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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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13th Jun 2019, 4:40 pm | #1 |
Tetrode
Join Date: Apr 2014
Location: Essex, UK.
Posts: 70
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Quartzlab 2A 01 Off Air Frequency Standard
The above kit is locked to Droitwich on 198KHz. I notice lf jitter when driving/phase locking my generator at 1.295GHz, about 100Hz, is this normal?
Regards Kevin |
13th Jun 2019, 4:53 pm | #2 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: Quartzlab 2A 01 Off Air Frequency Standard
Does Droitwich still carry the low-deviation phase-modulation data signal that was used to operate the old "Radio Teleswitch" things used for economy-7 electricity-meter control and suchlike? That could be the cause of the jitter.
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13th Jun 2019, 11:42 pm | #3 |
Heptode
Join Date: May 2015
Location: Chatham, Kent, UK.
Posts: 947
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Re: Quartzlab 2A 01 Off Air Frequency Standard
Hi not noticed this on mine i have the service man if needed Mick
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14th Jun 2019, 1:55 pm | #4 |
Dekatron
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
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Re: Quartzlab 2A 01 Off Air Frequency Standard
At work we have several of these old OAFS units. I think most are the 2A-Y version with an OCXO. The 2A-Y units use a huge loop antenna made from coax cable and also they have the decent 10MHz OCXO fitted.
However, we do still have at least one early 2A-01 unit. This uses the little white ferrite rod antenna at the rear of the unit and the performance isn't that great compared to the 2A-Y. With the 2A-01 a lot depends on the time of day (propagation) and also if there are any nearby sources of LF interference. This could be a laptop PSU or a wallwart charger etc. Also, the ferrite antenna needs to be rotated and placed somewhere to get a strong signal on the Rx s meter on the 2A-01. If any of these are sub optimal I think the performance suffers in terms of output stability. Typically it will still show a fair bit of jitter/wobble at 10MHz when working correctly and this covers about +/- 0.15Hz on peaks across a few seconds. Over maybe 10 seconds the peak wobble might hit +0.2Hz but this will be a very brief event. The average of all this should be within maybe 0.02Hz of 10MHz over several seconds. When used to lock a sig gen up at 1.295GHz I'd expect it to be 129 times worse than this. Therefore, the typical wobble would be expected to be +/-20Hz at 1.295GHz. I'd expect to see it wobble back and forth several times across this range over a few seconds.
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Regards, Jeremy G0HZU |
14th Jun 2019, 3:59 pm | #5 |
Tetrode
Join Date: Apr 2014
Location: Essex, UK.
Posts: 70
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Re: Quartzlab 2A 01 Off Air Frequency Standard
Thanks Jeremy,
Think they do jitter a bit, mine is more or less in the right area. Sig Gen better with no standard connected as far as jitter goes, but slightly off frequency. Settled on a 10 Megs output Mini GPS unit by Leo Bodnar, much better, no jitter and very small! Kevin |
15th Jun 2019, 12:33 am | #6 | |
Dekatron
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
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Re: Quartzlab 2A 01 Off Air Frequency Standard
Quote:
This starts off with a 20kHz span so the LF phase modulation isn't visible at first. Also, the response of the display isn't very fluid because my old PC struggles to process the data, display it and then capture it with Camstudio. But it can still show the LF phase modulation once the span is reduced to 1kHz or less. https://www.youtube.com/watch?v=xrVp...ature=youtu.be It is also possible to see that the main 198kHz carrier doesn't stay at a constant level and they presumably dip the carrier power where the regular AM signal has high peak power in order to try and improve efficiency on speech peaks. So I guess the combination of the LF phase modulation, the carrier dips and the phase and amplitude variations due to propagation effects will all contribute towards the overall jitter on the 10MHz output of the OAFS. If a regular frequency counter with a 10 second gate time is used to look at the 10MHz output of the OAFS then the effects of all this jitter tends to average out across the 10 seconds and it isn't obvious on the counter display that the wobble and jitter is there. So the jitter becomes less of an issue here. I think the best use for this type of OAFS is simply to average the results over maybe a minute or so with a logged frequency counter and use the long term average to calibrate the reference OCXO in a counter or a signal generator etc. I don't think it's a good idea to try and use the 10MHz from the 198kHz OAFS as an external reference for a decent sig gen or a spectrum analyser because the jitter and phase noise of the test gear will be degraded as kkyahoo has found out.
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Regards, Jeremy G0HZU Last edited by G0HZU_JMR; 15th Jun 2019 at 12:38 am. |
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16th Jun 2019, 6:46 am | #7 |
Tetrode
Join Date: Apr 2014
Location: Essex, UK.
Posts: 70
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Re: Quartzlab 2A 01 Off Air Frequency Standard
Good video Jeremy. Also your 2017 one on Off-Air Standards is very informative, thanks.
Kevin |