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dspira-lessons/forum/antennas/ #3
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The instructions for the horn antenna can say to use 5-1/4 inches for dimensions. Shouldn’t the instructions say 5.25 cm (=2-1/16”)? |
Yes, of course! Thanks for pointing that out. It's been fixed. |
UK based teacher here finding it hard to find an F style 1 gallon can. Any suggestions where to get one? Thanks |
If you have access to tin plate at a diy store you can make the equivalent
of one. In the US we can get them on Amazon but it is cheaper to buy a can
of paint thinner and toss it or put it into bottles. That’s what I did.
On Tue, Sep 7, 2021 at 1:35 PM Tynetenna ***@***.***> wrote:
UK based teacher here finding it hard to find an F style 1 gallon can. Any
suggestions where to get one? Thanks
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Thank you. It’ll need soldering presumably? How precise do the dimensions need to be? |
Actually you could metal tape it like the foam walls and it’ll be fine. You
can look up the dimensions of an f-can on google or I can measure mine and
let you know.
On Tue, Sep 7, 2021 at 10:33 PM Tynetenna ***@***.***> wrote:
Thank you. It’ll need soldering presumably? How precise do the dimensions
need to be?
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16.9cm x 10.5cm x 26.2cm
The 26.2 can be 26.0cm with no problem.
On Tue, Sep 7, 2021 at 10:33 PM Tynetenna ***@***.***> wrote:
Thank you. It’ll need soldering presumably? How precise do the dimensions
need to be?
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Hello Tynetenna, Neil and everyone,
Good questions concerning the size of the metal container to use
for your radio astronomy horn.
In general the needed dimensional accuracy is only about 1/20 of a wavelength,
or 1 cm, for the dimensions of the horn. The feed probe is 1/4 of a wavelength,
so the length accuracy should be a 20th of that or 21/(20*4) = .26cm
Note that the metal can was not optimum size, but was available. The optimum shape
is twice as wide as tall. The attached table shows that WR650
waveguide is used for L-band (1.42 GHz), and the size is 6.5 by 3.25 inches
which corresponds to 16.5 by 8.25 cm.
So, If you’re going to make a can, make it that size. The optimum length (depth) depends
on the material you have, but the longer the can, the more rejection of low frequency
interference you have, so I’d say at least 25cm would be good, with a little longer
being a little better.
Good Luck
Glen
Glen I Langston, Ph. D.
Galactic Astronomy Program Director
National Science Foundation
304-456-3032
[cid:57D569F0-D1BF-40C0-AE3E-8A5D4D9A5FA7]
On Sep 8, 2021, at 1:46 AM, nmaron ***@***.******@***.***>> wrote:
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16.9cm x 10.5cm x 26.2cm
The 26.2 can be 26.0cm with no problem.
On Tue, Sep 7, 2021 at 10:33 PM Tynetenna ***@***.***> wrote:
Thank you. It’ll need soldering presumably? How precise do the dimensions
need to be?
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Thanks Glen and Neil. Glen, did you say there was a table attached to your message, I’m afraid I can’t see it. Thank you very much, Guy |
Hi
Here’s the table, again. It is an image of the table.
FYI I’m a little surprised the optimum size is not exactly half a wavelength
in width. Not sure why that is, but the experts must be correct.
Glen
Also note that I actually use a cylindrical horn, 6inches in diameter == 15.2cm
The feed probe is 5cm long and 7.5cm from the end of the cylinder.
With this design we can get to a system temperature*Gain of about 150K.
I also had fairly good (but un documented) luck with building a rectangular feed
that included a wave-guide band pass filter.
***@***.***
Glen I Langston, Ph. D.
Galactic Astronomy Program Director
National Science Foundation
304-456-3032
… On Sep 8, 2021, at 4:05 PM, Tynetenna ***@***.***> wrote:
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Thanks Glen and Neil. Glen, did you say there was a table attached to your message, I’m afraid I can’t see it. Thank you very much, Guy
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Hi I just received the email I sent. It appears
that all attachments are now being removed from the emails.
