RF Ammeter

[Jim Wiley-2]

As everyone knows, "real" RF ammeters are becoming scarce,  or very
expensive.  Does anyone out there have info on where to find a circuit
that is relatively inexpensive that I could use as a substitute?  
Something using a toroid core plus diode, or something like that,  would
be what I am looking for.   Not too complicated in any case, and  
absolute accuracy is not needed - a relative indication would be fine.  
The application is measuring RF current for a trailing wire antenna  
from an airplane.    Transmitter power is in the 100 watt range.


Thank in advance


- Jim, KL7CC


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[Phil Kane-2]

On 12/18/2011 11:17 AM, Jim Wiley wrote:

> As everyone knows, "real" RF ammeters are becoming scarce,  or
> very expensive.  Does anyone out there have info on where to find
> a circuit that is relatively inexpensive that I could use as a
> substitute? Something using a toroid core plus diode, or
> something like that,  would be what I am looking for.

  RF ammeters - direct reading or remote reading - are used
  extensively in AM broadcast antenna arrays.  In most cases they
  are available off-the-shelf but cheap they are not.  I'm sorry
  that I don't have a convenient URL to point you to but check the
  sites of AM BC transmission equipment suppliers.

--  73 de K2ASP - Phil Kane
    Elecraft K2/100   s/n 5402

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[Jim Brown-10]

On 12/18/2011 11:17 AM, Jim Wiley wrote:
> Does anyone out there have info on where to find a circuit
> that is relatively inexpensive that I could use as a substitute?
> Something using a toroid core plus diode, or something like that,  would
> be what I am looking for.

Yep. Google to find GM3SEK's excellent website.

73, JimK9YC
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[Doug Faunt N6TQS [phone]]

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


On 18-Dec-11 19:17, Jim Wiley wrote:

>
> As everyone knows, "real" RF ammeters are becoming scarce,  or very
> expensive.  Does anyone out there have info on where to find a circuit
> that is relatively inexpensive that I could use as a substitute?
> Something using a toroid core plus diode, or something like that,  would
> be what I am looking for.   Not too complicated in any case, and
> absolute accuracy is not needed - a relative indication would be fine.
> The application is measuring RF current for a trailing wire antenna
> from an airplane.    Transmitter power is in the 100 watt range.
>
>
> Thank in advance
>
>
> - Jim, KL7CC
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>

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[Rick WA6NHC]

A short Google search found:

http://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm 

Merry/Happy Christmas,

Rick WA6NHC

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Doug Faunt N6TQS
[phone]
Sent: Sunday, December 18, 2011 12:54 PM
To: [hidden email]
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


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[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: [hidden email]
>[mailto:[hidden email]] On Behalf Of Doug Faunt N6TQS
>[phone]
>Sent: Sunday, December 18, 2011 12:54 PM
>To: [hidden email]
>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
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[Jim Wiley-2]

Thanks to all who responded.  Several circuits to try, so I am sure one
of them will work for what I have in mind.  Again, thank you.


-- Jim,  KL7CC


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