[ARC5] Fw: Receiver current drain (AF output)

[WA5CAB at cs.com]

Well, that's true but 4000 ohm units could have been built using the newer 
approach.  And further, magnetic material developement (the higher Hc and Br 
Alnico and probably specifically Alnico 5) made possible the newer design 
(decent performance with fewer turns in the coils).  But the lower impedance 
audio lines also decreased noise pickup problems (from relatively long runs 
in aircraft and AFV's).

In a message dated 1/7/2011 10:26:09 AM Central Standard Time, 
jfor at quik.com writes: 
> I think the headphone impedance change could well have resulted from an
> earphone design change.
> 
> Prewar, earphones used a "U" metal structure wound with a coil on each leh
> and a metal disk diaphragm. I suspect this design does not work well at
> high noise levels as might be found in AFVs ot planes.
> 
> So, they went to the small loudspeaker design, and hence a much lower
> impedance.
> 
> FWIW,
> 
> -John
> 
> 

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480