In article ,
"gareth" wrote:

"Scott Dorsey" wrote in message
...
gareth wrote:
"Scott Dorsey" wrote in message
Perhaps you, as indeed do others seem, are trying to interpret a
technique
from
the 1930s and 1940s in terms of the multi-pole Xtal filters that are the
norm today?
Well, yes. That is the point of this thread, isn't it?
No, it isn't.
I have a junk box going back 50 years from which I intend to make the sort
of RX that I dreamed of as a teenager in the 1960s, on the basis that if I
do
not make use of all those museum bits and pieces, the executor of my will
will be likely to bin the lot.
I am inspired by the ham-bands only Eddystone EA12 and am making slow
progress
in a DIY effort to manufacture the gears for the dial drive and am now
considering
the manufacture of a Catacomb along the lines of the National NC100X.
One technique from those pre-mechanical, and multi-pole or monolithic
Xtal, filters was to use a _SINGLE_ crystal early on in the IF chain, and
it
is that
single crystal together with its phasing control that interests me at the
moment.
Yes, and you would like to understand how that device works in terms of
modern nyquist filter theory, correct?

Harry Nyquist is far from modern, I have somewhere an essay of his from
1924,
something along the lines of, "Certain topics in telegraph theory"


What I was after was the standard way of setting up the phasing together
with
the BFO for eliminating an interfering carrier that was equally spaced from
the BFO
frequency on the other side.

Once you have tuned the radio (VFO) to get the wanted signal at the
centre of the crystal passband, you can set the BFO to taste and
altering the phasing of the crystal will not alter the IF frequency of
the wanted signal so won't alter the beat note. If the phasing shifts
the crystal pass band significantly (which it probably won't) you might
need to retune the radio (VFO) slightly and then the beat note would
alter so you might have to adjust the BFO to taste again. But the BFO
won't alter where the signal is in the passband, and the crystal phasing
won't alter the beat note when it is adjusted. Only changing the VFO
could do that.

--

Percy Picacity

"Percy Picacity" wrote in message
...
Once you have tuned the radio (VFO) to get the wanted signal at the
centre of the crystal passband,

There is no passband, it is a single sharp peak.



you can set the BFO to taste and
altering the phasing of the crystal will not alter the IF frequency of
the wanted signal so won't alter the beat note.
If the phasing shifts
the crystal pass band significantly (which it probably won't) you might
need to retune the radio (VFO) slightly and then the beat note would
alter so you might have to adjust the BFO to taste again. But the BFO
won't alter where the signal is in the passband, and the crystal phasing
won't alter the beat note when it is adjusted. Only changing the VFO
could do that.

Sorry OM, but you're way off topic.

A single-Xtal series resonant XTal has a sharp peak, and then a deep null at
the parallel resonant frequency, and the phasing control adjusts the
position of the null.

My assumption, which is where I came in, is that the BFO would be centred
between
the two frequencies so that an interfering signal at the audio image
frequency would
be nullified.

"gareth" wrote in message
...

A single-Xtal series resonant XTal has a sharp peak, and then a deep null
at
the parallel resonant frequency, and the phasing control adjusts the
position of the null.

My assumption, which is where I came in, is that the BFO would be centred
between
the two frequencies so that an interfering signal at the audio image
frequency would
be nullified.



You might choose to do this - particularly if, understandably, you find
interference at the same beat frequency makes copy of the wanted signal more
difficult.

This approach, though, has no obvious merit over *normal procedure and has
the distinct disadvantage of forcing you to listen to audio at one half the
difference between the wanted and unwanted signals.

*peak the wanted signal, adjust the BFO to give the optimum audio frequency
while adjusting phasing for maximum readability.

PA

"Peter Able" stuck@home wrote in message
o.uk...
*peak the wanted signal, adjust the BFO to give the optimum audio
frequency while adjusting phasing for maximum readability.


What do you mean by, "adjusting phasing for maximum readability", if the
signal is already
peaked at the series resonant frequency?


And where do you derive your opinion that this is normal?

"gareth" wrote in message
...
"Peter Able" stuck@home wrote in message
o.uk...
*peak the wanted signal, adjust the BFO to give the optimum audio
frequency while adjusting phasing for maximum readability.


What do you mean by, "adjusting phasing for maximum readability", if the
signal is already
peaked at the series resonant frequency?

If you need to ask this question, I think that you would benefit from
directed experience of working with this sort of filter. Remember, we are
talking Readability, not Strength.

And where do you derive your opinion that this is normal?

From my lengthy experience as a successful professional engineer and from
holding a licence - Amateur (Sound) A and its successors - for many more
years than yourself. Also from what ability I have to assess and learn from
the opinions of others.


You asked for input from "experienced and senior" folk and yet you've been
rude and dismissive of such input. Why do you act down to Mr. Reay's
earlier characterisation of yourself? I'd like to see him proved wrong -
but that is a matter entirely in your hands, Gareth.

