[ARC5] Rollerductor setting

[Kenneth G. Gordon]

On 22 Apr 2017 at 14:55, J Mcvey via ARC5 wrote:

> 
> I , too, am reluctant to add turns or modify the transmitters. These poor things 
> have been hacked enough over the years!
> Here is an observation that I 've made with the series cap and unun setup:
> While the watt meter on the 50 ohm line shows 50 watts the BC-441 ammeter 
> looks to be much  less than 1 amp!

I have mentioned more than once that this is because an RF ammeter's reading depends on 
the impedance it is "seeing". Those in the ARC-5 (generic term) are setup for a LOW 
impedance antennas. I=E/R, therefore, the smaller the R the greater the I for the same 
voltage, which in the case of our transmitters, translates to P or power output. 

So, for the same power output into a LOW impedance, the CURRENT must be greater, and 
vice versa. P= I^2*R, so, again, the lower the R the higher the I.

Simple.

> This does not square with a straight 12.5 ohm match which should be just under 
> 2 amps.

But where in the circuit is your RF ammeter? Before or after the cap and/or un-un? If before, 
then you have a legitimate question. If AFTER then the RF ammeter is "seeing" the higher 
impedance.

I suspect, given the way the circuit seems to be laid out, that your RF ammeter is AFTER 
the cap and/or un-un, in which case what you are seeing is correct.

Ken W7EKB

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