[TowerTalk] 40M FD Antenna & CQ Article Reference
K7GCO@aol.com
K7GCO@aol.com
Fri, 29 Jun 2001 20:04:07 EDT
Field Day or Base Antennas
The Post below on 40M FD Antennas created a lot of response to me for
which I appreciated. In the July CQ p44 a "very timely article" appeared
that "paralleled exactly" the very suggestion I gave. It's called "A Large,
Remote-Tuned Loop for HF DX" by R Stroud W9SR. It used a fancy remote tuner
also for 160-6M. An open wire line 137' long into the shack into a Johnson
Match Box would work just fine also except on 160M. I've modified a Match
Box with 2 toroid wound coils on each end of the 80M tank coil at right
angles to the tank coil that could be shorted out with a knife switch and I
paralleled a 100 uufd vacuum into fuse clips. I use an open box on all my
tuners and have no TVI even on 6M. It can then be used 160-10M for this
antenna. I have a 6M only Match Box. This antenna is what I call a "Tuned
Log Periodic." With a Match Box and if you can match the Z at the "end of
the feedline," you can use it on "any frequency" in between the ham bands
like for the SW bands to make use of the "progressive gain" and "lower angle"
all around the loop as you use it progressively higher in frequency. The SW
BC stations really boom-in. Before the Match Box it was very slow tuning up
various antennas with plug in coils and switching between "Series and
Parallel" before the Jones Micro-Match SWR Bridge and then out of the ham
bands. You had to keep data for each frequency. I used a Grid Dipper and
Antenna Scope (50 ohm RF Wheatstone Bridge) to get a 50,75,100 or a 300 ohm
match. Before that the Surplus Command Transmitters like the BC696 for
80/75M and adjacent frequencies sometimes VFO modified and the BC-459 for 7-9
MHz that I modified also for 20&15M using a buffer tube. This provided a low
power RF source with the variable link for quick tune ups using the 300 ohm,
50 and 75 ohm "Twin Bulb SWR Indicator" I built right in a dielectric slot I
carefully cut with a Pen knife in 50&75 ohm coax. Before that you "tuned by
ear dB's" out of the ham bands.
There is no simpler way to get horizontally polarized gain on the low
frequencies. The author found DX routine on 40M and not unusual to open the
band(s) with 135' on a side. That is routine with great antennas. With the
270' per side model, DX could be a whole lot easier on 80/75M in particular
at 100' high. It's a great DX listening antenna with the mostly even
patterns all around progressively higher in the band. What a listening
antenna for 6M DX--from all directions. Are you getting the picture of what
a great antenna is? I don't recommend so-so antennas.
In absence of light poles, 3 or 4 trees can usually be found on FD to throw a
line over with the "Wrist Rocket." Back in SD prior to 1956 I lived on main
street and 300' from the railroad. I used high elevators for 2 of the
supports and regular light poles for the other 2. I lived 600' from the ball
diamond and used the poles in the winter time. I was the pitcher for the
Town Team and never even had to ask to use them hi. Open wire line is a
"great and inexpensive feedline." You don't have to worry about feedline/SWR
loss or antenna length and it's complex Z if you know how to use tuners that
certain TTer's have problems with. I haven't found a feedline load that
couldn't be matched with a change of the number of turns in the link, tank
coil or in a few cases a reversal of the Differential Variable Leads. I had
a dual switch that could switch in different lengths of feedline but the
Match Box did way with that for all practical purposes. Remember this:
"If you can match the Z at the end of the feedline, you will have 100 percent
transfer of power to the antenna less the losses in the tuner and feedline.
If the tuner coil is cold to the touch (with power turned off) you have a
very efficient system. No more TT coax loss charts are needed. Coax is just
an unbalanced fad Art Collins designed for using a Pi Network (just kidding).
