From: G0MRF@aol.com
Message-ID: <39.3c35684.2629b33c@aol.com>
Date: Sat, 15 Apr 2000 07:57:48 EDT
Subject: Re: LF: Field Strength G3WSC in DL
To: rsgb_lf_group@blacksheep.org
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

In a message dated 4/15/00 6:10:06 AM GMT Daylight Time, DK8KW@compuserve.com 
writes:

<< G3WSC Beacon 
 Saturday morning                ?               34.1 dB microVolt/m
 
 
 at a distance of 697 km
  >>

Hi Geri.

Some information which may help:
As of last night at 00.50  local  I had set up the system as follows.

Transmitter.  My old MRF linear fitted with class D drive and 4 STW34NB20 FETs

    36V supply  at  20 Amps.      i.e. 720 W  DC input.

estimated efficiency  85% after the LPF.  or  612 W out.  (let's say 600)

efficiency of mast at 137k  (Decca figures) 15%   so   90W radiated    
BUT.......
losses in matching coils are suggested to reduce this to 10%   or 60W.

For a 15% efficient antenna to radiate 60W from a 600W transmitter, then the 
loss in the loading coils etc. must be 200W. 

( since 600 from tx - 200 losses = 400 and 15% of 400 equals 60W radiated)

By 00.30 local we had already bypassed the variometer's antenna current 
circuit to save the electronics, but had watched the fwd / ref network expire 
in spectacular fashion.

After all those estimates. some more real measurements to ~proove~ them.

The antenna current overnight was measured at 9A.
hence:

9 x 9 = 81    and 81x 5 ohms =  405 Watts (after losses) delivered to the 
antenna which at 15% efficiency is just about 60W radiated.

and yes, the variometer ( A litz wire professional unit)  was quite warm.

As for radiation pattern / ERP / and the path loss over 697km.. I'll leave 
that to the you and the group. - I look forward to seeing the data on the 
website.

YXM's TX will take over today.

Hope that helps.

73

David   G0MRF