[time-nuts] Re. DIY atomic "resonator"

[Scott McGrath]

One of the challenges with todays new WiFi standards i.e. 802.11ac/ad/ax is the doppler from office fluorescent lighting systems so much so that channel emulators like the Anite Propsim F8 emulate it at various pseudoranges to the AP and STA

That said old school noise sources were indeed gas discharge tubes

> On Apr 12, 2017, at 2:18 PM, jimlux <jimlux at earthlink.net> wrote:
> 
>> On 4/12/17 10:28 AM, Dave B via time-nuts wrote:
>>> On 12/04/17 17:00, jimlux wrote:
>>> 
>>> Subject: Re: [time-nuts] Re. DIY atomic "resonator"
>>> Message-ID: <b3926cda-b4ff-2508-1be6-57c2fecf0ad6 at earthlink.net>
>>> Content-Type: text/plain; charset=utf-8; format=flowed
>>> 
>>>> On 4/11/17 11:09 AM, Mark Sims wrote:
>>>> Apparently fluorescent tubes continuously emit a lot of other microwave signals.  I once built a  homodyne doppler "speed" radar kit (used a coffee can for the antenna).  The way you calibrated it was to point it at a florescent tube and and adjust the reading to a specific value.
>>>> 
>>>> --
>>> That's not because the tube is emitting..  It's a target reflector
>>> turning on and off at twice line frequency.
>>> In most homodyne radars, you filter out the DC (the reflections from
>>> stuff that's not moving), so anything that pulses on and off creates
>>> nice output.
>> 
>> This patent would seem to confirm that discharge tubes do generate
>> microwave noise, and with a DC powered tube too.  (Would different
>> gasses produce different microwave spectra?)
>> 
>> http://www.google.co.uk/patents/US2942204
> 
> They generate broadband noise - they're used as high power noise sources for calibration.
> 
> Bracewell (I believe) used fluorescent tubes (driven by a reasonably stable source) as a calibration and timing reference at a astronomy array -
> http://articles.adsabs.harvard.edu//full/2005JAHH....8...75B/0000077.000.html
> 
> R. Bracewell and G. Swarup, "The Stanford microwave spectroheliograph antenna, a microsteradian pencil beam interferometer," in IRE Transactions on Antennas and Propagation, vol. 9, no. 1, pp. 22-30, January 1961.
> doi: 10.1109/TAP.1961.1144935
> 
> I particularly like the inclusion of "milling machines" in the keyword list
> keywords: {Microwave interferometry;Planar arrays;Radio telescopes;Reflector antennas, arrays;Solar radiation;Brightness temperature;Corona;Frequency;Microwave antennas;Milling machines;Monitoring;Moon;Phase modulation;Sun;TV}
> 
> And fluorescent tubes have been used as a broad band source in a classroom demo
> https://www.researchgate.net/publication/276280926_Demonstrating_the_Principles_of_Aperture_Synthesis_with_the_Very_Small_Radio_Telescope
> 
> 
> 
> I would suspect that the radiated field has some spectral bumps in it, probably related the physical dimensions.  I doubt it would have any discrete lines (although maybe it does..)
> 
> 
> 
> 
> 
>> 
>> I recall seeing such things sold surplus back in the early 70's, pity I
>> didn't know what they were back then.
> 
> There are also gas tubes in waveguides used as Radar T/R switches. when the main bang happens, the tube ionizes shorting the waveguide and protecting the receiver downstream.
> 
> 
>> 
>> There is also mention of huge mismatches in the guide when the tube was
>> not powered, that would support the homodyne speed calibration comment
>> by pointing it at a working (AC powered) florescent tube.  As Jim said,
>> a 100 (or 120) Hz "modulated reflector."
> 
> Yep.  There's been a fair amount of work over the past decades on using modulated reflectors for measuring antenna patterns (e.g. on phased arrays).  You can have a diode/dipole suspended by resistive leads (with an impedance of 377 ohms/square that are invisible) and turn it on and off.
> 
> Bolomey (I think) had an array of modulated reflectors, so you could measure multiple points in the near field at the same time, and only need to scan in one dimension. I can't remember if the reflectors were modulated at different rates or with PN codes - either would work to separate the responses.
> 
> 
>> 
>> Regards to All.
>> 
>> Dave G0WBX (or G8KBV both still valid.)
>> 
>> ~~~
>> 
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> 
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