John Fields wrote:
On Tue, 13 Mar 2007 18:00:15 -0500, "Anthony Fremont"
wrote:

Eamon Skelton wrote:
On Tue, 13 Mar 2007 12:02:38 -0500, Anthony Fremont wrote:


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 then
the adjustable cap should be able to tweak it back down.

Use less inductance or replace it with a wire link.

I did this and now I'm up to 3580.050; an increase of about 70Hz or
so.. I don't understand how this was designed to work. What is
making the crystal oscillate above its design frequency? I thought
the inductor had something to do with it, obviously not. Is it
being operated in series mode instead of parallel?

I tried putting small cap in series with the adjustable one and that
just greatly narrowed the tuning range and only slightly raised the
frequency. It seemed to be getting unstable at that point as my old
frequency counter started showing variations of quite a few hertz
each update instead of remaining steady. It could be the amplitude
is too low and the counter is missing ticks.

---
Your color burst crystal is ground to ring at 3.579545 MHz, and if
you try to run it at another frequency you'll run into drive and
tempco problems which will make it worthless.

I know that I'm "violating the specs", but that's the intent here. Most of
the circuits I've encountered tend to pull the xtal down in frequency (just
add capacitance), but this case is odd in that W1AW transmits just above the
colorburst frequency. I can pull it down several kcs pretty easily, I just
can't get it above the specced value by more than about 500Hz. I think I
just need to try a different crystal or maybe two in parallel. The parallel
inductance idea is interesting as well, never done anything like that
before.

As for stability, as long as it's not causing warbling audio, I'm not too
concerned. :-)

"John Fields" wrote in message
...
On Tue, 13 Mar 2007 18:00:15 -0500, "Anthony Fremont"
wrote:

Eamon Skelton wrote:
On Tue, 13 Mar 2007 12:02:38 -0500, Anthony Fremont wrote:


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 then the adjustable
cap should be able to tweak it back down.

Use less inductance or replace it with a wire link.

I did this and now I'm up to 3580.050; an increase of about 70Hz or so..
I
don't understand how this was designed to work. What is making the
crystal
oscillate above its design frequency? I thought the inductor had
something
to do with it, obviously not. Is it being operated in series mode instead
of parallel?

I tried putting small cap in series with the adjustable one and that just
greatly narrowed the tuning range and only slightly raised the frequency.
It seemed to be getting unstable at that point as my old frequency counter
started showing variations of quite a few hertz each update instead of
remaining steady. It could be the amplitude is too low and the counter is
missing ticks.

---
Your color burst crystal is ground to ring at 3.579545 MHz, and if
you try to run it at another frequency you'll run into drive and
tempco problems which will make it worthless.

Its only a pull of ~100ppm, this should be easily pullable for most
fundamental xtals.
ofc if the tolerenace all add up against you you might find it hard.

I would also try reduce the 100pf caps on the sa602 too.
100pf is higher than most crystals I use would like,
50pf or 20pf or if youve got some spare trimmers ...
you can adjust the ratio too, say just reduce the one accross pin 6-7

Colin =^.^=

colin wrote:

Its only a pull of ~100ppm, this should be easily pullable for most
fundamental xtals.

I'd like to get close to 500ppm if possible.

ofc if the tolerenace all add up against you you might find it hard.

I would also try reduce the 100pf caps on the sa602 too.
100pf is higher than most crystals I use would like,
50pf or 20pf or if youve got some spare trimmers ...
you can adjust the ratio too, say just reduce the one accross pin 6-7

I figured that they were voltage dividers to set the amount of feedback, but
I can certainly see how they could have an effect. Since I'm close to where
I need to be, I will try a couple of 33pF caps to see what happens.

"Anthony Fremont" wrote in message
...
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 then the adjustable cap should be able to tweak
it back down. Higher capicitance does result in even lower frequency. I
made the 20uH inductor by wrapping 17 turns on an old amidon FT50-61
ferrite toroid. I don't have any way to measure the inductance, but by my
calculations it should be approximately 20uH. Is the ferrite saturating
and messing things up? I see that touching the 20uH inductor it will
cause the frequency to shift down as much as 4-5kHz.

I believe this is direct conversion and that the crystal should exactly
match the desired station (3581kHz) I want to recieve, that's right isn't
it? Maybe this is close enough? I have to wait til tonight to see if I
can actually hear anything.

I mostly tinker with PIC chips so this is pretty much out of my league. I
just wanted to throw it together and listen to the nightly report. It
seems to be working as I can touch the 7.8uH coil (40 turns on a T50-2
toroid) and I get increased noise out of pins 4 and 5 on the NE602 (hey
it's what I had in the box ;-). I haven't added the 386 yet, I just
wanted to test the front end first. I'm cramming it all on a RS 276-259
pc proto board, but the layout is coming along pretty well for not
planning it out. ;-) Thanks for helping.

maybe the Q of you inductor is too low, try an air core,
needs lots more turns, a trimmer core as a core is good too.

