Thank's for the description , Mike , the distributed inductance on the
vertical is interesting , I use a top loading coil with the inv L on
500 ... I did have 2 parallel top wires in rectangular loop till the
wind snapped the coil connection of one side , making it into a U
shape .. which seemed to work better , the final config , is the far
end dropping at 90 deg to the ground , stops about 8 feet up , making
a |''''''''!
shape , fed at one end , top is 40 ft , vertical just 40 ft ..which
may be slightly better again..
I assume the top inductance , changes the array to a series L+C
network , so the feed to the coil is quite low .....match is good
with very little reflected power , only real problem is Rx , a very
high noise level , 3/4 scale on the ra1778 s-meter ..im sure it was
not that bad when the 500 nov was first issued.. :(
73 -G.
--------------------------------------------------
From: "Mike Dennison" <[email protected]>
Sent: Sunday, March 04, 2012 9:56 AM
To: <[email protected]>
Subject: Re: LF: Permissible QSY limits for 136
On 4 Mar 2012 at 2:09, Stefan Schäfer wrote:
Am 04.03.2012 02:01, schrieb Graham:
> Permissible QSY limits for 136
> Q what is the average Q of a 136 Khz Ae system ? (back
> garden + larger)
Maybe arround 50.
My very rough tests here suggest that a Q of 50 is about right. My
current reduces to approx 70% at 1.5kHz off the antenna's tuned
frequency. This is a Q of 1.5*2/137 = 46%. It is raining at the
moment and I would expect the Q to rise when it is dry.
The antenna is in a small back garden. It is an inverted-L, with a
14m vertical wire, and five roughly parallel top wires each 14m long.
Lots of trees around help to reduce the Q. Inductive loading is
distributed over several coils, small ones at the bottom and top of
the vertical section, and most inductance some 3m up.
The original question referred to SWR, which in most cases is
irrelevant. In practice, my PA makes worrying noises when the antenna
detunes by only a couple of hundred Hertz.
Mike, G3XDV
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