Cygnus A Observation Validation

[Anthony]

Hello SARA Members!

I need your help, please to validate a Cygnus A observation. A PDF is attached along with embedded images.

Thank you!

[Marcus D. Leech]

On 21/07/2023 18:59, Anthony wrote:

Hello SARA Members!

I need your help, please to validate a Cygnus A observation. A PDF is attached along with embedded images.

Thank you!

The interferogram during Cygnus A transit is basically non-existent.    Are you sure you're pointed correctly?

I think you're in Atlanta, which means you'd point about 7 deg north of straight up.

I'll note that in your spectral data, one of the two antenna inputs has noticably higher SNR compared to the other.  This
  may just be that one of your dishes is seeing a bit more noise than the other...

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[Anthony]

Thank you, Marcus!

I will double check tomorrow the dish's location in the sky.  An equatorial mount would sure be handy. It is raining hard tonight! If the weather permits, I'll hook up the satellite dish movers, hopefully they are still functioning.

There are four wireless security cameras nearby, I'm aware of one or two causing RFI. I've accessed one and watched the RFI spike and fall once the camera portal is closed, another on my to do list.. 

Since I'm without an EL/Azimuth mount, could an inclinometer be leveraged?

Security Cam RFI

 

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[Anthony]

Since Cygnus A is a broadband source, would the emission cause the correlator to rise as in the GIF attached, Marcus?

I'm aware Cygnus X (complex is nearby) and potentially causing the rise in the correlator output? If you notice in the Gif, left screenshot, you'll see Cygnus A above my antenna beam, or close. I'll check again the dish's location in the sky. 

They are pointed up at an angle of 88.9 degrees. 

On Fri, Jul 21, 2023 at 8:51 PM Marcus D. Leech <patchv...@gmail.com> wrote:

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[Marcus D. Leech]

On 21/07/2023 22:22, Anthony wrote:

Since Cygnus A is a broadband source, would the emission cause the correlator to rise as in the GIF attached, Marcus?

I'm aware Cygnus X (complex is nearby) and potentially causing the rise in the correlator output? If you notice in the Gif, left screenshot, you'll see Cygnus A above my antenna beam, or close. I'll check again the dish's location in the sky. 

They are pointed up at an angle of 88.9 degrees. 

If you're in Atlanta (which is what i recall about your location), your dishes should be pointed about 7 degrees north of Zenith.
  Or about 97 degrees away from the Southern horizon--assuming they're meridian aligned.

I don't see anything that immediately hits me as "interferometer fringes", which is what we'd be looking for.  With the spacing
  you have, I think it should be about 10 minutes peak-to-peak per fringe.

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[Anthony]

I'm close to Atlanta. My location is Roswell, GA. 

Will check everything tomorrow, thanks again!

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[fasleitung3]

Hi Antony,

From your location with 88.9° elevation and assuming your dishes are pointing south, at 4:28 UTC on July 20th you would be pointing towards RA 18.7, Dec 32°. Since Cygnus is at RA 19.99, Dec 40.7 you are not pointing quite correctly.

What I am also struggling with is your pointing for the hydrogen spectrum. With the same parameters of the dish, at 16:58 on July 6th, you would be pointing towards RA 6.27, Dec 32.8 which is ~ 180° longitude and 7.7° latitude in galactic coordinates. In that direction, the spectrum would look substantially different, it would be essentially a single line rather than two lines. You spectrum is certainly coming from hydrogen, but this looks more like what is would be in the direction of 120° longitude.

I hope my calculations are correct. If that is the case, then there might be something to sort our with respect to where you are pointing.

Best regards,

Wolfgang

[Anthony]

I really appreciate this Wolfgang, that was very helpful!!

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[Marcus D. Leech]

On 22/07/2023 08:53, Anthony wrote:

I really appreciate this Wolfgang, that was very helpful!!

Hey, are there any other SARA members in the Atlanta/Roswell GA area who might be able to help Anthony get his
  setup "sane" ??   There was Paul Oxley, but, sadly, he's no longer with us.

If I lived within 100km of him, I'd be out there myself, but, alas....

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[Anthony]

Hey Marcus,

Finally woke up and saw your email, thank you so much!!

Wow, a mild drink and a good long nap, gives you a better perspective! Ok, took a look at the dishes, took a really good look and they are not oriented correctly to each other and location for drift scanning, obviously! 🙂

One dish's (Western) landing pad is not aligned properly (didn't measure) to the Eastern dish, which by the way looks pretty good, probably why the SNR has a better performance than the Western dish; in addition the LNA was replaced and it's not so close to the Western dish side of the RFI. The feed horns aren't the best. In other words, I need to go back to the basics:

• Understanding Baseline - in terms of resolution, longer baselines provide better resolution
• Determine the optimal Baseline - which will depend on the radio sources I wish to observe and taking into consideration proper dish aligned and phased
• Orientation - East-West or North-South and since both dishes use actuators and not an EL/Azimuth drive, drift scans are probably what I'm left to do, which means an orientation of East-West, am I correct in this thinking?
• Location - RFI, not much I can do about that, no place to move the dishes, but the upper part of the backyard. My better half (wife) has enforced no satellite dishes in the lower part of the backyard or hunting for aliens.. Joking 😊 But she's serious!
• Calibration and testing - something a lot of the SARA members do, calibration, testing and calibration, testing...

