My homemade 3m parabolic radiotelescope

[Mario M.]

Hi

I always wanted a radio telescope. Ever since I saw movie "Contact" when I was around 10. Large dishes were really expensive so I decided to build my own. I settled on 3m diameter. 2m would also be fine, but I decided, when I'm making it I might as well make it 3m. It's F/D= 0.4 dish. 

I'm planning to listen to 1420MHz frequency, and I have a Nooelec SawBird amplifier for it. 

I didn't have a lot of free time to work on it, so this took about 1.5 years up to this moment. I decided to share some photos now that the dish is mounted on the mount and it actually looks like a radio telescope instead of looking just like a bunch of parts!

My dad helped me with welding and other stuff. The dish weights around 40kg.

Better picture of the dish while it was on the ground. 2/8 of the wire mesh were temporary removed to allow for easier acces inside the dish.

I took every precaution to make it as accurate as I can, but in the end I don't know how it will behave. Hopefully the wooden parabolic parts will be strong enough and not distort too much under weight.

It's located in a quiet little village in mountains of Croatia. 

[B & MR Randall]

Your construction job is impressive.  Hope ypu get feed and radio together soon

Bruce Randall

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[Mathew George]

Dear Mario,

It is inspiring to see your work. I wish you all success with your endeavour. It should not be hard to see first light, but it might take a while until you optimise your setup. 

All the best,

Mathew

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[Anthony]

That's nice!!

--

[Mike]

Wow, that truly is a beautiful construction. Well done Sir. Please keep us posted on your efforts. This is very inspiring.

Mike Thompson

KG4JYA

Mikeasphere

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[djl]

Very Nice!

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"It's always something."
Roseanne Rosannadanna
----------------------"
Dr. Don Latham  AJ7LL
PO Box 404, Frenchtown, MT, 59834
VOX: 406-626-4304

[Michael Perkins]

Mario,

That is a fantastic job well done!

We look forward to seeing more as your project progresses. 

Michael

KB1PQS

On Fri, Aug 11, 2023 at 12:40 PM Mario M. <mariom...@gmail.com> wrote:

--

[Alex P]

Hello Mario,

Congratulations :it looks very well made.  

If the feed is tuned, the next step will be to adjust the dish<>feed spacing ..

Start with perhaps 3 cm steps and refine from there. 

Pick a bright spot in the MW and optimize the difference between cold sky and peak H1 readings.

Post some data when  you get all operational.

Regards

Alex KK4VB

[Marcus D. Leech]

On 11/08/2023 17:33, Michael Perkins wrote:

Mario,

That is a fantastic job well done!

We look forward to seeing more as your project progresses. 

Michael

KB1PQS

I similarly echo those sentiments.  It is a thing of remarkable beauty.  Looking forward to some "first light" data!

To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/CACZunDa%3D4-oGvHZwcgNkaCUZ_0CTdBeza01pqfnkV3ghqmQAgg%40mail.gmail.com.

[fasleitung3]

Hi Mario,

Just like everyone else here I find this is excellent work. You should be very close to seeing first light.

Good luck and if there is anything where we can be of assistance just let us know.

Best regards,

Wolfgang

[Mario M.]

Thanks for the kind words, it means a lot.

Yes, the feedhorn is about 70% complete. I need to install the antenna and solder the aluminium parts and that's done. Then digging out and putting a electrical conduit in the ground. I think I'll get first light in about 1-2 months.

[Mario M.]

Thanks for the advice, I'll try that.

[Lester Veenstra]

Mario:   Would you be willing to publish a drawing.  I would particularly like to see how the mount was designed.

Thanks

   Les

 

Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)

les...@veenstras.com

 

452 Stable Ln

Keyser WV 26726 USA

 

GPS: 39.336826 N  78.982287 W (Google)

GPS: 39.33682 N  78.9823741 W (GPSDO)

 

 

Telephones:

Home:            +1-304-289-6057

US cell          +1-304-790-9192

Jamaica cell:    +1-876-456-8898

To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/e10b751b-85ae-345f-dc78-e8c97c490904%40gmail.com.

[Mario M.]

I don't really have a drawing, but I do have some close up photos. The base for the mount was the bearing from the car wheel. On top came a steel holder for a wooden pillars, and on it I put some other regular bearings for another axis. There's a cog wheel for future, when I put motors on it.

Forgive the junk on my garage shelves :)

[Lester Veenstra]

Thanks

 

Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)

les...@veenstras.com

 

452 Stable Ln

Keyser WV 26726 USA

 

GPS: 39.336826 N  78.982287 W (Google)

GPS: 39.33682 N  78.9823741 W (GPSDO)

 

 

Telephones:

Home:            +1-304-289-6057

US cell          +1-304-790-9192

Jamaica cell:    +1-876-456-8898

 

From: sara...@googlegroups.com [mailto:sara...@googlegroups.com] On Behalf Of Mario M.
Sent: Saturday, August 12, 2023 10:13 AM
To: Society of Amateur Radio Astronomers
Subject: Re: [SARA] My homemade 3m parabolic radiotelescope

 

I don't really have a drawing, but I do have some close up photos. The base for the mount was the bearing from the car wheel. On top came a steel holder for a wooden pillars, and on it I put some other regular bearings for another axis. There's a cog wheel for future, when I put motors on it.

