It appears to me that a potential down
side might be that overall BSEF array performance is more compromised when
set up for multi-band use as compared to staggered receive 4-squares. I
believe it is possible to consider interlacing two sets of the DXE receive
4-squares with either remote feedline switching or two independent feedlines
and a switch in the shack. This may provide a better overall solution
depending on how you want to optimize your performance.
A related consideration that I discovered through modeling is pattern
deterioration (and noise increase) due to interactions with other resonant
transmit antennas. Pattern disruption can be pretty severe when there is a
resonant antenna nearby - including 2nd and 4th harmonics. For example,
when modeling my sight, I find that patterns for 2 staggered sets of receive
4 squares become distorted at 80m in two directions and at 40m in many
directions from interaction with an 80m transmit 4-square at 200 ft of
separation. At the same time, a shortened 160m antenna has little
predicted effect at the same distance because it is not resonant on the
primary or harmonic frequencies. A crank-up tower on site with a resonance
at near 1.75 mhz is also predicted to cause similar significant pattern
distortion on 160m, 80m, and 40m receive.... at least I can change the
resonance by cranking down the tower. In any event - I have come to the
conclusion that for my station, about 11-12 dB RDF is a realistic target to
have coverage in all directions - so I plan to optimize for this performance
level. To get there am planning two sets of 4-square receive antennas
covering 160m and 80m (except 2 directions) and then use my Beverages for
40m instead of trying to cover three bands on the receive 4-squares. I can
extend the length of Beverages in the two directions that I can't cover well
on 80m to pick up the performance there without getting the corresponding
40m patterns too narrow.
Hope this info is of some use to you and perhaps gives you some ideas on
what might work best for your station. Good luck with it.
73
Matt
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Paul
F. Merrill
Sent: Tuesday, December 06, 2016 3:54 PM
To: towertalk@contesting.com
Subject: [TowerTalk] DXE RX Antenna Systems
I sent this to DXE first, but I'd be interested in hearing opinions and
experiences. Thanks.
I have two DXE RX 4 squares. I bought the second one used thinking that I
may gather the parts so as to make a 8 antenna system using the controller
that came out after I bought my 4SQ.
Do you guys have an opinion on these three things:
1) My main focus will be 80 and 160, and will take what I can get on 40.
The 4 directions will cover pretty well from my QTH in Central W6...not sure
if I need 8 directions. Would I be better off with a SQ optimized for
160 and one for 80 than on compromise 8L system?
2) Can I nest these two squares to save space, cable runs, etc.? 80 inside
the 160.
3) Are there any available systems to share (Multi2 contesting) and take
advantage of diversity RCV and/or share the various RCV antennas? I plan to
put them far enough away from the XMIT antennas that I won't need the
sequencer, since I wouldn't want the 80m op to lose his RX antenna when the
160m op transmits.
Rigs now are K3's, but I foresee 6700's in my future.
I am fortunate to have some acreage, so I plan to have a couple of beverages
and maybe an AS Shared Apex Loop, but I have a lot of money in these
new/used DXE systems and want to make the best of them.
Thanks, Paul / W7IV
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