[600MRG] RF Ammeter

[John Langridge]

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
>