165 CM PRIME FOCUS SATELLITE C/ KU BAND DISH ANTENNA 1.65 Meter W/ POLE FTA

[Pablo Lewin]

Hi I just pulled the trigger on the following antenna... 165 CM PRIME FOCUS SATELLITE C/ KU BAND DISH ANTENNA 1.65 Meter W/ POLE FTA

https://www.ebay.com/itm/222981273600

I hope it will be easy to modify to do some radio Astronomy with it (H-Alpha and maybe other radio sources?

Thoughts?

Pablo Lewin WA6RSV

[djl]

2 of these would make a dynamite interferometer.

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Dr. Don Latham  AJ7LL
PO Box 404, Frenchtown, MT, 59834
VOX: 406-626-4304

[Marcus D. Leech]

Good for introductory work at the hydrogen line--which is NOT H-Alpha.
H-Alpha is a visible-light (deep red) ionization line unrelated to
the neutral hydrogen line--which is due to the so-called "hyperfine"
transition.

Here at CCERA (http://www.ccera.ca) we use a 1.8m dish for our permanent
21cm dual-polarization spectrometer. So 1.65m is not
too small to be useful, certainly.

[Pablo Lewin]

Thank you Don and Marcus for the explanation. I guess I will have to build an active element for it...I'm going to have to find the different focus points for different frequencies? Also Pulsars do hapen near the 1.4ghz frewuency right?

Thanks again.

Pablo Lewin (WA6RSV).

[Marcus D. Leech]

On 09/28/2020 05:15 PM, Pablo Lewin wrote:

Thank you Don and Marcus for the explanation. I guess I will have to build an active element for it...I'm going to have to find the different focus points for different frequencies? Also Pulsars do hapen near the 1.4ghz frewuency right?

Yes, the focal point will be slightly different for different frequencies.

Pulsars DO have energy at 1.4GHz, but with a 1.65m dish, it would take 10s of hours of integration to detect them, which implies being able
  to track.

Thanks again.

Pablo Lewin (WA6RSV).

On Monday, September 28, 2020 at 2:07:12 PM UTC-7 Marcus wrote:

On 09/28/2020 03:22 PM, Pablo Lewin wrote:
> Hi I just pulled the trigger on the following antenna... 165 CM PRIME
> FOCUS SATELLITE C/ KU BAND DISH ANTENNA 1.65 Meter W/ POLE FTA
>
> https://www.ebay.com/itm/222981273600
>
> I hope it will be easy to modify to do some radio Astronomy with it
> (H-Alpha and maybe other radio sources?
>
> Thoughts?
>
> Pablo Lewin WA6RSV
>
Good for introductory work at the hydrogen line--which is NOT H-Alpha.
H-Alpha is a visible-light (deep red) ionization line unrelated to
the neutral hydrogen line--which is due to the so-called "hyperfine"
transition.

Here at CCERA (http://www.ccera.ca) we use a 1.8m dish for our permanent
21cm dual-polarization spectrometer. So 1.65m is not
too small to be useful, certainly.

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[Paul Oxley]

Pablo

The focal point of the parabola should be the same regardless of frequency. It is at a point where it is equal distance to all points on the dish.

Paul

[Pablo Lewin]

Thank you Paul and Marcus..well the Ebay vendor just informed me that he doesn't have that dish anymore!..so that's that, it was a good thought and learned lots. I'll keep looking for a cheap dish

take care

Pablo

[Marcus D. Leech]

On 09/28/2020 05:21 PM, Paul Oxley wrote:
> Pablo
>
> The focal point of the parabola should be the same regardless of
> frequency. It is at a point where it is equal distance to all points
> on the dish.
>
> Paul
>

The optical focus isn't necessarily where the ideal position is for the
feed antenna--it depends very much on the style of feed, and whether
you're contemplating multiple feeds at the notional feed-point. Which
is why I said "it can vary a bit".

Consider two concentric loop feeds made for different frequencies. The
feed pattern will be optimized for a specific height above the
reflector plane, and if you have more than one loop, you'll need to
"futz" with it to get a compromise focal position that makes both
feeds operate reasonaby efficiently.

Similarly, you nearly always have to "futz" with a circular (or other)
waveguide feed to find the optimal phase center. That "futzing" can start
at the notional optical focus and creep a bit away from or towards the
dish to find the sweet spot.

[Jim Abshier]

For an alternative, you might try:

https://www.rfhamdesign.com/products/parabolicdishkit/

Jim Abshier

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[Paul Oxley]

Marcus

Yes a given feed has a sweet spot. For a waveguide feed, it is located inside the waveguide tube, not at the end of the waveguide.

The sweet spot always needs to be at the focal point where the RF and physical distance is the same for all points on the dish. If this is not true, the dish is not a parabola (by definition).

Paul

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[Paul Oxley]

Pablo

Where are you located? People on this list sometimes have dishes that they will give away. It you are within driving distance, it makes for a very low cost alternative.

