On Mar 13, 12:02 pm, "Anthony Fremont" wrote:
Hello all,

I was playing around and saw that my junk box had all the parts so I started
tossing this together:http://newenglandqrp.org/files/w1aw-receiver.jpg
The problem is (well I think it's a problem) is that I'm all the way down to
a 10pF cap for the crystal trimmer and the highest frequency I can get out
of it is still less than 3580kHz. Pleae correct me if I'm wrong, but I'm
thinking that the 20uH inductor is supposed to pull the colorburst crystal
high in frequency

The inductor will pull the crystal down in frequency, as others have
suggested.

In fact it is extremely difficult to pull a crystal's series resonance
up in frequency more than a few Hz. This is because the crystal's
parallel resonance is just above its series resonance. If you put a
capacitor in series with the crystal the series resonant frequency
goes up...BUT...if you approach the parallel resonant frequency you
can no longer get a low impedance resonance condition since the
crystal's parallel resonance makes the crystal look like an open
circuit, regardless of what you put in series with it.

If you want to understand this better, try to find a reference with a
good discussion of the equivalent circuit of the quartz crystal
resonator. the only one I know of at present is Kenneth K. Clarke and
Donald T. Hess, Communication Circuits: Analysis and Design, Addison-
Wesley Publishing Co., 1971. It may be a bit hard to find outside a
good university library.

As Ian Jackson suggested a parallel inductor might work....this
modifies the parallel resonance. Ian..is there a schematic available
for that ? I'd be interested in what actually worked.

Steve

wrote:
On Mar 13, 12:02 pm, "Anthony Fremont" wrote:
Hello all,

I was playing around and saw that my junk box had all the parts so I
started tossing this
together:http://newenglandqrp.org/files/w1aw-receiver.jpg
The problem is (well I think it's a problem) is that I'm all the way
down to a 10pF cap for the crystal trimmer and the highest frequency
I can get out of it is still less than 3580kHz. Pleae correct me if
I'm wrong, but I'm thinking that the 20uH inductor is supposed to
pull the colorburst crystal high in frequency

The inductor will pull the crystal down in frequency, as others have
suggested.

I understand now. I knew that adding capacitance tended to slow xtals down.
I was unfamiliar with how an inductor would act in series. I knew that this
circuit was trying to pull the crystal higher than spec so I, quite wrongly,
assumed that the inductor would have the opposite effect of capacitance.
And it seems that it does when used in parallel and that seems sensible to
my feeble mind. But in series, it has the opposite effect. What still
throws me is that raising series capacitance doesn't have the opposite
effect of adding parallel capacitance.


In fact it is extremely difficult to pull a crystal's series resonance
up in frequency more than a few Hz. This is because the crystal's
parallel resonance is just above its series resonance. If you put a
capacitor in series with the crystal the series resonant frequency
goes up...BUT...if you approach the parallel resonant frequency you
can no longer get a low impedance resonance condition since the
crystal's parallel resonance makes the crystal look like an open
circuit, regardless of what you put in series with it.

Hmm....food for thought. :-)

If you want to understand this better, try to find a reference with a
good discussion of the equivalent circuit of the quartz crystal
resonator. the only one I know of at present is Kenneth K. Clarke and
Donald T. Hess, Communication Circuits: Analysis and Design, Addison-
Wesley Publishing Co., 1971. It may be a bit hard to find outside a
good university library.

As Ian Jackson suggested a parallel inductor might work....this
modifies the parallel resonance. Ian..is there a schematic available
for that ? I'd be interested in what actually worked.

Doodling with reactance formulas, it appears that 20uH (coincidence?) would
offset 100pF of capacitance fairly well by having a an opposing reactance
(well resistance at this point) of about 450 Ohms at 3581kHz, the same as
100pF. I'll try putting the coil I made in parallel and see what happens.
Hopefully it won't short the oscillator and kill my 15 year old NE602, I
only have two spares.

