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Message-ID: <000601c7dac7$f7491f20$5042383e@Tom>
From: "Tom Boucher" <tom@telemetry.demon.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <Pine.LNX.4.64.0708091508540.10082@lurcher.twatt.local> <00a501c7dac2$b551dc60$517d383e@Tom>
Date: Thu, 9 Aug 2007 21:57:57 +0100
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Subject: LF: Re: Re: Antennas & ERP
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Status: O

Thank you John - have just proved you are seeing my signal by turning it off 
for a few minutes.

73
Tom/G3OLB

----- Original Message ----- 
From: "Tom Boucher" <tom@telemetry.demon.co.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, August 09, 2007 9:20 PM
Subject: LF: Re: Antennas & ERP


> 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
>>
>>
>
>