Checking Xtal Freq W/ a GDO?

[W1UJR]

Hey guys,

Is it true that you can check the operating freq of an xtal with a Grid Dip Oscillator?
I heard about that somewhere, but can't see to find the docs or circut diagram of how to do so.
I've got a nice Millen GDO stashed away that would work perfectly for this.

I'm working on my rock collection for the new 30K-4 rig, its a 160 meter only set up at this point.
Have been gutting out the FT-243 holders to install the rocks in the larger Collins 3 pin holders, working well, but I am 1886 rather than 1885.

Also have a "dead" 1945 rock that just will not oscillate, tried cleaning with alcohol, still no activity, any suggestions?


-Old Buzzard Bruce

[W1DAN]

Hi Bruce:

I tend to think a GDO is not that accurate. Never done it though.

 You can put the xtal in an oscillator and then to a freq counter, or pass a sig gen through the xtal and see where it resonates.

73
Dan
W1DAN

[W1RKW]

I can be done but it isn't easy unlike determining the resonance of an LC network.  The reason being is a crystal has a very narrow bandwidth or response and seeing where it resonates and peaks on a GDO, you could actually go right by it's point of resonance and not see the peak and you may think the crystal is dead.  Very fine tuning of the GDO is essential.  And whatever you use to couple the GDO to the crystal will alter it's resonant freq somewhat so determining it's actual operating freq won't help to much.  Probably the best thing to do is stick it in the osc circuit and measure it with a freq counter.  If it's off a bit it can be rubbered into position with a small amount of capacitance or inductance in either parallel or series with the crapstal. Of course introducing some capacitance or inductance will introduce or change the drift characteristics.  Experimentation.

[WA1GFZ]

Bruce the circuit will have a big effect on the oscillator frequency. You can pull a crystal down by adding a small cap in parallel or series....or wait for it to age.
The angle cut of the quartz has a big effect on performance. Also if you add a little mass to the rock like a little pencil lead can pull it.
I would put the crystal in the rig and check it with a frequency counter or accurate RX. Most 36 degree cut crystals go down in frequency either side of about 30 degrees C. So if it warms up or cools down it will drop in frequency.
The best way to check is a network analyzer.
Try grinding the outside of a crystal to bring it back. Old timers would hold the outside so the center ended up a bit thicker. The FT243 has contacts on the edge to contact the corners in the ones I have moved.
Crystals are still a real art and SAW devices are even cooler.  

[W1UJR]

Bruce the circuit will have a big effect on the oscillator frequency. You can pull a crystal down by adding a small cap in parallel or series....or wait for it to age.
The angle cut of the quartz has a big effect on performance. Also if you add a little mass to the rock like a little pencil lead can pull it.
I would put the crystal in the rig and check it with a frequency counter or accurate RX. Most 36 degree cut crystals go down in frequency either side of about 30 degrees C. So if it warms up or cools down it will drop in frequency.
The best way to check is a network analyzer.
Try grinding the outside of a crystal to bring it back. Old timers would hold the outside so the center ended up a bit thicker. The FT243 has contacts on the edge to contact the corners in the ones I have moved.
Crystals are still a real art and SAW devices are even cooler.  

Thanks guys!

SAW devices?

[Steve - WB3HUZ]

Surface Acoustic Wave

[W2JBL]

     Bruce- try to keep them in the FT243 holders, and make up an adaptor for the
Collins socket. as mentioned before- the correct FT243 plates contact at the four coners in most, so try to stay with those. you have a few old buzzard options to lower the 1886 to 1885: lightly rub some pencil lead on the crystal, a bit on each side near the center. you lose activity when you do this, so go easy. this is what my Dad taught me to do. another one i found recently in a 30's QST works better: dip the crystal in IODINE, and let it dry. you can go a few coats before it loses activity. spring tension is critical in pressure type holders. if you have a few different FT243 holders, try different springs in the one you want to lower. more spring tension=-lower freq. 

     your dead 1945 may have been ground non paralell. a regrind on a truly flat grinding plate, taking care to make each side perfectly flat may bring it back, but it will be up the band a bit. grinding at 160 is a bunch more forgiving than 80 and 40, so it's a good place to learn the skill. use powdered carborundum in a paste mix of alcohol or natptha, grind on a thick FLAT glass plate. go for the finer grits- 600 for fast grinding, 800 and 1000 for fine and finish work. finer grit cuts slower. build an oscillator similar to the one in your rig and test frequently while grinding. stick the crystal under your finger and go in figure 8 patterns in the cutting goo, while counting them. do an equal number on each side. when testing clean the blank, dry and assemble in holder then test to keep track of frequency. put a grid current meter in the test osc. to monitor activity. are you having fun yet?