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[Dimitry UA3AVR]

Good luck to see first light ... nice work, Mario.

пятница, 11 августа 2023 г. в 19:40:26 UTC+3, Mario M.:

[b alex pettit jr]

Mario,

Are you going run the 1.42 GHz signal via a long coax or install the SDR near the antenna and have the long run digital ?

What is the length of the buried conduit ?

Alex

On Saturday, August 12, 2023 at 11:17:01 AM EDT, matovin...@gmail.com <matovin...@gmail.com> wrote:

Thank you so much for all the nice comments. It means a lot :)

Regarding the feedhorn, It's about 70% done. What's left to do is to put the antenna and connector and solder the aluminium parts together. Should be done soon.

And then a nice workout - putting the power cable and its conduit under ground.

I'll keep you posted and until then here are some more old photos .

The mount

Soon-to-be-operational feedhorn

Early phase of dish construction. I used a line to align all the parts together. This part of the build was a nightmare. It took so much time.

Closeup of the feedhorn mounting spot

[Eduard Mol]

Amazing work, Mario, well done! That dish looks really good.

Looking forward to your first light and subsequent results.

Best,

Eduard

[Mario M.]

I will have amplifier on the side of the feedhorn and SDR also very close, probably on the feedhorn too.

Conduit is about 50m long, from the house.

[b alex pettit jr]

Hello Mario,

How do you plan to transfer USB data over 50m ? 

I found USB over Cat Cable Extenders work fine but radiate significant noise from the Cat  cable. 

I tried 4 different brands of USB over Cat Extenders .. the AV Star had the least noise, but still Way Too Much,

and the only solution I could find was to move it away from the antenna.

I moved the SDR and USB Extender ~ 7m away from the antenna using LMR 400 .

( There is 12V power in/out of the box to power the WD5AGO LNA and WideBand Amps on the antenna. )

  >>   Perhaps you should run some tests before finalizing the design...

Alex

[Nathaniel Butts]

Love it.  Gives me good inspiration for a future big dish.  Super interested to see your first signals.

USB to CAT can be problematic if wire pairs aren’t twisted, as alex said.  Not sure what you’re using to process the SDR signal, but if you digitize at the source that will help with the signal loss.

Thanks,

Nathan Butts

Wannabe Astronomer

Bowling Green, KY

[Mario M.]

Sorry, I didn't explain good enough. I will have raspberry pi in a (hopefully) waterproof enclosure on the dish pillar. That way I will only have 3-4 meters of USB coming from feedhorn to raspberry pi. I will control raspberry pi over wifi. I have a small wifi extender so I will use it.

[Mario M.]

I'm interested as well. Do you think I would get anything if I point feedhorn (no dish) directly to the milky way? Just to test it before I put everything on the telescope.

[Eduard Mol]

Yes, you will see the Milky Way HI signal with just the bare feedhorn.

Op zo 13 aug. 2023 om 09:24 schreef Mario M. <mariom...@gmail.com>

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[b alex pettit jr]

Hi Mario,

Pre Test everything ... 

H1 Signal Levels are much lower than even the blackbody emission from room temperature objects.

 = You  need to verify the WiFi signal does not overload the LNA.

1) Try your planned design.

 2) If there are RFI  problems, use coax and move the SDR to a location 'shielded' by the dish screening.

     Since the data will have been amplified by 40 dB,  few m of LMR240 will not affect performance.

A useful tool to locate RFI sources is to make a simple 21cm long Loop Feed connected to

the LNA  and hold it near suspected sources.  ( any flexible coax to the SDR is fine )

Regards,

Alex

[Larry Mayfield]

Alex, great idea regards the loop antenna. I’m gonna make one!

But will make it so that I can use the actual hardware in the system so that  I will hopefully know how the system works together and then for bad places, and then I can do to experiment to reduce the RFI.

Sound?

 

Larry

Pahrump

 

From: 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Sunday, August 13, 2023 3:19 AM
To: sara...@googlegroups.com
Subject: Re: [SARA] My homemade 3m parabolic radiotelescope

 

Hi Mario,

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[Douglas Decker]

I like Alex had to do some extending. Some information that may help others.

The above shows my rough one line.

Systems working fine.

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[Marcus D. Leech]

On 13/08/2023 11:30, Douglas Decker wrote:

I like Alex had to do some extending. Some information that may help others.

The above shows my rough one line.

Systems working fine.

