Greetings from the High Desert!
I sure am enjoying my first year of semi-serious DX'ing on Top Band and
thus feel the need to make some antenna system improvements. I've been
kicking around a few alternatives and would appreciate some "words of
wisdom" from fellow Top Banders prior to charging off in any one particular
direction.
First a little background info. My QTH is in Southern California near
California City, in the Mojave Desert. I'm about 40 miles North of Earl,
K6SE whom many of you know. It's hardly a good spot when it comes to decent
ground/soil conditions, but at least it's quiet on receive! I put up a full
size Inverted Vee for 160 with the apex at 100' and the ends up about 30'.
I use it for transmitting and for receiving most of the time. However, I
have found that my 80M Delta Loop works very well on receive, especially
towards Europe. The noise output from the Delta Loop is very low, and the
overall Signal to Noise Ratio of received signals is much improved; at least
in the NE/SW directions. Since I more or less stumbled on to this, I would
definitely recommend that folks try receiving on other antennas they may
have available to them. You might be pleasantly surprised at the results!
I have managed to work all continents and a total of 50 countries in the
last 2 months with this setup, primarily due to receiving on the 80M Delta
Loop. Although it works reasonably well, I hope to get a few 585' 2 Wire
Beverages up soon as well.
Even though the "low" Inverted Vee has worked out fairly well as a
transmit antenna, it seems I could make better use of the tower I have the
Inverted Vee hung on. The tower is 102' of Tri-ex T-15 (similar to Rohn
25/45) with 15' of 2" mast above that. The tower is topped off with a KLM 4
element 40M beam at 103' and a Hygain 204BA at 116'. The tower is grounded
at the base, but I did insulate the guy wires from the tower when I built
it. The primary options I've been kicking around are:
1. Shunt load the tower. My instincts, research and modeling efforts tend
to point me in this direction. I would need to somehow isolate my VHF and
UHF PacketCluster Node antennas from the tower, and probably take some steps
to ensure a better bond between tower sections and between the tower and the
mast/rotator. Is there anything special that needs to be done to protect
the rotator and/or control box from the high amounts of RF flowing through
the tower structure? Also, since the 40M and 20M yagis are top loading the
tower, should anything special be done with their feedlines down in the
shack? Seems like there could be problems if they are connected to a
grounding type antenna switch? Lastly, I would have to do something about a
decent ground system for this critter. I suppose the optimum thing to do
would be to put in 120 or so ground radials. That will be very difficult to
do at this location with driveways, buildings, horse corrals, etc near by.
So how about 4-8 elevated tuned radials up about 10-15' with a similar
number of ground radials? Wasn't sure if elevated radials are doable with a
shunt loaded tower? Maybe I could run them up from the bottom of the tower
out at a 45 degree angle or so, then straight out horizontally to the
supports. It seems like this would be the best approach. By the way, would
aluminum electric fence wire be acceptable for ground radials? I have a
mile or so of it on hand if it's usable.
2. Next option, forget loading the tower and go with an elevated Inverted-L
with 4-8 elevated radials. This is obviously simpler to implement, but I
was curious how much of the radiated energy would be soaked up by the tower
structure and shunted straight to ground! I'm guessing this would not work
out as effectively as loading the tower itself? More aperture using the
tower?
3. The last alternative I was considering is using several Quarter Slopers
with a remote switch box at the top of the tower. I suspect, however, that
the performance would not be very hot as compared to full size slopers.
Maybe turn things upside down and use Quarter Slopers fed at the bottom end
using elevated radials under each one?
I suspect that loading the tower, if done correctly, would outperform
any of the options listed. Any tips on feeding this critter would be
helpful as well. Comments and/or suggestions regarding these or other
alternatives that I may be overlooking would certainly be appreciated. I'm
having a great time on Top Band and am looking forward to the remainder of
the season. The night I first worked into Europe, I worked about 5 stations
and was hooked. I was so pumped up I couldn't sleep for the remainder of
the evening. I doubt that I'll make it to 100 this season, but I'm going to
give it a good try! Thanks for reading.
73, Bob K6ZZ
w9nq@ccis.com
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