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From: "Dick" <knaap159@zonnet.nl>
To: <rsgb_lf_group@blacksheep.org>
Date: Sun, 14 May 2006 21:58:23 +0200
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Subject: LF: 'meter problem' 
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Status: O

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 using
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
resistamce.
This also effects the SWR protection circuit........

So, I did some experiments by using a FET or transistor as a driver for the
meter.
The measurment circuit voltage is almost not effected by the meter circuit
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........

73

Dick, PA4VHF