Re: LF: QRP RF Ammeter

[hajo.brandt.dj1zb@t-online.de (Hans-Joachim Brandt)]

Dear Weazle,

 

the general rule for current transformers is that for frequency independant operation the inductive reactance of the secondary coil should be at least five times the parallel resistor. The other aim ist to employ a ferrite toroid giving the highest inductance with the least number of turns. Therefore the Amidon material -75 should give best results (from those materials I know, there may be even newer toroids with even higher AL values, for switch-mode power supplies). Optimum choice of the parallel resistor will depend on the sensitivity of the meter available and its internal resistance.

 

OKP

 

73 Ha-Jo, DJ1ZB 

 

 

  "J. B. Weazle McCreath" <weazle@hurontel.on.ca> schrieb:

Hi Guys,

 

I'm in need of the details on how to build an RF ammeter for the Lowfer freqs.

Surfing the web has yielded plenty of info for the 137 band units, but they're

meant for much higher power.  I expect that I'll need a lot more turns on the

secondary of the current transformer, and likely a more sensitive movement

for the indicator.  Any and all help is appreciated.

 

73, J.B., VE3EAR - VE3WZL
Solar and wind powered
EN93dr