[TenTec] 80 meter loops

[Billy Cox]

>Billy, without getting too far into the technical, your answer to

Getting into the technical is not a problem ... it's one of the
parts of the hobby I still enjoy even after all these years. B-)

>Why does not the 20m dipole work twice as well on 10m, (hope I am
>summarizing your thought correctly) is that Antenna effective area differs
> from geometric area by a k factor.

OK ... now you are using effective area, before some were saying
that because the larger antenna's capture area is bigger, it will work
better ... <and I agree with your k factor note above as the key is the
actual EFFECTIVE area ... not the total length of conductor(s)>

One of the "ham lore's" that seems to continue to be passed
along ... goes to the tune of ... bigger/longer is better, just as
higher is better ... when the reality can be much different.

>However, in dealing with wire antennas such as horizontal loops over equal
>ground, & equal other parameters, you will have greater and worthwhile gain
>as you go higher in frequency, i.e. an 80m loop used on its harmonics.
>There are indeed pattern differences in the classic modeling.  In actuality
>of operation, ionospherics are so non uniform that pattern lobes do not
limit
>usability of a given azimuth direction from the loop on the harmonic bands.

Not just with horizontal loops though ... use a 40m dipole on 15m
and you will have a different pattern on 15m than on 40m, and in
theory, some gain. Ditto for the 20m dipole, with a proper matching
network <be it a rig's  internal tuner with coax or open wire and a
Matchbox>, it will radiate with a different pattern on 10m, than on
20m due to the total EFFECTIVE area of wire now being 1.0 wave
on 10m or roughly 33-36'. Yet ...

It may not "work better" <now there's a moving target!> due to
having a larger 'capture area' ....

>his is a topic of ongoing experiments, from a uniform site used each year.

And as I recall ... there's been past discussion about those results too.
B-)

>It has been a rewarding finding of going to the large horizontal loop,
>(several wavelengths on the frequency in use).  However, as in all antennas
>there is no free lunch, and you must live with mechanical demands of wire
>tension limits, sag, static build up and dissipation, etc.  In a free space
>case, lobing and nulls are shown, but less a problem in wide area use such
>as Field Day.

Agreed!

>Loop Symmetry is important we find in the achievement of best operations as
>a near omnidirectional radiator.   Other geometries can be effective in the
>directions of longest sides, but you give up some gain in other directions.

Or the changes may be what is needed for the desired purpose of
the loop ... I used a 80m vertically polarized loop at another QTH,
fed on purpose/design 0.25w down from the apex to ensure the
horizontal radiation was min, and the vertical was max. In this case,
the pattern was broadside and not near omnidirectional which is
what the goal was to achieve.

There may or may not be any "gain" ... that takes us back to the
effective area of the antenna on the desired freq. and as well a
very good point that you mention next. ... Antenna siting.

>One must steer the lobes as needed by careful siting, and have the
>antenna free of outside influence, just as in any antenna.

QSL! ... It would be very interesting to study this very point with the
various loop experiences that have been posted ... as a large 80m
loop when used say on 10m ... could indeed have observable gain
on specific headings. So how the loop were oriented verses the
observed results "I was loud into DL6" would confirm such parameters.

Likewise ... random antenna positioning could make NULLS appears
into the desired heading ... "I put up a loop just like his, but it really
stinks into DL6" ... Why? Due to the orientation of the loop's pattern
at the second op's QTH ... with to the siting <heading> being different.

The W8JK's book that was mentioned ... and also
various ARRL texts, including ON4UN's works and
certainly W4RNL's site ... all of these are great places
to spend some time browsing during the next solar flare
for those who would like to learn more about this topic
currently being discussed in this thread.

Antennas ... one of the final frontiers we can still explore!

73 Billy AA4NU