Anthony Fremont wrote:

Doodling with reactance formulas, it appears that 20uH (coincidence?)
would offset 100pF of capacitance fairly well by having a an opposing
reactance (well resistance at this point) of about 450 Ohms at

s/.well resistance at this point.//
It's just inductive reactance, I need more coffee. ;-)

3581kHz, the same as 100pF. I'll try putting the coil I made in
parallel and see what happens. Hopefully it won't short the
oscillator and kill my 15 year old NE602, I only have two spares.

Should I be afraid to do this? Does it need something to block DC current?

"Anthony Fremont" wrote in message
...
Anthony Fremont wrote:

Doodling with reactance formulas, it appears that 20uH (coincidence?)
would offset 100pF of capacitance fairly well by having a an opposing
reactance (well resistance at this point) of about 450 Ohms at

s/.well resistance at this point.//
It's just inductive reactance, I need more coffee. ;-)

3581kHz, the same as 100pF. I'll try putting the coil I made in
parallel and see what happens. Hopefully it won't short the
oscillator and kill my 15 year old NE602, I only have two spares.

Should I be afraid to do this? Does it need something to block DC
current?


the trimmer should block all the dc.
im not convinced about the inductor in parallel with the crystal
it might work though.

On 14 Mar, 07:42, "Anthony Fremont" wrote:
Anthony Fremont wrote:
Doodling with reactance formulas, it appears that 20uH (coincidence?)
would offset 100pF of capacitance fairly well by having a an opposing
reactance (well resistance at this point) of about 450 Ohms at

s/.well resistance at this point.//
It's just inductive reactance, I need more coffee. ;-)

3581kHz, the same as 100pF. I'll try putting the coil I made in
parallel and see what happens. Hopefully it won't short the
oscillator and kill my 15 year old NE602, I only have two spares.

Should I be afraid to do this? Does it need something to block DC current?

Anthony

Your trimmer cap will block any DC flow to ground. If you are really
paranoid then put a 0.1 mfd in series with the crystal.

If you do accidentally ground the crystal input terminal on that
SA602, it only pulls the base of a transistor to ground and thus turns
it off. That shouldn't hurt anything.

While you may not be able to purchase new "602's" now (they are long
ago declared obsolete) the Phillips SA-612 is the same unit and is
readily available from a number of outlets.

A datasheet for this device is located at:

http://www.nxp.com/pip/SA612AD_01.html

Arv - K7HKL
_._

Arv wrote:
On 14 Mar, 07:42, "Anthony Fremont" wrote:
Anthony Fremont wrote:
Doodling with reactance formulas, it appears that 20uH
(coincidence?) would offset 100pF of capacitance fairly well by
having a an opposing reactance (well resistance at this point) of
about 450 Ohms at

s/.well resistance at this point.//
It's just inductive reactance, I need more coffee. ;-)

3581kHz, the same as 100pF. I'll try putting the coil I made in
parallel and see what happens. Hopefully it won't short the
oscillator and kill my 15 year old NE602, I only have two spares.

Should I be afraid to do this? Does it need something to block DC
current?

Anthony

Your trimmer cap will block any DC flow to ground. If you are really
paranoid then put a 0.1 mfd in series with the crystal.

Doh, I see that now. For some reason I was thinking that they crystal had
both pins connected to the oscillator on the 602, and not with one leg
grounded as the circuit has it. Having yet another senior moment I guess.
Only about the tenth one so far this week.

If you do accidentally ground the crystal input terminal on that
SA602, it only pulls the base of a transistor to ground and thus turns
it off. That shouldn't hurt anything.

While you may not be able to purchase new "602's" now (they are long
ago declared obsolete) the Phillips SA-612 is the same unit and is
readily available from a number of outlets.

I saw that 612 part when I was poking around on the net. A fellow ham gave
me three NE602s about 15 years ago. I had fogotten about them and recently
found them. I even have a couple of tuning cap vernier drives he gave me.

A datasheet for this device is located at:

http://www.nxp.com/pip/SA612AD_01.html

Thanks

Arv - K7HKL
_._

_.. . _. ..... __._ __ __.

