Crystal Control

got my novice class license back in February 1970.  Back then novice class hams were limited to CW operation on portions of the 80, 40, and 15 meter bands.  By this time voice privileges in the 2 meter band had been withdrawn.  The purpose of the novice class license, created in 1951, was to allow the applicant to increase his (or her) CW skills via on the air practice with the goal of upgrading to a general class ticket.  The novice license was granted for a one year period, and was not renewable.

I upgraded to an Advanced class license within six months of getting my novice license.  The FCC had announced that license fees for the amateur service would be going up for the first time in several decades, from $4 to $9.  With that incentive, I studied the written test questions for both the general and advanced class exams, and managed to copy CW at a solid 15 WPM, a sizable safety margin.  I made the trip down to the NYC FCC office in lower Manhattan on the last day that the $4 license fee would be in force, and I managed to pass the 13 WPM code element, and both the general and advanced class written elements.

Since then, both the novice and advanced class licenses have been eliminated (though anyone holding such  tickets could renew them forever).  The privileges allocated to both of these license classes still apply, how strange that the only way a general class licensee can now gain privileges in the advanced class band segments would now be to obtain an extra class ticket!  I was in a special league here.

Even more recently, the CW requirements for all ham licenses have been removed (thought the CW band segments remain, now shared with new ‘digital’ modes that don’t require CW knowledge).  Since I’d never increased my abilities in CW beyond the 15 WPM plateau (and have probably gotten more than a bit rusty as well), the extra class license had remained an elusive goal.  However with the CW requirement now history, it was within reach.  The written test for the extra was a cinch for me, having a BS degree in electrical engineering.

Nostalgia is a strange beast.  The recent resurgence of home brewing has resulted in many hams building simple QRP rigs.  What is QRP?  Back in the early days of CW when power tubes were scarce and expensive, anything over 100 watts was considered QRO (high power).  If you operated with less than 100 watts, that was QRP.  With the onset of SSB, building a legal limit station became easy.  You no longer needed a heavy, expensive modulator (which was actually a very high powered audio amplifier, about 500 watts worth).  The same tubes that were in the old modulator, plus an additional copy in the final amplifier (2+2 = 4) would run the legal limit, no modulation transformer required.  But it was also discovered just how well SSB cut through the QRM and QRN compared to AM.  You really DIDN’T need the full gallon (most of the time).  The 100 watt output of the average transceiver was more than enough (except for the contest nuts or DXCC hunters).   Today, a new term has come up, QRPP.  If QRP means a 100 watt station, then QRPP would be < 10 watts.

I’ve collected quite a lot of parts over the years.  Even though I’ve pruned my junk box of a lot of the old tube related stuff, I still have a good assortment, including some old NOS octal tubes.  Why not build something that would be a throwback to the novice days?  That would probably mean a crystal controlled transmitter.  There is a problem though, have you checked to see what those old FT-243 crystals cost these days?  Even back in the 1970’s, with quite a few crystal houses still turning out such crystals for the novice class, the supply was mostly made from re-processed WWII surplus.  Needless to say, that supply has dwindled down to a trickle, especially since the demand slackened off following the removal of the crystal control requirement for the novice licensees back in the 1980’s.  As a result, FT-243 crystals on Ebay often fetch upwards of $20 each, especially for those in the heart of the amateur QRP CW band segments.

Looking in my junk box, I see that I have quite an assortment of these old crystals, few of which are cut for amateur frequencies.  I do have some crystals that could end up in an amateur band if used on their second or higher order harmonics (especially for the ‘newer’ WARC bands).  I also have quite a few more that could be made to work by grinding or etching them higher in frequency.  THAT will be my next project.  If I succeed doing this, I will then consider building a simple tube transmitter and receiver (more on that in a future post).

I’ll go into the process of re-working those old crystals in a future post, for now I need a way to test all those old crystals.  I need to separate the good ones from the dead ones.  (Actually the first two ‘dead’ crystals I discovered were only dead because one of the two pins had become electrically ‘open’.  Moving the actual crystal into another case brought it back to life.  I can repair the broken crystal holder).

A search on the web found a project by W5USJ on QRPME.com for a crystal checker.  This gizmo includes a test oscillator, a crystal activity indicator, and a frequency counter.  I didn’t need the frequency counter, I already own an old Leader 250 mhz counter.  I did need the test oscillator however.  The circuit of this tester, as I built it, plus some pictures of its construction are shown below:

CrystalChecker

P1030026P1030027

The circuit contains an oscillator (Q1), an activity indicator (Q2, two small signal diodes and an LED indicator), and a buffer amplifier (Q3) to drive an external frequency counter.  I added a 5 volt regulator (7805) so I could power the tester from a 9v ‘wall wart’ or a 9v battery.  I built mine on a small copper chassis I made from a scrap of copper plate (from a hobby shop).  The transistors are mounted in sockets (salvaged from old TV set PC boards).  While PN2222 and 2N3904 transistors are specified, really ANY common small signal silicon NPN transistors with an FT of 150 mhz or more can be used.  I have metal cased 2N2222’s in the oscillator and indicator positions, but the 2N3904 would work there as well.

Operation is simple, connect power (the red LED should light), and plug a crystal into the socket.  If the crystal is oscillating, the two diodes will rectify the signal and develop a turn on bias for Q2, which will the conduct lighting the green LED.  Transistor Q3 along with the diode from its base to ground will square up the signal to provide a clean waveform to drive a frequency counter.  The circuit as designed by W5USJ included a PIC microcontroller programmed as a frequency counter good for up to (at least) 10 mhz.  He didn’t provide the source code, but I’ve seen other examples of PIC frequency counters on the WEB if you need one.  (https://sites.google.com/site/vk3bhr/home/fm2)   I just use my Leader LDC-823S I bought used many years ago.

Note that 6740 khz crystal in the socket.  I intend to try and move that (and a few others like it) into the 40 meter CW band.  Many years ago as a novice, I did mange to move one surplus crystal a few hundred khz higher in frequency.  Several others were ‘bricked’ in the attempt.  I’ve later read about using an etching solution to chemically thin down crystals, a process that should offer a higher rate of success.  We’ll see.  I have some etching solution on order.  I’ll report on how this all works out in a part two.  Stay tuned.

 

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