An approach that is becoming more economical is to have SDR+computer in a shielded box behind the dish--so you
  only have a few m of cable between the LNA output and the receiver.   Then carry your ethernet connection from the
  computer via fiber -- 1Gig  fiber bridges are now fairly cheap.   Aggressively decouple the power feed going into the
  computer box and make sure your fiber goes through the smallest possible hole in the shielded box.

We sorta-kinda use this at the CCERA observatory in Carp, ON.   The LNAs are at the feedpoint, then there's about 10m
  of cable that feeds our 4-channel SDR in the elevation cabin behind the dish, then a 10G fiber going to our computer
  downstairs.

To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/5140c1c8-a6a6-a041-8bf0-fbdad1d52dce%40gmail.com.

[Mario M.]

Hopefully the wifi doesn't interfere with the amplifier and SDR. Otherwise I won't be able to use my raspberry pi zero which only has wifi, and doesn't have ethernet port.

[Nathaniel Butts]

If it does, this may help. 

Ethernet/USB HUB HAT Expansion Board for Raspberry Pi 4B/3B+/3B/2B/Zero/Pi Zero W/Pi Zero 2W,with RJ45 10/100M Ethernet Port (Based on RTL8152B Chip) and Three USB Ports,Compatible with USB2.0/1.1 https://a.co/d/36QwBV7

I made a router/hub for traveling with one and I like it. 

Thanks,

Nathan Butts

Wannabe Astronomer 

Bowling Green, KY

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[b alex pettit jr]

Hello Larry,

 Exactly . 

 It is best to see how Your System responds to the RFI

Alex

========================================================

[Mario M.]

Good idea! That or USB extender.

[Mario M.]

My SDR receiver is in metal case, but while working it still heats up. How will that heat affect its ability to detect hydrogen line?

[Mathew George]

It is normal that sdr heats up a bit. You can optimise cooling by attaching it to the metal box.

For initial testing you can keep it in the open. There could be temperature fluctuations, which affects your noise floor, but one needs to measure it to optimise the setup.

All the best, Mario

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[mike....@gmail.com]

Heat makes amplifiers' gain drift.

Ambient temperature changes  will change the gain  of amps both in the LNA and in the SDR.

To smooth these out:

1) active temperature control using  peltier devices or resistors to maintain a constant temperature  (costly ) 
2) Thermal Mass,  large metal heat sinks or just metal bars  or water bottles

3) Shading from Sun

4) Shading from drafts, cardboard box

GL

Best regards

Mike

[b alex pettit jr]

Does Temperature primarily shift Gain or Noise Floor ??

For Example

[Lester Veenstra]

https://spaceweatherarchive.com/2023/08/15/ham-radio-operators-hack-a-nasa-spacecraft/ 

 

 

Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)

les...@veenstras.com

 

452 Stable Ln

Keyser WV 26726 USA

 

GPS: 39.336826 N  78.982287 W (Google)

GPS: 39.33682 N  78.9823741 W (GPSDO)

 

 

Telephones:

Home:            +1-304-289-6057

US cell          +1-304-790-9192

Jamaica cell:    +1-876-456-8898

.

[fasleitung3]

I would not be concerned about a noise figure drift of the SDR with temperature: The noise figure is determined by the LNA anyway, so there is no impact. Of course there may be some noise figure degradation of the LNA at higher temperatures. The example shown by Alex demonstrates it is not that significant.

A different story is gain stabililty: Most SDRs I have tested show a significant decrease in gain as soon as you start pulling data and the chip heats up. One can mitigate this a bit by letting it run for a while before taking actual data.

However, in Mario's first application this does not really matter. He wants to observe the Hydrogen emission and if there are some changes in gain this would only affect any quantitative brightness temperature measurements, but not the detection itself. Gain stability is much more an issue for continuum observations.

All these effects are no show stoppers for getting first light from Hydrogen.

Good luck,

Wolfgang

[tedcl...@gmail.com]

Professionals attack system gain variations due to temperature changes, with hardware.

ezRA tries attacking the same with free software and frequent Reference samples.

Good enough for slow drift-scans ?

---
Ted Cline   N0RQV

[fasleitung3]

Ted, what is your reference then?

Wolfgang

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[Marcus D. Leech]

On 16/08/2023 12:29, 'fasleitung3' via Society of Amateur Radio Astronomers wrote:

Ted, what is your reference then?

Wolfgang

Indeed, unless the reference is:

  (A) Very stable with temperature
  (B) Producing a noise temp that is comparable to the observed Tant

They don't do that well in providing gain stabilization.

To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/94aa4bf939190aeaa140e5f6754d3a5a8023e642.camel%40googlemail.com.

[fasleitung3]

On our 25-m dish we have a noise source which is injected into the feed horn.

