WW2RDO

“In matters of style, float with the current. In matters of Principle, stand like a rock. “. - Thomas Jefferson

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On Oct 5, 2025, at 7:51 AM, Christopher Bowne <[email protected]> wrote:

Re tactical communications use of a BC-221 frequency meter - have seen mention of use of them for communication with the tower at airfields from incoming B-17s that had lost both their command set and liaison transmitters. Mention was made of keying the transmission on CW simply by making and breaking the connection of the antenna lead in to the output terminal on the 221.

Chris AJ1G

Stonington CT

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On Oct 5, 2025, at 00:39, Dennis Monticelli <[email protected]> wrote:

I like this thread. Here are some additional details regarding using the CMS on 80M CW.

The transmitter module was removed from the case and used standalone. I left it 100% stock. Receiving was ably handled by a restored BC-348-N. The manual states that one could use 6L6's at 450V from a line operated supply or 6V6's at 250V from a battery or hand crank gen. I used a bench PS. First up was the 6L6 and it had keying problems with a crystal. I switched to a pair of JAN metal 6V6's and it keyed beautifully with a rock or as a VFO. There was a lot of pulling with the VFO and a thermal warmup period so I elected to go with an FT-243 rock. Using the lowest Z output coil tap I was able to get 5W output with a little over 300V applied (max rating for a metal 6V6).

I will admit that I did make one teensy weensy temporary mod. I snuck a thin pair of wires through a factory adjustment hole in the rear. The wires were tack soldered to the B+ ON/OFF slide switch on the front panel. This allowed me to use a foot-switch operated T/R relay for snappy QSO exchanges.

With my antenna tuned to 50 ohm and measuring 5W, I then swapped the antenna for the 50 ohm input of my spectrum analyzer. This is how I recorded 1.6mW of backwave. The 200 mi path between my friend and I is a good one around dawn. When he copies me 599, the backwave is heard. It's not a one time event; it happens month after month. There is a ceramic neutralization trimmer in the CMS circuit that I left untouched. Was it adjusted for 6V6 or 6L6? I don't know. I did not readjust it for fear of breaking that cap.

Note that the telegraph key switches the B+ line. That is why I chose the Navy flameproof. Lots of fun using this little rig. I welcome comments on the usage of the CMS set.

Dennis AE6C

On Sat, Oct 4, 2025 at 5:35 PM Hubert Miller <[email protected]> wrote:

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-------- Original message --------

From: Frank Barnes <[email protected]>

Date: 10/4/25 15:03 (GMT-08:00)

To: Hubert Miller <[email protected]>

Cc: [email protected], ARC5 <[email protected]>

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 <[email protected]> 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

Chapel Hill, NC

Grid Square FM05

Cell 919.260.7955

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