Thread: Hi-Fi AM Radio.
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Henry Kolesnik
 
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HiFi AM is stretching the definition of HiFi! Designing and building a good
receiver is not a trivial task. When I was a kid in Jr High and didn't know
any better I used whatever was at hand or I could scrounge and most projects
usually worked, and even worked better when certain parts were substituted
by trial and error. But in reality none compared to the war surplus
receivers I converted.
Later in when I was in the RCAF radar school and had more knowledge and
parts I did much better. But still not as good as commercial units.
After college I made a few attempts getting into the details of
characteristic curves for tubes and transistors, load lines and calculating
component values. It's a very big task to select the best tube or
transistor for each stage and decide on stage gain, distortion, etc. But
once that's done, physical layout is very important. After design and
layout the unit is built and it's generally not a proto-type, it's the
final prize. After changing part values to optimize performance one finds
that many things should have been done differently. And I know guys who
have built several re-designs till they were satisfied but again I never saw
one that outperformed a commercial unit.
It's a lot of fun to take an idea from concept to a working unit but anyone
who thinks they're going to build something better than what's available
should learn how to engineer by going to school or get a job around a lot
real smart designers.
These days I know the challenge but I still pick up project parts at
hamfests knowing full well that I may never get around to using them. Mind
games are entertaining but not as much as plugging a project in to listen
for the crackle of static and hoping like hell the smoke stays in. It's
long road from concept to enjoyment with lots of disappointment and
surprises in between.
I've resisted the temptation to post this to the shortwave group so Telamon
could gripe.

--
73
Hank WD5JFR
..
"Steven Swift" wrote in message
...
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. 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.

Build it; they will come.

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