When turned on it will provide a signal which is in the order of magnitude of Tsys. Since it is very stable, it can serve as reference. We use this as calibration reference. Of course, this again has to be calibrated against a know calibration source (such as 3C353). We do not use this, however, to permanently correct the gain. We just do it prior to an observation run.

Since we hardly ever do continuum observations cycling between on and off is not what we need to do.

Wolfgang

[tedcl...@gmail.com]

ezRA chose (B).

ezCol currently collects frequent Reference samples through the same RF path, either from

      1423 MHz (no hydrogen ?)

or

      a resistor at the front of the first LNA

      (pin 4 of https://www.nooelec.com/store/sdr/sdr-addons/sawbird/sawbird-h1-barebones.html)

Maybe from a local calibration transmitter (noise source) ?

Maybe from a true frequency-tuned Dicke Reference circuit ?

(page 11 of https://123.physics.ucdavis.edu/week_10_files/microwave/microwave_notes.pdf )

Comments ?

This is similar to a previous Jun-2021

https://groups.google.com/g/sara-list/c/tdI2XwWCWMQ

---

Ted Cline   N0RQV

[djl]

Is that like a tribble?

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------------
"It's always something."
Roseanne Rosannadanna
----------------------"
Dr. Don Latham  AJ7LL
PO Box 404, Frenchtown, MT, 59834
VOX: 406-626-4304

[Mario M.]

Eventually if it works fine I want to do scans of the entire sky, so I guess by that time I should deal with the heating. Also I plan on moving away from RTL SDR and possibly use dedicated detector. 

[matovin...@gmail.com]

Today and last night I tried testing my radio telescope. First I tested bare feedhorn with LNA. No signal whatsoever. Yes, I can see an increase in noise level when I turn on the LNA (about 30dB). But there's no characteristic signal from Milky way 21cm radiation. Next I tried putting it on the dish, in case the feedhorn alone is not able to see the hydrogen line radiation. Still nothing. Entire spectrum from 1410-1430 MHz or even wider is just a flat line. No signals, no nothing except for some very narrowspikes here and there. I don't have to say this is very depressing. 

I did detect a Sun with the dish, but it's about 10dB increase in noise. Somehow I think the signal from the Sun should be a lot stronger than 10dB increase above the rest of the sky.

First question is: how easy is it to completely mess up a feedhorn while constructing it so that it can't receive anything? My feedhorn is SETI feedhorn, I used their excel sheet to calculate the dimensions and I got it reasonably accurate. Is there some obvious thing that I might be doing wrong so that the feedhorn isn't receiving at all, or receiving very very poorly?

Second question: Should I insulate feedhorn from the rest of the dish? Right now, it's all connected, feedhorn and feedhorn supports and wire mesh.Not on purpose but It turned out that way.

What would you recommend, how should I test my feedhorn to check if it's getting any signal into it? Is bare feedhorn really able to receive 21cm signal from Milky way?

I attached the photos of my feedhorn, can you see anything obviously wrong with it? I checked the probe, it's not in contact with the feedhorn metal.

[Marcus D. Leech]

The brightness temperature of the SUn is about 100,000K -- you'll only
see half of that.  The Sun occupies about 1/100th of your
  beam area with a 3m dish.  So, 50,000 / 100 is about 500K Tant, so a
roughly 10dB rise, given a good LNA is about right.

Keep in mind that the hydrogen spectrum will cause, at most, a 2dB
"bump" in the spectrum.   Make sure you're integrating
  for long enough (a few 10s of seconds), and that you have your
spectral display scaled appropriately.

[Mario]

I may have made a big mistake. I didn't integrate the signal at all. I just turned on SDR sharp and looked at the signal and expected to see it there...

[Marcus D. Leech]

On 08/10/2023 17:22, Mario wrote:

I may have made a big mistake. I didn't integrate the signal at all. I just turned on SDR sharp and looked at the signal and expected to see it there...

I think on SDRSHarp, there's an "IF Average" plug-in that folks use.  But I don't know anything about it.

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[Nathaniel Butts]

Mario,

You will will need to do a couple of things to increase your chances of seeing the line:

1. Perform cold sky reference measurement. Measure a part of the sky far away from galactic plane. 

2. Perform integration measurements. The smaller your device the longer you will need to integrate to get “good” results, but if you’re just attempting to see the line then a 10-30 second integration time may be enough. 

You may need to record over a several hour period to make sure you see the galactic plane, since that waveguide will be hard to aim. 

Thanks,

Nathan Butts

Wannabe Astronomer

Bowling Green, KY

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[Anthony]

I think this was the old link from a while ago on the IF plug for SDRSharp. My apologies if someone else already addressed this, didn't look at all the threads. There is also a zadig USB driver that may be required. It's been several years since I've used SDRSharp. 

Double check the links to make sure they are valid and safe.. 

