Backyard Radio Telescope

[Makarand]

I have been wanting to set up a radio telescope in my back yard. I have been reading up on radio astronomy. Not much guidance in my area. Can someone in this form please guide me on specifics parts and procedure to build one? Thanks in advance.

[robin_astro]

Radio astronomy is a big field and It depends on what you want to measure. In your reading up have you come to a conclusion about the sort of kit  you want to build?  wavelength, size of antenna etc?

If you are looking at a relatively modest 21cm Hydrogen setup for example this thread gives an idea of what is involved and some of the pitfalls. (Spoiler alert, the setup ended up significantly different to that at the top of the thread)

 

[Ed astro]

Hi,

as Robin already stated, the design of the radio telescope or antenna really depends on what you aim to observe. For a beginner I think that detecting the hydrogen line at 1420 MHz is a good starting point. You could start by making a simple “cantenna”, once you have detected the hydrogen line with it you can mount the antenna in the focal point of a dish for more serious hydrogen line astronomy. If you are interested I can give more details on how to make a  relatively simple setup for hydrogen line detection.

 

[RadioJoe]

I found your call for help late
but yet no reply form you
so hope you have not deserted hi HI

May I suggest a project that produces almost immediate results

Radio Jove

https://groups.io/g/radio-jove/topics

Juipter was in opposition 220926 (September 26) https://stellarium.org/
  a free open source planetarium for your computer
  !!opposition!! = Sun angle at 180 degrees...
...that is Earth is between Sun and Jupiter for best signal to noise observation
And will stay close for several months (Stellarium)

The project can be as simple as a home brew 20 meter dipole set up in special orientation and cut for 20.1 MHz has a length of 23.28 ft (23’ 3” or 7.09 m) as measured from tip to tip of the wire ...see Figure 3-1 here...
(https://radiojove.gsfc.nasa.gov/radio_telescope/manuals/RJ_ant_manual_2.0.pdf)

And I suggest start with a single element (just one dipole vs two) for your first telescope
Two dipoles plus that delay line (special length of coax measured in wavelength degrees) makes the two element array steerable, so depending on you 'back yard' obstruction (if any) and elevation (Earth's latitude) you may choose to change or modify your second telescope elevation (height above ground) and lQQk angle (delay line length) for better observation

You will also need...
HF receiver that tunes 20.1 mHz and best if you can disable AGC
PC with sound card for recording observations to apps such as
       https://www.audacityteam.org/download/ (free)
Check out RSS (Radio-Sky Spectrograph) discussed on RadioJove link above
Plus tons of other free apps on the web


Again, this telescope project can be as simple (few $$) as home brew above
    ... or as complex (more $$) as a complete kit...

https://radiojove.gsfc.nasa.gov/
https://radiojove.gsfc.nasa.gov/radio_telescope/manuals/
https://101science.com/radiojove.html



Now for the gQQd stuff
This HF radio telescope can be multi purpose such as target;

1)   Solar storms

2)   Solar gray line ('rise and 'set are very dynamic)
    https://en.m.wikipedia.org/wiki/Terminator_(solar)#:

3)   Aurora (depending on your latitude for best dynamics)

4)   The up comming Solar eclips (depending on your Latitude and Longitude )... https://hamsci.org/article/hamsci-use-grape-personal-space-weather-stations-study-2023-and-2024-solar-eclipses

5)   My bucket list includes ... EME/echo (EarthMoonEarth)
... https://physics.princeton.edu/pulsar/k1jt/wsjtx.html

yet just another 'facet' on this marvoules ham radio hobby

Enjoy

73
John
N3AAZ

[RadioJoe]

I notice Makarand's post  Backyard Radio Telescope  increased from  290  views to  442  since my   Oct 26  reply

I wonder if there is enough interest here to share   "your"    experience? 

John
N3AAZ
 

Edited November 2, 2022 by RadioJoe

[Ed astro]

Hi,

The OP has not replied anymore to this thread, but it seems there are still a lot of other folks who are interested in radio astronomy here on this forum. This evening I had some time to put together a simple hydrogen line "cantenna" from parts I had already sitting around, as an example of what a beginner could easily make. It is effectively a metal can, 15 cm wide and 27 cm long. I made it from a thin sheet of galvanized steel, but one can also use something like a paint bucket of approximately the right dimensions (width should be 15 plus or minus 1 cm, the length is not very critical). Inside the can is a small, 4.9 cm long monopole antenna (the probe), which was made from a piece of 7 mm wide copper rod soldered to an N-connector. The probe length is somewhat critical, the width is not as important but should be atleast 3 millimeter. The distance between the probe and the bottom of the can should be close to 8.3cm.

The antenna was placed outside on a spot away from trees or buildings which could block my view of the sky. The hydrogen line signal is rather weak compared to the noise of the receiver, so a low noise amplifier (LNA) must be used. I used a nooelec SAWbird HI LNA, which also includes a filter for blocking unwanted signals at frequencies away from the hydrogen line. The LNA is connected to the antenna via a N-to-SMA adapter and a short piece of SMA cable (the cable between the LNA and the antenna should be kept as short as possible to reduce cable losses!). After the LNA cable losses are not as important, so several metres of coax cable can be used between the LNA and the SDR receiver and computer. In fact it is better to keep at least a few metres distance between the antenna and the computer in order to prevent interference.

