Re: What's difficult in DIY audio?

"John Byrns" <byrnsj@xxxxxxxxxxxxx> wrote in message
news:byrnsj-AE00F5.10245030052007@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
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?

No reason.

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.

I agree with the gist of this.


.

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