SDR# IF Plug sites - trust but verify! 

https://www.dropbox.com/sh/v3ul0a8x9ofagej/AADwDWqiuGUZexueFzfqEGGva?dl=0

https://github.com/DanielKami/SDR_AVE_new

Not sure if this driver is required, can't remember. 

https://zadig.akeo.ie/

This was a very old on RTL that may help with SDR# and the Hydrogen line observation

https://www.rtl-sdr.com/cheap-and-easy-hydrogen-line-radio-astronomy-with-a-rtl-sdr-wifi-parabolic-grid-dish-lna-and-sdrsharp/

And last but may not be relevant, a list of RTL-SDR supported software, may not work for Radio Astronomy, unfortunately I've only looked at a few, several years ago. 

https://www.rtl-sdr.com/big-list-rtl-sdr-supported-software/

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[Eduard Mol]

Hi,

The latest version of IF average can be found here: https://github.com/DanielKami/SDR_AVE_new

You should be able to detect the HI signal quite easily even with the bare feedhorn if you integrate the spectrum for a few seconds or longer. It will appear as a small bump near 1420.4 MHz typically a few hundred KHz wide and no more than 1- 2 dB, on top of the SDR bandpass response which is always there.

To remove the SDR bandpass response you can do a background correction (cold-sky reference measurement), as others already pointed out in this thread. 

Good luck with your observations,

Eduard

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[Mario]

OK, I will repeat the experiment, this time actually integrating the signal instead of just expecting to see a strong signal from live FFT view.

Another thing, does the feedhorn need to be somewhat watertight or is it a non issue? I thought about putting a little bit of silicone on the edges, for example the edge where a feedhorn cylinder meets the circular top part (hat). So that when it rains the water doesn't drip into the feedhorn.

And one other question that I asked, which probably got burried among other things I asked: Right now the metal wire mesh is connected to metal feedhorn supports which is connected to feedhorn. Is that a problem if it's all electrically connected?

In yagi antennas, the reflector can't be connected to active element, not sure how things go with parabolic reflectors.

[Mario]

The 21cm line is that small bump under the yellow line?  And there's about 0.5dB difference from minimum to maximum of bandpass response curve?

[Eduard Mol]

Yes it’s the small hump around the yellow line. Vertical scale is in dB amplitude.

This spectrum was made with a small (ca. 35 cm) conical horn antenna.

Op ma 9 okt. 2023 om 11:54 schreef Mario <matovin...@gmail.com>

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[Mario]

Did you use LNA or was that directly from the horn to the SDR? What was the integration time?

[Eduard Mol]

I used a nooelec sawbird HI LNA. Don’t remember the exact integration time but it was in the order of ~60 seconds.

Op ma 9 okt. 2023 om 12:06 schreef Mario <matovin...@gmail.com>

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[Andrew Thornett]

I am not an expert by any means but I haven't found it too difficult to pick up hydrogen from centre of a modest size town with plenty competing signals - however initially I had problem getting it to work and turned out one of SMA patch cables wasn't working - plus I've had couple of those cables break on me with very minor pulling on them. Plus some of sma connectors don't work at all. So the quality control on these things is really poor. Buy a few and try changing them around would be my suggestion but please can someone correct me if this advice is poor.

Also check LNA LED light is on - did you turn the bias tee on perhaps using the bias tee on python script online?

As mentioned by others check your SDR is picking up local FM Station without the dish - any simple SMA aerial will do.

I have also added pre-amp into my flow before SNA between it and aerial - dobt know if that is making a difference.

You need to test each individual item to limit variables

SDR# is really good here BUT latest version does something strange with bias tee so older version given out with the SARA Scope in a Box software package is MUCH easier to use - this is my opinion based on VERY limited knowledge and experience and understanding on the whole thing but I hope it helps!

Andy

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From: sara...@googlegroups.com <sara...@googlegroups.com> on behalf of Eduard Mol <eddiem...@gmail.com>
Sent: Monday, October 9, 2023 12:08:29 PM
To: sara...@googlegroups.com <sara...@googlegroups.com>
Subject: Re: [SARA] My homemade 3m parabolic radiotelescope

 

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[Andrew Thornett]

NB My website will show you what sort of traces you should obtain.

www.astronomy.me.uk - I only started just over a month or so ago.

Andy

M6THO

Don't get taken in by my radio ham moniker - this is the foundation licence in the UK which means I hardly know anything at all!!

Sent from Outlook for Android

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From: Andrew Thornett <andrew....@googlemail.com>
Sent: Monday, October 9, 2023 1:13:00 PM

[Mario]

Yes, the SDR light is on. I'm not using bias tee to power the SDR, I'm using micro USB. And SDR is receiving local stations just fine. I'll double check cables and connections.

Also, I said I used SDR Sharp to check the signal. But the only reason I used SDR sharp is that I didn't have my laptop with me. On my laptop I wrote a program that uses rtlsdr library to get raw data from SDR, does FFT on the data and calculates power spectral density. I can also easily change number of samples there to get longer integration time.  I was experimenting with using more samples for FFT vs using less samples but doing an average of those results. It seemed like doing the average of FFTs produced smoother graphs. I still have to check if it's good or not.

