Mark: I must agree with Mike here. Your measurement result is very unlikely, but at this point, I cannot tell what is wrong.The fact that you got two quite different results from two supposedly near-identical meters is "interesting".The technique you used, i.e. two resistors, etc. is certainly correct.Ken W7EKBSent via the Samsung Galaxy S21 5G, an AT&T 5G smartphone-------- Original message --------From: Mike Feher <n4fs@eozinc.com>Date: 6/16/25 07:09 (GMT-08:00)To: 'Mark K3MSB' <mark.k3msb@gmail.com>Cc: "'Charlie L.'" <mjcal79@gmail.com>, milsurplus@mailman.qth.netSubject: Re: [Milsurplus] RE2/ARC5Mark –
It still sounds unlikely to me. Did you try to measure the total current using a current probe or another milliamp meter in series, like 10 MA full scale? I recently measured the internal resistance of a 0 to 1 ma meter using a bridge/Kelvin technique to minimize the current, and measured around 340 ohms. 73 – Mike
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ 07731
908-902-3831
From: milsurplus-bounces@mailman.qth.net <milsurplus-bounces@mailman.qth.net> On Behalf Of Mark K3MSB
Sent: Monday, June 16, 2025 9:53 AM
To: Mike Feher <n4fs@eozinc.com>
Cc: Charlie L. <mjcal79@gmail.com>; milsurplus@mailman.qth.net
Subject: Re: [Milsurplus] RE2/ARC5
Hi Everyone.
My apologies for not replying sooner.... Hamfest yesterday as well as Father's Day activities.
There were no typos in my original email. I was just as surprised at the internal resistance value as you were.
This morning I performed the same measurements on a second relay unit.....
Again, 5 mA full scale deflection.
On the 2nd unit, I could get the FS reading to go half scale if I SHORTED the meter leads with a twenty inch alligator clip jumper.... this is repeatable with different sets of alligator clips.
For the 1st unit (original email)... I used three 0.1 ohm resistors in parallel as a shunt to give me the reported 0.033 ohm value.
For the 2nd unit (tested this morning).... four 0.1 ohm resistors in parallel as a shunt did not even give half scale deflection.
I don't know what the resistance of the alligator clip jumper is, but it (obviously) has to be low.
Just for fun, I directly shorted the meter leads together (no jumper). The meter went from FS to zero.
What this is telling me is that the internal resistance of the relay meter is very low, much lower than I expected.
73 Mark K3MSB
On Sat, Jun 14, 2025 at 8:42 PM Mike Feher <n4fs@eozinc.com> wrote:
Mark –
I must have misunderstood what you said. The way I read it is that when the meter read 5 ma you measured 0.033 ohms. That comes out to 165 microvolts for full scale. Just does not seem right. 73 – Mike
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ 07731
908-902-3831
From: milsurplus-bounces@mailman.qth.net <milsurplus-bounces@mailman.qth.net> On Behalf Of Mark K3MSB
Sent: Saturday, June 14, 2025 7:25 PM
To: Charlie L. <mjcal79@gmail.com>
Cc: milsurplus@mailman.qth.net
Subject: Re: [Milsurplus] RE2/ARC5
Hi Charlie
I have a new, probably never used, BC-442-A Relay unit.
I measure 5 mA FS meter deflection with an internal meter resistance of 0.033 ohms.
These were measured by the usual means of a series resistance to give FS deflection then a shunt to give half-scale deflection.
Across the meter leads of the thermocouple, I measure 1 ohm (meter disconnected).
Across the other leads I measure about 0.7 ohms (wires also disconnected).
There lead resistances were subtracted out to give the above two measurements.
Remember, the meter face reads Antenna Current Indicator -- there are no units given.
As mentioned in other posts, at home I go through a 4:1 UNUN then through an air variable series capacitor (an old HT-37 cap with some rotors removed...) to get to 50 ohms to feed my home antennas.
Sometimes I see my BC-442 hit '2", other times it just budges a little, yet my wattmeter shows 40 to 50 W out. I think the current distribution depends upon what antenna you are using and the matching network.
LIke others have said, one can ignore the relay meter reading when you have a wattmeter in line further downstream.
As posted a few weeks ago, I experimented with a 45 foot random wire antenna as that is what the B-24 used, but I did not have a counterpoise (I didn't think about the fuselage being the counterpoise.....).
I plan to recreate that later this month with an insulated counterpoise and see if that has any impact on the relay meter movement.
I hope this helps.
73 Mark K3MSB