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LF: Re: 'meter problem'

To: <[email protected]>
Subject: LF: Re: 'meter problem'
From: "F6CWN" <[email protected]>
Date: Mon, 15 May 2006 09:53:30 +0100
Delivered-to: [email protected]
References: <[email protected]> <[email protected]>
Reply-to: [email protected]
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15./05/2006   0934z

 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
> 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



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