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Dear forum,

I try to measure my 12 MHz IF-crystals with method here,

for purpose selection within 30 to 50 KHz ( is this value right ? ).

But the problem is:

Frequency reading is still moving / drifting,

although circuit has been warming up about 5 minutes.

Q: How do you "note/catch" the frequency in this situation ?

( like Hans Summer's ...:? Here are my measurements in ascending order:
9,994,677
9,994,704
9,994,733
9,994,747
9,994,799??? 0
9,994,811??? +12
9,994,821??? +22
9,994,829??? +30
9,994,874
9,994,887
You can see the chosen 4, which are within 30 Hz.

I wouldn't have been able to match a second set within 45Hz... )
===
My measurement method:

I have?modified BITX-VFO with 3 transistors Q5, Q6 and Q7.

But?I remove the coil L4?and T1 etc.,

replace it with crystal for the purpose of measurement as :

NB:

- I use 12.00 MHz?crystals for my BITX.

- My counter is homemade, One 7 segment counter by PA2OHH

since the 7 segment diplay is 100 Hz accuracy (ex. : 12 000.0 KHz),

I use RS232 for display frequency at computer for more accuracy

as ex. : 12. 123 456 MHz ).

Hans Summers

#196

开云体育

?

> Frequency reading is still moving / drifting,

> although circuit has been warming up about 5

> minutes.

> Q: How do you "note/catch" the frequency in this situation ?

?

Your circuit and method look Ok to me... how bad is the drift, and what happens if you wait longer than 5 minutes? The drift could also be in your frequency counter (or PC if you are using that as a frequency counter). The crystal itself will also drift, we tend to think of crystals as rock stable but they aren't at all. Relative to an LC oscillator maybe, but not in absolute terms. Just read about the problems I had getting a stable frequency in my 30m QRSS beacon (?and ).

?

In my BITX20 evaluation, I managed to find a socket which fit the crystals. If you are soldering the crystals in, you might find that the initial drift is rather high due to the crystal being so hot from the soldering iron and needing to cool back down to room temperature. A socket is better for testing. My socket was a proper HC49 socket temporarily "borrowed" out of a different unfinished project. But you can hunt around the junk box and another type of socket which will work Ok. The wires of the crystal are long enough that you can bend them slightly to fit in whatever socket you find to be suitable. Even with a socket, there was some initial drift due to the temperature stabilisation after me holding the crystal in my fingers.

?

73 Hans G0UPL

http://www.HansSummers.com

MILAREPA

#202

开云体育

Dear forum,

?

==About Crystal Measurements==
At the time I mail to BITX about this subject,
'actually' I was using a 3.579545 MHz crystal, that available
at my junkbox and drifting is in this frequency.
( not 12 MHz... ).
?
After that email I buy some crystal,
each 10.00 MHz, 12.00 MHz, 12.288 MHz, and 14.00 MHz.
and make some test for each crystal, using my vfo and socket
as?Hans's suggest, then connect / monitor at :
shortwave rx, counter 8 leds, counter one-7segment, and
rs232 - pc monitor ( this rs232 is part of one-7segment counter's add on )
here are the results:
?

?
The measurements stop at 10.00 MHz on 8 led cntr,
since the 8 led accuracy is 10.xxx MHz, and I need to
check them on rs232-pc but happened not displayed.
?
Please suggest what is possible here.
-Why for 10 MHz higher the circuit doesn't works normally ?
I have read that for a higher frequency, the vfo gain could be drop.

-Does vfo design limit is at 10 MHz ?
-How to fix this ?

?

Thanks.

MILAREPA

#209

Dear forum,

The problem of my crystal measurements has solved :-).
Thank you for your advice :-).

I try change the transistors from BC547B to 2N3904.
(maybe I got 2nd grade quality of BC547B)
Then vfo works with crystals : 3.5 ~ 14 MHz, 
and frequency could also displayed at my pc monitor counter.

Yours,
Milarepa

Show quoted text

----- Original Message ----- 
From: Arv Evans <arvevans@...>
To: <BITX20@...>
Sent: Friday, July 16, 2004 11:19 PM
Subject: Re: [BITX20] CRYSTAL MEASUREMENTS

  (2)  If the transistor you are using for the Crystal oscillator is not
capable of operating at 10 MHz or above, it may be not oscillating with
the higher frequency crystals.  The solution for this is to use a better
transistor.  In the US we have 2N2222 and 2N3904 available for very
reasonable prices so this is what I use for most of my HF work.  These
devices are rated to 150 MHZ, and will usually oscillate at even higher
frequencies.I hope this helps.

Arv - K7HKL
_._  

On Fri, 2004-07-16 at 04:30, MILAREPA wrote:

Dear forum,

==About Crystal Measurements==
At the time I mail to BITX about this subject,
'actually' I was using a 3.579545 MHz crystal, that available
at my junkbox and drifting is in this frequency.
( not 12 MHz... ).

After that email I buy some crystal,
each 10.00 MHz, 12.00 MHz, 12.288 MHz, and 14.00 MHz.
and make some test for each crystal, using my vfo and socket
as Hans's suggest, then connect / monitor at : 
shortwave rx, counter 8 leds, counter one-7segment, and
rs232 - pc monitor ( this rs232 is part of one-7segment counter's add
on )
here are the results:

The measurements stop at 10.00 MHz on 8 led cntr,
since the 8 led accuracy is 10.xxx MHz, and I need to
check them on rs232-pc but happened not displayed.

Please suggest what is possible here.
-Why for 10 MHz higher the circuit doesn't works normally ?
I have read that for a higher frequency, the vfo gain could be drop. 
-Does vfo design limit is at 10 MHz ?
-How to fix this ?

Thanks.
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