Re: What's difficult in DIY audio?

In article <465D9174.45D1729A@xxxxxxxxxxxxxxxxxx>,
Patrick Turner <info@xxxxxxxxxxxxxxxxxx> wrote:

John Byrns wrote:

In article <esmdnfnEPoXU5MDbnZ2dnUVZ_hOdnZ2d@xxxxxxxxxxx>,
"Arny Krueger" <arnyk@xxxxxxxxxx> wrote:

"Peter Wieck" <pfjw@xxxxxxx> wrote in message
news:1180491734.775980.124750@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
On May 29, 4:28 pm, robert casey <wa2...@xxxxxxxxxxxxx>
wrote:
For some real fun, build a high performance FM tube
tuner from scratch. Getting 100MHz circuits to behave
is another ballgame.

There is a crystal FM tuner out there. I wonder if it is
powerful enough to drive a multiplex adaptor...

http://solomonsmusic.net/FM_CrystalRadio.html

I have to try that some time.

It needs a really strong signal to work at all.

It produces audio based on slope detection, which fails to exploit FM's
resistance to interference.

It's not really because of the slope detection that it fails to exploit
FM's resistance to interference, after all the traditional discriminator
circuit used in tube FM radios is little more than a push-pull slope
detector and doesn't provide resistance to interference at sideband
frequencies. The real reason it fails to exploit FM's resistance to
interference is because it lacks a limiter circuit. Slope detectors
work just fine interference wise when proceeded by a good limiter.

Solomon forgot to include the audio de-emphasis circuit in his
schematic.

But because of gross conversions of the recieved FM into AM,
the diode peak detector works.

If the circuit limited, and the RF had the same amplitude,
the peak detector wouldn't work.

Why wouldn't a slope detector work with a limiter? Keep in mind that a
"slope detector" places the carrier on the sloped skirt of a tuned
circuit, that's why it's called a "slope" detector. The slope provides
FM to AM conversion, the resulting AM is then detected by by the "peak
detector". A "slope detector" will still work just fine when preceded
by a limiter. The traditional "discriminator used in tube FM radios
also depends on FM to AM conversion via tuned circuits which feed a pair
of AM "peak detectors" connected in push-pull. The main difference
being that the push pull connection of the discriminator reduces even
order distortion and cancels noise at the carrier frequency, although
not at the frequencies occupied by the modulation sidebands.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/
.

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