[time-nuts] 40MHz source

Grant Hodgson grant at ghengineering.co.uk
Mon Mar 25 13:34:54 EDT 2013


I think you're going down the right road with the Chris Bartram transceiver.

My suggestion for a 40MHz source would be to take a 10MHz source and  
feed it into two successive doublers, with a bit of inter-stage and  
post-stage buffering and filtering.

Frequency doublers can be very simple indeed - as simple as a  
full-wave rectifier.  It's the sort of thing that somebody in the  
local radio club might be interested in building, even if they are  
afraid of the 'scary' microwave stuff.  Lot's of possibilities for  
experimentation there.

As for a 10MHz source - I'd be tempted to go for either a good quality  
OCXO, or maybe a GPSDO such as the Trimble Thunderbolt (which has a  
fairly good 10MHz OCXO inside it).  Many Rubidium sources are designed  
for medium-long term stability, at the expense of close-in phase  
noise, and that might be a problem in this application, as the 10MHz  
oscillators in many rubidium sources don't have as low phase noise as  
the 10MHz oscillators in the good GPSDOs.

A good quality 10MHz frequency standard will also have other uses in  
the lab, of course.

To answer Jim's question - 'inside the box' is an LTC6946-3 integrated  
Frac-N PLL/VCO with an o/p at 5GHz, then feeding into a sub-harmonic  
mixer to get to 10GHz.  The PLL uses a 40MHz reference, which I  
believe is also the PLL comparison frequency.  I think that the  
supplier might be reluctant to change the software to use a lower  
comparison frequency, but I haven't asked.

The loop bandwidth of the PLL is somewhere in the 10kHz-20kHz range,  
so any close-in phase noise from the reference will get multiplied up  
to the final frequency, hence the need for a reference with good phase  


Subject: [time-nuts] Are there any rubidiums
         programmahttps://mail.google.com/mail/?shva=1#inboxble to 40 MHz?

I'm possibly looking for a 40 MHz source and I know some of the
rubidiums are programmable. But can any of the affordable ones be
programmed to work at 40.0 MHz?

I was looking for a source to drive this 144 MHz -> 10 GHz transceiver.


The TCXO oscillator is off the board and a separate item, but costs
?40 and then one ideally wants to lock that to a more precise source.
The oscillator will lock to an external 10 MHz source, but then one
needs to buy both a 10 MHz rubidium as well as this 40 MHz TCXO. Hence
I was wondering if there was a cheaper more compact solution, which
just used a rubidium, and dispensed with a TCXO.


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