The 50 ohm output rigs have created a huge antenna tuner market in the shack
for coax but the coax still has progressively higher loss with SWR which is
certainly negligible with open wire line. Long Live Open Wire Line and the
Johnson Match Box--With Modifications." (Old K7GCO Axiom)
The CQ article shows the E-plane and ground reflection patterns on all bands
along with the very impressive and progressive gains and their angles. His
patterns are a bit different from mine as he fed it off center some. The
only TT Nit Picking that can be done is, it didn't show patterns for 17&12M
but one could interpret them. He installed 4 telephone poles that gave a 54'
height. They were quickly installed at $150/hr with no concrete in the
ground expense or water on the legs to ever worry about. I suggested in the
previous post below for FD using the wide spaced baseball field or more
available football field light poles for this very antenna only one size
longer cut for 900 KHz. The higher light poles would lower the CQ article
angle data even more on 80-6M and would perhaps be a disadvantage on FD and
SS contests (try different heights during the contest) but even better for
DX. It wouldn't be used in the BC band but the gains would be one more notch
"progressively higher" on each higher band which is very useful on 160&80M if
you can use 270' on a side +/-. A 1 WL horizontal quad at Fo gives a "figure
8 pattern" broadside and reflecting off the "reflector ground" really gives
it a big "Jump Start" straight up and out and does a great dominating job
locally and out a fair ways. But at 2F (2 WL and longer) and higher in
frequency, the free space pattern is "end fire" with 1.6 dBi free space gain
and about 6.5 dBi at 50 degrees 54' high after ground reflections. The
270'/side version would have a similar end fire pattern on 160M which is very
useful--gain on 160M. The reflective gains increases progressively to a very
high 15.27dBi and the angle lowers to about 5 degrees on 6M. The authors 1st
contact was on 6M with 5W with WP4O in Puerto Rico who could not even be
heard on his trusty 5 element at 45'. I worked 6M DX using a Harvey Wells
TBS-50 on AM into a similar antenna. Things like this happen when you have a
great antenna with what I call the "K7GCO RF Clout." Would you believe the
angle is so low (in particular if mounted on 100' light poles and the "K7GCO
2X" version is used) it kicks up dust--RF Dust that is. You can see the RF
Pattern in the RF Dust Devils.
135' on a side (average) can be obtained in many locations using trees and
I've used it as low as 20' with great results on 160 and 80/75M 3 years ago.
In SD I ran it across the street to 2 trees just to keep my back yard clearer
for 4 other antennas. Review the article give this antenna a try. The
higher it is the better it works higher in frequency for DX. K7GCO
In a message dated 6/26/01 8:36:06 PM Pacific Daylight Time, n4kg@juno.com
writes:
<< A current fed Long Wire is an OK antenna, but probably NOT at 20 ft.
There will be DEEP NULLS broadside to the wire and lesser nulls
off the ends of the wire.
I installed a 2L wire beam composed of an inverted VEE plus
Reflector with 150 degree apex angles and 21 ft of separation
supported by a rope boom between two 50 ft high light poles
for adjacent baseball fields. The ends were tied off 200 ft from
the center of the antenna. This beam was aimed due NORTH
from North Alabama (K4BFT 5A AL). Performance was AMAZING -
we had W1's answering CQ's an hour before sunset and VE1,2,3,
5,7, KL7, and even a few Europeans after dark. With a single inv vee
we usually work far fewer W1's and VE's. For the West Coast,
we use a vertically polarized Delta Loop which is usually about
6 dB stronger to W6 / 7 after 11 pm. It was interesting to note
that we still had many Tex, NM, Ariz, CA stations call after
CQing on the 2L wire beam aimed North. Some FL stations
were somewhat weak but still called in and were worked off
the back of the beam. We have used this antenna for the last
2 years and both times beat the 20 / 80 CW station for the first
and second time. Peak 10 QSO rate was 140, our best ever.
BTW, we also used the 40M wire beam on 15M and worked all
over the country, jumping from W1/2 to W6/7 to W4. A 3/2 WL current
fed Long Wire (e.g. 40M straight dipole used on 15M) has 6 lobes.
