Amps
[Top] [All Lists]

[AMPS] New member and Drake L7 questions

To: <amps@contesting.com>
Subject: [AMPS] New member and Drake L7 questions
From: Ian White, G3SEK" <g3sek@ifwtech.com (Ian White, G3SEK)
Date: Tue, 26 Sep 2000 08:07:13 +0100
Peter Chadwick wrote:
>A lot depends on what the meters are. If the shunt is internal and it's a
>'standard' 100mV meter, then increasing the drop isn't very practical.

Many "1A" meters are actually a 100uA, 1mA or 10mA movement with an
internal shunt. Open the meter and snip the shunt, and you're back on
track.

> A 5x
>overload may not be a brilliant idea for the meter, but it's not normally
>disastrous - or not as much as no protection. A Schottky rectifier across the
>meter gets around the problem 

Only partly - remember that the voltage drop at surge currents of 40-50A
will be a lot higher than the rated Vf, for all types of diode.

>(or a pair of them in reverse parallel).

Hmmm... I thought about this long and hard. Can you see any way that a
surge from HV+ to the HV- rail could go in the opposite direction? 


>Incidentally, I'm assuming that 100mV is the standard drop for moving coil
>meters in the US.
>
It hardly seems to be a standard anywhere, if it ever was. High-cost
meters (surplus of course) seem to vary considerably, but have a lower
voltage drop than the far eastern imports which typically run 300-400mV. 

>Do people still manufacture moving coil meters, by the way, or have electronic
>meters taken over completely?
>
Come on, Peter - they're still in the component catalogues, but good
ones cost a fortune at full price. That's why they're worth protecting.

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)
                           http://www.ifwtech.com/g3sek

--
FAQ on WWW:               http://www.contesting.com/FAQ/amps
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com


<Prev in Thread] Current Thread [Next in Thread>