Thread: Hi-Fi AM Radio.
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Patrick Turner
 
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Steven Swift wrote:

rar+p and rats:

Okay, here's the answer directly from the Radiotron Designer's
Handbook, fourth edition, pages 1226 and 1227:

"Section 3: The Synchrodyne"
[...]
"and hence the synchrodyne is likely to be most popular for
high-quality local-station reception."

There you have it. Are we done.


No we are not.
Mr Noring will be submitting test results on the prototype receiver he
is nutting out.

This is a 3-tube design for
local stations. One RF amp, 2 12au7s. Use an IC or two in the
oscillator loop and its perfect, almost a Costas Loop.


The synchrodyne never became commercially viable for home radios
in the old tube era, just twice as expensive to make and adjust.

But when PLLs became easy with chips there were a few synchrodynes made
but I have never seen a synchrodyne AM radio yet.

I tried to make one with RF amp and 6BE6 but it was a poor performer.

The selectivity depends on the audio filter, and when two stations are
9 or 10kHz apart, and both are strong,
you get some weird monkey chatter.
But they should be good for locals which are at least 45 kHz apart;
If they were only 27 kHz apart, the unwanted station modulation appears
at the detector
as a 27 kHz carrier modulated by its audio signal, and if the audio
filter has a pole at 12 kHz, and a steep roll off, the other station is
thus filtered out
by the audio filter, not the RF or IF filter.
This may sound strange, but the wanted station's carrier is locks a
local oscillator's
F to its own F, and so you get the modulation imposed on an "exalted
carrier".
A station 27 kHz away beats with the oscillator F.

RDH4 says very very little about synchrodynes.

But Wireless World ran some very big articles on them
and some very complex (and mostly incomprehensible) circuit designs were
published.

Its all there in the right libraries.



Build it; they will come.


Maybe not many :-/

Patrick Turner.



Steve.

--
Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA