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Old 25th Oct 2018, 11:27 am   #1
Vintage_RC
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Default Quartzlock 2A off air standard and MSF?

I've got a Quartzlock 2A off air (BBC 198KHz) standard which works well after minor tweaking. In the light of the potential shut down of the 198 service I was wondering if it could be converted to use MSF 60KHz. You can download the manual with circuit for the near identical 200KHz version from ElektroTanya. It works by crystal filtering and amplifying/limiting the 198 signal and dividing it down to 1KHz. A 10MHz xtal oscillator is also divided down to 1KHz and the phase difference between the signals is used to bring the 10MHz oscillator into lock. Some mods are obvious such as changing the front end including the crystal filter to 60KHz and altering the divide ratio but:

1) Would the time modulation on MSF make this fairly simple approach impossible?

2) If it is possible would there be enough front end gain as I believe the MSF Tx is much lower power and further away than Droitwich?

Alan
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Old 25th Oct 2018, 7:42 pm   #2
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Default Re: Quartzlock 2A off air standard and MSF?

Although locking to MSF is possible the ON-OFF keying of the carrier means that this is not so simple.
There is an old design by G4JNT here and I've attached another version be G4OEP which seems not to be on-line any more.

If you have a view of the sky then a cheap NEO-6M v2 module (from ebay?)
can be configured to output a 1kHz signal which would give the option of easy switching between GPS and Droitwich.
(The 1kHz will have some jitter on it but the pll wil attenuate this.)

I believe the NEO-6M can save its configuration to eprom on the module, the later NEO-7M doesn't appear to be able to do this.


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File Type: pdf MSF_Ref G4OEP.pdf (74.5 KB, 312 views)
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Old 26th Oct 2018, 10:05 am   #3
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Default Re: Quartzlock 2A off air standard and MSF?

Thanks for your reply Jim. I was familiar with the G4JNT design but not the G4OEP one (thanks for the attachment). The G4OEP design is interesting and neatly solves the on/off data problem by using a tri-state phase comparator to hold the control voltage in the absence of signal. Looks like an interesting winter project! I'll take a look at the NEO-6M v2 module although the need for an external antenna is a bit of a minus compared with MSF.

Alan
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Old 27th Oct 2018, 1:15 pm   #4
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Default Re: Quartzlock 2A off air standard and MSF?

The other option would be to find out how accurate your local radio 5 live transmitter is on 693kHz. I think the 693kHz transmitter near me is at Droitwich so it may well be locked to the same frequency reference as 198kHz. The last time I checked BBC R5L at 693kHz with data from a decent (real time) spectrum analyser it seemed to be very accurate and this is what makes me think it might locked to the same or similar reference as the 198kHz transmitter. But other 693kHz transmitters across the UK might not be as accurate.

However, a lot obviously depends on what accuracy you want.

For the majority of home applications an accuracy to within maybe 10Hz at 10MHz would be OK to calibrate a fairly modest/classic frequency counter. So it might be possible to use 693kHz even if the reference they use isn't as accurate as Droitwich. I'd hope they are all well within 1Hz at 693kHz for example. But I could be wrong!

Here's a quick video showing the lock time and short term stability of my old homebrew 198kHz OAS. I made this back in the 1990s and it works very well on a good day. On a bad day/night when propagation is not as predictable it won't be as stable as in the video. If the 198kHz transmitter goes off air then I'll probably modify this one to 693kHz if they keep R5L as accurate as it appears to be at the moment.

https://www.youtube.com/watch?v=F5gNe3OIdsc
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Old 27th Oct 2018, 5:22 pm   #5
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Default Re: Quartzlock 2A off air standard and MSF?

I had pondered with the idea of using a BBC MW Tx. This would get around the on/off modulation problem with MSF and might be an easier way of adapting the Quartzlock 2A. I do wonder, however, that when 198KHz goes off air how long the MW stations will carry on for.
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Old 6th Nov 2018, 12:48 pm   #6
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Default Re: Quartzlock 2A off air standard and MSF?

"High power MF sync groups with the same programme eg) the R5 693 and 909 kHz etc networks are accurate to 1/5th Hz ie) +/- 200 mHz off channel maximum."

I asked a similar question on the VMARS forum some time ago and the response above came from Dave G4OYX who is a broadcast engineer.
My local R5 transmitter on 909kHz at Moorside Edge seems to be quite a lot better than this and very stable - at least as far as my counter is concerned! 200mHz is good enough for me as most of my work is at HF and its a lot easier to count 909kHz than to start building GPS disciplined oscillators etc.
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Old 7th Nov 2018, 2:38 pm   #7
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Default Re: Quartzlock 2A off air standard and MSF?

Hi Jeremy,
That's a very interesting video. Was this your own design or a project available elsewhere please?
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Old 7th Nov 2018, 6:25 pm   #8
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Default Re: Quartzlock 2A off air standard and MSF?

Quote:
Originally Posted by G8BBZ View Post
I asked a similar question on the VMARS forum some time ago and the response above came from Dave G4OYX who is a broadcast engineer.
My local R5 transmitter on 909kHz at Moorside Edge seems to be quite a lot better than this and very stable - at least as far as my counter is concerned! 200mHz is good enough for me as most of my work is at HF and its a lot easier to count 909kHz than to start building GPS disciplined oscillators etc.
What did you do about the modulation and the resultant sidebands?
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Old 8th Nov 2018, 4:50 pm   #9
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Default Re: Quartzlock 2A off air standard and MSF?

Quote:
Originally Posted by See_Mos View Post
That's a very interesting video. Was this your own design or a project available elsewhere please?
It was my own design. It is fairly crude in that it is just a TRF receiver/limiter and a /99 stage and so it phase detects at 2kHz. It also has a homebrew 10MHz VCXO and uses 74HC390 chips to do the division and it uses a classic HC4046 phase detector. I designed and built it in an evening in dead bug style and it has remained like that ever since. It really is a bit of an ugly (but reliable) mess. I did keep meaning to make a tidy version but the threat of the 198kHz transmitter being closed down meant that I didn't want to make a tidy version of something that could go obsolete at any time.
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Old 9th Nov 2018, 11:15 am   #10
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Default Re: Quartzlock 2A off air standard and MSF?

At the moment I just need a very accurate signal to check a low frequency generator / DFM.

I found an article online which uses a ZN414 and a high speed comparator for a 198KHz front end.

I am now working on coding a Microchip PIC as a variable frequency divider referenced to one of the BBC stations.
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Old 9th Nov 2018, 1:03 pm   #11
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Default Re: Quartzlock 2A off air standard and MSF?

See Mos - I'd love to hear how that goes. I tried a similar front end with the TA7642, but any attempt to get a reasonable amount of 198 KHz from the output pin (by reducing the decoupling) caused instability. Still, that website seems to indicate the ZN414 design works.
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Old 9th Nov 2018, 6:47 pm   #12
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Default Re: Quartzlock 2A off air standard and MSF?

My old receiver design used a very narrow BPF at 198kHz using RM cores and a Philips NE604A limiter/FM chip to try and limit out the AM. The NE604A also gives an RSSI output for a signal meter. However, If I was starting again I think I would have designed a discrete limiter to try for even more AM rejection. However, the output of the 604 is good enough to drive a reciprocal frequency counter direct and I get a stable 198.000000kHz display on the counter with only the LSD flicking by one or two digits. So the TRF receiver + limiter on its own would be good enough for some people if they have a suitable counter to read the 198kHz directly.
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