An RTL-SDR receiver was used with the SDR# program and the IF average plugin to detect the hydrogen line. The hydrogen signal is weak, so you need to average the spectrum over several seconds to minutes with a program like IF average to get a good signal-to-noise ratio. Even then the hydrogen line is often only visible as a very small bump in the spectrum near 1420.4 MHz. The larger bumps and crests in the spectrum are artifacts of the SDR, which make it more difficult to recognise the hydrogen line. Unfortunately there were also some troubles with the power cirquit in my old LNA, so the results were not as nice as I hoped.

To get rid of the SDR artifacts, a "dark" spectrum whithout the hydrogen line signal needs to be made and subtracted from the spectrum. This can be done by shifting the frequency 1- 2 MHz away from the hydrogen line and clicking "background" in IF average. When the background is corrected the spectrum can be centered at 1420.4 MHz again to record the hydrogen line. The spectrum can also be exported as a text file containing the frequency and intensity values. These can then be copied over to for example Excel for further analysis and plotting. 

[Miguel_EA1HTA]

I can't try to make any of the suggested solutions at the moment (no room, no time...), but I just wanted to let you know that I'm really interested in hearing your experiences, how you made it, what can be made, from the begining point of view...

 

So for all of this, I can't do anything else but saying to you: THANK YOU for SHARING !!

 

Regards,

 

Miguel (EA1HTA)

[RadioJoe]

Yet no response from  OP Makarand
My BIG Thanks go to the OP for rekindling a fire in this 'ole stove'

Ed astro,
re your ""SDR artifacts""
Thanks for the interesting technique

Quite coincidental I was just reading about 'self calibration'
 = SELF CALF
 https://forge.oca.eu/trac/fitOmatic/wiki/self-cal
""Self-calibration is a method first developed in radio-astronomy to produce radio-interferometric images of an astrophysical object""

As Miguel_EA1HTA ... noted ...  (and I paraphrase ** because this is true for me too**)
**the redeeming factor is almost always the learning** while implementation comes later ...
 
72 73
John
N3AAZ
 

[SteveBz]

Here's an thread from earlier on in the year talking about my experiences in Sussex. 

And uses exactly the cantena above.

The final output was this small section of the milky way.  It would have been more if it hadn't been for the trees and house

Good luck.

Steve.

[Steve714]

Great 21cm work! Also from Sussex (East), I thought some measurements at ~3.3GHz on usual suspects (thermal (Moon)and supernova remnant(Taurus A)) might be of interest. This drift scan was made using a 1.9m diameter dish and LimeSDR receiver.  The moon was 1.4 degrees lower in the sky than the dish elevation which was set for Taurus A. Happy to provide details of system (LNAs, filters, software etc).

 

[ZiHao]

11 hours ago, Steve714 said:

Great 21cm work! Also from Sussex (East), I thought some measurements at ~3.3GHz on usual suspects (thermal (Moon)and supernova remnant(Taurus A)) might be of interest. This drift scan was made using a 1.9m diameter dish and LimeSDR receiver.  The moon was 1.4 degrees lower in the sky than the dish elevation which was set for Taurus A. Happy to provide details of system (LNAs, filters, software etc).

 

Nice observation. I think it's quite rare to see someone observing in the S band so I am interested in the details of the hardware and software used! 

[Steve714]

Hi, Thanks for that. I'll quickly write out a few details in addition to the components used so that there is some context for anyone who might be interested in this area of work. I've also attached a more representative graph of  Taurus A . This method can be used to perform drift scans on thermal sources (Sun and Moon) and supernova remnants such as Cassiopeia A, Cygnus A and Taurus A. Virgo A is probably a challenge too far as the flux density is around an order of magnitude lower than that of Taurus A.

 

Dish

1.9m diameter prime focus mesh (3mm) dish f/d=0.35 coupled to an EQ6 mount.

Circuits

Two circuits were used. The first received signals from the dish and the second with identical components was connected to a 50 ohm matched load termination and acted as a reference.

Circuit 1:- A WR229 waveguide to coaxial adapter (3.3-4.9GHz) with feedhorn and scalar ring was positioned so that the dish focal point was 0.7cm inside the feedhorn. The first low noise amplifier (Mini Circuits ZX60-63GLN+, Gain 28dB, Noise Figure 0.8dB) was connected directly to the WR229 output. A semi-flexible 50 ohm coaxial cable with sma connectors, positioned along the dish strut, connected the output to a second LNA (Avantek AWT6032, Gain 20dB). The outputs of both LNAs had attached dc blocking components.  A 3m length of high quality, heavy duty cable then delivered the signal to the receiver housing where it connected to a narrow bandpass filter (K&L X5FVSP-3316.5/E67, 3.27-3.37GHz) and then to the Limesdr Channel 1 receiver input.

Circuit 2: The reference circuit with identical coaxial lines and components to the active Circuit 1 was terminated with a 50 ohm matched load. This circuit was placed on a tripod approximately 3m from the dish and connected to Channel 2 of the LimeSDR receiver.

The receiver communicated with a high spec PC via a 15m USB3 (56bps) cable with inline amplification.

Of critical importance to the sensitivity of this system were the noise figures of the first LNAs in each circuit which should be as low as possible and the bandwidth of the receiver which should be as high as possible. The noise specs of the second LNAs are not critical.

The open source software employed for data capture was the excellent SDR_Angel with the Radio Astronomy plugin. Data analysis and presentation was performed using a program written in R.

Reference data was subtracted from Sample (Dish) data to provide results relatively free from the effects of drift in the receiver output due to temperature fluctuations. (NB this must be performed after the two datasets have been converted to linear format; the result can then be transformed back to a log format).

[Steve714]

Update:- I managed to source a couple of LNAs with a lower noise figure (~0.3dB cf 0.8dB).