In message , Anthony Fremont
writes
Anthony Fremont wrote:

Doodling with reactance formulas, it appears that 20uH (coincidence?)
would offset 100pF of capacitance fairly well by having a an opposing
reactance (well resistance at this point) of about 450 Ohms at

s/.well resistance at this point.//
It's just inductive reactance, I need more coffee. ;-)

3581kHz, the same as 100pF. I'll try putting the coil I made in
parallel and see what happens. Hopefully it won't short the
oscillator and kill my 15 year old NE602, I only have two spares.

Should I be afraid to do this? Does it need something to block DC current?



If you do try an inductor across the crystal, make sure that you still
do have a DC blocking capacitor somewhere in the path to ground (as
provided by the existing C2 trimmer).
Ian.
--

In message .com,
writes
On Mar 13, 12:02 pm, "Anthony Fremont" wrote:
Hello all,

I was playing around and saw that my junk box had all the parts so I started
tossing this together:http://newenglandqrp.org/files/w1aw-receiver.jpg
The problem is (well I think it's a problem) is that I'm all the way down to
a 10pF cap for the crystal trimmer and the highest frequency I can get out
of it is still less than 3580kHz. Pleae correct me if I'm wrong, but I'm
thinking that the 20uH inductor is supposed to pull the colorburst crystal
high in frequency

The inductor will pull the crystal down in frequency, as others have
suggested.

In fact it is extremely difficult to pull a crystal's series resonance
up in frequency more than a few Hz. This is because the crystal's
parallel resonance is just above its series resonance. If you put a
capacitor in series with the crystal the series resonant frequency
goes up...BUT...if you approach the parallel resonant frequency you
can no longer get a low impedance resonance condition since the
crystal's parallel resonance makes the crystal look like an open
circuit, regardless of what you put in series with it.

If you want to understand this better, try to find a reference with a
good discussion of the equivalent circuit of the quartz crystal
resonator. the only one I know of at present is Kenneth K. Clarke and
Donald T. Hess, Communication Circuits: Analysis and Design, Addison-
Wesley Publishing Co., 1971. It may be a bit hard to find outside a
good university library.

As Ian Jackson suggested a parallel inductor might work....this
modifies the parallel resonance. Ian..is there a schematic available
for that ? I'd be interested in what actually worked.

Steve


I'll try and draw what I have in mind, and post it in
alt.binaries.schematics.electronic. However, in the meantime, let me try
and explain. The explanation may not be absolutely 100% complete, or
even 100% correct, but it may help in moving a crystal more HF than it
wants to go. Sorry that it's a bit rambling!

In Anthony's circuit (http://newenglandqrp.org/files/w1aw-receiver.jpg),
the crystal will probably be functioning as a series-tuned circuit.

As Steve has stated, a crystal suddenly goes into parallel resonance
just HF of its series resonance. This limits how far the series
resonance can be pulled HF by the addition of a series trimmer
capacitor. However, if this parallel resonance can be removed (or moved
further HF), it should be possible to move the crystal further HF. The
technique described certainly does work with VHF overtone crystals
(between 50 and 200MHz), but should also work with HF crystals working
on their fundamental frequencies.

A crystal is a mechanical device, but can be represented as being a
series-tuned L-C circuit. (Call these L1 and C1.) Also, across the two
is a parallel C (C2). Forget about losses (represented by a resistor).
[Note: L1 and C1 are not actual electrical components, and only appear
to have these values at or near to the L1-C1 resonant frequency.
However, C2 essentially is a physical electrical capacitor consisting of
the plating on each face of the crystal, with the crystal as the
dielectric between.]

L1 is very large (possibly 1H or more, depending on the frequency). C1
is very small (say only a few pF or even a fraction of a pF - again
depending on the crystal frequency). [So adding a relatively large
series trimmer capacitor has very little effect on the frequency.] C2 is
typically around 5pF, regardless of frequency.