This is different behavior than before.
Maybe include your email address again and I’ll re-send.
Pranav, Maybe you can fix the email exploder to have it
forward attachments.
Thanks
Glen
… On Sep 9, 2021, at 11:25 AM, Glen Langston ***@***.***> wrote:
Hi
Here’s the table, again. It is an image of the table.
FYI I’m a little surprised the optimum size is not exactly half a wavelength
in width. Not sure why that is, but the experts must be correct.
Glen
Also note that I actually use a cylindrical horn, 6inches in diameter == 15.2cm
The feed probe is 5cm long and 7.5cm from the end of the cylinder.
With this design we can get to a system temperature*Gain of about 150K.
I also had fairly good (but un documented) luck with building a rectangular feed
that included a wave-guide band pass filter.
***@***.***
Glen I Langston, Ph. D.
Galactic Astronomy Program Director
National Science Foundation
304-456-3032
> On Sep 8, 2021, at 4:05 PM, Tynetenna ***@***.***> wrote:
>
> This email originated from outside of the National Science Foundation. Do not click links or open attachments unless you recognize the sender and know the content is safe.
>
>
>
>
> Thanks Glen and Neil. Glen, did you say there was a table attached to your message, I’m afraid I can’t see it. Thank you very much, Guy
>
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Hi Glen this service is based of github issues specifically for this thread #3 Within email it seems to strip all attachments and formatting and sends a plain text. any attachments I believe can added from the issue itself via that link. I shall look into fixing this seems like a github quirk. best, |
I wonder if the horn can be constructed from fine galv "chicken" wire mesh say 15mm? It would obviously need support ribs in the corners. The foam board doesn't seem to be common in my country and mesh would have an advantage in wind. |
I think 15mm might be a little too large. Could you cover it with aluminum
foil?
Neil
On Wed, Sep 22, 2021 at 8:46 PM ZL4DK ***@***.***> wrote:
I wonder if the horn can be constructed from fine galv "chicken" wire mesh
say 15mm? It would obviously need support ribs in the corners. The foam
board doesn't seem to be common in my country and mesh would have an
advantage in wind.
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Maybe, that would certainly solve the problem. I have a 1 metre diameter solid aluminium dish I might try first. It has a feed that is supposedly OK for 1.4 to 1.8 GHz |
A 1 meter dish is a nice size. That should work well. It will depend on
your receiving electronics, but that’s not too hard either.
Neil
On Wed, Sep 22, 2021 at 9:28 PM ZL4DK ***@***.***> wrote:
Maybe, that would certainly solve the problem. I have a 1 metre diameter
solid aluminium dish I might try first. It has a feed that is supposedly OK
for 1.4 to 1.8 GHz
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I'll comment on my electronics on the Electronics forum |
I have built a small radio telescope using the DSPIRA GNU Radio-based software running on a Raspberry Pi, a Nooelec SMART SDR module, a Nooelec Sawbird LNA for the 21 cm hydrogen line, and a satellite antenna, not the DSPIRA horn antenna. The software ran correctly but I was unable to see the 21cm hydrogen bump in the spectrum plot. I am thinking that my problem is either the antenna and/or my location. I am in a densly populated city near Boston and my backyard is closely surrounded by other houses although I have a clear view of the sky. Any ideas on what could be the problem with my system would be appreciated. Here is a link to the antenna specs. https://www.amazon.com/gp/product/B005M8KU3W/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1 This antenna was used successfully by amateur radio astronomers, see this link: Thanks! Tom Consi |
Hi Tom,
Sounds like you’ve done everything right and should easily see signal in just a
few minutes.
One suggestion is to first check that their is really enough gain in your system.
The 50 Ohm termination load, will produce more signal than you will
see with your telescope, (if all goes well).
These are not too expensive, $7 for two. You can check whether your system has
sufficient gain. There should be a major increase in signal with the termination
on the input.
See how to run the tests, look at this LightWork memo:
https://github.com/WVURAIL/lightwork/blob/master/memos/LightWorkMemo028-r7-NoiseTemp.pdf
and
https://github.com/WVURAIL/lightwork/blob/master/memos/LightWork0030-r1-ATaleOfThreeLNAs.pdf
Good luck with you telescope.