PA

On 26/08/2013 09:48, Peter Able wrote:
"gareth" wrote in message
...
"Peter Able" stuck@home wrote in message
o.uk...
*peak the wanted signal, adjust the BFO to give the optimum audio
frequency while adjusting phasing for maximum readability.


What do you mean by, "adjusting phasing for maximum readability", if the
signal is already
peaked at the series resonant frequency?

If you need to ask this question, I think that you would benefit from
directed experience of working with this sort of filter. Remember, we are
talking Readability, not Strength.

And where do you derive your opinion that this is normal?

From my lengthy experience as a successful professional engineer and from
holding a licence - Amateur (Sound) A and its successors - for many more
years than yourself. Also from what ability I have to assess and learn from
the opinions of others.


You asked for input from "experienced and senior" folk and yet you've been
rude and dismissive of such input. Why do you act down to Mr. Reay's
earlier characterisation of yourself? I'd like to see him proved wrong -
but that is a matter entirely in your hands, Gareth.

PA


Oh dear Peter, don't be surprised if your employer is added to the list
who receives an Email.

I've copies of several so far. If you need advice on how to proceed when
it happens, feel free to contact me.

"Peter Able" stuck@home wrote in message
o.uk...

You asked for input from "experienced and senior" folk and yet you've been
rude and dismissive of such input. Why do you act down to Mr. Reay's
earlier characterisation of yourself? I'd like to see him proved wrong -
but that is a matter entirely in your hands, Gareth.

Infantile

PLONK!

"gareth" wrote in message
...

Infantile

PLONKER!



We know you are.

In article ,
"gareth" wrote:

"Percy Picacity" wrote in message
...
Once you have tuned the radio (VFO) to get the wanted signal at the
centre of the crystal passband,

There is no passband, it is a single sharp peak.

Sorry that is a passband, unless it is an ideal infinitely narrow
filter, in which case you would not be able to hear the morse characters!



you can set the BFO to taste and
altering the phasing of the crystal will not alter the IF frequency of
the wanted signal so won't alter the beat note.
If the phasing shifts
the crystal pass band significantly (which it probably won't) you might
need to retune the radio (VFO) slightly and then the beat note would
alter so you might have to adjust the BFO to taste again. But the BFO
won't alter where the signal is in the passband, and the crystal phasing
won't alter the beat note when it is adjusted. Only changing the VFO
could do that.

Sorry OM, but you're way off topic.

A single-Xtal series resonant XTal has a sharp peak, and then a deep null at
the parallel resonant frequency, and the phasing control adjusts the
position of the null.

My assumption, which is where I came in, is that the BFO would be centred
between
the two frequencies so that an interfering signal at the audio image
frequency would
be nullified.

The crystal nulls the signal that *leads to* the audio image, not the
audio image itself. The only effect of putting the BFO half way between
the wanted and unwanted signal is to give them the same beat note and
therefore make them harder to distinguish. If the BFO is elsewhere they
will have different pitches. But the position of the BFO frequency has
no effect on the the crystal nulling the unwanted signal. If you
actually wanted to null the audio image (or any other audio frequency)
you would need to use DSP.

--

Percy Picacity

"Percy Picacity" wrote in message
...
In article ,
"gareth" wrote:
"Percy Picacity" wrote in message
...
Once you have tuned the radio (VFO) to get the wanted signal at the
centre of the crystal passband,
There is no passband, it is a single sharp peak.
Sorry that is a passband, unless it is an ideal infinitely narrow
filter, in which case you would not be able to hear the morse characters!
you can set the BFO to taste and
altering the phasing of the crystal will not alter the IF frequency of
the wanted signal so won't alter the beat note.
If the phasing shifts
the crystal pass band significantly (which it probably won't) you might
need to retune the radio (VFO) slightly and then the beat note would
alter so you might have to adjust the BFO to taste again. But the BFO
won't alter where the signal is in the passband, and the crystal
phasing
won't alter the beat note when it is adjusted. Only changing the VFO
could do that.

Sorry OM, but you're way off topic.
A single-Xtal series resonant XTal has a sharp peak, and then a deep null
at
the parallel resonant frequency, and the phasing control adjusts the
position of the null.
My assumption, which is where I came in, is that the BFO would be centred
between
the two frequencies so that an interfering signal at the audio image
frequency would
be nullified.
The crystal nulls the signal that *leads to* the audio image, not the
audio image itself. The only effect of putting the BFO half way between
the wanted and unwanted signal is to give them the same beat note and
therefore make them harder to distinguish. If the BFO is elsewhere they
will have different pitches. But the position of the BFO frequency has
no effect on the the crystal nulling the unwanted signal. If you
actually wanted to null the audio image (or any other audio frequency)
you would need to use DSP.

You're still missing the point that in addition to the peak response, there
is
also a deep null.