[Milsurplus] RE2/ARC5

[Mark K3MSB]

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 at 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 at mailman.qth.net <
> milsurplus-bounces at mailman.qth.net> *On Behalf Of *Mark K3MSB
> *Sent:* Saturday, June 14, 2025 7:25 PM
> *To:* Charlie L. <mjcal79 at gmail.com>
> *Cc:* milsurplus at 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
>
>
>
>
>
>
>
>
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