Anthony Fremont wrote:
Telstar Electronics wrote:

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


It's interesting that I don't see that oscillator circuit arrangement
at http://www.ace.ual.es/~jgazquez/icons/ne602.pdf
I guess you're attempting to drag the xtal off freq? Why not just use
a tank?


Thanks for the reply. I should have been more clear, the desired frequency
is 3581kHz so yes I need to pull the crystal up in frequency about 1.5kHz.
Right now I'm only able to get to just under 3580. It seems that much
inductance should have more effect than moving it up only about 500Hz, but
this isn't my bag.

By tank I guess you mean to rid myself of the crystal and use an ordinary LC
circuit? I think I can come up with something simple, but I'd rather just
get this working if at all possible. Do you have any idea what impedance
the 602 wants to see on it's oscillator? I have a couple more chips and I
could try and cobble something together if I knew what impedance to target.


You need to reduce the inductor.. that is causing a down swing in your freq.


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Jamie wrote:

You need to reduce the inductor.. that is causing a down swing in
your freq.

Thanks, I took it out and the frequency increased by only about 70Hz, but it
did increase. :-) Do you know of anything else I can do to increase the
frequency by about another couple of kcs?

"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 =^.^=

Anthony Fremont wrote:

Jamie wrote:


You need to reduce the inductor.. that is causing a down swing in
your freq.


Thanks, I took it out and the frequency increased by only about 70Hz, but it
did increase. :-) Do you know of anything else I can do to increase the
frequency by about another couple of kcs?


try a different Xstyle, it sounds like your at the limits..
it's possible the chip has too much capacitance on the
osc legs, i suppose you could try a stand alone osc with a
high freq transistor to lower the cap. use a buffer on the
stage to drive the chip .
Also, have you considered the board mounting? you could
have to much cap via your board construction.


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

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
_._

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.


--
JF

Jamie wrote:
Anthony Fremont wrote:

Thanks, I took it out and the frequency increased by only about
70Hz, but it did increase. :-) Do you know of anything else I can
do to increase the frequency by about another couple of kcs?


try a different Xstyle, it sounds like your at the limits..
it's possible the chip has too much capacitance on the
osc legs, i suppose you could try a stand alone osc with a
high freq transistor to lower the cap. use a buffer on the
stage to drive the chip .
Also, have you considered the board mounting? you could
have to much cap via your board construction.

Looks like you are quite likely correct. Without the inductor and with a
10pF cap in place of the variable cap, I can get the frequency up to just
over 3580kHz. I did some looking around and it appears that if I were to
parallel another crystal, I could get a bigger spread on frequency. Or I
could just try a different crystal too. I think I will tinker on a
breadboard to see how high in frequency I can get the crystal to vibrate.

Charles Schuler wrote:
Try going smaller than 10 pF (you can put a 10 pF fixed capacitor in
series with the trimmer).

I did this and it will go slightly higher in frequency, but it gets a tad
unstable (could be the counter too, I wish my new scope would get here). I
guess I'm at the limits of that particular crystal.

Ian Jackson wrote:
In message , Uncle Peter

Get rid of the series choke and just use the small value variable
capacitor to go higher in frequency. I believe the inductance will
lower the frequency--the combination works to give an increased
VXCO range if I am not mistaken.

If the series capacitor is very small, the oscillation will stop. In
these circumstances, I have successfully pulled VHF crystals (3rd, 5th

It hasn't stopped, but it has gotten weak or unstable (I can't be sure right
now) with capacitance below 10pF.

and 7th overtone, between 70 and 200MHz) HF by adding an inductor IN
PARALLEL with the crystal. The value will be somewhat less than that
required to neutralise (ie parallel resonate with) the parallel
capacitance of the crystal. The lower the inductance, the higher the
frequency.

Are you referring to the capacitance inside the crystal, or the 100pF
external cap? Do you have a ballpark number on the inductance value I
should try?

Andrew Holme 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.

You have a capacitor and inductor in series.
Capacitive reactance = -j/(wC)
Inductive reactance = +jwL
The net reactance [jwL-j/(wC)] may be capacitive (negative) or
inductive (positive).

I understand that, but I don't use values like j and w, just 2, f and PI.
;-)

Reducing the inductor makes it less inductive i.e. more capacitive.
Reducing the capacitor also makes the net reactance more capacitive.

You turned your trimmer all the way down to 10pF and it wasn't
enough, so try taking a few turns off the inductor.

I took it out, and it's still too low in frequency. :-( Back to the
drawing board I guess.