Imagine doing a test where you look at the resonant frequency of a
crystal, using a signal generator. This feeds an RF signal through a
crystal, into a 50 ohm load. You measure throughput of the crystal by
measuring the voltage across the load.

Swing the sig gen frequency slowly from LF to HF, through the resonant
frequency of L1-C1. [Let's forget about C2 for the moment.] Below the
resonant frequency of L1-C1, the L1-C1 circuit acts like a small
capacitor, so there is very little throughput. Above the series resonant
frequency of L1-C1, the L1-C1 circuit acts like a large inductor, so
again there is very little throughput. However, when you hit the series
resonance of L1 and C1 (F1), reactance of L1 and C1 cancel. The crystal
acts like a short-circuit (or nearly so) and there is a large
throughput. Because the L-C ratio is very high, the resonance peak is
very sharp.

The effect of C2 across the L1-C1 circuit is to produce a second
(parallel) resonant circuit. VERY slightly HF of the L1-C1 resonance, C2
resonates with effective inductance of the L1-C1 circuit. This produces
a parallel resonant circuit (F2). Another way of looking at it is that
L1 resonates with the series combination of C1 and C2 (so F2 must be
higher than F1). The parallel resonance is, of course, a high impedance,
where there is almost no throughput through the crystal.

As a result of this double resonance, the crystal acts as a series-tuned
circuit at F1 (one you want), and a parallel-tuned circuit at F2. The
transition between the two is very sudden. The frequency response peak
of the throughput is very lopsided, and gets chopped off suddenly on the
HF side.

The difference between F1 and F2 is very small (a few Hz to a few kHz,
depending on the frequency and type of the crystal). If F1 is lower than
you want, and you add an external series trimmer capacitor to try and
pull the crystal L1-C1 series resonance HF, you effectively hit a brick
wall with the parallel resonance at F2. The parallel resonance will
block any throughput at (or near) this frequency.

A possible solution is to neutralize C2.
[Note: Neutralization is a technique sometimes required when using VHF
crystals, as C2 may be large enough to allow the oscillator to free-run,
instead of being locked to the frequency of L1-C1. However, it may also
be used with advantage, as described below.]
You can neutralize C2 by adding an inductor across the crystal (ie in
parallel with C2). The value required is that which parallel-resonates
with C2 at the crystal frequency. In effect, C2 no longer exists. With
C2 neutralized, there is no longer a sudden transition from the wanted
series resonance F1 to the unwanted parallel resonance F2. The peak the
response curve of the throughput of the crystal (at F1) is now nice and
symmetrical, without the sudden cutoff at F2. In practice, the actual F1
peak will probably be somewhat more HF than before, and the crystal
should be more pullable with a series capacitor.

Finally, if you reduce the value of the inductor so that its resonance
with C2 is somewhat higher than the crystal frequency, this tends to
pull the F1 resonance peak even higher in frequency. However, if you
overdo this, the oscillation will probably unlock from the crystal, and
start to free-run.

As I said, sorry for the ramble.
Ian.
--

Ian Jackson wrote:
In message .com,
writes
On Mar 13, 12:02 pm, "Anthony Fremont" wrote:
Hello all,

I was playing around and saw that my junk box had all the parts so
I started tossing this
together:http://newenglandqrp.org/files/w1aw-receiver.jpg The problem is
(well I think it's a problem) is that I'm all the
way down to a 10pF cap for the crystal trimmer and the highest
frequency I can get out of it is still less than 3580kHz. Pleae
correct me if I'm wrong, but I'm thinking that the 20uH inductor is
supposed to pull the colorburst crystal high in frequency

The inductor will pull the crystal down in frequency, as others have
suggested.

In fact it is extremely difficult to pull a crystal's series
resonance up in frequency more than a few Hz. This is because the
crystal's parallel resonance is just above its series resonance. If
you put a capacitor in series with the crystal the series resonant
frequency goes up...BUT...if you approach the parallel resonant
frequency you can no longer get a low impedance resonance condition
since the crystal's parallel resonance makes the crystal look like
an open circuit, regardless of what you put in series with it.

