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[TowerTalk] 40M FD Antenna

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Subject: [TowerTalk] 40M FD Antenna
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Date: Wed, 27 Jun 2001 11:07:15 EDT
 In a message dated 6/26/01 8:36:06 PM Pacific Daylight Time, 
  << 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 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
  > 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 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 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 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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