The AM Forum

  Got this Antenna Current Meter mounted in a box with this shunt, pictures of both, the shunt is labeled .75 Amp which doesn't show in the picture well.

  Question is a 10 Amp Meter and a .75 Amp shunt? Is that correct?


                                       

Looks to me like the meter shunt itself is shunted with a piece of wire in an attempt to make the 0.75 amp shunt work at 10 amps. At a full 10 amps the shunt should be carry 0.75 amps and the piece of wire the other 9.25 amps.

The linear meter scale is making me wonder how the thing works.

Yo'


    Looks like the shunt is "shunt'ed" with a tinned
chunk o' #12...  Read "Crap Shoot".

     I concur that any RF AMP meter I have ever
seen is Non-Linear. In a 50 ohm environment. I
have no experience with meters set up for both
sides of a balanced feed...  "I don't know what
I don't know", and freely admit it!  I do know
these meters are non-linear...

in order.

ART-13
BC-939
TCS


73

/Dan

I agree,  the scale was the first thing I noticed.  Looks to be a DC movement.  Could be the shunt doesn't belong to the meter.

I have GE antenna current meter, but they are direct reading meters, no external shunt needed and the scales are not linear.

You need to figure out what piece of military gear the meter was used in.

The needed info is not shown on the face of the meter, what's the full scale current of the meter.  Normally, if there is no other ratings shown along the bottom of the face, you can assume it is a direct reading meter, whereas no shunt needed.  But, like Dave points out, the linear scale doesn't seem correct.

Fred

Dan posted a picture of the ART-13 antenna current meter.  The meter reads to 5 amps, but, that meter is only a .25 amp movement.  The meter works off a current transformer in the xmtr.  Look close at the face and it states full scale is .25 amp.

I use that meter in my HB xmtr and I made a HB current xfmr to make it read correctly.  I actually set it up to have full scale to be exactly 1/2 the meter scale.  A 5 amp reading is really only 2.5 amps.  The lower range works better with lower powered xmtrs.

Your 10 amp range meter has very limited value for ham xmtrs where the power level is up to about 400 watts.  A 3 amp meter will read 450 watts at 50 ohm load.  The 10 amp meter will read up to 5KW at 50 ohm load.

I'm thinking your meter works off a linear shunt and then was rectified to dc and feed to the meter as a DC voltage.

Fred

It's not a 10 amp meter. It is a relative antenna current indicator as in "tune for max smoke".

concur, relative, with a reading goal provided in the instructions for the equipment is was in.