[TowerTalk] Re: Physically Low--Low Frequency Antennas
K7GCO@aol.com
K7GCO@aol.com
Thu, 17 Feb 2000 23:52:30 EST
TT: I worked 2 weeks on this Post and forgot to add the Subject. Please
delete previous post. Sorry about that. K7GCO
"There are also tricks I've used to make horizontal antennas close to the
ground on 160-40M complete with the higher ones. It's rare fun beating the
higher antennas." K7GCO
In a message dated 09.02.00 13:33:20 Pacific Standard Time,
redpines@cybrzn.com writes:
Dear Ken: I would love to hear about these! I have 2-70 foot towers
about 120' apart and they need some wires to be attached to them! 73 Tom
K0SN
Physically Low and Effectively High Antennas for the LF’s. Part 1
Gee Tom, I thought you would never ask!! I put a lot of bait on the hook and
even sprayed it with WD-40. At the Sportsman Show I got further confirmation
that it enhances fish bate. One guy said that "when fish weren’t biting he’d
dunk the bait in the oil bilge." It may also be that oil covers up human
scent completely and is less objectionable. Humans have a certain scent that
fish can smell. That tends to support it’s a petroleum base in WD-40—not a
fish base oil. Even Paul Harvey verified WD-40 works on arthritis.
You won't even need those towers. For starters, review the article "A Half
Square Array for 40M" in 1/98 QST for one (I added another element).
Unfortunately, the balanced feed point is not fed with a balun and there is
the "Dreaded RF Spill Over" on the coax shield. It’s in the "K7GCO Top 5 All
Time Antenna Dummities." None have ever succeeded these top 5. On any
directive antenna it upsets the SWR and pattern—in particular the F/B. It
can excite the whole tower. I entered the "equivalent circuit" of this and
several other antennas into Eznec and it shows what happens. I was going to
send my correction data--before and after balun--to QST but they don't open
your mail after that. If Attachments were possible I could have included
some of that in E-mails. When I get them all assembled I’ll offer them on
E-mail.
In Eznec there are no feedlines. The RF Source is placed right at the
feedpoint and one gets the correct pattern as if there is no feedline, an
open wire balanced line, a balanced coax or coax with balun. The "Dreaded RF
Spill Over" has never been recognized by QST and degrades every balanced feed
point antenna described fed directly with coax (again in the 2/00 issue) they
and other mags have printed. There has only been 2 articles on the "Dreaded
RF Spill Over". One was in 1938 Radio Mag by Bailey and one in a ’52 QST by
Remington Rand--both about VHF verticals. I’ll have to write the 3rd
one—when I get time. Rand put the Dreaded RF Spill Over to work cleverly by
reversing the phase 180 degrees every ½ WL down the mast so it gave 6 dB
broadside gain over the a high angle lob—on the horizon. It actually gave 4
S-Units over the high angle lobe without the modification on the horizon.
Now you see how torturous RF Spill Over can get. This unique trick is in the
"K7GCO Top 5 All Time Cleverties" of Antenna Design. I still have the 2M
antenna described. Both addressed the affect of typical 10M and higher
frequency verticals on a mast with RF Spill Over. Radials don’t take it all
off. They even add to it if they run down close to the coax—Another RF
Dummity--#8.
Bailey made a very profound statement over 60 years ago I have never forgot
to this day. "Most vertical antennas are nothing but a 50 ohm matching
device for the coax--to the mast and tower." He should have got a "Nobel RF
Prize" of some kind for his "Astute RF Wisdom". The vertical antenna
radiates broadside but the "Dreaded RF Spill Over" by the J-Pole vertical
referenced on the mast and tower cause a lift off of the over all free space
vertical pattern. Many of the VHF/UHF verticals still do today. Actually
Bailey used the "2nd All Time Worst RF Spill Over Vertical"—"The Sleeve
Vertical" so only got a small improvement. That ended up disqualifying him
from the Nobel RF Prize. It was Rand who cleverly corrected the "RF Sins" of
Bailey’s J-Pole Antenna with 3 more sleeves and some radials and got 6 dB
gain from it making it a 4 element collinear on the horizon.