[Andrew Thornett]

On the basis of removing variables, I suppose it is theoretically possible there might be problem woth your software so is it worth trying to detect hydrogen first with IFAverage on SDR# with 902000 integration as recommended in Scope in a Box?

Also - and this is beyond really.what I know - maybe someone else will comment - can you use a handheld transceiver to produce signal source to test rig against? I have a Chinese Baofeng handheld 1mW that will tune to ANYTHING (built for Chinese Market and they don't care about regulations...) so I thought I'd give that a try....other folks reading this -.would that work? And would it be better to replace aerial on the Baofebg with a dummy load to try and attenuate the signal given the gain on the 1420MHz antenna?

Andy

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[Mario]

Of course it's possible my software doesn't work. But I only tried with SDR sharp, not yet with my software. But of course, I will try first with SDR sharp, to be sure it's working.

I will first try with a bare feedhorn and lots of integration time.

I do have Baofeng UV-5R, but it doesn't trynsmit on anything other than 2m and 70cm bands.

[fasleitung3]

Hi Mario,

Indeed a lot of comments and questions have been going back and forth here. So my apologies if I am adressing things that have already been answered/resolved. Just a bit of a summary in random order:

You should be able to observe the hydrogen line with just the bare feedhorn, an LNA and a RTL-SDR. Even if the feedhorn design/craftsmanship is not ideal, it should still be good enough to observe hydrogen.

Because the RTL-SDR has this very "bumpy" baseline it is sometimes a bit difficult to actually see the signal. I understand SDR# with IF average have to functionality to take a reference spectrum and substract this from the spectrum when pointing towards the galactic plane. This would help. I do not have hands on exeperience with it since I do not use SDR#, though.

You will need a bit of intergration time, 10 to 60 seconds should be ok.

When you try to record the spectrum you should make sure that your feedhorn is actuall pointing roughly towards the galactic plane.

When the Noolec LNA is powered via the Micro-USB port you need to remember that then DC voltage is fed back into the coaxial output of the LNA. Depending on your RTL-SDR, this may cause a problem if there is no DC-blocking in between.

When you put the feedhorn on the dish it is perfectly ok if there is electrical connection to the feed support structure. No need to isolate.

You may want to take a precaution that not too much water is dripping into the feedhorn. When it is mounted on the dish there should be little problem since the opening is pointing downwards. However if there is some gap between the cylinder and the back plate, some sealing would be useful. Make sure though, that there is no major gap as this might degrade performance. When you use the dish alone, then you could put just some wrap foil over the mouth. There is no attentuation by the foil.

Overall, I do not see anything that is between yourself and the first light :-)

Best regards,

Wolfgang

[Nathaniel Butts]

Mario,

Some troubleshooting steps I learned the hard way:

Grab a multimeter, a VNA helps as well.  Set the multimeter to test continuity.

Using the image and table below, test the continuity between each end of the cable.  Do this for all cables in your system (element to LNA if you have one, LNA to SDR).

If all turns out well there, attach the cable to your connector on your feedhorn.  Repeat the test, replacing the End A Pin with the element in your feedhorn, and End A Nut with the casing of the feedhorn.  Do the test from casing of feedhorn to End B Nut on all different panels used to construct your feed.  

If all these pass as anticipated, then the horn and cable should be electrically conductive and no crossed wires, per se.  If it fails anywhere, there is most likely a problem with the connection in the wires (i.e. a piece of the shielding got into the male pin, or something).  I used RG136 cables and build them myself, so this happens to me a lot. 

Second, if you're using the Sawbird LNA, make double sure the light is on.  My mini-usb connection failed a lot and I would lose power, losing an entire day's worth of scans at a minimum.  I eventually hard wired mine in, but make sure the led is on when you're scanning for now.

Third, you may need to let it collect data for an hour to make sure you're actually hitting the hydrogen part of the galaxy.  It can be a little tricky to aim it right, using a smaller section like that.

Patience is a virtue......and I'm low on virtue.....

Thanks,

Nathan Butts

Wannabe Astronomer

Bowling Green, KY

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[Mario]

Thanks for your answers! 

I didn't know SawBird LNA puts out DC voltage on the output. I know it supports bias tee, but I thought when I'm using micro USB there's only RF on the output. But I think I'll just stop using micro usb for power. RTL SDR supports bias tee and can give enough current. I'll use that and get rid of one extra cable going into feedhorn.

You say, make sure there's no major gap in the feedhorn. I don't have large gaps but I do have areas where there isn't direct electrical connection. Like between the round back plate and cylinder walls. I soldered those on 4 points around the circle. I didn't solder it all around the circumference. Should I have done that? Same goes for feedhorn choke ring. It also isn't continuosly soldered around the circumference.

