In a message dated 9/8/01 11:04:10 AM Pacific Daylight Time, i4jmy@iol.it
writes:
<<
>> Actually my first gain antenna was a 2L triband quad and K7WA
> > and I spent a whole Saturday screwing around with the tuning.
> > That was it for quads. That and the fact that I wanted to put a
> > 40M yagi up too and couldn't do it with the quad.
> > Cheers, Steve K7LXC
> > Tower Tech
> >
> Are you saying that you still can't just "cut and play" with 2L Quads?
> What about W4RNL's website, or others, for a good set of dimensions.
> Tom N4KG
I don't know what Steve meant, I know that even a 2L multiband quad is a
challenge and final F/B fair when some band is close to each other or
harmonically related.
Modeling and tests proved to me that 12m and 10m loops doesn't live
happily
together, expecially in 3 or more elements loop antennas and particularly
when same parasitic type loops are on a single cross arms.
I had a 5x10/4x15/3x20 multiband delta loop on a single boom that worked
fine, but 10 meters stopped (refused) to work properly when the 40m loops
were added, no matter everything was tried to refine 10m loops.
People often think that's all right with their multiband directional antenna
because of a low SWR and some F/B exist, but if they could compare with a
reference antenna, in some cases the disillusions could be many and big.
73,
Mauri I4JMY
>>
This 12/10M interference is a puzzling concept. In all the 5 band 2 element
tune ups I've done in Eznec I've been able to get clean patterns adjusting
the reflectors on every band. So has the W6 that had a 2 element 5 band quad
in QST. If 12M affects 10M, why doesn't 15M affect 12M, 17M affect 15M and
20M affect 17M? Or the reverse? I find very little RF on the off band
elements. I even added 6M which is further way frequency ratio wise. I'm
adding 144/455MHz in the rear.
Here's another one I did just to check out a theory I had. I drove the
higher off band DE and then the off band lower DE and got great
patterns--sometime better F/B. The Z's were way off but fed with open wire
line and into the proper tuner it will still put max RF into the DE. I will
check out the patterns in actual practice.
Now Exnec hasn't lied to me yet. Since this produces great patterns without
any retuning I would then have to assume there is some querk of 12&10M that
does this that is compensated for by retuning the 12M reflector the right
amount. So I have to ask--"were the 12 or 10M elements ever retuned. If it
works in Exnec I'm taking bets it works in actual practice. Are there any
betters? k7gco
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