[Milsurplus] Fwd: Substitute for CRYSTALS

[William Cromwell]

Hi Ron,

I have been considering something similar and I have much of the 
information you have posted. The trick with the pin diode/key jack 
voltage is new to me and very useful. Thank you for posting.

73,

Bill KU8H

bark less - wag more

On 5/27/21 4:23 AM, Ron De Silva wrote:
>
>
>     Perhaps this is nothing new to most of you..But I'll share it.
>
>     Wth the death of our beloved International,JAN and Bomar crystal
>     providers...a lot of us have had to wait for months to get
>     crystals from Europe.
>
>     A simple,flexible and inexpensive work around is the readily
>     available DDS waveform signal generators you can get on Ebay.
>
>     Here is an example..( but I don't see what the MAX sig generator
>     putput of this particular one is,contact seller for specifics)
>
>     https://www.ebay.com/itm/DDS-Signal-Generator-Counter-Dual-Channel-Arbitrary-Frequency-Counter-60MHz-a11-/353502878077?_trksid=p2349624.m46890.l49286
>
>     They are extremely stable and mine puts out up to 20vpp of rf.
>
>     Plenty to drive any of the boat anchor crystal sockets I've tried.
>
>
>     The signal generators have a grounded output, and for some xtal
>     oscillator circuits that have an ungrounded "floating"
>     crystal...You may have to wind a simple balun to drive the xtal
>     socket.
>
>     In the case of the GRC9, it's not needed.
>
>
>     As an example,here is what I did on my GRC9.
>
>     No mods were needed to the radio, except to lift the ground lug on
>     the "BATTERY" Canon jack of the transmitter.
>
>     I then got a spare battery connector and added a female BNC to it.
>
>     The shell of the cannon plug  provides the ground for the BNC.The
>     old GROUND pin of the battery is what I used for a "no holes" way
>     to get the DDS xtal signal into the radio.
>
>     Then,I just routed a small piece of RG174 coax from the battery
>     jack inside the radio  to my small crystal substitute pcboard that
>     plugs into any socket.
>
>     Operation is simple enough..Dial up the crystal frequency you need
>     and start with 1volt or so from the sig generator while keying the
>     radio.
>
>     On the GRC9, it took about 6vpp output to give a consistent rf output.
>
>
>     The reason I used the  DDS source for the GRC9 is because of the
>     really bad CW note from a GRC9 MO.. Chirp is really bad,and I am a
>     99% cw op.
>
>     By using the DDS source,you end up with a pure ,chirpless stable
>     cw signal...
>     Without having to butcher the radio.
>
>     One oddity of tuning on the GRC9 in this mode is that you tune up
>     the rig with the normal MO, and then when you switch to the XTAL
>     position, you will seem to have to crank the Sig gen output VERY
>     high in level.
>
>     Instead,set it lower,like 5 or 6vpp and then turn the MO VFO dial
>     of the GRC9 just a turn or two below where it was running and you
>     will note that you need very little rf from the DDS to get full rf
>     output.
>
>     I have not noticed this on other rigs of mine.
>
>     But it's a simple tune up procedure to remember.
>
>     Depending on your radio and cable shielding you may be hearing
>     your sig generator when you switch back to receive.
>
>     To deal with that,you can use an external relay or opto isolator
>     to SHORT the signal generator output when you are NOT in key down
>     mode.
>
>     I decided to use a small RF PIN diode I had on a simple pc board
>     and a bias pot.
>     I added a T cable and 1/4 inch key jack for my bug,the DDS and the
>     1/4 inch jack to the radio key jack .
>
>     Open circuit voltage across the key in receive mode is plenty to
>     bias the PIN diode to an rf short...
>
>     I added a small trimpot to adjust the PIN diode bias when I switch
>     to other rigs I use this on.
>
>     So,on receive I hear no sig generator.On key down,the PIN diode
>     fwd bias short is removed and the transmitter works normally.
>
>     So,if you don't want to invest in crystals ...this is a simple way
>     to get some of your fleet back on the air.
>
>     Ron
>     NU6F
>     Reno,Nv
>
>
>
>
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