[Mario]

Sure, I'll try that. I'll power my LNA from bias tee from RTL SDR. And place my feedhorn somewhere and let it do a drift scan and see what I get.

[Alex P]

Hello Mario,

Your  feed looks Very Well Made . No Issues

You should be able to readily detect a shift in background level from pointing overhead ( measuring Cold Sky ) 

to then placing your hand under the feed . 

And Pointing the antenna from overhead to  horizontal to pick up ground noise should result in a Major level shift in the spectrum.

( on my 1.2m dish  system there is a difference of 7.0 dB in overall background level shift between Cold Sky and Ground Noise [nearby grass/trees/bushes] )

( see attached photo )

 Yes, when uUSB powered, the SAWBird backfeeds 5V into its "Output" SMA connector ..

 try a DC Block .    nooelec $24 ( there is another brand on Amazon @ $11 I've used also )

https://www.amazon.com/Nooelec-SMA-DC-Block-50kHz-8GHz/dp/B07YYLHJKS/ref=sr_1_3?crid=CNVW76V1TRZ1&keywords=sma+dc+block&qid=1696929470&sprefix=sma+dc+block%2Caps%2C347&sr=8-3

Nooelec SMA DC Block in-Line 50 Ohm 50kHz-8GHz Connector 

Blocks DC Voltage from Your Radio or RF Test Equipment.

 Regards,

Alex

[Andrew Thornett]

This discussion thread is very interesting! I am learning a lot from it too.

Andy

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Sent: Tuesday, October 10, 2023 11:32:48 AM

To: Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: Re: [SARA] My homemade 3m parabolic radiotelescope

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[Mario]

Today I tried detecting hydrogen line with my feedhorn. There was a lot of noise, and I mean it. This was taken from my apartment in the city, with lots of people around having routers, phones, remote controls etc... Do you think I actually detected hydrogen line? Seems to be at  somewhat accurate position in the spectrum. And I get it every time I point the feedhorn south-west. Sometimes with more noise, sometimes a bit less.

 I used H-line software

[b alex pettit jr]

Hello Mario,

I would say YES !  congratulations

What was the total time for this sample ?  It might improve with more averaging time ..

Alex

[Mario]

50 000 FFT's of 2048 samples each. Around 50s I'd say. But as I said there's a lot of noise. I'll try again in 2 weeks when I get to my parents' house in the country side, where my dish is. I'm hoping for a much better result.

[b alex pettit jr]

Try taking measurements from either of these bright areas

Use Stellarium to locate them

http://stellarium.org/

Regards,

Alex

[Mathew George]

Simply covering the feedhorn with aluminium foil or suitable metallic lid, should make the peak disappear. This can be a confirmatory test. 

If the peak is not disappearing with feedhorn covered, it has to be from the electronics itself, I guess.

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[Marcus D. Leech]

On 07/11/2023 20:16, Mathew George wrote:

Simply covering the feedhorn with aluminium foil or suitable metallic lid, should make the peak disappear. This can be a confirmatory test. 

You don't want to do this with a strictly-conductive "cap".  Many times, it will kick the LNA into oscillation--sometimes
  destructively.   Because a short across the waveguide constitutes and profound impedance-mismatch.

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[Mario]

I'd say this is pretty much confirmed to be Hydrogen line. Yesterday I tried to point my feedhorn as best I can in the direction of maximum brightness (RA: 20.5, Dec: 40)

This is the result, pretty nice signal, 50 000 FFT's averaged

And then I tried covering the feedhorn with my hands and this is the result, no signal.

What is the next step, should I adjust choke ring to get better signal or just leave it where SETI feedhorn sheet says and put it onto the dish and test entire setup?

[fasleitung3]

Put it on the dish first before you do something with the choke ring. The idea of the choke ring is to adjust the feed beam pattern to the dish.

Wolfgang

[b alex pettit jr]

** YES **

Since it is Much easier to adjust the choke ring with the feed UnMounted, 

Perhaps make a series of short tests .. say sliding the

choke ring in 2 cm steps over say +- 4cm and document the change... 

That way, you have some idea of what to expect when it IS mounted.

Alex

=======================================================================

On Thursday, November 9, 2023 at 03:19:58 AM EST, Mario <matovin...@gmail.com> wrote:

I'd say this is pretty much confirmed to be Hydrogen line. 

Yesterday I tried to point my feedhorn as best I can in the direction of maximum brightness (RA: 20.5, Dec: 40)

This is the result, pretty nice signal, 50 000 FFT's averaged

And then I tried covering the feedhorn with my hands and this is the result, no signal.

What is the next step, should I adjust choke ring to get better signal

 or just leave it where SETI feedhorn sheet says and put it onto the dish and test entire setup?

--
-

.

[b alex pettit jr]

THIS is the Answer.

