Message-ID: <4ACD0AA3.30507@charter.net>
Date: Wed, 07 Oct 2009 17:39:47 -0400
From: John Andrews <w1tag@charter.net>
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To: rsgb_lf_group@blacksheep.org
References: <57a24ca70910070818o2e4adde4k1c8daa318eb2eb30@mail.gmail.com> <006001ca4763$a69a1290$0301a8c0@mal769a60aa920> <002601ca4766$1ff29bb0$6c01a8c0@DELL4> <4ACCD7FA.5080501@ukonline.co.uk> <4ACCB110.8A4E.00FD.0@globalstar.com> <F1FBC7A69D7E409DA52460C6547DC64B@JimPC> <4ACCBFC9.8A4E.00FD.0@globalstar.com>
In-Reply-To: <4ACCBFC9.8A4E.00FD.0@globalstar.com>
Subject: Re: LF:  Re Propagation report
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David,

You might try some web searching on the subject, as there is some 
material on calibrating receiving setups and making field measurements. 
Here's one possibility:
http://www.w1tag.com/LF_FSM.htm

John, W1TAG

David Weinreich wrote:
> Jim,
>  
> Thanks very much for the explanation it's very helpful. Too bad there 
> aren't very many calibrated receivers and antennas.
>  
> 73,
>  
> David Weinreich
> WA2VUJ/3
> 
>  >>>
> *From: *  "James Moritz" <james.moritz@btopenworld.com>
> *To:*     <rsgb_lf_group@blacksheep.org>
> *Date: *  10/07/09 4:02 PM
> *Subject: *   Re: LF:  Re Propagation report
> 
> Dear David, LF Group,
> 
> There are basically two ways of determining ERP, briefly:
> 
> Method 1 is to calculate the radiation resistance (Rrad) of your antenna,
> which can be done using various text-book formulae, or using antenna
> simulation software like EZNEC or similar. Then you measure the RF current
> flowing in the antenna (Iant). The ERP is then Iant^2 x Rrad x 1.8 (1.8 is
> the directivity of electrically small vertical or loop antennas, which in
> practice is what all amateur 136kHz antennas are).
> 
> Method 2 is to measure the field strength some km from the antenna. The ERP
> is then (E x d)^2 /49, where E is the field strength, d distance in metres.
> This requires a calibrated antenna and measuring receiver, so is more
> complicated to do.
> 
> Method 1 is simpler to do, but yields ERP results that tend to be lower 
> than
> those obtained by method 2. This is thought to be due to various combined
> environmental effects on the antenna, which are not accounted for in the
> simple calculation. So to get a more accurate and definitive figure, you
> need to do method 2, but as far as compliance with licence conditions is
> concerned, method 1 is a conservative way of checking.
> 
> Good luck in your efforts!
> 
> Cheers, Jim Moritz
> 73 de M0BMU
> 
> ----- Original Message -----
> but From: "David Weinreich" <David.Weinreich@globalstar.com>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Wednesday, October 07, 2009 8:17 PM
> Subject: Re: LF: Re Propagation report
> 
> 
> Peter,
> 
> As an interested observer from the other side of the pond, how do you
> determine that you are close to the ERP limit?? I'd be interested in 
> knowing
> as I am trying to do some pro-bono work for the ARRL on getting use of 137
> kHz here in the USA.
> 
> Tnx & 73,
> 
> David Weinreich
> WA2VUJ/3
> 
> 
> 
> 
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