----- Original Message -----
Sent: Tuesday, May 12, 2009 2:16 PM
Subject: Re: LF: Re: Re: 500kHz
Portable
A full quarter wave inverted L with sloping end is starting to become a
loop with the ground path forming part of the loop conductor, rather than a
vertical. ANY antenna that approaches more than about a tenth of a
wavelength cannot be treated as small any more, and must be considered in its
entirety. Such is obvious even before resorting to modelling. Mike
was referring to electrically short antennas where the downward sloping part
simply opposes the current flow in the upward path.
A small amount of slope on a large capacity hat might not be too
noticeable in practice, as a lot of extra capacitance at the top could do more
good than its slope undoes.
Please stop and actually think, and perhaps before being so rude
and treating all why don't own millions of hectares of farmland as
second-class radio-ams, you stop and read the exam question.
I QUOTE from emails sent on the reflector by the
man himself, but forgot to mention the TOOTHBRUSH
INSULATORS.
If one is serious about LF/MFantennas and putting
out a respectable signal then perhaps some hectares would be an
advantage.
Now is the time to buy.
G3KEV
Andy G4JNT
wobbleU
cubed .g4jnt.kom
2009/5/12 mal hamilton
<[email protected]>
You
are certainly NO EXPERT at amateur radio never mind LF/MF and especially
antennas.
I have worked the world on LF/MF using Inv L antennas with the
far end just above ground , and in normal CW mode.
Some time ago it was
Comics, elevated lemonade bottles as coil formers, thought an AR88D
was a diversity fly catcher.
What is coming next? The diversity
UMBRELLA!!!!
My current MF antenna is a full 1/4 wave inv L, 100 ft high
and performs well but for some this might be difficult, therefore use what
you can get on your property and let the far end tilt down if
necessary.
G3KEV
----- Original Message ----- From: "Mike
Dennison" <[email protected]>
To: <[email protected]>
Sent: Tuesday, May 12,
2009 10:29 AM
Subject: Re: LF: Re: Re: 500kHz Portable
You
do not need 2 masts for an inv L or T antenna.
The so called
horizontal wire(s) can slope down and the far end tied
to a bush or
tree, or a stake in the ground via an insulator, as far
away as
possible from the vert section, the longer the better. Keep
it
simple. mal/g3kev
This is quite wrong. Any slope
downwards will reduce the effective
height of a Marconi. Since ERP is a
function of the square of the
effective height this is extremely
important. An umbrella is far
preferable to an inverted-L in a single
mast situation because a
large amount of capacitance to ground can be
achieved without much
reduction of effective height.
Based on my
experience of LF portable (both on 73 and 136kHz), my
advice is to make
very sure that the remote ends of a Marconi are
very well insulated as
they carry large voltages. Keep well away from
wet trees. This is not
just a safety issue; any voltage leaked is
power lost.
Mike,
G3XDV
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