Hello Dick and the list,
I suggest a converter U/I with AOP the drive the galva in current.
73: Jeff F6CWN
> ----- Original Message -----
> From: Dick <[email protected]>
> To: <[email protected]>
> Sent: 14 May 2006 20:58
> Subject: LF: 'meter problem'
> Hello all,
> I almost finished my new 136kHz transmitter, and after several hours of
> fault-finding it seems to work upto
> 600-700Watt DC input.
> However, I do have a 'problem' ..........
> Instead of using a 200uA meter for the forward and returned power, I'm
> a 10mA meter.
> This 10mA meter needs 53mV for full scale, internal resistance somewhere
> around 6 Ohm.
> When I put this meter into the G0MRF design it is a to heavy load for the
> measurement circuit.
> Open voltage drops from 13V to almost 0 V due to the low internal
> This also effects the SWR protection circuit........
> So, I did some experiments by using a FET or transistor as a driver for
> The measurment circuit voltage is almost not effected by the meter
> now, however
> it is very difficult to find a good setpoint for the meter.......
> i.e when doubling the power, the meter must read also twice the power.
> Somehow I'm not able to get the right linearity or what ever.
> Anyone out there with a circuit diagram that does work? or suggestions.
> It is difficult to exchange the meter because I cannot easily reach the
> mountingscrews anymore.....
> So I have to use this 10mA meter........
> Dick, PA4VHF