[fasleitung3]

Alex, the optimum position of the choke ring is not a matter of centimerters but rather a fraction of cm. If you want to optimize the choke ring postion while off the dish then you need to have the capability to actually measure the beam pattern of the feed horn. This means to rotate the feed horn around it's phase center. Ideally this is done in an anechoic chamber, but doing it outside and reasonably far away from structures which could reflect will work also.

We have done this, it is cumbersome and requires adequate equipment.

So I still recommend to put the feed onto the dish with it's nominal position and then take it from there.

Best regards,

Wolfgang

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[Mario]

Thanks Alex and Wolfgang for your answers. I appreciate it.

[b alex pettit jr]

Hello Wolfgang.

1) I was writing the reply suggesting off-dish tests as You were posting = we were out-of-phase.

2) Fractional cm !  that is difficult to perform on a larger dish system.

Regards,

Alex

[Mario]

When using RTL SDR to power SawBird LNA via bias tee, I noticed SDR gets quite hot. How will that affect noise floor and picking up faint signals? How will that affect the frequency stability or accuracy? 

Would it be a better idea to power LNA with a separate power supply?

[Alex P]

Hello Mario,

 I do not know what effect the heating will have on the performance, but the small SDRs get Hot

 Yes, you could power it independently..      Two Methods

1)  Power the Sawbird over the coax using an External BiasT  to prevent the power from backfeeding the SDR

2)  Power the SAWbird directly via its mini USB connector and add a DC_Block at the input of the SDR

Either Way it might be beneficial to mount the SDR on a HeatSink .

Alex

=========================

[Mario]

Thanks Alex. SDR already has a heatsink, it's this type. Do you mean I need even larger heatsink? 

[b alex pettit jr]

Yes, a real Heat Sink .. whatever it takes.

Use Heat Conductive Paste and attach with aluminum tape or brackets

Heat Conductive Tape is not a good solution as it slides/debonds over time.

[Mario]

Any ideas on how to protect LNA from rain and other weather? I thought about putting it in a waterproof box and then on the feedhorn, but then I have a problem of sealing the box around the hole for the antenna connector... 

[fasleitung3]

Mario, we are using aluminum die cast hosings with N-flange connectos for our LNA housings. Some of these have been sitting outside for several years with no issue.

You can find a picture at https://astropeiler.de/wp-content/uploads/2020/01/Hydrogen_2.pdf in figure 13.

Best regards,

Wolfgang

Am Dienstag, den 28.11.2023, 23:17 -0800 schrieb Mario:

Any ideas on how to protect LNA from rain and other weather? I thought about putting it in a waterproof box and then on the feedhorn, but then I have a problem of sealing the box around the hole for the antenna connector... 

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[Mario]

Thanks! I'll do something similar with mine. 

Any reason why everybody is using N type connector on feedhorn? I use SMA right now and wondering if I made a mistake with that connector.

[fasleitung3]

The reason for using N-Connectors is that they are watertight and are
designed to be used outside. SMA-Connectors are intended for indoor
use.
Wolfgang

[Mario]

How do you make a good connection (electrical and mechanical) when the feedhorn is curved and the connector plate is flat? It's not a problem with smaller SMA connectors, but N type are about 20x20mm at the connector plate.

[b alex pettit jr]

washers / shims and Coax Seal ?

[Mario]

Good idea, thanks.

[Mario]

First light of the telescope:

Feedhorn, LNA and SDR receiver were finally placed on the radio telescope.

It was pointed to about 45 Alt, 202 Azimuth. It's also temporary setup because I need some new connectors and cable. Don't pay attention to that wooden fence, it's temporary and I will make it wider later.

First thing I noticed were that there are some peaks in the graph, my guess is that they are from some source. Wifi amplifier or maybe SDR receiver that's placed right under the dish. This was the result of about an hour of Milky way crossing the field of view

Overall not a bad start, although it can be a lot better. I was surprised how strong the hydrogen line signal was.

[Anthony]

Very nice setup!

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[Clint Jeffrey]

I think this email came from Mario?....anyway, the spikes in your spectrum chart look awfully like power supply noise such as what a switch mode source might produce, power derived from USB connections aren't necessarily the cleanest....just a thought...😉

Cheers
Clint - VK3CSJ

On Mon, Feb 5, 2024 at 5:25 PM Mario <matovin...@gmail.com<mailto:matovin...@gmail.com>> wrote:
First light of the telescope:

Feedhorn, LNA and SDR receiver were finally placed on the radio telescope.

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It was pointed to about 45 Alt, 202 Azimuth. It's also temporary setup because I need some new connectors and cable. Don't pay attention to that wooden fence, it's temporary and I will make it wider later.


First thing I noticed were that there are some peaks in the graph, my guess is that they are from some source. Wifi amplifier or maybe SDR receiver that's placed right under the dish. This was the result of about an hour of Milky way crossing the field of view

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