Dear Christer,
In the Dutch Magazine "Radio-Nieuws"of 1 April 1925 I found a treatment of
the multiple tuned antenna by Ir. (later Prof.) Huijdts. It confirms what
Rik, ON7YD, expected: In a multiple tuned antenna with N radiators each one
has a loading coil of N times the selfinductance of the coil for a single
radiator. For our amateur antennas on 137 kHz, having small capacitance
speaking in LF terms, a single coil already has awkward dimensions, not to
speak of coils of N times as large!
As to the distance between the radiators we can look at the antenna of
station SAQ at Grimeton. It is obviously a multi tuned one, also called an
Alexanderson antenna after its inventor who also designed the alternator
used at Grimeton. From the description on the website we learn that there
are six vertical radiators at intervals of 380 metres. That is for a
frequency of about 19 kHz. Scaling the antenna for 137 kHz yields a distance
between radiators of (19/137) * 380 = 52.7 metres.
I don't think the voltage on the antenna increases as Rik says. In a single
radiator with a coil of X ohms and I amps current the voltage is I * X .
With N radiators the current in each one is I/N but the reactance of the
coil is N * X. So the voltage is (I/N) * N * X = I * X as before.
73, Dick, PA0SE
-----Oorspronkelijk bericht-----
Van: Rik Strobbe <[email protected]>
Aan: [email protected] <[email protected]>
Datum: maandag 23 augustus 1999 10:41
Onderwerp: Re: LF: Multiple tuned vertical
At 08:43 21/08/99 +0200, you wrote:
I would like to hear if anyone have tested the Multiple Tuned Vertical in
some form.
I have understood that the antenna transforms the feed impedance with a
factor equal to the square of the number of wires used. E.g.10 wires would
raise the feed impedance about 100 times.
I'm just rebuilding my LF-station and this antenna looks very interesting.
However, not much information has been found in my litterature. Links or
articles would be much appreciated.
73,
Christer / sm6pxj
I found a brief decription of a vertical antenna with multiple tuning in
the "Handbuch der Hochfrequenztechnik" by Meinke/Gundlach (p. 531 in in the
1968 edition).
I think it works quite similar to the open / folded dipole system where a
folded dipole also has 4 times the radiation resistance of an open dipole.
So having 2 tuned vertical wires connected to 1 topload will multiple the
radiation reststance by 4, 3 wires will multiple by 8 etc ...
If each vertical wire is well separated and has its own groundsystem you
will also reduce losses.
So far 2 things stopped me from testing this system :
1. How far do the vertical parts have to be separated to be effective ?
Looking at folded dipoles for HF/VHF the 2 parallel parts are at least 1%
spaced, this would mean about 22m on 136kHz.
2. On first sight (and doing some simple calculations) the total antenna
capacitance is 'divided' over the multiple verticals. So that would mean
that not only each vertical part will need its own loading coil but also
that for a 'double tuned' antenna each loading coil will need the double
inductance compared to a 'single loaded'. For a 'triple loaded' antenna the
inductances of the loading coils will need to be 3 times bigger etc ....
Also, if you feed the same current into the antennasystem the
antennavoltage will double for an 'double tuned' and triple for a 'triple
tuned' antenna. This might also created some practical problems.
I am a bit sceptic about the practical use of this antenna, but this should
stop nobody from testing it and reporting results to the reflector.
73, Rik ON7YD
Rik Strobbe ON7YD
[email protected]
Villadreef 14 B-3128 Baal BELGIUM (JO20IX)
|
