[ARC5] [Milsurplus] SCR-287 (BC-375 & BC-348) WW II Operational Question

[Frank Barnes]

I attach the output of my shop LM-8 (similar to the BC-221) to a random
wire antenna about 20 feet long, strung along the floor joists in the
ceiling of my indoors basement shop.  My understanding is that the output
of these units is something like 10-15 milliwatts.   I receive the signal
on my shop's Yaesu 840 and if the LM-8 is set to 7.04 Mhz (base frequency
is 3.52 Mhz), I get receivable harmonics all the way into the 30 Mhz range.
Some time ago, I keyed the LM-8 antenna while testing another receiver
tuned to 7.04, and to my surprise, a station came back to me from well out
of town.  Very surprising. Wonder what would happen if I coupled the LM-8
to my twinlead-fed 144' Delta "loop"? - but too many harmonics!  Time to
build an LC circuit to restrict the output to the desired frequency?  Might
be fun.  QRPP  The only problem will be how to use my electronic keyer to
send the code by breaking the antenna connection - I can't use my old J-38
hand key much any more, due to a nerve injury, but I can loaf along with
the keyer.

On Sat, Oct 4, 2025 at 4:01 AM Hubert Miller <Kargo_cult at msn.com> wrote:

> Your post is interesting but doesn't address my question. I imagine the RF
> route for osc to antenna in the CMS is via grid-plate capacitance in the
> 6L6 final
> and thence to the output circuit. With the LM or BC-221 as transmitter, as
> Bill related, i tend to think this would only work with a high Z antenna,
> like 1/2 wave.
>
> I also have the CMS, never used it tho. The black plastic sheet for
> covering the key, to keep hands off, got the sticky disease, so i discarded
> it. I am thinking
> i will plug in 1 volt receive tubes in the xmtr; maybe improve the
> stability that way.
> I wonder how the regen works with no actual gain control. That circuit
> design is very old.
> I suspect the CMS was intended for Philippines. It is a U.S. Navy radio.
> The Navy also owned the MBM, which seems not to have been the insurgents'
> answer
> to prayer either. I further suspect the CMS was just too hobbyist - like
> for a radio issued to people with only a basic operator level training. My
> speculations
> only. The CMS did stay in the Navy catalog for some years after the war,
> apparently; witness that AC supply for it, which is clearly of a newer
> generation of
> electronics.
> -Hue Miller
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-- 
Frank Barnes
www.W4NPN.org <http://www.W4NPN.net>
Chapel Hill, NC
Grid Square FM05
Cell 919.260.7955
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