[Test-Equipment] Frequency Measuring Test

Tue, 24 Sep 2002 10:21:34 -0400

Francesco -

Totally agree with all you had to say. I agree about holdover, and in that
case the Rubidium would be the better choice. I was comparing working
(locked) systems. A Costas loop is similar to what I had in mind for the
original frequency recovery. It just seems that there are too many of us
with the essentially state of the art equipment that it is hard to imagine
what the ARRL has in mind. Dino mentioned that the ARRL does have a Z3801A
in their lab. I also have two. I put a self contained AC PS in one of them.
It will be interesting to see how this plays out. 73 - Mike

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ, 07731
(732) 901-9193

----- Original Message -----
From: "Francesco Ledda" <[email protected]>
To: "Mike Feher" <[email protected]>; <[email protected]>; "Glenn Little"
<[email protected]>
Cc: "Gary Chatters" <[email protected]>; <[email protected]>
Sent: Tuesday, September 24, 2002 9:46 AM
Subject: RE: [Test-Equipment] Frequency Measuring Test

> As you well siad,  a Rubidium has better long term stability than a
crystal
> oscillator.  This means that if the GPS RX goes down for any reason, the
> Rudium long term stability provides better accuracy than a crystal
> oscillator.  This is called holdover ferformance.
>
> The best way to lock to an incoming radio station is to have a I&Q
receiver
> with a Costas frequency loop.
>
> Regards, Francesco Ledda
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of Mike Feher
> Sent: Tuesday, September 24, 2002 8:10 AM
> To: [email protected]; Glenn Little
> Cc: Gary Chatters; [email protected]
> Subject: Re: [Test-Equipment] Frequency Measuring Test
>
>
>
> Hi Guys -
>
> I do not believe that propagation delays will cause frequency measurement
> errors. Unless we are talking about something like doppler. Plain delay
> should have no effect. It will however have an effect on any time related
> information sent along at the same time. I have a Cesium, about a dozen
> rubidiums, and a pair of GPS disciplined double oven crystal types. I
really
> also do not fully appreciate the advantage of a GPS disciplined Rubidium
> over a GPS disciplined crystal in a double oven. We all know that for real
> short term stability a crystal is hard to beat. Rubidiums become better in
> the long term and Cesiums ever better yet. But in the short term, within
the
> loop bandwidth, they all have crystals, so not much difference. In the
long
> term, the GPS takes over. As pointed out, the biggest problem would be to
> somehow lock on to the actual signal to be measured and then compared. I
> really wonder if the ARRL has the equipment necessary to determine their
> transmitted frequency to these accuracies, or if they are going to
> coordinate with NIST or some equivalent. Additionally, at these accuracies
> only a statistical measurement, like an Allen Variance, or even a simple
> average, would be of use, as there would be too much fluctuation in the
> comparison device. I'll have to dig out my last issue of QST to see what
> they have in mind. Thanks & 73 - Mike
>
>
>
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell NJ, 07731
> (732) 901-9193
>
>
> ----- Original Message -----
> From: "Dave Emery" <[email protected]>
> To: "Glenn Little" <[email protected]>
> Cc: "Gary Chatters" <[email protected]>; <[email protected]>
> Sent: Tuesday, September 24, 2002 1:40 AM
> Subject: Re: [Test-Equipment] Frequency Measuring Test
>
>
> > On Tue, Sep 24, 2002 at 12:13:43AM -0400, Glenn Little wrote:
> > > I wonder if they have the ability to measure their reference frequency
> as
> > > well as some in the field. There are a number of people with GPS
> disiplined
> > > Rubidium standards. Unless you have a Hydrogen MASER, they are hard to
> beat.
> >
> > So the real issue for those with modern technology frequency
> > standards is actually not the raw time base accuracy but figuring out
> > how to make a reliable measurement of the unknown signal with anything
> > like the accuracy of their house standard.
> >
> > Certainly a HF signal received by skywave is only easily measured
> > to maybe one part in 10^7 or 10^8 due to propagation effects which is
> > a long long way away from a couple of parts in 10^11 that a GPS
> disciplined
> > rubidium standard will do routinely.   I suppose figuring out an
algorithm
> > to filter out the propagation induced errors might be interesting, but
> > certainly something very different from the frequency measuring tests
> > of past years, which stressed skills at calibrating and setting up
> > hardware and using it skillfully.
> >
> > I could - and I suppose many many others with fully synthesized
> > HF rigs referenced to a 10 mhz input from a rubidium GPS disciplined
> > standard could too -  measure a HF signal by just tuning it in with a
> > known BFO offset and processing the resulting audio with a soundcard to
> > make a best estimate of the frequency of the beat note minus propagation
> > related shifts.  And if I really was anal, I could hack the soundcard to
> > derive its sample clock from a synthesizer driven off the 10 mhz
> > rubidium standard too (eg replace the crystal osc used for timing with a
> > clock input from a synthesizer or even just a DDS NCO chip driven from
> > the rubidium).
> >
> > I suppose a local VHF or UHF signal might be measurable with
> > much greater accuracy, but then one gets into multipath and all sorts of
> > other  effects and of course the test signal only reaches a few people.
> >
> >
> >
> > >
> > > 73
> > > Glenn
> > > WB4UIV
> > >
> > > At 11:35 PM 9/23/02 -0400, Gary Chatters wrote:
> > > >The latest issue of QST announced that ARRL is bringing
> > > >back the frequency measuring test.  Anyone here thinking of
> > > >participating?
> > > >
> > > >Gary
> >
> > --
> > Dave Emery N1PRE,  [email protected]  DIE Consulting, Weston, Mass.
> > PGP fingerprint = 2047/4D7B08D1 DE 6E E1 CC 1F 1D 96 E2  5D 27 BD B0 24
88
> C3 18
> >
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> >
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