Glen
PS which software did you download?
The Raspberry Pi code is completely ready to download.
It is rather specifically configured for Radio Astronomy, but anyone could build other designs
in it using Gnuradio 3.10.
It is available for download (2.2GB) at:
https://docs.google.com/document/d/1T_IJhRzMmsDWOqOOUYMyr36vEMxKXEbWL_G2tNK9Os8/edit?usp=sharing
The installation guide (pdf) is here:
https://drive.google.com/file/d/1tF6BaEj1Sabq6fJXeNpMsqcb8RStfqJs/view?usp=sharing
Hope this is useful to you.
… On May 18, 2022, at 12:31 PM, TomConsi ***@***.***> wrote:
I have built a small radio telescope using the DSPIRA GNU Radio-based software running on a Raspberry Pi, a Nooelec SMART SDR module, a Nooelec Sawbird LNA for the 21 cm hydrogen line, and a satellite antenna, not the DSPIRA horn antenna. The software ran correctly but I was unable to see the 21cm hydrogen bump in the spectrum plot. I am thinking that my problem is either the antenna and/or my location. I am in a densly populated city near Boston and my backyard is closely surrounded by other houses although I have a clear view of the sky. Any ideas on what could be the problem with my system would be appreciated.
Here is a link to the antenna specs. https://www.amazon.com/gp/product/B005M8KU3W/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
This antenna was used successfully by amateur radio astronomers, see this link:
https://www.rtl-sdr.com/cheap-and-easy-hydrogen-line-radio-astronomy-with-a-rtl-sdr-wifi-parabolic-grid-dish-lna-and-sdrsharp/
Thanks!
Tom Consi
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Hi Tom, |
Glen and ZL4DK, Thanks for the advice and the speedy respones to my post. Another question: what are the specifications of the DSPIRA horn antenna such as the gain beam pattern? I can't find that information on the DSPIRA website. Such information would be useful to compare the homemade horn to other types of antennas, in particular, dish antennas. Cheers! Tom Consi |
Hi Tom,
The main advantage the horn has over a dish is the rejection of Interference (RFI) coming
in from diffraction around the edge of the dish and the feed support. The beam shape
is pretty much lambda/diameter, so for a 2 foot diameter horn about 30 degrees wide.
I think that ZL4DK is probably correct that the difficulty of detecting the galaxy
is mainly from the loss due to the cable and the feed match, so that the galactic signal is probably there
but very, very weak. You would not see the signal unless you did the
full calibration, but would need a 10 minute average.
So, I’d consider first testing the system gain, then
look at downloading the whole PI OS and then doing a 10 minute
average, after calibration.
Good Luck
Glen
From: TomConsi ***@***.***>
Sent: Thursday, May 19, 2022 6:52 AM
To: WVURAIL/dspira-lessons ***@***.***>
Cc: Langston, Glen ***@***.***>; Comment ***@***.***>
Subject: [EXTERNAL] - Re: [WVURAIL/dspira-lessons] dspira-lessons/forum/antennas/ (#3)
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Glen and ZL4DK,
Thanks for the advice and the speedy respones to my post.
I will try the 50 Ohm termination test to see if my electronics are working correctly.
If the problem is my antenna then I will dissect the feed and try to modify it to be more efficient at 1.4GHz.
Another question: what are the specifications of the DSPIRA horn antenna such as the gain beam pattern? I can't find that information on the DSPIRA website. Such information would be useful to compare the homemade horn to other types of antennas, in particular, dish antennas.
Cheers!
Tom Consi
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Hi Tom, Regards |
Glen & David, Thanks! Tom |
Hi Tom,
I just noticed your comment about the hot load (calibrated) plot showing a straight line.
That is as it should be. The calibration method assumes the “hot” is constant value and
that any variations are due to the gain variations of the system. The hot “counts” plot
should show variation of intensity, but the deduced hot load plot (in Kelvins) will
always be a constant for any amplifier and telescope combination. The cold load calibration
plot (in Kelvins) is what is important.
