Message-ID: <9803ED54134D412AAA065AE40A233841@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <12959492286D45E9BB24E80CE57644CD@AGB>, <4F52C0BB.3010505@iup.uni-heidelberg.de> <4F533C5B.14115.450D3B1@mike.dennison.ntlworld.com>
In-Reply-To: <4F533C5B.14115.450D3B1@mike.dennison.ntlworld.com>
Date: Mon, 5 Mar 2012 01:12:23 -0000
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Subject: Re: LF: Permissible QSY limits for 136
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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" <mike.dennison@ntlworld.com>
Sent: Sunday, March 04, 2012 9:56 AM
To: <rsgb_lf_group@blacksheep.org>
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
> ==========
>
>
>
>
>