If you want to understand this better, try to find a reference with a
good discussion of the equivalent circuit of the quartz crystal
resonator. the only one I know of at present is Kenneth K. Clarke
and Donald T. Hess, Communication Circuits: Analysis and Design,
Addison- Wesley Publishing Co., 1971. It may be a bit hard to find
outside a good university library.

As Ian Jackson suggested a parallel inductor might work....this
modifies the parallel resonance. Ian..is there a schematic available
for that ? I'd be interested in what actually worked.

Steve


I'll try and draw what I have in mind, and post it in
alt.binaries.schematics.electronic. However, in the meantime, let me
try and explain. The explanation may not be absolutely 100% complete,
or even 100% correct, but it may help in moving a crystal more HF
than it wants to go. Sorry that it's a bit rambling!

In Anthony's circuit
(http://newenglandqrp.org/files/w1aw-receiver.jpg), the crystal will
probably be functioning as a series-tuned circuit.
As Steve has stated, a crystal suddenly goes into parallel resonance
just HF of its series resonance. This limits how far the series
resonance can be pulled HF by the addition of a series trimmer
capacitor. However, if this parallel resonance can be removed (or
moved further HF), it should be possible to move the crystal further
HF. The technique described certainly does work with VHF overtone
crystals (between 50 and 200MHz), but should also work with HF
crystals working on their fundamental frequencies.

A crystal is a mechanical device, but can be represented as being a
series-tuned L-C circuit. (Call these L1 and C1.) Also, across the two
is a parallel C (C2). Forget about losses (represented by a resistor).
[Note: L1 and C1 are not actual electrical components, and only appear
to have these values at or near to the L1-C1 resonant frequency.
However, C2 essentially is a physical electrical capacitor consisting
of the plating on each face of the crystal, with the crystal as the
dielectric between.]

L1 is very large (possibly 1H or more, depending on the frequency). C1
is very small (say only a few pF or even a fraction of a pF - again
depending on the crystal frequency). [So adding a relatively large
series trimmer capacitor has very little effect on the frequency.] C2
is typically around 5pF, regardless of frequency.

Imagine doing a test where you look at the resonant frequency of a
crystal, using a signal generator. This feeds an RF signal through a
crystal, into a 50 ohm load. You measure throughput of the crystal by
measuring the voltage across the load.

Swing the sig gen frequency slowly from LF to HF, through the resonant
frequency of L1-C1. [Let's forget about C2 for the moment.] Below the
resonant frequency of L1-C1, the L1-C1 circuit acts like a small
capacitor, so there is very little throughput. Above the series
resonant frequency of L1-C1, the L1-C1 circuit acts like a large
inductor, so again there is very little throughput. However, when you
hit the series resonance of L1 and C1 (F1), reactance of L1 and C1
cancel. The crystal acts like a short-circuit (or nearly so) and
there is a large throughput. Because the L-C ratio is very high, the
resonance peak is very sharp.

The effect of C2 across the L1-C1 circuit is to produce a second
(parallel) resonant circuit. VERY slightly HF of the L1-C1 resonance,
C2 resonates with effective inductance of the L1-C1 circuit. This
produces a parallel resonant circuit (F2). Another way of looking at
it is that L1 resonates with the series combination of C1 and C2 (so
F2 must be higher than F1). The parallel resonance is, of course, a
high impedance, where there is almost no throughput through the
crystal.
As a result of this double resonance, the crystal acts as a
series-tuned circuit at F1 (one you want), and a parallel-tuned
circuit at F2. The transition between the two is very sudden. The
frequency response peak of the throughput is very lopsided, and gets
chopped off suddenly on the HF side.

The difference between F1 and F2 is very small (a few Hz to a few kHz,
depending on the frequency and type of the crystal). If F1 is lower
than you want, and you add an external series trimmer capacitor to
try and pull the crystal L1-C1 series resonance HF, you effectively
hit a brick wall with the parallel resonance at F2. The parallel
resonance will block any throughput at (or near) this frequency.