Also you should test it with the crystal shorted,
then when you get close to the frequency you want put the crystal back in.

Colin =^.^=

On 13 Mar, 17:52, "colin" wrote:
"Anthony Fremont" wrote in message

...

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 then the adjustable cap should be able to tweak
it back down. Higher capicitance does result in even lower frequency. I
made the 20uH inductor by wrapping 17 turns on an old amidon FT50-61
ferrite toroid. I don't have any way to measure the inductance, but by my
calculations it should be approximately 20uH. Is the ferrite saturating
and messing things up? I see that touching the 20uH inductor it will
cause the frequency to shift down as much as 4-5kHz.

I believe this is direct conversion and that the crystal should exactly
match the desired station (3581kHz) I want to recieve, that's right isn't
it? Maybe this is close enough? I have to wait til tonight to see if I
can actually hear anything.

I mostly tinker with PIC chips so this is pretty much out of my league. I
just wanted to throw it together and listen to the nightly report. It
seems to be working as I can touch the 7.8uH coil (40 turns on a T50-2
toroid) and I get increased noise out of pins 4 and 5 on the NE602 (hey
it's what I had in the box ;-). I haven't added the 386 yet, I just
wanted to test the front end first. I'm cramming it all on a RS 276-259
pc proto board, but the layout is coming along pretty well for not
planning it out. ;-) Thanks for helping.

maybe the Q of you inductor is too low, try an air core,
needs lots more turns, a trimmer core as a core is good too.

Also you should test it with the crystal shorted,
then when you get close to the frequency you want put the crystal back in.

Colin =^.^=

My W1AW receiver uses the crystal with just a 5-47 pf variable
capacitor...no inductor, and it nets right on frequency. Try shorting
the inductor and see if this gets you closer to the required
frequency. Not all color burst crystals were created equal. If you
have another crystal you might want to try it.

Your ferrite will not be saturating at the small amount of signal you
are sending through it as part of an SA-602 oscillator.

Arv - K7HKL
_._

Arv wrote:

My W1AW receiver uses the crystal with just a 5-47 pf variable
capacitor...no inductor, and it nets right on frequency. Try shorting

Story of my life. ;-)

the inductor and see if this gets you closer to the required
frequency. Not all color burst crystals were created equal. If you
have another crystal you might want to try it.

That seems to be the common consensus. I suspect my crystal is just too
good. ;-)

Your ferrite will not be saturating at the small amount of signal you
are sending through it as part of an SA-602 oscillator.

Thanks, I know very little about these things.

Arv - K7HKL
_._

On Wed, 14 Mar 2007 06:26:39 -0500, "Anthony Fremont"
wrote:

Arv wrote:

My W1AW receiver uses the crystal with just a 5-47 pf variable
capacitor...no inductor, and it nets right on frequency. Try shorting

Story of my life. ;-)

the inductor and see if this gets you closer to the required
frequency. Not all color burst crystals were created equal. If you
have another crystal you might want to try it.

That seems to be the common consensus. I suspect my crystal is just too
good. ;-)

Your ferrite will not be saturating at the small amount of signal you
are sending through it as part of an SA-602 oscillator.

Thanks, I know very little about these things.

---
Here's a good tutorial:

http://www.foxonline.com/techdata.htm
--
JF

John Fields wrote:
On Wed, 14 Mar 2007 06:26:39 -0500, "Anthony Fremont"
wrote:

Arv wrote:

My W1AW receiver uses the crystal with just a 5-47 pf variable
capacitor...no inductor, and it nets right on frequency. Try
shorting

Story of my life. ;-)

the inductor and see if this gets you closer to the required
frequency. Not all color burst crystals were created equal. If
you have another crystal you might want to try it.

That seems to be the common consensus. I suspect my crystal is just
too good. ;-)

Your ferrite will not be saturating at the small amount of signal
you are sending through it as part of an SA-602 oscillator.

Thanks, I know very little about these things.

---
Here's a good tutorial:

http://www.foxonline.com/techdata.htm

Thanks John. :-) I was referring to core saturation and when to suspect
it/materials/etc, but I can sure stand to learn a few things more about
crystals too. That's pretty good information in the link you posted. If
anyone knows about crystals it should be Fox. ;-) I had never tried
pulling one high before, only tweaking them down a little to get them on
frequency. I can pull this one low several kcs without much of a problem
other than stability, but it sure doesn't want to go any higher than about
500Hz above spec. I'm going try the parallel inductance trick to see if I
can get the frequency higher, that should prove interesting. I like doing
reality vs. theory experiments. ;-)

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.