For starters, I'm no longer going to grab my pickaxe, shovel, carry multiple (28, 50lb bags) cement bags up a hill to do the work myself. I'll contact a professional cement service and have them lay down the cement pads for both dishes, but making sure to determine the optimal baseline and orientation. 

I'll add in the new LNAs & BPF, after rebuilding the feedhorns and using a VNA to determine the best/optimal VSWR and so forth..... All of this should have been done in the first place, sigh! Radio Astronomy is unforgiving for the newbie! 

Thanks everyone for the help and especially Marcus, and Dr. Wolfgang, for your support!! 

I've got a lot of work to do and I have several cement services lined up, hopefully they can start work next week.  

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[Marcus D. Leech]

On 22/07/2023 22:35, Anthony wrote:

Hey Marcus,

Finally woke up and saw your email, thank you so much!!

Wow, a mild drink and a good long nap, gives you a better perspective! Ok, took a look at the dishes, took a really good look and they are not oriented correctly to each other and location for drift scanning, obviously! 🙂

One dish's (Western) landing pad is not aligned properly (didn't measure) to the Eastern dish, which by the way looks pretty good, probably why the SNR has a better performance than the Western dish; in addition the LNA was replaced and it's not so close to the Western dish side of the RFI. The feed horns aren't the best. In other words, I need to go back to the basics:

• Understanding Baseline - in terms of resolution, longer baselines provide better resolution
• Determine the optimal Baseline - which will depend on the radio sources I wish to observe and taking into consideration proper dish aligned and phased

You aren't going to come even *close* to "resolving" any discrete sources, except for the Sun and Moon, and even those,
  at 21cm, would require (rough guess) about a 30m baseline.   So the "optimal baseline" is the one you can fit along
  a good east-west line in the space you have available to you.

• Orientation - East-West or North-South and since both dishes use actuators and not an EL/Azimuth drive, drift scans are probably what I'm left to do, which means an orientation of East-West, am I correct in this thinking?

For a simple two-element interferometer, east west is the best orientation.  It will give you the nicest-looking fringes.  With only
  two dishes, doing actual synthesis imaging would be a significant challenge, so I wouldn't worry about any N-S orientation.
  The main advantage to an interferometer in an amateur setting is that it allows you to detect discrete sources that would
  otherwise be buried in the background for a small single-dish instrument.  Even with a 3m dish, being able to definitively say
  "hey, look, I captured Cygnus A" is next to impossible because you are mostly seeing the combined emission of Cygnus A
   and the the galactic background.  With an interferometer, larger structures are mostly suppressed.

• Location - RFI, not much I can do about that, no place to move the dishes, but the upper part of the backyard. My better half (wife) has enforced no satellite dishes in the lower part of the backyard or hunting for aliens.. Joking 😊 But she's serious!
• Calibration and testing - something a lot of the SARA members do, calibration, testing and calibration, testing...

For starters, I'm no longer going to grab my pickaxe, shovel, carry multiple (28, 50lb bags) cement bags up a hill to do the work myself. I'll contact a professional cement service and have them lay down the cement pads for both dishes, but making sure to determine the optimal baseline and orientation.

When I poured the base for my first 3.7m dish all those years ago, I started out with bags of concrete and naive
  enthusiasm.  My "better(???) half" wouldn't let me spend money out of household funds on this, so I had to
  sell one of my Yaesu radios to pay for a commercial concrete delivery.  Even back then (2001 or so?), 9 tonnes of
  high-strength concrete was about $600.00.   The forms (and resultant block) were much larger than needed for
  a 3.7m dish, but I was looking ahead to a future that never really happened where I might get my hands on a bigger
  dish.  So the entire structure was wildly over-built.

Again, if you can manage a strictly east-west baseline, where the dishes will have an unobstructed view to the south, and
  to perhaps 15 degrees to the North (total of 105 degrees from the southern horizon), you'll be well set. Having a skew
  in the baseline away from East-West will tend to produce an asymmetry in the fringes--which is one of the ways you can
  tell that your baseline is skewed.   For amateur work, "mostly east-west" fulfills the gross requirement of producing
  acceptable fringes that allow you to confirm detection.

I'll add in the new LNAs & BPF, after rebuilding the feedhorns and using a VNA to determine the best/optimal VSWR and so forth..... All of this should have been done in the first place, sigh! Radio Astronomy is unforgiving for the newbie! 

Thanks everyone for the help and especially Marcus, and Dr. Wolfgang, for your support!!

I think your HVAC-based feed-horns are probably adequate -- not perhaps "spectacular" but adequate.   Really, once
  you have a working interferometer, it will just "want" to work.  You'll quickly be able to detect most of the
  "usual suspects" of brighter discrete sources out there.   They really do just "want to work" once they're
  set-up correctly.   A feed-horn that isn't quite optimal will NOT be the determining factor.    Our 611MHz interferometer
  at our previous observatory site was made, to a first approximation, with "baling wire and chewing gum".  It worked
  "out of the gate". 

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[Anthony]

Thanks again, I really appreciate your tremendous insights, and experience, Marcus! 

I'll take your insights and get the baseline corrected.

I was using high-tensile concrete at 80lbs a bag! My enthusiasm has worn down a bit,  from hauling those bags up a steep hill! 

I'm starting to feel, to much money is being put into this, and will use what current equipment i have. I'm glad to know the feed horns are ok,not spectacular but after all this is only Amateur stuff. 😁

It maybe time to take inventory of the vast amount of electronics I have and sell them.

If anyone is interested please let me know. The pricing well be attractive...

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