[Boatanchors] Glen's FT-243 crystals questions

[Flowertime01 at wmconnect.com]

Glen,

I'm not much on CRYSTAL THEORY so I am wondering what is involved in using 
the smaller size Crystals such as the CR-18, CR-23, or whatever the number for 
FT-243 crystals.
---------------------------------
Grab all the FT-243 crystal cases you can.
The side package comes off with some small screws.
you can heat the pins and remove all the guts.
Any new small crystal socket with wire leads can then be soldered into the 
holder.
If the cover fits, OK. You can always cut the case so the pins can be used.

There are some metal cans that have pins the same as the FT-243 cases.
These will plug and play as Ft-243.

There are some other metal cans that have smaller pins.
You can build an adapter socket from some 9 pin tube socket pins and a 
FT-243 case. These crystals then become plug and play.

Most crystals have a frequency marked on top or side.
Over tones will likely work at the marked over tone if you get the 
circuit capacitance close.

You can plug almost any crystal into any crystal oscillator circuit and get 
it 
to work.

A better capacitance match will get you a stronger (larger voltage) output.
The frequency will be close, the difference will again be from circuit 
capacitance
or inductance values being off just a bit.


Since, a crystal operates on a Fundamental Frequency and also on Harmonics, 
which I understand is determined by the "Cut" of the Quartz.  

Once the crystal gets packaged, it is going to operate on the frequency
marked on the can. If you have an overtone crystal and place it into a
circuit where the capacitance is just to far off, it just will not oscillate.

The fundamental and the overtone are different.
An over tone is not the harmonic of the fundamental.
You get the harmonics out of the oscillator by tuning the output
of the oscillator to the to the harmonic.
You get the overtone out of the oscillator by tuning the crystal socket 
capacitance 
and using a unturned (broadband) output on the oscillator.

Also, the Frequency determines the thickness, plus probably other physical 
dimensions of the crystal as well.

Do not worry about these elements. The package will operate in most
crystal oscillator circuits.

Then there are voltages and associated circuitry necessary to drive the 
crystal into oscillation, and a feedback necessary to sustain oscillation. 

If you have an oscillator circuit, like in a transmitter where you are just 
plugging
crystals in to get a fixed frequency out, the circuit is designed and you are 
ready t go.

If you are building your own circuit, start with a good design, do use a nice 
variable capacitor that you can tweak around.

Now we add a trimmer capacitor to fine tune the oscillator frequency.  

No not really, the trimmer capacitor is to balance the tube, tube socket, 
crystal package, crystal socket and wiring capacitance. Once you balance the 
circuit, you can swap crystals and not rebalance. All the FT-243 packages have a 
characteristic capacitance and pretty much interchange. The other "standard" 
packages have their 
characteristics and will also interchange.

So the real question to the group is, "WHAT CRYSTALS WILL WORK WITH DIFFERENT 
SETS, or is there a table defining Crystal Characteristics for a given 
crystal type?

Almost any crystal will work in a FT-243 circuit.
Different package types (military small pin, FT-243, CB, Wire Lead) will work.
However, you may need to tweak the trimmer capacitance to match the package.

The operative here was to match the package, not maximize the frequency, not 
tweak the frequency. Matching the capacitance will get you the maximum output 
from the package. Two identical crystals in matching packages will not have 
the same maximum output voltage. (unless you get lucky.) Some do work better 
than others. Most transmitters have a buffer stage and some drive adjustment. 
This means most any crystal that will operate will provide enough drive, that you 
can get
full transmitter output.

Picking crystals for receivers and mixer stages is a bit more complex. 
The crystals are usually tested in a circuit to ensure the package will have
the required drive for the design before it solder in. Or in the old days 
plugged
into the socket. If you are building your own, you need to test the as built
circuit. You can adjust the feed back and get more or less gain.

You will also likely use two capitulators. One will neutralize the circuit 
capacitance for maximum crystal output. The second will actually change the 
circuit resonance frequency a few hertz to a maybe a few hundred hertz to get the 
crystal circuit exactly on the frequency you expect.

Most of the new stuff is so close it ain't funny. 
There are some nice 4 pin chips to be had from computer boards.
These things have +5, ground, signal and signal ground.
They run at 10, 20, 40, 60, 80 Mhz as square wave outputs. you can use these
in phase lock loops to get almost any frequency.

Strange, you can run a square wave into a mixer and do RF analog receiver 
mixing
with these circuits.  You can run the square into a tuned circuit and pick 
off a 
very nice sine wave. You need to work on the circuit values to get a sine 
wave.


Hope this helps.

Roger L. Ruszkowski KC6TRU