[Elecraft] RF Ammeter

[Ian White GM3SEK]

Rick Bates wrote:
>A short Google search found:
>
>http://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm
>
>Merry/Happy Christmas,
>
>Rick WA6NHC
>
>-----Original Message-----
>From: elecraft-bounces at mailman.qth.net
>[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Doug Faunt N6TQS
>+1-510-655-8604
>Sent: Sunday, December 18, 2011 12:54 PM
>To: elecraft at mailman.qth.net
>Subject: Re: [Elecraft] RF Ammeter
>
>I couldn't locate the GM3SEK article (is it still there?), but this is
>also useful:
>http://www.w8ji.com/building_a_current_meter.htm
>
>And I believe that QST and/or the ARRL Handbook has information on this,
>also.
>
>73, doug


You're there ahead of me.

The typical clamp-on RF current meter with a 10-turn secondary and a 
50-ohm terminating resistance has a theoretical insertion resistance of 
0.5 ohms, so it doesn't disturb the antenna very much. In practice the 
resistance is increased by the gaps in the core, so if possible I'd 
suggest threading the antenna wire through a ferrite toroid instead 
(probably #43 material for general HF use - NOT iron dust).

The article by G0SNO on the page referenced above shows how the RF 
current meter can be quite accurately calibrated using a transmitter, 
wattmeter and dummy load.




-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek