In article ,
Patrick Turner wrote:
On Jul 10, 1:09*pm, John Byrns wrote:
In article
,
*Patrick Turner wrote:
Don't worry, when, or if I become senile, i'll not recognise 5% ona
CRO when its there. But most waves at that site showed slew
distortions and cut off distortions and so forth, all of which can
easily be avoided or minimised to be below 1% with my circuit over a
wide AF range and if the output voltage 1 Vrms.
Yes, there are plenty of distortions shown to illustrate the various
problems
that can occur in a poorly designed detector, and what causes the
distortions. *
There are also plenty of undistorted waves shown at that site, with
distortions
of less than 1%, to illustrate the good results that can be achieved with
careful design.
Because my home brew test signal of modulated RF waves isn't perfect,
the distortion within the envelope is probably 1%, and hence if I
measured the THD of the AF after its been through the AM radio i would
get THD of detected AF 1%, certainly at say 95% modulation.
So to see how much THD is introduced by the radio set one may use a
dual trace CRO to display both test
signal at the radio input and the detected AF and overlay the waves to
see how they compare. Using as much of the screen as possible, its not
difficult to see if there is less than 1% of additional THD added by
the radio set. All that takes time but its a very simple thing
Unfortunately it is also somewhat subjective.
and I
cannot understand why you would not have tried out all sorts of AM
detector ideas like I have to see what works best for you.
I already know that a well-designed diode detector works best for me; at least
since I regressed to tubes, in my IC days I would have answered differently.
You say that you ³have tried out all sorts of AM detector ideas², besides your
spin on the diode detector, and your ill fated attempts at building a syncrodyne
receiver, what have you tried?
What the
**** impedes your progress to your workshop and soldering iron?
Two things, first the fact that AM detectors are of academic interest only, as
there has been no AM broadcasting around this area, that needs anything better
than the crudest AM detector, for at least 15 years or so. Second, I think I am
more interested in putting my soldering iron to work on the John Stewart
inspired ³improved 25L6² amplifier. There are three binary design decisions to
be made before I purchase a chassis and begin punching it.
If you
have a broken leg, or are impaired or disabled in some way, then let's
hear about it.
Ah, you think you can drag me into an off topic discussion, it won't work, if
you want to explore that kind of discussion, please take it to email.
But even where one
listens to short wave where AF detector output 0.1Vrms, the sound is
good, although rather mauled by having travelled so far and being so
riddles with noise and fading up and down. I have never ever seen any
old radio or any old schematic of what was used for detecting AF for
use in re-broadcasting.
I found a schematic for an old Telefunken AM rebroadcast receiver, a.k.a.
"Ballempfänger", on the web. *It was a rather complex radio although IIRC
it
used a straightforward vacuum diode detector.
Nothing wrong with vacuum diode detectors if used wisely. They might
be used instead of how I have used Ge diodes with CF. They all work
best with low Z signal sources.
I googled Telefunken AM rebroadcast receiver "Ballempfänger"
Nothing to be seen.
You weren't persistent enough, for a general description go he
http://www.radiomuseum.org/r/telefun...faenger_b.html
If you aren't a member, I'm not, you won't be able to see the schematic. The
schematic is available from several other web sites though, you can find it in
two parts he
http://www.tsf-radio.org/schph.php?f...anger-E1-1.gif
and he
http://www.tsf-radio.org/schph.php?f...anger-E1-2.gif
While the design looks like the ³bean counters² were kept at a safe distance,
there still isn't a cathode follower in sight!
AFAIK, not one single commercial example
exists of a radio with "infinite impedance detector" even though the
Selsted & Smith example is given in RDH4, page 1,495, Figs 27.56,
27.57
RDH4 does not have anything that works as well as what I invented for
myself 14 years ago.
In the US J.W. Miller offered both commercial AM tuners and Radios using
the
infinite impedance detector, I have one of their AM Tuners. *Altec Lansing
also
offered an AM-FM tuner that used the infinite impedance detector in the AM
section. *Sargent Rayment also offered a line of tuners and receivers that
used
the Selsted & Smith detector in the AM sections. *Ampex also built an AM-FM
tuner that used a perverted variant of the Selsted & Smith detector, I also
have
one of these.
I've never seen any of these things in Oz or any of their schematics.
Infinite Z detector isn't bad, but gives very low output.
That's an interesting comment as the output level depends on the input just as
with a diode detector. My experiments with the circuit suggest that it does
exploit the characteristics of the low mu triodes to improve operation at low
carrier levels.
It's hard to beat a carefully designed diode detector though.
Depends. Most are distortion generators.
Those are not ³carefully² designed, it is easy to screw up a diode detector, it
is equally easy to build a good one but it costs a little gain. This and the
output transformer are the areas where the work of ³bean counters² can be most
easily seen.
Most bean counters justify their employment by being able to reduce
the parts and labour needed to make something, and therefore
increasing shareholder profits and most often reducing the sound
quality and reliability in electronics produced by the company.
The opposite approach, of adding components that serve no useful function
is
just as bad, actually worse.
Each unto their own. everyone has a different way of doing things, and
commercial competition stifles anyone who dares to use one more nut,
bolt or resistor than the ****ing opposition brand. The result is that
they all have competitions to seewho can dumb **** down the most while
maintaining enough sales for the shareholders to dine well.
Hardly, commercial products today are overflowing with every imaginable feature,
each of which adds to the parts count. Competition today seems to be based more
on features, with cost as a secondary issue, why make something more expensive
than it needs to be to provide the required features and performance?
If it makes you ill to use one more cathode follower than someone
somewhere said could be superflous, then don't. But I will. In my
vicinity there are no shareholders or bean counters, and my clients
get a good deal without having to pay for someone's Cadillac or
expensive lunches, neither of which contribute to sound quality.
An unneeded cathode follower doesn't contribute to sound quality either. I
won't bother to ask who pays for your lunches and transportation, least it take
us off topic again, but I am reasonably sure they are accounted for in the price
of the amplifiers you build.
--
Regards,
John Byrns
Surf my web pages at,
http://fmamradios.com/