[WA1GFZ]

Chris,
Your OM taught you well. I learned at Andersen Labs back in the 70s. tuning glass delay line transducers.  Bruce SAWs are very cool. The transducers are on one side of the quartz only. The quartz oscillates like watching waves on the beach. My second time at Andersen I worked on SAW VCXOs. Imagine a 1GHz oscillator as clean as a 10 MHz crystal oscillator. No multiplier stages. A great reference for a DDS. I collected a few of those gems for the junk box. Anytime we had one out of spec after the case was welded I would keep them from hitting the bottom of the trash pail.
BTW I heard vodka also works well as a quartz cleaner.

[W1UJR]

     Bruce- try to keep them in the FT243 holders, and make up an adaptor for the
Collins socket. as mentioned before- the correct FT243 plates contact at the four coners in most, so try to stay with those. you have a few old buzzard options to lower the 1886 to 1885: lightly rub some pencil lead on the crystal, a bit on each side near the center. you lose activity when you do this, so go easy. this is what my Dad taught me to do. another one i found recently in a 30's QST works better: dip the crystal in IODINE, and let it dry. you can go a few coats before it loses activity. spring tension is critical in pressure type holders. if you have a few different FT243 holders, try different springs in the one you want to lower. more spring tension=-lower freq. 

     your dead 1945 may have been ground non paralell. a regrind on a truly flat grinding plate, taking care to make each side perfectly flat may bring it back, but it will be up the band a bit. grinding at 160 is a bunch more forgiving than 80 and 40, so it's a good place to learn the skill. use powdered carborundum in a paste mix of alcohol or natptha, grind on a thick FLAT glass plate. go for the finer grits- 600 for fast grinding, 800 and 1000 for fine and finish work. finer grit cuts slower. build an oscillator similar to the one in your rig and test frequently while grinding. stick the crystal under your finger and go in figure 8 patterns in the cutting goo, while counting them. do an equal number on each side. when testing clean the blank, dry and assemble in holder then test to keep track of frequency. put a grid current meter in the test osc. to monitor activity. are you having fun yet?

Guess I know what I will be doing this weekend, now if I can find some plate glass and carborundum paste...

Tnx again !

[WA1GFZ]

I bet rubbing compound, Valve lapping compound would work. I've even used comet cleanser. The whole thing is to go slow and make sure you clean it well.
I wonder if 600 grit wet dry paper would cut quartz?

[The Slab Bacon]

I bet rubbing compound, Valve lapping compound would work. I've even used comet cleanser. The whole thing is to go slow and make sure you clean it well.
I wonder if 600 grit wet dry paper would cut quartz?

That is the way that I have done them. I have reground lots of worthless CW band crapstals up to the fone bands with wet and dry sandpaper. Start with 400 for rough cut, then go to 600, and 800 for the final finish. Quartz is very soft and cuts easily.

I wanted some FT-243's for the AM frequencies. All i had was a ton of wierd freq crapstals and nothing to do one night, so I got creative. It wasnt hard to do, just time consuming.

                                                                         The Slab Bacon

[Carl WA1KPD]

Frank,
How liong dfoes it take to move a 80 mtr novice xtal up to the AM freqs?
Thanks

[The Slab Bacon]

Carl,
      I have brought a few up from around 3760 or 70 to 3885. It takes a while and a good bit of sanding but it is doable. Every once in a while you will get one that wont oscillate. But hothing from nothing leaves nothing. What do you have to loose! There are tons of CW band crapstals out there cheap or for free.

And besides, being able to say that you have ground your own crapstals is a nice
"notch in your gun" when it comes to bragging rights. I can uaually get them within a about a hundred cycles of what I want it to be doing it my way.
           
                                                                  The Slab Bacon

[W2JBL]

i have used Permatex Fine valve grinding compound, rubbing compound, and sandpaper. the carborundum paste made in alcohol or naptha works best. favorite cleaners for blanks is acetone or very pure alcohol. any finger residue on the blank raises hell too. non powdered latex gloves are good to use when handling. allways clean the crystal before inserting in the holder. if in doubt clean twice. getting from the 80 novice band to 3885 takes a while. be very careful of the activity as you make long excursions like that and check often. grinding your own? that's real ham radio!

[WA1GFZ]

I think you are supposed to hold the crystal around the corners not the center.