I am located near Atlanta and have two 6 foot dishes in a storage trailer. Any interest? I could pull the trailer a reasonable distance.

The price would be "free".

Paul

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.

[Pablo Lewin]

Thank you Paul and everybody on the list. I appreciate the information. I was able to negotiate with the merchant on Ebay and got the 2.1meter dish for $175 dollars more ($530) total..a good looking dish with a nice mount...I think it's a good price.

https://www.ebay.com/itm/2-1-M-PRIME-FOCUS-SATELLITE-C-KU-BAND-DISH-ANTENNA-6-9-FT-W-POLE-FTA-210-CM/382464598172?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3Df71d642d43ac4414abe77ae419125e41%26pid%3D100675%26rk%3D1%26rkt%3D15%26mehot%3Dpp%26sd%3D382464598172%26itm%3D382464598172%26pmt%3D0%26noa%3D1%26pg%3D2380057%26brand%3DLEXX&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3A254dc6ba-01e3-11eb-abea-3a08f185a008%7Cparentrq%3Ad7113f9b1740aa465e79c98afff459f1%7Ciid%3A1

These are last night results with my little wifi modified antenna

https://www.youtube.com/watch?v=zXGQAEMd2Yo&feature=youtu.be

[Pablo Lewin]

Oh by the way, I'm located in Glendora,CA. (Los Angeles County).

[s57uuu]

In fact it is the sum of distances of a point on the parabola from the
focal point and the aperture (or any parallel) plane.
Thus the path from the focus to the aperture is the same for any point
on the dish - and you get a plane wave.
The dish's focal point is independent of frequency, but the phase center
of the feed is not. Log periodic feeds are worst in this respect.
If you have multiple feeds, place the one for the highest frequency
closest to the focal point, because the distance measured in wavelengths
is the important thing.
Also, deeper dishes (lower f/d) are more critical regarding the focusing
accuracy.

Marko Cebokli

> --

[Pablo Lewin]

Thank you Marko!

[Hamish Barker]

I have had good results with my 0.85m offset feed dishes which I got for $10 from local junkyard, then built my own horn and waveguide feeds. The horn was dimensioned about 30cm diameter so as to give significant taper to the feed pattern at the dish edge, reducing ground noise and rfi from outside the beam entering the feed. Supporting the feed usually requires some macguver work.

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[Hamish Barker]

The other thing I meant to say was that I have seen plenty of 2.5 to 3m old satellite dishes for sale on trade me ( sort of ebay new Zealand style) but not in my city. Some people ask for $150 for them, others just want them removed as it seems they are for some now- superseded type of satellite TV system. 

Building a feed isn't too hard. Start with something basic and then start studying antenna books to understand the theory behind feed taper, optimum horn angle etc, and incrementally improve. Tin snips and a pop riveter are your friends ( and gloves, and a file to dull cut edges.) 

For higher frequencies such as 10 ghz+ when the feeds can be smaller, it might be worth soldering brass sheet etc since it won't be possible to place rivets less than say wavelength/10 apart to avoid leakage at riveted joints. But I only mention this from what I've read so far, I have no operation experience other than at the 1420mhz hydrogen line.

[Michiel Klaassen]

Hi Pablo, Hamish and All,

Using the mentioning of the Ku band in your post subject I remember that you also can try to capture 12GHz masers.

You do not have to build a frontend; you can just buy a standard LNB;  Avenger LNB with pll.

We captured W3(OH) with our 10m dish with 1 (minimum) to 5 minute integration  time at 12 GHz. see

http://parac.eu/projectmk23.htm

When you try to capture it with a 3m dish, then with the simplified formula A*sqrt(t), the integration time would be 1.6H (minimum) to 10H.

Regards,

Michiel

parac.eu

Op wo 30 sep. 2020 om 09:19 schreef Hamish Barker <hamish...@gmail.com>:

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[Pablo Lewin]

Hi Hamish, Michiel et al..thank you for the plethora of great information. I'm at the VERY beginning of my Radio Astronomy journey (Still fascinated by my little 2.4ghz antenna and LNA getting H-Line readings every night).

Right now my plan is to install the 2.1 meter looking up to the Zenith to keep recording H-Line data for that I'm going to need a link to a simple H-Line feed plans, directions, thoughts (Of the tin can version or cheap off the shelf that can be easily modified.)

My second step will be to fashion some way to motorize it without spending thousands of US Dollars and I have some idea on how to do it with step motors and reduction gear.

lastly I will need Different targets to observe and possible LNBs that can be modified.

I am also planning to use this dish for EME work which I always dreamed of accomplishing.

Other than the immediate H-Line goal the rest will take time and experience to accomplish and I deeply value your help.

Thank you so much!

Pablo Lewin (WA6RSV)

The Maury Lewin Astronomical Observatory

Glendora.CA. USA