If the ends are dropped SLIGHTLY (15 to 30 degrees), the nulls
are filled in. If the ends are dropped too much (45 degrees) it
becomes much less effective.
K4BFT 40 / 15 / 10 CW station results using 100W output:
40M CW QSO's 738 2L40 Inv Vee + Vert Polarized Delta Loop
15M CW QSO's 355 40M Inv Vee
10M CW QSO's 15 40M Vertically polarized Delta Loop)
Total station QSO's 1108
On Tue, 26 Jun 2001 EDT N4CW@aol.com writes:
> Out of curiosity, what antennas were truly outstanding during Field
> Day this > year? I used a full-wave, fed a quarter wave from one end
(up 20
> feet!) and it performed "just okay", judging by how long it took me to
get
> responses to my CQ's.
> You can E-mail your responses directly to me to save on bandwidth.
> 73, Bert N4CW (N4CW@AOL.COM)
>
The inverted vee beam does indeed work very well. In support of the the
above report, some time after my first article on the inverted vee in 8/60
QST, someone came out with a phasing box that would phase and match 2 similar
inverted vees about .2 WL apart with separate coax feed. You could reverse
the pattern, adjusts for max gain or F/B or the 8JK configuration. For
someone in the Midwest this would be a great FD or anytime antenna to meet
all the different conditions. I used it on 160-40M and will use it again.
Another favorite "Hard Butt Kicker" for year around base use and for Field
Day, I have used horizontally oriented quads on 160,80&40M .1-.2 WL high.
Their vertical and broadside "figure 8" pattern uses the ground as a
reflector to give the RF a "jump start" up to the reflecting medium in the
sky and back down to the receiving antennas "Without Passing Monopoly Ground"
again with very very good strength out to 3000 miles much to my surprise.
The high angle pattern is fairly broad and the very low loss path seems to
make up for reduction of gain at say 45 degrees. I call it the "Slam Dunk
Antenna." There is a lot of signals on 40M all over the country on FD night
on (also160&80), so a good signal is needed to work the East coast and
Midwest from Seattle on 40M. It's a great antenna locally 24 hours a day
I've used 100 ohm balanced coax into a Match Box for example on a 40M quad
loop on 40,20,15&10M. It's a great match on all 4 bands and fairly quiet
also with balanced 100 ohms coax and the selectivity of a Match Box. I've
also used a 1/2 wave of 450 ohm open wire line cut for and Grid Dipped at 7.1
MHz into the Match Box for all these bands and it repeats the quads Lo-Z at
the end of the feedline which the Match Box matches on all bands--only if you
try it.
An interesting concept occurs on 75M--not needing the Match Box. The 40M
quad loop is a 1/2 wave long on 80M presenting a very high Z at the balanced
feedpoint. It's a bit lower Z at about the right value if a 2 wire loop is
used spaced about 6" to simulate a fatter dipole and the Z was about 4050
ohms. The open wire line is now a 1/4 wave long on 80/75M and inverts the
Hi-Z to a Low Z. Guess what the Lo-Z was? Are you setting down? It was 50
ohms--I lucked out. If it wasn't I'd have adjusted the spacing of the 2 wire
quad loop so the Z there inverted down to 50 ohms. I could also adjust the
spacing of the open wire line to fine tune the Z seen at the end of the
feedline--but I didn't have to. Now using a technique I used in another
application I hooked one wire to my IC-720 50 ohm input and the other lead to
a 3 gang BC variable stator and the rotor/frame to the rig ground lug. The
variable has a plate bent over so that when it's closed it's shorted out. As
you go higher in frequency the inductive reactance reflected at the end of a
1/4 wave feedline is canceled out by the right setting of the Xc depending
what frequency you are on above the lower resonant frequency of the loop and
open wire line--all the way to 4 MHz. Resonant low and tune high. The
remaining Rt value doesn't change much all the way to 4 MHz allowing one to
operate the entire 80/75M band-even with no tuner other than the BC 3 gang
variable. It's a great concept. I've never tried a typical rigs tuner on
this as when I first did this they didn't have them internally. It works
great even though it's a balanced feedline into an unbalanced xmiter output.
