In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

John,

You seem to be limiting your considerations to the 'tangential
clipping'
and not to other distortions that will occur.

On the contrary I alluded to the other problems in my post above where I
said "while the traditional RC circuit has its problems". The
problem is
that Patrick has a very thick head, so I am trying to keep things simple
so he might get the point.

Unfortunately, you have not yet done a proper comparison measurement
of a traditional detector driven off an IFT secondary, and compared
the results to what I have proposed and posted using two CF tubes.

I'm not sure what "proper comparison measurements", or "CF tubes", have to
do with the theoretical aspects of tangential clipping?

It means to build samples of two comparable circuits, and
thoroughly measure and observe the workings of each,
and make your conclusions.

That isn't too hard now surely?

That is not responsive to my question as asked, and I am not talking about
answering a question with a question.

Unfortunately I
don't possess an AM generator that is adequate for making these
measurements, that is a generator that will do 100% negative modulation,
or anywhere near it, with low distortion. It isn't clear that you possess
such a generator either, and you seem to have engaged in a certain amount
of shucking and jiving with respect to the actual performance of your
detector.

I have two such generators, a old Topward, which uses chips to easily get
100% modulation of any signal between 2 Hz and 2 Mhz with a 400 Hz tone.

Is "2 Hz" a typo? If not the resulting wave form at 100% modulation with
a 400 Hz tone would be interesting to observe on the CRO. Do you know
what the distortion for this "old Topward" is at 100% modulation? It
would be nice to be able to get away form subjective CRO measurements and
use a distortion analyzer instead.

The other is a tube one I built, which is also capable of 100% modulation,
but the thd in the AF envelope is around 3% at the onset of 100% modulation.

Its a simple triode oscillator with a grid LC, with tap on the LC for
the cathode
current.

This feeds a 6BX6 RF amp, which has an LC in its anode circuit.

The AF is fed into the 6BX6 grid circuit to alter the anode current at AF, and
modulate the output at the anode.
The anode LC has a secondary winding to reduce the output impedance.

One two gang tuning cap from an old radio is used.

It took about a fortnight to build, and a fortnight to de-bug, and to get the
sawtooth oscillator working, so when switched to 455 kHz,
the Fo could be wobulated 40 kHz each side to display the IF bandpass contour.

I used about 10 x 68v zener diodes operating at a DV lower than the
zener voltage
to make a varicap diode to give a high enough C shift to cause the wanted F
deviation.
Some wobulators use a spinning tuning cap driven by a motor, but I wanted
no mechanical parts which could wear out.

Thanks for the description of your AM generator, or AM/FM generator as it
sounds like it actually is.


As they say, "if the shoe fits wear it"! I remember the "thick as a
brick" thread from earlier this year, where you clearly demonstrated the
thickness of your skull. For those don't remember, that adventure might
have been called the "octave" matter. It was related to the slope of the
attenuation curve of an RF tank circuit, IFT, or other similar circuit.

Phil Allison and I were quite correct in our assessment about
attenuation rates in RF tank circuits, and I was the one to measure a typical
LC taken from an old radio and post the results at the binaries groups,
to prove and define what I was saying, leaving no room for any doubt, or BS.

But that was my point, you were quite correct using your frame of
reference, on the other hand my assessment of the attenuation rates in RF
tank circuits was also correct, and also perfectly described your measured
data, even though it used a different frame of reference. Your position
was, and still seems to be that anyone who takes a different perspective
on a matter is of necessity wrong, even if the alternate perspective
explains the data as well, or even better than your perspective does, you
need to learn to think outside the box, and be more creative as it were.

Workshops, simulations, and what not didn't enter into the matter because
you had conveniently measured, plotted, and posted the response curves for
an AM aerial circuit which made a perfect example for discussion. The
trouble started when you and your fellow countryman Phil Allison claimed
that the slope of the attenuation curve of a tank circuit was stepper
close to resonance and that the slope of the attenuation progressively
became less steep as you moved away resonance.

Well indeed the rate of attenuation is steeper near Fo, and then becomes less.

There is only 6 dB /octave attenuation when you are 20 dB or more away
from Fo.
Say you have a tuned LC with Fo = 1,200 kHz, then at 600 kHz, the rate of
attenuation
is 6 dB /octave, so that between 600 kZ and 300 kHz, there is only 6 dB of
attenuation.

But close to Fo, within a few kHz, and if the Q of the LC is say 50,
the rate of attenuation is far far greater than 6 dB / octave with
regard to RF
frequencies.

Again that is one perspective, but it doesn't mean there aren't over
equally valid perspectives, all that matters is that a view correctly
describes the measured data, which mine does, and IIRC yours does also.

The rate of audio F carried by a modulated carrier follows the RF attenuation
shape.

This statement is a little ambiguous, could you clarify it? It almost
sounds like you are claiming the rate of attenuation of the audio
recovered from a single tuned tank circuit will be greater than 6dB/Octave
near the corner frequency? Well actually now that I think about it that
probably is what you are trying to say.

I had been under the
impression that the slope of the attenuation curve actually increased as
you moved away from resonance, and asymptotically approached a slope
determined by the order of the filter. After a few back and forths it
became obvious to me that the problem was one of the different frequency
reference points we were using, you and Phil were using Zero frequency as
your reference, while I was using the center frequency of the filter as my
reference. At that point I said I completely agreed with your
conclusions, given your frame of reference, but you refused to accept my
concept of using the filter center frequency as an alternative view of the
situation, and told me it just wasn't valid. That is a perfect example of
a thick skull, since generally there are alternate definitions for things,
and as long as they are consistent with the facts, in that case your
measured and posted results, they are just as valid as what you may
consider to be a more conventional viewpoint, although in the case of the
"octave" matter I am not entirely sure yours was the conventional
viewpoint, but the bottom line was they both worked, and you denied that
my approach had validity.

I have seen no reference of your interpretive methodology in any text books,
and the text book methods to which I adhere to explain it all nicely,
and I don't have any intention of going right through all that long and
tortuous
discussion again.

And I wouldn't ask you to, if you notice I am not disputing your method, I
am simply disputing your apparent claim that my method is invalid. I
would ask you for one favor though, could you cite some of the textbooks
that explain your method so nicely? I have suddenly realized that in the
previous furor that you and Phil raised about my method not being in
textbooks, no one asked if your method was actually presented in any
textbooks, and I have suddenly realized that I have never seen it in a
textbook, although that certainly doesn't mean it isn't. Does the RDH4
describe your method? As far as my method not being in text books, I
think that notion was thoroughly debunked in the earlier thread when both
myself and another poster provided references to textbooks that explained
my method. In fact my method is the basis of several filter design
techniques. I suspect the problem is that you are restricting your
reading to radio design textbooks, when you should perhaps be looking in
filter design textbooks for this information, which is where you can
easily find it. I don't remember seeing your method explained in any
radio design textbooks, and I have a whole shelf full, but that doesn't
mean it isn't in one somewhere because I certainly haven't read every page
of each one, and that is why I asked for a citation, so that I can become
more familiar with your approach. My reaction to your approach is the
same as yours to mine, namely assuming it is equally valid, it does not
appear to have any practical application, and tends to confuse the issue
of what is really going on.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/