"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.

--

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?

"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.

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.

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.

Uncle Peter wrote:
"Anthony Fremont" wrote in message


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.

Ok, just like an antenna

A capacitor in series will raise the frequency.

Same thing again, just like an antenna. However, when I increase the series
capacitance, the frequency drops instead of going higher. This I don't
really get.

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.

Did this, it helps, but when capacitance is below about 10pF, it seems to
get unstable and I still can't achieve the frequency I desire.

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.

Can you suggest a value to start with?

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.

That's what I'm thinking now, it just won't pull that far high. I can sure
pull it low though. Maybe I should try a 4MHz crystal and pull it down to
3990, this is where the voice transmissions are anyway.

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