[Boatanchors] RF current sensor

[GGLL]

May I add something?. The readings will be more accurate at higher 
frequencies if you put a faraday shield between the conductor and 
winding (sort of coaxial cable, center hot, shield to ground AT ONLY ONE 
end) to diminish capacitive coupling.

Best regards
Guillermo - LU8EYW.


Dave Brown escribió:
> Roger
> It certainly would be OK.
> Put as many turns as you can easily- number of turns not critical in 
> your case as calibration is not an issue- on the toroid and load the 
> winding with a shunt resistor. A series diode from one end of that 
> winding to the meter and a cap across the meter (say 0.1 uF) with the 
> other end of the winding going to the other meter terminal. Add series 
> resistance between diode/cap junction and meter terminal if needed - 
> maybe a pot- and/or juggle the shunt resistor on the toroid winding to 
> get whatever reading you want on the meter.  The toroid is threaded onto 
> the conductor you want the current indication from, of course!
> The resistor values to use will depend on the sensitivity of the meter 
> movement and the rf power in use- all values non critical in your 
> (uncalibrated) case.  Try 4k7 across the winding for starters (assuming 
> say 100 watts rf) and maybe a similar value pot to set the meter reading 
> as required.  Be aware that the reading will be frequency dependant-you 
> can reduce this effect by keeping the shunt resistor across the winding 
> as low as possible.
> 73
> Dave, ZL3FJ
> 
> 
> ----- Original Message ----- From: "Roger Basford" <roger at new-gate.co.uk>
> To: <boatanchors at mailman.qth.net>
> Sent: Thursday, May 03, 2007 6:40 AM
> Subject: [Boatanchors] RF current sensor
> 
> 
>> Hi All,
>>
>> I've been looking without success for an 15 amp RF meter for my BC-939 
>> ATU. As I'm not really bothered about a calibrated scale for the 
>> meter, just tuning for maximum output, I think that a current sensor 
>> driving a milliampere meter would probably be OK. I used to have a 
>> simple design used on a VLF TX using a toroid with a link passing 
>> through the centre carrying the RF current. Unfortunately, I can't 
>> find the circuit again. Anyone tried a similar method of replacing an 
>> RF ammeter?
>>
>> Regards,
>>
>> Roger Basford/G3VKM
>>
>>
>>
>>
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