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10 Mhz clock distribution for a double conversion upconverter

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kurtulmehtap

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Hi All,
I have designed a double conversion upconverter. Both PLL's use a 10 Mhz TXCO as reference.
I should also be able to use an external 10 Mhz reference.
Any suggestions on how to use only one 10 Mhz TXCO for both PLL's and to how to switch to an external reference?
 

kurtulmehtap said:
Hi All,
I have designed a double conversion upconverter. Both PLL's use a 10 Mhz TXCO as reference.
I should also be able to use an external 10 Mhz reference.
Any suggestions on how to use only one 10 Mhz TXCO for both PLL's and to how to switch to an external reference?
Click to expand...

Most PLOs utilize 0+/- 6 dBm for 10 MHz reference input. I have used a simple quartz oscillator (low-cost versions are available for < $10.- from Digi-Key, etc.), with an attenuator added to obtain ~ 0 dBm (usually the quartz modules generate ~+10-+13 dBm). To switch to external (other than my) reference source, I simply connect the "output wire" to another SMA connector, and use a switch to power my 10 MHz reference, or, switch it off.
Equally easy is to feed two PLOs from one internal/external 10 MHz source. Only some PLOs are radiating signals back to their reference inputs, so I would recommend to use a 10 MHz power splitter with some isolation, like Mini-Circuits ZMSC-2-1, and adjust the output power from 10 MHz source to get ~0 dBm to each PLO reference input.
 

Or you can use some LC Pi circuits to divide it into 2 way.
 

jiripolivka said:
Most PLOs utilize 0+/- 6 dBm for 10 MHz reference input. I have used a simple quartz oscillator (low-cost versions are available for < $10.- from Digi-Key, etc.), with an attenuator added to obtain ~ 0 dBm (usually the quartz modules generate ~+10-+13 dBm). To switch to external (other than my) reference source, I simply connect the "output wire" to another SMA connector, and use a switch to power my 10 MHz reference, or, switch it off.
Equally easy is to feed two PLOs from one internal/external 10 MHz source. Only some PLOs are radiating signals back to their reference inputs, so I would recommend to use a 10 MHz power splitter with some isolation, like Mini-Circuits ZMSC-2-1, and adjust the output power from 10 MHz source to get ~0 dBm to each PLO reference input.
Click to expand...

That is the approach I plan to use. However, in one article I saw this phrase:"OCXO is phase locked to external
source when present." How do we achieve this?
 

kurtulmehtap said:
That is the approach I plan to use. However, in one article I saw this phrase:"OCXO is phase locked to external
source when present." How do we achieve this?
Click to expand...

There are some OCXOs with a fine-tuning voltage input. By adding a phase-lock external circuit, you can lock such OCXO on a lower-frequency reference. For instance, Wenzel and Luff Research offer commercial "sub-reference-locked" OCXOs, with e.g. 100 MHz output, locked to a 10- MHz sub-reference, to achieve an extremely low phase-noise perfgrmance.
 

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