Re: Locking 25MHz Octagons

Brian Flynn GM8BJF

Hi Andy,
This may not answer your question but for the record I have just spent some time setting up a 27 MHz Octagon. I found that it would only lock with a sine wave on 27 MHz into it. I tried using a square wave on 27 MHz but it did not like that which seemed odd. Earlier I found that sub-harmonics (3MHz) upset the PLL and appeared as a comb either side of the main carrier on a downconverted signal. I ened up generating 54 MHz using an ADF4351 and dividing that by two and filtering it to get rid of the harmonics. I also noticed that my Octagon did not like having its reference interrupted. It would not re-lock until the power was cycled. Presumably the PLL has quite a narrow B/W and some frequency sweep is done to lock it at power up. Loss of reference wil not be a condition that it experiences in normal operation. BTW I have removed the xtal (plus its PCB pads  ;-( ) so am not injection locking. I found it likes about 10 - 13 dBm into it.
Brian GM8BJF.

On Wed, Jan 16, 2019 at 07:53 AM, Andy G4JNT wrote:
Has anyone tried injection locking the 25MHz crystalled version by injecting a SQUARE WAVE at 5MHz?
May make for a simple solution with a 10MHz reference and 74AC74.

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