Date: Fri, 2 Nov 2007 10:13:13 +0000
From: John GM4SLV <gm4slv@sighthound.demon.co.uk>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: RE: 500 kHz report /  Great expectations
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On Fri, 02 Nov 2007 09:40:31 -0000
"Dave Sergeant" <dave@davesergeant.com> wrote:

> On 2 Nov 2007 at 9:00, John Pumford-Green GM4SLV wrote:
> 
> > However, I don't think Dave runs even 25W though, and his antenna,
> > by his own admission, is very inefficient due to his sandy soil so
> > he's doubly handicapped:- 
> > 
> > Low TX power and poor efficiency. 
> 
> I run around 6W output.

Hello Dave, LF,

Thanks for your comments and explaination of your setup and experiences.

I only "butted" in after seeing your (tongue in cheek) comments about
moving house to improve ground losses!

I note your NoV purpose of investigating the use of 500kHz from a
'typical urban property'.

6W seems painfully low. I wonder what your estimated ERP is given what
you know of the ground losses and antenna dimensions. I'd guess it sub
10mW. No wonder I can't hear you!

My suggestion that more power is necessary in your situation is still
valid if the purpose is to investigate anything beyond the "comfortable
ground wave" zone that you're able to happily work.

I understand the feeling that it's poor practice to generate power
simply to heat the ground up, and that the correct approach is to reduce
ground losses. As you've observed this isn't practical so I see nothing
wrong with using raw TX power to push enough current into the antenna.
I'd not worry about how much was being dissipated in the losses, I'd
care about how much was being radiated. The more of the latter the
better!

My own antenna has no real "horizontal section" but has enough capacity
loading added to the already necessary upper guys to improve the ERP by
6dB over the straight vertical wire. I initially thought the steeply
sloping capacity wires would to some extent screen the vertical and
have a negative impact on the ERP. My measurements prove that they are
very, very worthwhile. I wonder if you could try that approach? If you
have to guy your 32 feet vertical (I certainly have to - at 4 levels!)
then using 7m of wire as the first part of the upper guys makes a
tremendous difference to ERP. I can't run any horizontal top loading
either.

>
> Since I shall be changing the antenna over to 160m before CQWW at the 
> end of the month, it is probably fairly academic.
> 

Hope to see you back on 500 afterwards. I'd give some thought to the
sloping capacity wire approach if more TX power is not acceptable.

I'm thinking of going QRP for a while - reducing TX power enough to
reduce my ERP to the 10mW range. I doubt anyone will then hear me
either but it'll be interesting to find out....


Cheers,

John