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[TowerTalk] P.S. on Comtek & Quad vs. Yagi

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Subject: [TowerTalk] P.S. on Comtek & Quad vs. Yagi
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Date: Tue, 27 Mar 2001 19:47:56 EST
Brief summary of this weekend antenna tests and WPX SSB adventures.
(For those who care.)

After finding out that Comtek phasing unit needs between 30 to 50 ohm 
impedance antennas, I reconfigured (degraded) my 4 square vertical radiators 
for about 50 ohm impedances and used 1/4 wave radiators with single elevated 
sloping radials. I pruned the individual radiators with MFJ antenna analyzer 
(software was telling me wrong dimensions!!!) in the test setup in the 
backyard. I was able to get 50 ohms at the TX port of COMTEK phasing unit, 
but not the dip of power going to the dummy load port. Those two were offset, 
which indicates problems with 10m phasing unit (160 and 80m units don't do 
that), mirroring what I was getting when testing it with 50 ohms resistors.  
No time to mess around more, good enough for use in the contest fire. I tuned 
it for minimum SWR for phone band, not to worry about dumped power, had big 
enough resistor to consume it. There was finally directivity out of verticals 
(~25 dB F/B)! This was major difference from the triangular array using 
Stackmatch which sucked, I could hardly see ANY directivity (possible problem 
with shields of reflector's coax loading stubs being connected together?). 
Interesting thing was that both antennas produced about the same signals. Is 
it possible that triangular had "gain" in all directions, or 4 square 
consumes the gain to produce better F/B? :-) - Just crude observation, no 

Now on to "no good" quad!
Learning my software modeling lesson, no time to mess around to find out what 
is wrong with what (whom), I resorted to my good old 3 el. quad design done 
on 2m model way back (software was telling me different dimensions, to be 
verified on the 2m model later). I wanted to take advantage of dual 
polarization (that "doesn't work") and installed the quad about 1/2 wave 
above ground. Slapped together small tower, 3 el. quad on .43 wave boom, has 
50 ohm feedpoint, just like my old 2m model. Tested it in the backyard, 
forgot about insulated wire shortening factor, retuned smack into the 10m 
phone band. Quick comparison with 4 square, quad is beating the four legged 
animal by one to two S units on RX, same on TX. (Hold your flames, I know 
about miscalibrated Smeters and "impossible" dB differences.) Good enough, 
disassembled, loaded on the roof rack of my 72 Buick LeSabre Radiomobile and 
left at Friday 2 a.m. for Cape Hatteras. The rest of the adventures (almost 
set the car on fire) belongs to another reflector, but considering problems 
that I had, I was very happy to verify my design goals, see the antennas 
perform well and survive blowing winds and for the first time to hear the Sun 
noise on HF so loud! The quad was mounted on the boat ramp over salt water, 
sure looked cool!

Forgive me but my conclusions are: that parasitic vertical arrays on the 
beach suck (or I am dummy who can't make them work), forced feeding is the 
way to go; that properly oriented parasitic 3 el. Quad is excellent performer 
and this is the base on which I can further develop beachy arrays for more 
kick. Looks like I have to be very careful when using software for designing 
antennas for the salt water environment, or close to ground, it might not 
know what is doing. I will trust more my instruments than them fancy computer 
pictures. This finally turned out to be the winning combination I was looking 
for, polarization diversity, combination of rotatable RF beam with quick 
switchable array for two rig operation on the same band. And yes Virginia, in 
real life Quad shows more dBs than what software states with better pattern 
than similar Yagi (yea, I know, itsa "folklore" :-) 

When I clear backlog of work that piled up in the mean time, I will try to 
elaborate more. 

Thanks to those who had mercy and gave me a point. If there are any 
observations and comparisons of signals, I would appreciate hearing (reading) 
about them.

Yuri, K3BU
one of Tesla Contest Sparks - N2EE, NT1E

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