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Message-ID: <00a501c7dac2$b551dc60$517d383e@Tom>
From: "Tom Boucher" <tom@telemetry.demon.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <Pine.LNX.4.64.0708091508540.10082@lurcher.twatt.local>
Date: Thu, 9 Aug 2007 21:20:19 +0100
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Subject: LF: Re: Antennas & ERP
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Status: O

John

I've been beaconing all evening on 503.5 slow CW. According to your grabber, 
you are either transmitting yourself on the same frequency, or you are 
receiving me at 90dB over 9!

73
Tom G3OLB

----- Original Message ----- 
From: "John Pumford-Green GM4SLV" <gm4slv@sighthound.demon.co.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, August 09, 2007 3:27 PM
Subject: LF: Antennas & ERP


> Hello LF group,
>
> I had another 2-way CW QSO with Finbar last evening at around 11pm Local
> Time. His signals were on the whole a bit better than the previous night
> and I think mine were better too at the start, although the QRN and QSB
> eventually took me down into the noise by the end.
>
> During the day I did some measurements of antenna current vs TX DC input
> power (easier to measure) and based on them (and a knowledge of PA
> efficiency) I have graphed I^2 against Power to come up with a straight
> line, the slope of which should correspond to overall antenna system
> resistance.
>
> This has given me a set of figures from where I can quantify
> improvements. It has also showed me that tne new antenna installation is
> seriously in need of work!
>
> For 50W RF power I get 0.65A RF feed current which implies a resistance
> of 118 ohms!!
>
> Other data points for powers between 4W and 50W tend to agree with this
> figure. The best fit line is around 115 ohms.
>
>
> Calculation of likely radiation resistance gives me around 0.14 ohms,
> which might be a tad optimistic, so my EMRP will be around 50mW, for 50W
> TX power. Obviously I need to improve this, if for no other reason than
> that I don't particularly want to run high RF power just to heat up the
> worms.
>
>
> I will attempt to lay some more radials tonight, and add some more earth
> rods and then remeasure current vs power.
>
> Hopefully the QRN will be lower this evening for another QSO attempt -
> and hopefully make GW this time?
>
> Regards,
>
> John, GM4SLV
>
>