[600MRG] RF Ammeter

[Neil Klagge]

Scott, here is a link to W5JGV’s projects page  Showing how he made a homemade  meter. I have built several of these.

http://w5jgv.com/rfa-2/rfa-2.htm

You can calibrate it with AC through 100 W bulb if necessary. Of course be careful with the clip leads when you do that LOL.

Neil Klagge
w0yse
Northern Utah


Sent from Neil's iPhone

On Nov 21, 2020, at 05:51, John Langridge <kb5njd at gmail.com> wrote:

Hi Scott, the way to tell if its a thermo is to put a VOM across the
terminals.  If the R is very low or zero, its likely a thermocouple.
If you see winding resistance, like 20 ohms or 100 ohms, for example,
its just a volt meter with a current scale that will need to be tied
to a therm or a current transformer...  I often find that the meters
with deeper cases tend to be more likely to be a therm... Also, my
experience with buying working thermocouple at hamfess is about 50%..
often times they show up with a burned-up junction or coil...

W5JGV had a nice transformer-based current meter with remote sampling.
I dont have the link handy right now but it may be on my links page...

I use both here and monitor antenna current in the ham shack
religiously.  I calibrated a volt meter with a current scale to a
transformer in the ATU to  a thermocouple ammeter.  Its linear where I
use it.  but I find the information far better at determining system
health than SWR...

as you suggest, your meter may have a hard time at lower current
levels.  but determine what it actually is first.  A current
transformer and a volt meter can better resolve those low levels if
you have an accurate meter to calibrate with.

73!

John..






On 11/20/20, Scott Armstrong <aa5am at vntx.net> wrote:
Hi Guys,


A couple of questions....


Wondering if anyone has any information on this meter.

I have a Simpson Model 135 RF Ammeter.  Full scale is 2.5A
Does this meter have a thermocouple built in or did it use an external
thermocouple?



Can anyone point me to a schematic for a RF Ammeter that will work at 2200m
and 630m and has a top end of say 1-1.5 A.

The Simpson meter, if it does have a TC built in, will not work very well
for low power ~25Wapplication. The meter scale being non-linear  does not
have much resolution on the bottom end of the scale around the .7A range.

Thanks,
Scott AA5AM

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