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Author Topic: Source for I.F. crystal filters?  (Read 1208 times)
KC9KEP
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Posts: 208


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« on: December 05, 2007, 11:22:41 AM »

Hello all!

Would anyone have a good source for crystals?

I would like to experiment with crystal I.F. filtering.  I have a couple potential vintage
ARRL receiver projects that require a 1700 kHz
crystal in the I.F. chain.

I'm also interested in potentially building a vintage
SSB exciter that would also require a few crystals in
its filter.

In the past, I recall procuring crystals from CTS
Knight, etc.  You'd just send a post card and $5 and
the crystal would be mailed to you .. but them days
are gone!

Thanks!

--Tom Nickel KC9KEP
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W3LK
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Posts: 5639




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« Reply #1 on: December 05, 2007, 03:30:57 PM »

International Crystal in Oklahoma City.

73,

Lon - W3LK
Naugatuck, Connecticut
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
AD5X
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Posts: 1432




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« Reply #2 on: December 06, 2007, 04:55:17 AM »

Can you change the IF frequency and use those cheap (and plentifull) microprocessor crystals?  Check out Mouser and Digikey for a large selection of them.

Phil - AD5X
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KC9KEP
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Posts: 208


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« Reply #3 on: December 06, 2007, 06:55:14 AM »

Thanks for the replies!

I did check w/International Crystal.

They can whip me up a 1700 kHz xtal for the
mere price of $55.27!!  Ouch! .. Ouch! Ouch! Ouch!

For the price of 3 crystals, I could buy a mobile
2-meter transceiver :-(

But, I'll keep looking.

I just may try moving the I.F. frequency as suggested.

I've found some surplus electronic crystals that aren't
too far for 1700 kHz as well ..

Thanks!

--KC9KEP
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AG4RQ
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Posts: 300


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« Reply #4 on: December 06, 2007, 08:44:38 PM »

I have a 1.8432 MHz crystal that I got off an old computer card. I just looked on Mouser's site. They're available for a couple of bucks. 1.8432 MHz isn't far from 1.7 MHz. Maybe it will work for you. Mouser has some others that are close as well. They have 1.61, 1.8 1.84 and 1.8432 MHz crystals.
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WA7NCL
Member

Posts: 625




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« Reply #5 on: December 07, 2007, 08:18:14 AM »

You could by a DDS kit that is offered by some of the QRP kit guys.  A DDS will allow a wide range of frequencies to be produced.
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KA5UOS
Member

Posts: 3




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« Reply #6 on: December 13, 2007, 02:00:31 PM »

The classic 80/40M receiver using a 1.7MHz IF and a 5MHz LO can be created with using a slightly different scheme...actually reversing the local oscillator and filter frequencies.

To cover 40/80M:

The 1.7MHz IF filter can be changed to 5.185MHz and microprocessor crystals used in a ladder formation.

The LO will then change to 1.185MHz to 2.115MHZ or 930KHZ which is doable with proper reduction drives or a bandset/bandspread setup.

If CW is all that is desired, approx 1.485 to 1.915 is required or 430KHz.

Again, all that is being done is switching the IF and LO frequencies.

Ladder filters are very easy to build with microprocessor crystals and a complete filter can be built for under $3.

73 K5UOS
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KB1GMX
Member

Posts: 786




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« Reply #7 on: December 13, 2007, 07:15:34 PM »

Suggestion,

An IF of 1700khz when the reciver was designed was
outside the AM boradcast band, now it isn't.  So a
higher IF is advised.  Microprocessor clock crystals
are available in a huge range of frequencies from
various sources usually for under $1.  A good starting
point is 1.8432Mhz but the list of available crystals
is generally long and lots of choices.

Places Like:

  JDR micro
  www.bgmicro.com
 
and others are cheap.  Digikey and Mouser generally
have what you want but you will pay more.


Allison
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WD4HXG
Member

Posts: 186




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« Reply #8 on: December 29, 2007, 07:44:57 PM »

At the risk of showing my age here goes. Look for FT-243 rocks on e-Bay near your frequency of interest but below the actual frequency you want.

Once in hand measure the actual frequency. Then open the rock. Check the rubber seal, make sure it is still ok. Remove the quartz. Hand grind the quartz to move the frequency up.

I use optical grinding compounds to hand trim the quartz. Once near the actual frequency finish the trim with a ammonium biflouride paste and then wash in distilled water. If you just grind and don't use an acid etch the rock will drift over the next year and then fail. The military discovered this during WWII.

Ammonium Biflouride is available in small quantities from glass etching houses. DO NOT CALL A CHEMICAL SUPPLY HOUSE WHICH SELLS THE STUFF BY THE GALLON. Ammonium Biflouride is a precursor for producing chemical weapons. You can figure the response to someone seeking to buy lab grade stuff for home use. A little two ounce bottle is the way to avoid Imperial Entanglements.

Also wear an apron and eye protection.

73

Chuck WD4HXG
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