[Lowfer] This is getting interesting!

[Bill Ashlock]

Too late for my brain to be working, JD :)

I think you are right about the lack of lobes unless it's a really large 
loop.

I've never much understood how the popular little coupling loop actually 
works relative to my experiments at 185K. Even tried to make it work a few 
years ago at Medfer 1700K but the efficiency was way down compared to the 
transformer or capacity divider methods. I'm guessing that the inductive 
reactance of the small coupling loop has to be something like 4X the Z of 
the feedline and this turns out to be a rather large coupling loop at 185K. 
There's an article in QST's March 07 issue featuring a 1/5WL HF loop using 
3/4" Cu tubing and the same coupling loop. Apparently good performance but 
no trees to contend with. Also no real theory given.

Another thought about John's 53 ohms: I've found that if the loop isn't all 
that large relative to the distance above ground (say a 20ft diameter loop 
spaced 4ft above ground) the soil loss is very small. On the other hand a 
50ft diameter loop at 6ft above ground has measurable ground loss - maybe 
half of the total loss of a 1/2" Cu conductor loop at 185K. It's probably an 
area effect so at a given frequency the loss increases to the square of the 
loop diameter and a loop of twice the diameter has to be spaced 4 times 
higher above ground for the same loss. Probably gets even more severe when 
the loop is more like a squashed circle and the total area of ground under 
the loop increases over the circular loop. The equation for soil loss with 
frequency could be very interesting!

Bill


>> I'm guessing that the LF nulls will be filled in,
>> and that the pattern will be more circular.
>
> This may be.
>
> The 1/4-wave loop would exhibit a pattern in free space just like that of 
> a
> very small loop, as I mentioned a moment ago.  But of course, it's not in
> free space.
>
> The same environmental interactions that result in local loss will also be
> coupling power into the supporting trees, which will be re-radiating to a
> certain extent, and may thus perform some partial null fill.  Alas, this
> re-radiation will also reduce field strength in some other directions, but
> so inefficiently that there will probably not be new nulls.
>
> JD
>
>
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