[Antennas] typo - word processor bugsFw: synchronzied MLA/trasnceiver tuning

[DavidE Benedict]

Here is some interesting stuff about small magnetic loops I found on the
web. I think I might try one for 40M - 10M or so, keeping in mind the
information in this article...and remotely tune the capacitor via digital
motor.
David B
W7DBH

Small Magnetic Loops
The “Antenna Designer’s Notebook” (ARRL?) has a number of simulations of
magnetic loops. These antennas are a closed loop, but with a high Q, they
actually produce a significant E field voltage, though the near field is
predominantly H. A 10m band loop of diameter <2m qualifies as an ESA.
Their efficiency is good when thick copper material is used for
construction. Bandwidth is small, so easy retuning is essential. The book
shows designs with two capacitors, of which one could be switched and the
other mechanically tuned air-spaced.

Disadvantages with loops are they require high quality tuning capacitors,
and heavy gauge copper because radiation resistance is very low. Loops for
bands below 20m must be large to get good efficiency. The recommended
minimum is 0.1l measured on the circumference. That means a diameter of
>1.3m for 40m, and >2.6m for 80m. Such a lot of heavy copper would be
expensive to make and difficult to mount outside. They are thus only
really practical for the higher bands.

For the moment I am not pursuing loops, but if other things fail I will
come back to them. My feeling is they don’t offer “something for nothing”.
The size vs. bandwidth (Chu) limit for loops was quite recently revised by
H.Thal. His highly mathematical paper suggests (I think?) that the
effective Chu limit is worse for loops than dipole derivatives. So the
conclusion in terms of an amateur antenna is they have a lower “goodness”
in efficiency, but compensate by being less sensitive to local noise which
is largely E field.

There is a distinction between small and large loops. A loop of nearly 1l
(a quad) has E and H fields in similar proportion to a dipole, whereas a
much smaller loop is predominantly an H field device.



meils at get2net.dk writes:
>my MLA mail (May 24, 2011, 6:16 PM (CET))
>SHOULD have been signed:
>
>73
>Henry F. M.
>OZ3O N2NR
>
>
>----- Original Message ----- 
>From: Henry Frederick "Meils" Meiseles 
>To: antennas at mailman.qth.net 
>Sent: Tuesday, May 24, 2011 6:16 PM
>Subject: synchronzied MLA/trasnceiver tunig
>
>
>One of the major setbacks with MLA's is the need to retune even for small
>(5-15kHz) 
>QSY's.  Wouldn't it be possible to build a  device that would couple the
>remotely tuned  MLA
>driving motor to transceiver tuning, perhaps where a single synchronizing
>"zero-set" would be needed when starting up the transceiver and/or
>changing bands? I'm thinking of the digital remote tuning options on many
>modern rigs. 
>
>I'm not necessarily talking about conventional automatic (remote) ATU's
>but the control and sensing circuitry of such could also be applied to
>MAL's -- presumably running QRP  
>in tune-up & then automatically going to full power when the SWR is
>minimum.
>
>For all I know, some commercial MLA models may already offer this type of
>feature.
>
>(I take for granted that posting this idea on an open internet
>thread/reflector is considered
>making the idea public knowledge in terms of patent claims and thus is
>not patentable --- if not have fun because I have no patent ambitions on
>this
>nor do wish to write an article about it  -- I'm not too competent in
>digital control
>systems. Also, I am chronically lazy ;0) 
>
>74
>
>Henry F. M., Cph.
>OZ3O NAN
>
>
>
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***
day, May .2011



David B
W7DBH
971-322-7529   9 AM - 9 PM Pacific Time
820 NW Wade Street Unit 26
Estacada, Oregon  97023

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