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Old 1st Apr 2023, 2:33 am   #1
mickm3for
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Default Quartzlock 2A mod.

Hi with all the LW tx's going off air thoughts as to my Quartzlock 2a. The way it works is to rx 198khz using this to lock a 10mhz xtal osc ok so when 198 khz goes off this= no locking signal = no output . so to the mod put quatzlock back to 200khz using the internal jumpers , using one of the Ublock neo-7-m gps units (£ 7.99 ebay) this can be reprogrammed to output from.25Hz to 10MHz so configure to 200KHz , the reason 200KHz because neo-7 gps clock is 48MHz this being locked to gps, so a clean devide of 240 this gives a clean squarewave pass this through a lopass filter and you have a 200KHz signal that is locked to gps. The Qurtzlock should see this as a off air signal and work as normal ? You say why not use the 10MHz straight from the neo-7 well on frequency's that do not devide cleanly you get jitter on the signal. This did not cause my counter to show any eror on readings Mick
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Old 1st Apr 2023, 8:32 am   #2
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Default Re: Quartzlock 2A mod.

You're using the Quartzlock as a 10MHz VCXO getting locked to the GPS reference. One problem is that there is jitter and then there is jitter.

The awkward divider in the Ublox (I've used them in the past) gives an erratic output, but there is also slower jitter in the GPS system itself. Most usually in a good frequency GPS-disciplined reference there is a very high class ovened VCXO locked in a very slow loop. This is in order to handle the long period wandering.

I'm not sure that the Quartzlock unit can be made slow enough without introducing its own errors.

It may just be simpler to look into one of the existing purpose designed GPS based frequency standards. I suspect you'd wind up effectively developing your own.

David
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Old 2nd Apr 2023, 2:15 am   #3
mickm3for
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Default Re: Quartzlock 2A mod.

Well i dismantled the 2a-01 and found it to be nothing like the circuit of the 2a
or indeed the discription of the 2a-01 in the manual. This unit has a 198khz xtal in the rx with no jumpers to change to 200khz also has no pll chip all smd parts and around 16 ic's nor gates nand gates with schmitt triger dual decade counter and some op amps, on the pcb says 29/6/98 issue 4 and on a label says 2A-x4 sn00027 nothing on the internet that i can find also no reff to this on quartzlock website under discontinued items back to the drawing board will contact quartzlock on Mon Mick
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Old 2nd Apr 2023, 8:18 am   #4
Craig Sawyers
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Default Re: Quartzlock 2A mod.

Quote:
Originally Posted by Radio Wrangler View Post
You're using the Quartzlock as a 10MHz VCXO getting locked to the GPS reference. One problem is that there is jitter and then there is jitter.

The awkward divider in the Ublox (I've used them in the past) gives an erratic output, but there is also slower jitter in the GPS system itself. Most usually in a good frequency GPS-disciplined reference there is a very high class ovened VCXO locked in a very slow loop. This is in order to handle the long period wandering.

I'm not sure that the Quartzlock unit can be made slow enough without introducing its own errors.

It may just be simpler to look into one of the existing purpose designed GPS based frequency standards. I suspect you'd wind up effectively developing your own.

David
Indeed. I use a Trimble Thunderbolt with a bullet antenna on a pole on the end gable of the house. That gives a 10Mz external reference for my HP counter mainly.

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Old 2nd Apr 2023, 8:42 am   #5
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Default Re: Quartzlock 2A mod.

Sorry to tell you but contacting Quartzlock is a waste of time. The Quartzlock name was sold to HCD Research Ltd. a few years ago. All of the 2A paperwork was "binned" at the same time along with documentation for other obsolete products manufactured by Quartzlock. I actually acquired the old documentation plus some spares for the early Rb oscillators along with test equipment that was not part of the sale. There are several versions on the original 2A off air standard & documentation can be a bit vague. Being pragmatic the simplest option when the 198KHz signal is dropped would be to retire the 2A & use a GPS variant. At least some versions of the 2A were adapted to use 60KHz as the reference frequency but to modify one from 198KHz is not a trivial task if my memory is correct.

Phil Parsons
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Old 2nd Apr 2023, 12:12 pm   #6
mickm3for
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Default Re: Quartzlock 2A mod.

Hi thank you for info, i will not mod this untill 198khz goes off .MK2 idea i have some 10mhz ovxo units with control pin to set fx out so if i take this 10mhz divide it to say 10khz and phase lock to 10khz from gps neo-7 then use the error voltage to set ovxo to 10mhz ? well that is the idea, i could just not bother with the jitter at 10mhz from neo-7 or try and clean it up with a schmitt trigger or 2 Mick
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Old 2nd Apr 2023, 12:25 pm   #7
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Default Re: Quartzlock 2A mod.

You'll have to decide on the speed of your loop. Good ovened VCXOs can be so stable that you might question why you need to lock it to a caesium source. The jitter due to the simplistic divider is short-duration, but the slower wander in the GPS system forces a much slower loop. Most system designers seem to have looked at what the max rate of drift of the OCXO might be and planned a loop response just fast enough to take this out.

Get the loop design wrong and it can make a result worse than just using the OCXO on its own. Some of the more recent GPS-disciplined frequency standard designs use small microprocessors and DACs to control the OCXO from looking at the 1Hz from a GPS receiver and the divided OCXO.

There are several designs out there you can just build. All you might wind up using from the Quartzlock unit might be the box and power supply, though.

David
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Old 4th May 2023, 9:37 pm   #8
veedub565
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Default Re: Quartzlock 2A mod.

I heard they could no longer find replacement valves for the 198khz Tx equipment. And once their spares were exhausted then that was it. So it could run for a while yet.... or not.

We do still see the quartlock 2A and 2A-01 units coming in for test & cal at work (I did one last week) I've been unable to find any documentation for them though other than the user guide and cal/setup procedure.

At home I use a Rubidium standard. I do actually have a GPS disciplined rubidium too, but the lamp isn't lighting on it.
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Old 4th May 2023, 11:39 pm   #9
Cruisin Marine
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Default Re: Quartzlock 2A mod.

Surely a well designed 198 kHz oscillator (or higher in freq. divided down), and using a zero beat on a monitor receiver should be good enough to calibrate on a weekly or monthly basis?
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