Sacrilege, yes or no?

[sidspop]

I have a Racal 9081 that works, and a 9081 that doesn't, picked up for a tenner as spares.
I also have a number of frequency counters, ad they all give slightly different readings on an input, eg 100Mhz.
Given that the bank account will not quite stretch to a Rubidium Standard, I was toying with the idea of removing the 5Mhz crystal oven, adding a 12 volt PSU and sticking it in a case, for use as a calibrator.
But this seems to be sacrilidge in a way.
Your thoughts?

[Refugee]

Use a long wave radio and a signal generator to get a beat and see what your counters show from the signal generator.
Radio4 is 198Khz.
I have an earlier Racal and ran such a test on it with several radios.

[Diabolical Artificer]

Not really, especially if you make it reversable.

Andy.

[ukcol]

Originally Posted by Refugee

Use a long wave radio and a signal generator to get a [ZERO frequency] beat and see what your counters show from the signal generator.
Radio4 is 198Khz....

That's the way to do it! Perfectly accurate enough for our purposes. Just tweak the clock in the counter if required.

[Radio Wrangler]

Just because a crystal is in an oven does not make it accurate. It makes it much more stable. What frequency it's stable on depends on how well it was adjusted, what it was compared against, and then ageing effects.

A carrier beat on 198kHz with a broadcast radio is an easy check against what should be a well-maintained standard. The radio 4 carrier used to be derived from NPL, but I'm not sure whether that's still the case.

There are purpose made standard frequency transmissions on 60kHz, 2.5, 5 and 10MHz if you have a general coverage receiver. The low frequency one offers more stable propagation characteristics from a 'local' source (MSF, Anthorn, Cumbria).

Another reference is to use the counter in period mode to measure the time between the 1 second ticks from a GPS receiver module.

There are many ways of getting an external reference, all good enough for our purposes. The radio and 198kHz is the easiest.

If the aim is to get a high resolution counter within its original spec, then getting an external standard is a challenge. Fun if you like that kind of thing.

David

[barretter]

It's definitely not "sacrilidge".

[Nymrod121]

Upcycling is preferable to recycling!

In my personal opinion, not sacriledge at all. It's yours, so do with it as you think fit - and a 'plural, terse and spherical' response to the 'rivet-counters'.

West Brom ... hmm. Not that far from me (10 mins off M42 j3), so if you wanted to bring the finished item over I can run it on soak for a few days with my GPS-disciplined oscillator as a reference to assist in any fine tweaking you felt was needed. It depends upon how 'time-nut'-ish / perfectionist you feel about it - ?

Best wishes
Guy

[David Simpson]

Aye, sidspop - use the 198KHz as a reference. Back in the 60's we checked RAF frequency counters against the original Radio 4 at 200KHz, as it was supposed to be NPL monitored. There are several test frequencies broadcast, but I can't put my hand on the list just now. Perhaps another Forum guy can.

Taking up Guy's offer is a great idea.

Regards, David.

[MrBungle]

I would take up Guy's offer or you'll end up with all your frequency counters being wrong (been there)

I use a QRP labs QLG1 GPS receiver and their VFO kit. Total $56 for GPSDO

https://www.qrp-labs.com/vfo.html
https://www.qrp-labs.com/qlg1.html

Wait for it to lock onto GPS, then set it for 10MHz out, then cal the counter. Also acts as a handy 2.5KHz to 200MHz RF signal generator (if you add the LPF kits to it)

It's not as good as a nice old HP GPSDO or rubidium source but it's very much good enough for amateur use.

[trh01uk]

I wonder why you need better accuracy or stability than a crystal oven will provide? Typically that's about +-1ppm - or at 100MHz - about +-100Hz.

What are you doing that requires you to get a 100MHz signal better than +-100Hz?

Richard

Originally Posted by sidspop

I have a Racal 9081 that works, and a 9081 that doesn't, picked up for a tenner as spares.
I also have a number of frequency counters, ad they all give slightly different readings on an input, eg 100Mhz.
Given that the bank account will not quite stretch to a Rubidium Standard, I was toying with the idea of removing the 5Mhz crystal oven, adding a 12 volt PSU and sticking it in a case, for use as a calibrator.
But this seems to be sacrilidge in a way.
Your thoughts?

I wonder why you need better accuracy or stability than a crystal oven will provide?

For the sheer fun of it.

[MrBungle]

Not just for the fun of it either. Really narrow band digital radio modes are very sensitive to drift. It’s nice to be able to tell the difference between your XO, TCXO, OCXO, GPSDO performance here.

[Radio1950]

Originally Posted by merlinmaxwell

For the sheer fun of it.

Yes!!
Well said.
.

[MrBungle]

Worth mentioning time nuttery here: http://leapsecond.com/time-nuts.htm

[AC/HL]

Unless you intend to repair the non-worker and pass it on, the subject of sacrilege doesn't arise. As well as it being yours to do with as you please, it is fulfilling a useful purpose, if only that all your counters will agree with each other, and the standard you trim it against.

[sidspop]

Thanks for all the replies.
A couple of points.
GPS looks interesting, but my workshop is in the cellar, and although my mrs is tolerant, I somehow doubt she would like a load of test gear on he kitchen worktop whilst looking at the sky.
The gent on the M42, I may well take you up om your offer, once I have built it, if I do get around to building it, along with all the other stuff and trying to earn a living.
The spares unit is in effect a write off, I have been through parts of it and it seems to have multiple faults, with tantalum capacitors short all over it, so for a tenner I do not mind breaking it. I can always use the case for some other project, it's worth a lot more than a tenner when you factor in cost of RF connectors, PSU etc. Plus spares if anybody else needs them for this model.

The main reason for doing it is simply that it is annoying that test equipment is not quite bang on, which sort of negates it being test equipment.
Most ofmy activity is repair of CB and some amateur gear, so it would be nice to be accurate, ish...

[David Simpson]

Hello again sidspop, you mentioned being involved with CB & amateur equipment repair. Have you ever used "WebSDR" ? Its a multi-national facility, with a number of bases in the UK & Europe. Its software can actually analyse your transmissions over a broad spectrum of amateur, maritime & commercial bands.
Simply log on with your computer, PTT your Tx unmodulated & study your transmission. If, say its 3615KHz, & WebSDR tells you you're spot-on, then carefully loose-link a length of co-ax into your counter & see if 3615 comes up on the your counter's display - within the manufacturer's % accuracy.(You can also study your modulated transmissions in general). You'll probably need your Tx's full CW o/p wattage to reach a suitable WebSDR station(Hack Green, University of Twente in Holland, & so on), but for RF pick-up within your workshop/shack then a low power o/p, or dummy load should be used. Or even a loose pick-up near to the Tx's MO.
Yep - a bit of fannying about. But, if like me you're interested in both test equipment & R/T , then its a jolly good method of 21st century frequency measurement of 20th century vintage equipment.
It goes without saying - never transmit RF directly into scopes & counters. P -P voltage measurement of loose RF pick-up within range of a Tx can first be observed on a scope, and a suitable length of co-ax chosen to match the counter's i/p spec. I've got 3 counters - a Maplin MF100, a miniature Dong Kwang, and a Watson Super-Hunter. All respond to this method of freq measurement, and give sub-decimal indications of frequencies between them. As I acquired the Watson, new & pristine in its box, (seemingly un-used by the silent-key, several years ago), I take it as being the most accurate of the three.

Regards, David