Re: Availability of Mag Loop and other stuff...

ajparent1/KB1GMX
 

Jack,

Not aimed at you personally that was a general comment on some of the other loop vendors
that came from nowhere.  After all at this point you not selling anything.  If you telling people
how to do it [book] that's experimental electronics and encouraged.  

As to getting HOA/restricted people back on the air a loop is a possible choice but far from
the only one.  It has potential for a quick trip to the park, hill or other areas where ambient
electrical noise is much lower and its desirable to have minimal setup time.   Usually the
limitation is lack of imagination and maybe understanding of antennas in general.  Antennas
do not have to look like antennas and they can be reasonably efficient with a small amount
of work.  The key element is to look at the box and not be limited by it.  The biggest thing I
see is everyone wants every band even the inactive ones.  Two maybe three bands with a
reasonable antenna is far easier and more likely to be enjoyed.  

And being 10db down from a "good" antenna is not a crime.  I've worked a lot of DX from the
mobile on 40M QRP SSB with a center loaded 8ft whip.  Efficient?  No they are legendary for
being terrible as in easily 10db or more down from a full size vertical.  However the mobile is not
unlike the HOA, we just add it has to work at 80mph and clear a 12.6ft bridge (we have
low ones here!) when mounted on a truck more than 4ft above the road with a crappy
ground (counterpoise maybe?).  

As to commentary on exogenous factors, when you quote dB and people look at it without
understanding or knowledge of those factors it can look better than it is.  Fact is and I
already said that you cannot control the external factors as it would cost dearly, having
done it for MIL applications and budget.

Also I think it was Arv that suggested scaling it for low VHF and that can be done to show if
correlation holds true but its a lot of work to make a scale model and  test it against a vertical
dipole. 

I've done that and it can be close (usually +-1db) and the amount of room needed is a back
yard without metal fences or aluminum siding as reflections will make you nuts. Reflections
can make for errors as in higher or lower gain that should be expected.   The test is RF
source to a vertical dipole and a second dipole at a distance of 10-20M at 2m will do ok
and you get a RX measurement that will be the reference.  Dipoles vertical or horizontal if
resonant are predictable in gain and behavior.  A pair of ELK log periodic antennas would
work well for this, they just have to be the same.  I've used 4 element yagis for 2m and
432 as test antennas as they are simple and easy to make.  In any case directional
antennas  make for fewer issues with weak signals and reflections.    Now substitute the
antenna under test and  get new reading.   How to get an accurate reading is easy, on the
TX side use maybe 20dbm (100mw) and an attenuator to radiate a signal to the RX and
then use the attenuator as adjust the signal to S9. install new antenna at the RX end and after
recording the attenuator before then adjust it for S9 again.  The difference is gain or loss.
A SA can make that easier but any detector can do the job if sensitive enough and has
selectivity to avoid offending signals.  I've used a AD8703 for that with an input tuned
circuit [bandpass] added to keep it from hearing FM broadcast stations.    Don't try this
at HF you will go insane or expend much treasure and going end to end to read or
adjust will wear you out.

Allison

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