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.

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.

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

"Anthony Fremont" wrote in message
...
Hello all,

I was playing around and saw that my junk box had all the parts so I
started

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.

Pete k1zjh

In message , Uncle Peter
writes

"Anthony Fremont" wrote in message
...
Hello all,

I was playing around and saw that my junk box had all the parts so I
started

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.

Pete k1zjh



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

--

"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).

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.

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.

73, Ed. EI9GQ.



--
Linux 2.6.18
Remove 'X' to reply by E-Mail

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.

"Anthony Fremont" wrote in message
...
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.


If you want a VXCO, you use the capacitor and inductor to achieve
maximum range of the crystal frequency.

An inductor in series will lower the frequency.
A capacitor in series will raise the frequency.

Eliminate the coil and just use the series trimmer to see how
how high the crystal frequency can be raised before it becomes
unstable or quits oscillating.

As Ian suggested, you can add an inductor ACROSS the
crystal to raise the frequency. Think of the crystal as being
a parallel LC circuit (over simplification) and you'll
be better able to visualize how this works.

Try a few other color burst xtals in the circuit for the heck
of it. You may not be able to pull the crystal that far.