If you talk to the RF it will behave.
The pattern and gain of a 40M loop in Eznec is hardly different on 80/75M
than a 80/75M WL quad loop is on 75M. So a 40M horizontally oriented loop
operates on 80/75/40M with high/medium angle and on 20,15&10M end fire/low
angle with progressive gain. It's a great FD antenna. There is more. I
struck a "RF Gold Mine."
On 30,17&12 the 40M quad loop has a Hi-Z feed and the feedline is an odd
number of 1/4 waves which inverts the 40M loops Hi-Z to a Lo-Z at the end of
the feedline for the Match Box and easy matching. When I get time I'll write
this up with all the patterns and Z's. There is more.
A lower frequency version does the same on 160&80/75M. In SD 3 years ago I
had a 75M horizontal quad 20' high over the street fed with a 1/2 wave of 600
ohms Zo open wire line cut for 3.56 MHz into the Match Box. This Match Box
really gets a work out if you know how to use it. It would put a 20/9 signal
into Seattle on 75M running 100W. That's not exactly high angle.
On 160M a Match Box made just for 160M I'm sad to say--finally failed.
Using a UnUn mobile toroid with Z steps all the way down to 6 ohms, I
inserted it in one leg and it matched 1:1 at 17 ohms at 1.8 MHz and 23 ohms
at 2 MHz. That's too low for the Match Box. I used my trusty 1936 BC
variable once gain (everyone should have one) and it tuned out the reactance
all the way to 2 MHz. Now this is only the 2nd 160M antenna I've been able
to "use across the entire band" with a low SWR to coax. I calculated the 75M
single wire quads Z on 160M at about 21,000 ohms. The band width is very
narrow due the 1247/1 Z step down ratio but it sure worked well at 20' high.
I will make a "2 wire version" to decrease the Z to about 7000 ohms to give
50 ohms using 600 ohm open wire line. I have a model of this in Eznec.
That's only a 144 ohm step Z down and should give much better bandwidth and
no down step matching xformer is needed--just the BC variable.Xc. Very
simple indeed. I calculated that a 1025 Zo open wire line would have matched
the 21,000 ohms to 50 ohms. Unfortunately the Zo of open wire line tends to
top out at about 660 ohms with reasonable spacing wider than 6".
75M quad loop presents a Lo-Z on all bands now and a 1/2 wave open wire
line cut and grid dipped for 3.562 MHz will be a 1/2 wave or multiples on all
bands (close enough) reflecting the 1 WL quads Lo-Z at the end of the
feedline for easy matching into most any tuner in particular with a "2 wire
quad" to simulate larger diameter. Unbalanced tuners can even be used with
toroids on the coax. This is a great FD or Base antenna. Now this and the
previous 40M quad only works if you actually try it.
I want to erect again a 1 WL horizontal quad loop hung between the baseball
light poles at home in SD cut for 900KHz (292'/side). It's not for the BC
band but to have an "end fire pattern" on 160,80,40M with "progressive gain."
There are football fields with poles the right spacing that aren't used on
FD (baseball fields will be) that would be absolutely great FD sites. If the
football field light poles aren't wide enough make it rectangle. I'd like to
take that new Yaesu 5W rig to Safeco Field with the big roof during a game
and do some gamma matching with a tuner on 160,80,40M. Big bridges are
potential FD 160,80&40M antennas anytime as are water towers if there are no
other RF Service antennas on it. Those big cranes used in shipyards are
potential antennas with some "creative feedline matching" using a tuner and a
wire with a vice grip pliers to make a connection. I'd like to try the Space
Needle or the Narrows Bridge on 160M. Awesome! K7GCO
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