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Old 26th Dec 2007, 8:54 pm   #21
RobinBirch
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Default Re: Frequency Standards

Pete,
You have stated very exactly what the position is. We are in a curious position where officialdom is bringing under its control a large number of bits of kit that have been happily maintained for a long time on a largely amateur basis.

The route that we (all the guys who inspect gliders like myself) are taking is that we are submitting descriptions of what we are doing to officialdom and they are being asked to say yes or no. Up to now they are being very reasonable.

One of the reasons for the reasonableness is that we haven't had any incidents of getting it wrong in the past and that they have a mandate of not upsetting everyone with over officialdom and cost and highly expensive calibration costs would be one of those.

A further wrinkle in the future will be that we will have to fit transponders to the gliders which is not a test job that the average radio person will be kitted out for and we are not sure what the route through this will be.

Robin
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Old 26th Dec 2007, 9:52 pm   #22
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Default Re: Frequency Standards

I think you need to have and offer to the Men from the Ministry, a defensible position if anything goes wrong. This could be double-checking of everything and expensive calibration of all test equipment, or it could be something less, but which you could stand up in court and defend. The Men from the Ministry would have to explain why they allowed such and such a test regime to exist. Explaining how you tested tranceivers which may have failed and contributed to a crash, with home made equipment, might be a difficult line to argue.

Follow the other line to its conclusion and you have equipment in gliders being maintained to the same standards as trans-Atlantic airliners, glider tranceivers sent off to certified labs every 3 months or whatever and gliding made unaffordable.

As far as I know, gliding has never been regarded as a particularly dangerous business, but it only takes one freak accident to cause a complete over reaction. We live in risk averse and compensation sensitive times.

Pete.
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Old 27th Dec 2007, 3:55 pm   #23
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Default Re: Frequency Standards

IN essence you are right. The men from the ministry have been realising that they have bitten off more than they can easily chew in that every one (from EASA in Europe downwards) has been going mad in that they've realised that doing gliding, and a lot of sport aviation, in the same way that the big boys are done is very very difficult and could easily make the whole thing (not just us but the home build boys in the PFA and a lot of other people) totally uneconomic. As a result a lot of us have been writing up methods for doing things that are being submitted for approval so that we can keep things going in an economic way.

It may be that we have to do things using comercial kit rather than home built but we won't know until we've tried it. The CAA are actually being very reasonable and are not going overboard on any of this.

Everybody recognises that the existing standards are written for commercial aviation and are not directly applicable to sport aviation so we are kind of making it up as we are going along

Robin
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Old 27th Dec 2007, 9:08 pm   #24
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Default Re: Frequency Standards

Robin,

if you contact me via PM, I may be able to help with a couple of contacts, however, if it comes down to it, you will need to refer to the CAA document CAP670, which lays down the legal requirements and standards for aviation radio ground stations (and is guarenteed to cure insomnia), I believe that aircraft stations are covered in the Air Navigation Order, and derived from ICAO Annex 10 & 11. I suspect that the work you and your colleagues are doing will lead to an ammendment to some of that documentation.

Jim.

PS CAA CAP670 is available online
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Old 28th Dec 2007, 12:28 am   #25
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Default Re: Frequency Standards

When I worked in a cal lab we would send our standards receiver to a NAMAS calibration facility for accreditation. This was deemed acceptable by which to check all crystal sources in the sweepers, spectrum analyzers and counters our company used. As long as your standard is traceable to a NAMAS calibration house you should be ok.
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Old 28th Dec 2007, 6:48 pm   #26
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Default Re: Frequency Standards

NAMAS has now changed to UKAS (United Kingdom Accreditation Service) but is still based at NPL Teddington. All equipment used for 'legal' measurements should be calibrated in such a way as to be traceable to UKAS at a frequency stated in the relevant British or ISO Standard.
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Old 29th Dec 2007, 12:20 pm   #27
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Default Re: Frequency Standards

Quote:
The whole idea is to provide a calibration standard for some test gear. I have a comms tester that I use for my own ends - works well and is very accurate. however it is long out of calibration and I don't fancy stumping up the cash to get it professionally done. One of the things that i use it for is checking the frequency of tranceivers in gliders and up to now this state of affairs has been fine. Unfortunately they (the powers that be) are changing the regulatory environment under which we look after such things and so I will have to be able to state the calibration of the kit that I use. My intention is to say that I have checked the comms tester against droitwich, the error is x and so the results measured are good to y.
Going back to the original requirement, can your comms tester recieve off-air signals? If so you should be able to calibrate its' own frequency standard against against a known off-air reference. By using several transmissions you could justify the accuracy of calibration. You could then calibrate the comms tester's standard every time you wanted to use it, or else use the comms tester's accuracy and drift specs. to justify a particular caibration interval.
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Old 30th Dec 2007, 2:12 am   #28
RobinBirch
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Default Re: Frequency Standards

That's effectively what I want to do. It won't receive 198 kHz directly (only goes down to 400 kHz) but it will take an external 10 MHz.

So, build externally driven 10 MHz and then tie comms tester to it

Robin
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Old 30th Dec 2007, 10:44 am   #29
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Default Re: Frequency Standards

Going a bit OT now, but another possibility - Find a reciever that can pick up one of the WWV transmissions on 5/10/15Mhz http://tf.nist.gov/stations/wwv.html
Then loosely couple the output of your comms tester sig. gen. tuned to the same RF as the reciever and adjust the reference oscillator for zero beat. That ought to work in theory.
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Old 30th Dec 2007, 5:35 pm   #30
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Default Re: Frequency Standards

Hi Robin,

Whatever you build (externally driven 10 Mhz) , for your own piece of mind or even legal position it will have to be UKAS traceable.Their service is not to just check calibration from a measurement point of view but to also specify the method of testing and all of the theory to support required cal intervals and measurement errors. It is they that then take full technical and legal responsibility for the calibration.

How do the Germans cope with the legality, my understanding of their law is that they are far more restrictive and demanding.

Mike
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Old 30th Dec 2007, 6:47 pm   #31
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Default Re: Frequency Standards

WWV will work OK if you are in the USA. At this time of the sunspot cycle you will be lucky to even detect it over in the UK, never mind do any serious measurements from it. Since Rugby stopped transmitting MSF there has been a distinct lack of useful frequency standards in Europe - the only one I know of is the Moscow one on 9996kHz, but can't even hear that at the moment.

Dave
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Old 5th Jan 2008, 5:08 pm   #32
RobinBirch
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Default Re: Frequency Standards

Well MSF is still available from the new site. Also if you look at the NPL site their declared frequency standards are droitwich, MSF and GPS satellite based. They don't underwrite the other 198 kHz transmitters as they don't monitor them.

Robin
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Old 5th Jan 2008, 6:42 pm   #33
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Default Re: Frequency Standards

Guess you are talking about MSF on 60kHz - now from Anthorn. MSF used to also transmit on HF at 5MHz, 10MHz, 15MHz etc and was quite handy for checking frequencies of receivers. Now there is nothing in Europe on those frequencies and reception of WWV from the USA is pretty patchy until the sunspots return.

Dave
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