[time-nuts] Re: As there a hobby application of precise time or frequency measurement except for being a time nut?

[Lester Veenstra]

Paul:  Are you a member of SARA?
https://radio-astronomy.org/


Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG
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lester at veenstras.com

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-----Original Message-----
From: Paul Boven via time-nuts [mailto:time-nuts at lists.febo.com] 
Sent: Friday, April 25, 2025 7:34 AM
To: time-nuts at lists.febo.com
Cc: Paul Boven
Subject: [time-nuts] Re: As there a hobby application of precise time or
frequency measurement except for being a time nut?

As Jim (and others) have mentioned: Radio Astronomy.

I'm a volunteer at the historic 25m radio astronomy dish in Dwingeloo, 
the Netherlands, and I would consider myself our local 'time nut', 
amongst the many hats I wear in this group.

Some of the things we do which require accurate time or frequency signals:

Hydrogen line observing - the Doppler shift of the 21cm line at 
1420.40575 MHz can be used to model the spiral arms of our Milky Way. We 
also observe the redshift to other galaxies, and other spectral lines 
such as the OH lines. Accuracy requirements are quite modest, on the 
order of a PPM.

Satellite tracking - Doppler information is crucial to tracking your 
spacecraft. We were an official NASA (volunteer!) ground station during 
the ARTEMIS I mission, and are planning to join the future missions as 
well. The accuracy requirement here is much higher, ideally sub-Hz at 
2.5 GHz.

Pulsar timing - measuring the time of arrival of the pulsar signal 
allows you to determine many physical parameters, such as the size of 
the Earth's orbit, a very precise location of the pulsar in the sky, and 
the slowdown of the pulsar as it loses its energy. Here the requirement 
is very good stability over many years.

Interferometry: We've participated in VLBI observations, together with 
other professional dishes in the European VLBI network, and got great 
fringes. For us, this requires phase stability at up to 5 GHz, for 
periods of up to 15 minutes (after that, the ionosphere starts to 
destroy coherence anyway).

We're putting up a new 3m dish, and are planning to do interferometry 
and holography of our big dish this way.

We have several Rubidium clocks, but mostly we use a dark fiber White 
Rabbit link of 35km length, which is connected to a 'nearby' Hydrogen 
maser at the WSRT radio telescope. We ended up trenching and splicing 
the last 250 m of fiber ourselves, in 2018.

Regards, Paul Boven - 73 de PE1NUT.

On 4/11/25 19:26, Jim Lux via time-nuts wrote:
> 
> 	
> 
> 
> 
> A lot depends on what you consider "precise" of course...
> 
> Radio astronomy - more and more people (yeah, probably < 1/2 dozen, but..)
are setting up interferometers and precise time knowledge is important.
>   
> Radio amateurs on microwave frequencies with narrow band signals need good
frequency control (1ppm at 10 GHz is wildly insufficient - you'd like to be
within 10 Hz - 1E-9)
> 
> There seems to be a bunch of people doing direction finding with a
distributed system (perhaps collaborative drone flight) - it's unclear what
their requirements are.
> 
> There is a hobby radar community with bistatic radars - both at low
frequencies (chirp sounders) and at microwave frequencies. The performance
of the radar depends on both long term stability (for SAR) and closein
(phase noise).
> 
> I know a guy with a LTE base station he built in his house - granted he's
not putting up multiples, so he doesn't need precise timing (yet).
> 
> I suspect none of these are hundreds or thousands of people, but they all
have some need to understand time and frequency to a "more than you get with
a TinySA or oscilloscope" kind of performance.
> 
> 
> 
> On Fri, 11 Apr 2025 12:46:12 +0200, Erik Kaashoek via time-nuts
<time-nuts at lists.febo.com> wrote:
> 
> Maybe the subject line is a bit clickbait but this is a serious question.
> Hobby VNA are used to measure impedance for antenna, amplifiers,
> filters, PCB's and cables. Many applications for a VNA outside the
> professional world.
> Hobby spectrum analyzers are user for hunting RFI, measuring harmonics
> of active devices, assessing what part of the spectrum is still
> available for wireless devices, etc... Again many applications.
> But for time and frequency measurement the situation seems to be
> different. What are hobby applications for accurate assessment of
> stability, time or frequency?
> For radio amateurs that operate in the GHz bands the accurate assessment
> of the frequencies of their generators is such an application but what
> other applications do exist and what are their requirements regarding
> accuracy?
> I'm purposely excluding the applications where the accuracy is the goal
> instead of some usage for accuracy.
> Any input is welcome.
> Erik.
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