[CW] CW headphones

[Richard Knoppow]

     FWIW, I did a patent search for headphones a couple of times. There 
were commercial phones with adjustable resonance. I've forgotten the 
name but could find it again. Mostly magnetic phones had fixed 
resonance, usually around 1000 Hz.

On 2/11/2026 10:00 AM, Radio KH6O wrote:
> I'm enjoying the CW acoustic speaker discussion on the Topband list but 
> here's an entirely different idea: I was a US Coast Guard radioman back 
> in the 70s when almost all maritime traffic was conducted in Morse. We 
> were issued government headphones that had a metal diaphragm held in 
> place with a magnet.
> 
> A colleague used a pair of metal cutters to cut out a small 
> rectangular area from the diaphragm and riveted a reed from a harmonica 
> in its place, then reassembled everything. Adjusting the receiver BFO to 
> match the reed's frequency resulted in that reed acting as an incredibly 
> sharp and narrow bandwidth filter.
> 
> Pretty soon we were all bringing harmonicas to the station and removing 
> our favorite musical frequency reed to do the modification! This really 
> helped clear the pile ups on the HF maritime frequencies during the 
> every-six-hour weather OBS from the ships. (Ham pile ups are nothing 
> compared to what we encountered!)
> 
> Today's headphones no longer have metal discs so some other method would 
> have to be employed to implement this idea.
> 
> Station name: US Coast Guard Communication Station Honolulu, callsign NMO.
> 
> -- 
> 
> 72 / 73 / 3579,
> Jeff KH6O
-- 
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998