In a message dated 3/18/01 6:42:10 PM Eastern Standard Time,
jterleski@home.com 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
problem.
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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