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[TowerTalk] problems with 10m COMTEK 4 sq unit

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Subject: [TowerTalk] problems with 10m COMTEK 4 sq unit
From: (
Date: Sun, 18 Mar 2001 20:32:06 EST
In a message dated 3/18/01 6:42:10 PM Eastern Standard Time, writes:

<<  You mention that your dipoles have an impedance of 110 ohms, so the 75
ohm 1/4 transformers are transforming this to 150 ohms.  Not good, the
hybrid coupler is looking for 50 ohms and I am sure Comtek is using 50
ohm transformer windings in the coupler, at least that is the design I
have seen in ON4UNs book.  At 30Mhz things get worse than at 3.5 Mhz so
any stray inductance and capacitance in the coupler will magnify the

You may want to try to reduce the dipoles impedance by using a 2:1
broadband xfmr to take it back to 50 ohms first.  But you also state
that resistors plugged into the coupler are also not giving you the low
SWR you expect to see.

Thanks Jay for elaboration.
I think there is something wrong with ACB-10, unless there is something 
special that has to be done. I will wait for Jim's answer.

I was hesitant to use any matching devices (hate those things) to bring 
impedance down to around 50 ohms, maybe I am wrong. But when I look at the 
other two ports, they have way high impedances (when -90 and +90 feed), if I 
put some matching gizmo at that point, wouldn't it fry? If the phasing unit 
needs around 50 ohm radiators (nowhere in the manual does it say) then I 
rather redo the antennas to give me 50 ohms. I have that with triangular 
array (using 1/4 wave radiators and elevated 1/4 wave sloping radials). I was 
just wanting to try half wave dipoles, with their elevated high current part, 
aiming to gain some extra gain and further out reflection point at the salty 
beach and cleaner installation. I will try 3/8 verticals with elevated 4x 1/8 
radials, they give 50 ohms and I have modeled some other variations of 
vertical radiators that I can try. Another alternative would be to brew my 
own hybrid optimized for those weird impedances and "VHF" 10m band, but no 
time was this WPX. I will be interested to see your 4sq phasing gizmo. We 
don't mind to tweak or adjust as long as we know what's cooking. Selling 
boxes "that work, don't worry about it" is not good enough for some of the 
inquiring minds :-) Where are the days when things came with schematics, 
theory of operation, description, specs, etc.
       The objective here is to get best sharp and clean pattern, I want to 
use it on receive in SO2R on the same band setup. Need polarization diversity 
and quick switch for directions in addition to some rotary Razor stuff.
       From modeling, looks like triangular arrays are not very sharp, I am 
willing to go for extra element to gain that extra 20 dB in F/BS. 
       Statement from Comtek manual says that on high angle signals there is 
little directivity from 4 square (I can see that). How do we reconcile that 
with patterns shown by modeling software and books? Isn't antenna suppose to 
exhibit performance as indicated by the radiation diagrams? Are some signals 
sneaking in behind the pattern?  :-)  Polarization quirks?
       Can't wait for warmer days on the beach to do some experimenting and 
real life testing.

73 Yuri
to be, or not to be NT1E in WPX SSB on 10m from Cape Hatteras, NC
any comparison reports with KC1XX, K3LR, W3LPL, W4ZV and other "beacons" on 
the band would be appreciated

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