What tool to measure phase difference at 1420 MHz?

[Dr. Rich Russel]

I have built a 2 antenna phased array.

I have an RF phase shifter that I can shift the phase using 8 bit inputs.

What tool can I use to verify that I am shifting the phase?

I don't know of an oscilloscope that is at 1420MHz. (At least at my price range).

Thanks!

Rich

[Stephen Arbogast]

What  kind  of   accuracy  do you need?

A  long time ago  we measured phase  coherence by  down converting  both  signals   and  comparing.  It  was good enough   for us  at the time   but    probably not  acceptable today.

Stephen

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[Mike Otte]

The AD8302 measures phase up to 2.7 Ghz.

Your testing the phase shifter?   on the bench, correct?

mike

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Mike Otte W9YS

[Stephen Arbogast]

About  two years  ago   I built  a  phase locked  loop  using  a  standard component  I ordered  from   Digi  Key   I think  I still  have it   some  where  around here .......

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[Jacob Fernandez]

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[duncan campbell-wilson]

Hi Rich,

(1) Use a vna to measure the initial phase and amplitude.

(2) Insert a cable known electrical length of cable and adjust the phasing device to bring the signal back  to the initial phase.

(3) The cable dispersion (phase velocity and  dielectric loss are frequency dependent ) so only use a narrow band (monochromatic)  for the testing (don't sweep the frequency).

Null cancellation is a sensitive test.

Rgds Duncan

  

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[Neil Smith]

AD8302 phase comparator with a pair of matched logamps and a linear phase detector is what I use at 400 MHz, should go to 2.7 GHz ok. Lots of boards on ebay around $10. 

They have 60 dB dynamic range, so you need a reference signal into each input that's not too noisy and ideally at about -40 dBm to -10dBm

https://www.analog.com/media/cn/technical-documentation/data-sheets/AD8302.pdf

My scope samples at 8 GS/s, but can't go much above 350 MHz. Downconverting with a pair of mixers fed by a splitter from the same local oscillator with identical cable lengths and using a slower scope would work, but would need changeover switching to check for any phase offset with identical inputs

Neil

[Lamar Owen]

A wide bandwidth vector scope is made for this sort of thing.  Even a relatively inexpensive analog scope can be used; you might have to down convert to get the signals within the frequency range of the vector scope, but nothing is as good for a quick visual indication of phase difference.

Feed the pre-shift signal to X and the post-shift signal to Y.  The width of the ellipse will show the amount of phase shift.

Sent from Nine

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From: "'Dr. Rich Russel' via Society of Amateur Radio Astronomers" <sara...@googlegroups.com>
Sent: Tuesday, September 2, 2025 18:42
To: SARA Listserv
Subject: [SARA] What tool to measure phase difference at 1420 MHz?

[Stephen Arbogast]

I  found my old  PLL  project....   I used this.....  https://www.ti.com/lit/ds/symlink/cd4046b.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1756824078316&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%252Fwww.ti.com%252Flit%252Fgpn%252Fcd4046b

with my Siglent  SDS 1202X-E  At the time   I was just playing  around.....   Again  not  high accuracy   but fun to  play with.

[Stephen Arbogast]

What  about  phase locking  our   instruments  to a  GPS  disciplined  oscillator ?  I  am  using   a BG7TBL  from 2020...  provides     stability   and accuracy....   I hope...  What  standard  should I measure  against?

I hope  to add another  dish  some  day   and try  out   stuff like  BAA  Seminar  by   Marcus   Leech.   Why  can't this  be done?  We  would  synch  with GPS  time   keepers  and adjust   for    relativity   via  software.....

Lot's of  questions...... 

[Marcus D. Leech]

On 2025-09-02 21:11, 'Stephen Arbogast' via Society of Amateur Radio Astronomers wrote:

What  about  phase locking  our   instruments  to a  GPS  disciplined  oscillator ?  I  am  using   a BG7TBL  from 2020...  provides     stability   and accuracy....   I hope...  What  standard  should I measure  against?

I hope  to add another  dish  some  day   and try  out   stuff like  BAA  Seminar  by   Marcus   Leech.   Why  can't this  be done?  We  would  synch  with GPS  time   keepers  and adjust   for    relativity   via  software.....

Lot's of  questions......

I think this particular query is about phasing-up a couple of antennas for "stacking" the antennas, rather than interferometry.

Also, two radios that are each synched to a GPSDO won't actually agree on phase, and there will usually be enough  residual phase noise to render
  interferometry kinda problematic.

