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Test signal gen and several quartz

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Garyl

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Test signal gen and seeveral quartzs

Hey
I want to make a test signal generator with this schematic:
76431-004-CD643328.jpg
I want to use multiple crystals within 1MHz - 15MHz range.
The exact output frequency is not important.
I want to have 5 or 10 crystals and be able to select the active one with microcontroller.

My question is, how do I modify this circuit to handle multiple crystals?
I have two ideas.
IDEA 1 - just use many crystals and many transistors (I mean, repeat the circuit as many times as needed). Then just use microcontroller and extra transistor to power-on the desired sub-circuit when needed.
IDEA 2 - use multiple relays to select the crystal for the single shared transistor. Then just use microcontroller to drive the relays... in this case I am afraid about the noise...

What would you suggest?
 

Re: Test signal gen and seeveral quartzs

The usual way to do this type of switching is to **broken link removed**.
 

Re: Test signal gen and seeveral quartzs

PIN diode switching would be ideal but as losses are not much of a problem in an oscillator, you can probably use normal small signal diodes.

The more practical solution if you want 10 different frequencies is to use one crystal and a PLL or if they are harmonically related, to generate a comb and then filter the harmonic you want.

Brian.
 

Re: Test signal gen and seeveral quartzs

The usual way to do this type of switching is to **broken link removed**.
testsignalgen.png
This is almost exacly what I wanted, but why is there 12V connected directly on one side (crystal selection) and 9V regulator on transistor collectors? Is it correct? I mean... wouldn't it mean that the collector voltage is 9V and base voltage 12V?
 

Re: Test signal gen and seeveral quartzs

... wouldn't it mean that the collector voltage is 9V and base voltage 12V?

PIN diode voltage is blocked by C10. Q1's base voltage is generated automatically by R1 and DC feedback via R2 .
 

Re: Test signal gen and seeveral quartzs

They are using the unregulated +12 V to provide switching current to the pin diodes. It is no problem as mentioned because there is a coupling capacitor C10 which block the DC.
 

Re: Test signal gen and seeveral quartzs

Hi,

If the exact frequency is not important...
* why not use an RC oscillator, a VCO, a PLL?

Klaus
 

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