Industry has still not caught on. One exception is the AEA 2M Iso-Pole
designed by Dr Don Reynolds of Seattle with the 2nd skirt ¼ WL lower. That
kills it. The 2nd Sleeve deserved a Nobel RF Design Award of some kind. I
showed him a single radial version of that 40 years ago. I called it the
"Truman 2nd Radial"--"The RF Stops Here." Another term I had for it 40 years
ago was they were "RF Spill Over Trick Sticks." I used them several
different ways—even to change the length of LW Antennas on different bands.
Always put a balun or bazooka sleeve on the coax that feeds any balanced
dipole, beam or vertical feed point on a mast. Get yourself a "RF Sniffer"
and do some "RF Sniffing." Don’t get Zapped with the "Dreaded RF Spill Over."
Another feedline sin in the "K7GCO 5 All Time Dummities" is showing open wire
line and suggesting "any length" rather than the "K7GCO Magic 1/2 WL or
Multiple Length" they have been told about repeatedly. Random open wire
lengths frequently results in complex Z's presented to tuners they can't or
find very difficult to match or arcing. Since it is a tuned line with high
SWR at times, the length can be critical depending on the SWR. All this goes
away with my "Magic Length" (it repeats what it sees) with
multi-all-band-advantages. Random lengths of open wire line has done more to
discourage the use of open wire line than any other factor. Open wire line
properly used can match antennas low to the ground a lot better—if you know
how. I have a way to do it even without and tuner.
Assuming you are using the proper feed techniques of coax or open wire line,
an effective procedure on 75&40M, is to tip the director up of a horizontal
beam with good gain when real close to the ground. This reduces the ground
reflection gain of the final lobe by reducing the ground reflections. You
get 6 dB reflection gain over perfect ground, 3-5 dB over real ground for
horizontal polarization, broader final lobes and shallower nulls—even less
gain for vertical polarization. Tipping up at 45 degrees can take only 1 or
2 dB more gain from it but all of the free space pattern is working without
any losses on the way. It seems to end up getting more RF into 20-45 degrees
mostly by direct radiation rather than bouncing 50% off the ground as with a
horizontal boom. Optimum low angles typical on 20M, seem to be a little
higher on 75&40M. They certainly are for stateside I’ve found.
When a beam is tipped up there is less ground reflection gain and reshaping
of the free space pattern into reflection factors lobes for certain antenna
heights that normally happens when the boom is parallel to the ground.
If a lower gain beam is used, the vertical pattern is much broader and there
is less advantage of tipping but it still seems to help to better fill the
higher angles. A 2 element yagi or 40M quad of .12 WL boom close to the
ground tuned for best F/B has a broad vertical pattern and is a killer as it
already has a high level of RF going into the higher angle reflection factors
for the lower heights. I haven't tipped up a 40M quad yet but I will. I'm
going to build a tipped Moxon Version of a 2 element yagi close to the ground
for 75&40M which is 30% shorter due to folded elements and has a high 40 dB
F/B and a 50 ohm feed point. The Moxon 2 element is a very good design to
work with in any configuration. There is "critical coupling" between the
ends which actually improves F/B and gain from that of parallel elements but
has narrow bandwidth that I will broaden with a variable Xc and selsyn. This
or a quad close to the ground pointing straight up is a killer antenna.
RaiBeam is working on a shortened 40M 2 element beam and I would like to try
that close to the ground and tipped up. It’s a new concept o altering the
Refection Factors reflecting RF is a slave to on a 50/50 basis.
