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 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.

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?

www.telstar-electronics.com

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.

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:

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

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.

"Anthony Fremont" wrote in message
...
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?


Get the right freq crystal.

Jimmie