Message-ID: <4A30AEEB.1080700@dsl.pipex.com>
Date: Thu, 11 Jun 2009 08:14:51 +0100
From: tim hague <m0afj@dsl.pipex.com>
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References: <memo.20090610114023.3260A@Jodan.cix.co.uk> <B6744C828D0E46809F88181F89342AEE@JimPC>
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Subject: Re: LF: Re Welbrook Loops
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James Moritz wrote:
> Dear Tim, LF Group,
>
> I tried some expeiments with measuring loop antennas at LF and MF a 
> while back - changing the height above ground from 0 - 10m made 
> virtually no difference. The only thing that made a lot of difference 
> to signal levels is if the loop is very close to big metal objects, 
> but even then the difference is only minor unless the metal thing is 
> big compared to the loop, and within a loop diameter, say.
>
> I would agree with G3YXM about overloading - if you have an 
> oscilloscope, it is worth connecting it to the loop output to see if 
> any huge signals are present. I have used elliptic low pass filters 
> here to reduce the signal level from the local medium wave broadcast 
> stations to a reasonable level.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
> ----- Original Message ----- From: "Trevor Smithers" 
> <tsmithers@cix.co.uk>
> To: <rsgb_lf_group@blacksheep.org>
> Cc: <tsmithers@cix.co.uk>
> Sent: Wednesday, June 10, 2009 11:40 AM
> Subject: Re: LF: Re Welbrook Loops
>
>
>> I use a 1530 as well, its mounted on a rotator about 2ft above ground 
>> level on a Barenco
>> socket/spike. Works well 80m down to 500khz but being so close to the 
>> ground its a bit deaf
>> above 80m as you would expect. My understanding is that for hf it 
>> should me mounted high up but
>> for lf its better low down near the ground.
>>
>> A rotator isn't really necessary as the beamwidth is quite broad but 
>> where I do find it useful is
>> nulling out the local qrm, switch modes etc.
>>
>
>
>
Thanks Jim for the info, I'll get myself a length of Fibreglass pipe and 
put it up over the roof, just got it hanging off the gutter at the 
moment, can hear loads on NDB's during the day, now to find out when the 
500kz activity is on.
I've checked the output on a scope and it looks reasonable

73
Tim