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[Stephen Arbogast]

Will  Star Link  allow us to  synchronize   our  observations    to  form  a   planet  wide    network    for  our  observations?

[Marcus D. Leech]

On 2025-09-02 21:24, 'Stephen Arbogast' via Society of Amateur Radio Astronomers wrote:

Will  Star Link  allow us to  synchronize   our  observations    to  form  a   planet  wide    network    for  our  observations?

How?

I cannot imagine that it would be *better* than GPS, since it isn't designed to provide a synchronization services, as far as I know.

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[Stephen Arbogast]

I am  the   Physics   type , dreamer,  not  the  the  practical  Engineer. Would not  Star Link  need  to be   doing    some   general  relativistic    calculations   to  send  E&M  waves   through    space to  account    for  gravity  or  maybe this  is  negligible?

Yes  Star Link  is    out  to  make     $$$$  

Stephen

[Marcus D. Leech]

On 2025-09-02 21:48, 'Stephen Arbogast' via Society of Amateur Radio Astronomers wrote:

I am  the   Physics   type , dreamer,  not  the  the  practical  Engineer. Would not  Star Link  need  to be   doing    some   general  relativistic    calculations   to  send  E&M  waves   through    space to  account    for  gravity  or  maybe this  is  negligible?

Yes  Star Link  is    out  to  make     $$$$  

Stephen

No.  You don't need to account for GR just because you're in orbit sending radio signals.    GPS accounts for GR effects because at its core, it's a precision timing device,
  and GR effects can subtly affect that.

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[Stephen Arbogast]

If   I  am low  earth orbit   sending   a  signal   back to  earth about   what   I am  measuring   I     don't   need to   worry

   about  time...    Is  this  correct?

https://www.sciencedirect.com/science/article/abs/pii/S0263224124019201

[Marcus D. Leech]

On 2025-09-02 22:40, 'Stephen Arbogast' via Society of Amateur Radio Astronomers wrote:

If   I  am low  earth orbit   sending   a  signal   back to  earth about   what   I am  measuring   I     don't   need to   worry

   about  time...    Is  this  correct?

https://www.sciencedirect.com/science/article/abs/pii/S0263224124019201

We were talking about StarLink.  Which is sending radio signals, but it isn't sending precise positioning or timing information.   StarLink isn't a measurement platform.
  It's how you get your TikToks when you don't have other connectivity options.

GPS, on the other hand, IS a precision position/time measurement platform.  And they account for GR effects.

I'm starting to think we may be talking past each other...

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[Stephen Arbogast]

In Physics   time has no meaning..........   I  agree with you  in Engineering.   But  in  Physics  time is  very  important ....   maybe  it i s entropy!

[Stephen Arbogast]

Physics  teaches us to  keep  an  open mind.....   

I love   the work  that  Marcus  Leech has  done to  give  us his BAA  Seminar.  I am the    Physics type....... I have  some questions....... probably will  get in to  trouble.

Thanks   Marcus   for   your  work.

We need  General Relativity  even at low altitude, maybe  not  needed for  Amateur  Radio  but    necessary  for    precise measurements...

I might  have an opportunity   to use     some land  in  the  Animas Valley of South West Colorado. I cannot   put  up  big dishes on  this   land.. maybe  an array  of  small  antennae..   I am inviting suggestions.

Stephen

[Stephen Arbogast]

Also..   I tend  to not read  the  instructions first.  I just  experiment .. That  said   I recommend  that you take  a look at  Ted Cline's  source  code   for ezCon.py     It i s very well  documented.

[Neil Smith]

GNSS based timing is subject to a lot of variation at short time scales. If you compare your GPS time device with even just a good double-ovened quartz oscillator in a vibration-isolated and temperature  controlled rack enclosure, you'll see all the steps and wobbles of a simple GPSDO over short timescales. I have some rubidium clocks that are reasonably stable over timescales of up to a few tens of seconds, but even those are not good enough for long baseline work. Fine for 50 km baselines. Don't get me started about earth tides and other diurnal variations!  Then there are atmospheric variations, clouds and weather changes to deal with. I don't have a Caesium clock or a hydrogen maser in a rock-hewn basement like a proper time-nut, nor are my survey-quality multi-band GPS antennas mounted on a granite pillar grouted to bedrock.

Endless fun trying to get properly-stable time references to work over even county-sized scales at short intervals, never mind globally.

Neil