Message-ID: <006f01bf1ffd$55a92a80$4ff9abc3@default>
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: "rsgb_lf_group" <rsgb_lf_group@blacksheep.org>
Subject: LF: Musing on the data on CFH
Date: Tue, 26 Oct 1999 21:51:22 +0100
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

Dave and Dave have been kicking around some interesting thoughts about the
significance of hearing CFH to hearing WA2XTZ.
My own first thoughts put about 1.5kW into the radiation resistance, the
problem is that the ground losses will be quite low. Gamal quotes about
90%efficiency (ouch!) for commercial aerials which would mean more like 8kW,
say 40dB more than we have available.

On Dave G3YMC's point about aerial 'gain'.....
As an quick estimate I thought that a 200foot mast might generate a signal
3dB more efficiently than a 100foot mast.....I have no idea whether that is
sensible or not, but in other areas of radio, if you double the size of the
aerial you get 3dB more. (I dont have eznec or whatever!). That would mean
about a 7 or 8dB disadvantage for a 100foot 'T'. That makes a grand total of
about 48dB, or a signal -18dB relative to the noise in whatever
andwidth( Dave G3YMC quoting 30dB above the noise for CFH). I must admit
that that figure seems possible. WA2XTZ is about 10% further away, but again
due to the angle of the North American coast, the path is predominantly over
water.

If I work the figures corrrectly John Lamont's propagation chart for a water
path of 3000kms  suggests that the CFH signal should be between 90 and
900uV/m, so WA2XTZ should be somewhere in the 100nV/m to 1uV/m range. Maybe
some of the previous loggings of CFH could be worked back to test that
figure. Note that 2000kms over land (I to OH) has already been achieved the
graph predicts (assuming 1Watt ERP TX) a rx field strengh 30nV/m for that
path. I am making the assumption, because I can't find any counter-evidence
in the data I have available, that the graph in Lamont's paper ,derived from
CCIR recommendation 368, is independent of frequency (!) though it specifies
73kHz. I would say that with a signal approaching 1watt ERP it looks a
definite possibility.

I suspect my postage-stamp calculations make heavy use of the mathematical
operator  'O'
.......that golden multiplier called 'optimism'......but that is what it is
all about!
All we need now is to get Andre' burying a few tons of copper!
73 de Alan G3NYK
Alan.Melia@btinternet.com