Question on wattmeter
 

Hi Tony,

Most of the expense of the unit is in slugs and the base unit.
Certainly the diodes may be precious (I've rebuilt and calibrated
them), but in today's world you can replace them with garden variety
diodes and make up the difference with analog amplifiers with shaping
to conform to the meter scale. There is more than enough room in the
base unit to do this and the investment would pay off when you would
be tempted to just let it gather dust.

There's no such thing as magic diodes, merely mil-spec hand selected
ones that push cost through the roof.

Look at the meter movement for its full scale deflection current. From
there it is a rather simple matter to use one of several diode i/v
curves to reverse-engineer the solution. Buy pallet full of the
appropriate technology (Si/Ge/Tunnel/Avalanche/what-have-you) and
select. OR take one of those garden variety diodes and build a log
amp (or simply buy a log amp). Add a battery clip with battery and
move on.

73's
Richard Clark, KB7QHC

I was just interested in the theory of why that scale is linear. I have no
interest for modifications of or additions.

73

Tony I0JX

Question on wattmeter
 

"Owen Duffy" ha scritto nel messaggio
...
"Antonio Vernucci" wrote in news:4640a649$0$17940
:

We are talking about millivolt levels, but the good news is that today,
stable high gain DC amplifiers are a snack (see chopper stabilised Op
Amps).

Yes, but to my knowledge, the Struthers wattmeter is purely passive, no
amplifier whatsoever.


You have misunderstood me, my post was in answer to your more general
question "Does anyone know of special diodes resulting in a linear
wattmeter scale?" (which I quoted in my post).

If you weren't interested in the answer to the question, why ask it?

Owen

I am interested in answers specifically regarding diodes which may cause the
Struthers wattmeter scale to be linear.

Using modern electronics one can do almost everything, no big novelty.

73

Tony I0JX

Question on wattmeter
 

Antonio Vernucci wrote:


I am interested in answers specifically regarding diodes which may cause
the Struthers wattmeter scale to be linear.

Using modern electronics one can do almost everything, no big novelty.

73

Tony I0JX



Tony, see if this answers your question:

http://www.evaluationengineering.com...201sensors.htm
The Sharp End of RF Power Measurement

Note Figure 1.

Also, take a look at HP's AN986.

73,

Chuck NT3G

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Question on wattmeter
 

On Tue, 08 May 2007 20:47:31 -0400, Chuck
wrote:

Tony, see if this answers your question:

http://www.evaluationengineering.com...201sensors.htm
The Sharp End of RF Power Measurement

Hi Chuck,

Little do you realize (or you are especially diabolical to have
introduced it), but within this monograph offered is the heresy of the
Source mismatching the load (the heresy being that any source of
sufficient power does not embody the nominal 50 Ohms Impedance).

It even contains the classic math introduced by Stephen F. Adam back
in the mid 60s for the National Bureau of Standards - and later
published by Hewlett Packard (both notorious hotbeds of technical
corruption in the matters of source impedance).

73's
Richard Clark, KB7QHC

Question on wattmeter
 

Richard Clark wrote:
On Tue, 08 May 2007 20:47:31 -0400, Chuck
wrote:

Tony, see if this answers your question:

http://www.evaluationengineering.com...201sensors.htm
The Sharp End of RF Power Measurement

Hi Chuck,

Little do you realize

Very little, it appears.

(or you are especially diabolical to have
introduced it), but within this monograph offered is the heresy of the
Source mismatching the load (the heresy being that any source of
sufficient power does not embody the nominal 50 Ohms Impedance).

It even contains the classic math introduced by Stephen F. Adam back
in the mid 60s for the National Bureau of Standards - and later
published by Hewlett Packard (both notorious hotbeds of technical
corruption in the matters of source impedance).

73's
Richard Clark, KB7QHC

Thanks.

73,

Chuck

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