Yes I built a similar oscillator, a bit cruder though
I clipped my scope probe to the output and connected the
probe to the counter. I noticed that the frequency drifts somewhat
when the crystal is first plugged into the test oscillator.

Highly recommended reading;

"High-Performance crystal filter design" by Bill Carver, Communications
Quarterly, Winter 1993.

Addresses the same problem and lots more, and unless you plan on permanently
attaching your fingers to your filter, you'd better pay attention.

W4ZCB

"Ken Scharf" wrote in message
. ..
Yes I built a similar oscillator, a bit cruder though
I clipped my scope probe to the output and connected the
probe to the counter. I noticed that the frequency drifts somewhat
when the crystal is first plugged into the test oscillator. I
guess I need to let the frequency counter warm up for about a
half hour before taking any measurements, the oscillator may
also need a warmup period, and perhaps even the crystal.
If you handle the crystal while inserting it into the socket
the heat from your hands probably affects the crystal, though
I noticed that if I continue to hold the crystal with
two fingers things stablize more quickly (is my hand acting
as a crystal oven?) Total drift is under 250hz.

I used an untuned buffer. Listening on a receiver when I connect the
counter, I hear no pulling. Sounds like your counter needs an oven! Based on
what you're saying about hand temperature moving the frequency, I am
expecting to see an article on passband tuning using a lightbulb driven by a
variable regulator, mounted next to the filter and BFO xtal. "Passband
Tuning Via Thermally Induced Piezoelectric Deformation."

73,

"PM"

"Ken Scharf" wrote in message
. ..
Yes I built a similar oscillator, a bit cruder though
I clipped my scope probe to the output and connected the
probe to the counter. I noticed that the frequency drifts somewhat
when the crystal is first plugged into the test oscillator. I
guess I need to let the frequency counter warm up for about a
half hour before taking any measurements, the oscillator may
also need a warmup period, and perhaps even the crystal.
If you handle the crystal while inserting it into the socket
the heat from your hands probably affects the crystal, though
I noticed that if I continue to hold the crystal with
two fingers things stablize more quickly (is my hand acting
as a crystal oven?) Total drift is under 250hz.

I used an untuned buffer. Listening on a receiver when I connect the
counter, I hear no pulling. Sounds like your counter needs an oven! Based on
what you're saying about hand temperature moving the frequency, I am
expecting to see an article on passband tuning using a lightbulb driven by a
variable regulator, mounted next to the filter and BFO xtal. "Passband
Tuning Via Thermally Induced Piezoelectric Deformation."

73,

"PM"

"Paul_Morphy" ) writes:
"Ken Scharf" wrote in message
. ..
Yes I built a similar oscillator, a bit cruder though
I clipped my scope probe to the output and connected the
probe to the counter. I noticed that the frequency drifts somewhat
when the crystal is first plugged into the test oscillator. I
guess I need to let the frequency counter warm up for about a
half hour before taking any measurements, the oscillator may
also need a warmup period, and perhaps even the crystal.
If you handle the crystal while inserting it into the socket
the heat from your hands probably affects the crystal, though
I noticed that if I continue to hold the crystal with
two fingers things stablize more quickly (is my hand acting
as a crystal oven?) Total drift is under 250hz.

I used an untuned buffer. Listening on a receiver when I connect the
counter, I hear no pulling. Sounds like your counter needs an oven! Based on
what you're saying about hand temperature moving the frequency, I am
expecting to see an article on passband tuning using a lightbulb driven by a
variable regulator, mounted next to the filter and BFO xtal. "Passband
Tuning Via Thermally Induced Piezoelectric Deformation."

73,

"PM"


But is it temperature, or finger capacitance.

Look at any circuit board, and the crystals will have the case grounded.
Look in any old two-way radio, and there is a grounding clip at the crystal
socket. Now, maybe this is for temperature stability (connected a larger
mass to the case stabilizes it) but I think it's due to the case coming
into play.

Michael VE2BVW

"Paul_Morphy" ) writes:
"Ken Scharf" wrote in message
. ..
Yes I built a similar oscillator, a bit cruder though
I clipped my scope probe to the output and connected the
probe to the counter. I noticed that the frequency drifts somewhat
when the crystal is first plugged into the test oscillator. I
guess I need to let the frequency counter warm up for about a
half hour before taking any measurements, the oscillator may
also need a warmup period, and perhaps even the crystal.
If you handle the crystal while inserting it into the socket
the heat from your hands probably affects the crystal, though
I noticed that if I continue to hold the crystal with
two fingers things stablize more quickly (is my hand acting
as a crystal oven?) Total drift is under 250hz.

I used an untuned buffer. Listening on a receiver when I connect the
counter, I hear no pulling. Sounds like your counter needs an oven! Based on
what you're saying about hand temperature moving the frequency, I am
expecting to see an article on passband tuning using a lightbulb driven by a
variable regulator, mounted next to the filter and BFO xtal. "Passband
Tuning Via Thermally Induced Piezoelectric Deformation."

73,

"PM"


But is it temperature, or finger capacitance.

Look at any circuit board, and the crystals will have the case grounded.
Look in any old two-way radio, and there is a grounding clip at the crystal
socket. Now, maybe this is for temperature stability (connected a larger
mass to the case stabilizes it) but I think it's due to the case coming
into play.

Michael VE2BVW