[cctalk] Re: FM/Armstrong was: [ Great Vintage Computer Heist of 2012

[Paul Koning via cctalk]

> On Oct 19, 2022, at 3:10 PM, Chuck Guzis via cctalk <cctalk@classiccmp.org> 
> wrote:
> 
> Indeed, FM was one of the undesired side effects of AM unless you had a
> well-isolated or crystal-controlled frequency source for your transmitter.

I suppose so, but Idzerda's transmitter produces FM with essentially constant 
amplitude.  It's a bit surprising given that it uses a carbon microphone as an 
element in the tuned circuit, but that's what the oscilloscope shows.  And it 
works very nicely.

> As far as detection goes, a simple AM "slope detector" sufficed in most
> cases for getting intelligible audio.

True, and that's how his listeners heard his broadcasts, since the 
discriminator had not yet been invented.  That also means, of course, that the 
"capture effect" benefit of FM was not available to him, since you need 
limiters for that.

        paul