A possible solution is to neutralize C2.
[Note: Neutralization is a technique sometimes required when using VHF
crystals, as C2 may be large enough to allow the oscillator to
free-run, instead of being locked to the frequency of L1-C1. However,
it may also be used with advantage, as described below.]
You can neutralize C2 by adding an inductor across the crystal (ie in
parallel with C2). The value required is that which parallel-resonates
with C2 at the crystal frequency. In effect, C2 no longer exists. With
C2 neutralized, there is no longer a sudden transition from the wanted
series resonance F1 to the unwanted parallel resonance F2. The peak
the response curve of the throughput of the crystal (at F1) is now
nice and symmetrical, without the sudden cutoff at F2. In practice,
the actual F1 peak will probably be somewhat more HF than before, and
the crystal should be more pullable with a series capacitor.

Finally, if you reduce the value of the inductor so that its resonance
with C2 is somewhat higher than the crystal frequency, this tends to
pull the F1 resonance peak even higher in frequency. However, if you
overdo this, the oscillation will probably unlock from the crystal,
and start to free-run.

As I said, sorry for the ramble.
Ian.

OMG are you kidding, don't be sorry. Thank you way so much!!! :-))) You
should set your clock to way in the future and repost that message so it
sticks around for a while. ;-)

So to make a long story short I need to put an inductor of roughly 400uH
across the crystal to cancel the 5pF of C2. Wow that's a ton of
inductance, but about 27 turns on a FT50-43 ferrite torroid ought to do it.
I'll let you know how that works out. I found another crystal,
unfortunately it's identical and possibly from the same batch. I haven't
tried it yet, but I'm not expecting any miracles. I'm tired of burning my
fingers unsoldering parts, so I'm goint to tinker on the breadboard with
another 602 set up just for the oscillator testing with capacitor changes.
I will apply the new coil to the soldered up version though.

The receiver hears, as we just had a storm earlier and I could hear
lightning crashes in the distance. In my narrow tuning range, I can hear
what is likely the carrier of a broadcaster too, or maybe my TV. Later
tonight when the band opens up some more, I should hear something from W1AW
hopefully.

Thanks again

In message , Anthony Fremont
writes
Ian Jackson wrote:


As I said, sorry for the ramble.
Ian.

OMG are you kidding, don't be sorry. Thank you way so much!!! :-))) You
should set your clock to way in the future and repost that message so it
sticks around for a while. ;-)

So to make a long story short I need to put an inductor of roughly 400uH
across the crystal to cancel the 5pF of C2. Wow that's a ton of
inductance, but about 27 turns on a FT50-43 ferrite torroid ought to do it.
I'll let you know how that works out. I found another crystal,
unfortunately it's identical and possibly from the same batch. I haven't
tried it yet, but I'm not expecting any miracles. I'm tired of burning my
fingers unsoldering parts, so I'm goint to tinker on the breadboard with
another 602 set up just for the oscillator testing with capacitor changes.
I will apply the new coil to the soldered up version though.

The receiver hears, as we just had a storm earlier and I could hear
lightning crashes in the distance. In my narrow tuning range, I can hear
what is likely the carrier of a broadcaster too, or maybe my TV. Later
tonight when the band opens up some more, I should hear something from W1AW
hopefully.

Thanks again



As you say, at around 3.5MHz, you will need a fairly large inductor to
resonate with 5pF. An alternative might be to make a bridge circuit,
where you actually use another (5pF) capacitor to balance out the
unwanted 5pF. I used to use an extremely simple balancing circuit to
make accurate measurements of the resonant frequencies and ESRs
(equivalent series resistance) of VHF crystals, and it should be
possible to use something similar in an oscillator. However, maybe
someone out there can advise on a tried-and-tested circuit which will
definitely work. [There's no point in re-inventing the wheel!]
Ian.
--