An article in AntenneX on the Web every TT'er should be on, is a 75M ZL
Special of 5-6 dBi close to the ground and actually pointing straight up that
frequently beats the higher antenna guys even out there a ways. Any
horizontal beam with decent F/B can be real close to the ground if it points
up 45-90 degrees with little or no detuning of the beam. The F/B becomes a
ground reflection buffer both ways from any detuning affect. A vertically
polarized beam can be close to the ground and still have a low angle although
I'm going to see what that does when tipped up in Eznec. The final lobes
without tipping are a little sharper if it's high off the ground. Strike a
compromise of ground affects and orient any beam or any antenna 30-45-60-90
degrees and/or tipped or both and be prepared for some surprises.
A Horizontally Oriented Quad Loop about .15 WL above the ground is a killer
antenna and does great even 2-3000 miles away on 160-40M. Some nights on
160M it acts like a vertical--almost. It can reach out and be "Hush Hush" on
noise. I have a multi-band horizontal quad loop and system I'll be releasing
soon. I also have a way to get full power into a 40M quad loop of any
orientation on 80 and 160M. When I get time I will write it up.
There are 2 BC Radio Stations in the US with antennas that looks like the
horizontal quad but are different. It has less ground losses than a ground
plane and it puts out a stronger signal than a ¼ WL vertical for the BC
market. One’s in MT Vernon, WA. I drove by this station on 660 KHz and saw
4 towers 100’ or .067 WL high (37’ on 160M) in a square and I said to myself
"they have a 4 Square." Then I noticed the quad wires at the top and almost
drove off the road. I found out this is not the same design although it is
fed at the top in a different way. I noticed a Horizontal Quad Loops great
performance 50 years ago before the quad beam caught on and suggested my
Horizontal Loop for the BC Band over 40 years ago. I stopped and took
pictures and talked to the Engineer there. He told me the BC Engineer who
installed it and I knew him--George Frese of Wenatchee,Wa. I called it a
Horizontal Loop then and "that magazine" wasn't interested in that either or
the antenna people in the BC Radio area? We need more progressive editors
and others in the industry. It’s called the "Paran Antenna" and developed
over 20 years ago. It always takes 20-30 years to advance a new concept.
The Horizontal Square or Delta Loop has a figure 8 pattern broadside or up
and down in this case. The RF gets reflected off the ground just like a
normal reflector so it’s a "1 element beam with a ground reflector". The
broad pattern hits only 1 reflecting medium above and then back down without
ever encountering any resistance other than a weather head cloud or ever
going over ground. There are no polarization reflection factor ground rules
in this game. It comes down in the your antenna "top door" like heat from an
overhead register or "Blue Ice" from the Jets before it hits the
ground—rather clever I’d say. I call it the "K7GCO Slam Dunk Antenna." This
path has less attenuation day or night with no skip zones like that from a
vertical which has a lossy start, sees lossy ground all the way, has a skip
zone and costs a lot more $$$, space, height to create and waste power in.
Every ground contact vertical polarization has on the way takes something
from it. There has been too much bad mouthing of high angle radiation by
those who are as Mark Twain says, "are experts in everything from child birth
to reincarnation without ever experiencing either." One ham told me "every
time I come on with that Damn Slam Dung Antenna, it knocks the papers off his
table and he has to clean up the shack!". I finally got him to install one
and we had a private pipe line between us or I should--say above us. This is
a little used direction of communication. Mobile whips on 160, 75&40 often
work better tipped back 45-90 degrees. I think this antenna would be great
for a Net Control.
There is another receive antenna only that is startling at times. There is a
technique of coupling to the 110 VAC power line for a receive antenna on the
BC band and even 160&80M. Use a BC variable with all 3 gangs tied together
in series with a .5 ufd 600 V fixed Xc connected to one leg of the power
line. Use a neon tester to find the grounded leg for safety but there isn’t
any difference in strength. The center lead in a three wire sockets is a
ground. It’s a great receive antenna on the BC band—better than any wire
antenna I’ve had on my lot. After I had my power lines buried, it wasn’t as
effective. Connect to the telephone or the air ducts in the house as they
are great receive antennas also. I had an article on this in Radio Sporting
Mag about 20 years ago. Part 2 will follow. It gets even better. K7GCO
--
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