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

[Hubert Miller]

Sent from my Galaxy



-------- Original message --------
From: Frank Barnes <fbw4npn at gmail.com>
Date: 10/4/25 15:03 (GMT-08:00)
To: Hubert Miller <Kargo_cult at msn.com>
Cc: Milsurplus at mailman.qth.net, ARC5 <arc5 at mailman.qth.net>
Subject: Re: [ARC5] [Milsurplus] SCR-287 (BC-375 & BC-348) WW II Operational Question

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<mailto: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
______________________________________________________________
ARC5 mailing list
Home: http://mailman.qth.net/mailman/listinfo/arc5
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:ARC5 at mailman.qth.net<mailto:ARC5 at mailman.qth.net>

This list hosted by: http://www.qsl.net<http://www.qsl.net/>
Please help support this email list: https://www.qsl.net/donate.html


--
Frank Barnes
www.W4NPN.org<http://www.w4npn.net/>
Chapel Hill, NC
Grid Square FM05
Cell 919.260.7955
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20251004/0bc99b02/attachment-0001.html>