Note that the calibration method measures the ratio of system temperature to gain. Since
the actual hot load system temperature is about 300 K (room temperature), the gain of your
horn/feed is 300/730 => 0.4. So the LNA amplifier equivalent noise temperature is about
140K*.4 = 57K or so. (I think).
Please email the counts plot image directly. The GITHUB mail system removes all attachments.
THanks
Glen
***@***.***
… On May 23, 2022, at 10:26 PM, TomConsi ***@***.***> wrote:
Glen & David,
I ran NsfIntegrate24.py as per the instructions in Light Work Memo 28 (rev. 7). The window only had one gain box that was set at a default of 49.6. Keeping that gain I ran a test and got a cold noise of about 140K, the hot noise was 730K but the plot was a straight line with no variation. The median was centered around the cold noise line, which showed variation. I am testing a Nooelec Smartee SDR with a permanent bias T attached to a Nooelec SawBird H1 LNA. The SDR gets very warm, could that be the cause of the high hot noise?
Is there documentation on NsfIntegrate? If so please point me to it.
Thanks!
Tom
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Hi Tom, most SDR dongles run fairly warm so I think yours will be fine. A high "Hot" temperature reading is a good thing. I am not completely familiar with the NsfIntegrate software but I think those readings suggest everything is fine. Glen will be able to answer this one better. |
Glen & David, |
Hi Tom, Regards |
Thanks Tom and David,
Please let us know how your tests work out and
your best configuration
Best regards
Glen
Glen I Langston, Ph. D.
Galactic Astronomy Program Director
National Science Foundation
304-456-3032
… On May 28, 2022, at 3:00 PM, ZL4DK ***@***.***> wrote:
This email originated from outside of the National Science Foundation. Do not click links or open attachments unless you recognize the sender and know the content is safe.
Hi Tom,
Great stuff that you've got it working. I think there are some options to improve your dish by changing the feed antenna. The feed antenna needs to have a wide enough beamwidth to look at all the dish but not too wide that it looks past the edge of the dish. Unfortunately the beamwidth is never sharply defined and all feed antennas are a compromise. For radio astronomy it is best if we compromise on a narrower beamwidth that may not see all of the dish well, but reduces picking up signals from outside of the dish edge as usually these will be noise from the hot ground behind the dish.
Your dish is slightly unusual in that it is not circular. This means we need a feed antenna that has more gain (narrower beamwidth) in one plane than the other.
I am thinking something like the "more simple collinear ant for 1090" about halfway down this page
https://www.qsl.net/g4hbt/1090%20mhz%20ant.htm
This antenna is designed for 1090MHz so the wire lengths need to be scaled back by about 30% for 1420MHz. I would suggest making this out of a single piece of wire and instead of a connector block simply solder a SMA connector at the feedpoint.
You also need to mount a reflector in front of this feed antenna so that it looks towards the dish. A rectangular piece of metal about 300mm by 100mm should be fine. This could be anything metal, but thin aluminium sheet would be best. Even aluminium foil glued to a sheet of cardboard would work. It needs to be spaced about 50mm in front of the collinear feed antenna. The whole lot then needs to be mounted at the focus point of the dish instead of the feed you have at the moment.
I am keen to try this myself and will let you know how it works out.
Regards
David
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Hi All, I was interested to discover if a very small horn can still get useful signal. A small version would be easy to weatherproof and possibly automate for rooftop operation. Without doing any math, I made a truncated horn (15 inch diagonal, 5 inch depth) and attached it to the standard F-gallon can (see attached pictures.) I ran this using the RTL-SDR combined with the NOOELEC Sawbird and got signal levels which were quite good, even in comparison with a much larger horn that I typically use. The attached data file shows signal at galactic longitude=30 deg, galactic latitude=0 deg, averaged for 600 seconds. The background temperature is higher than when I run the larger horn (300 K compared to 180 K) but the overall peak intensity is similar (~35 K) with both horns. For an automated version, I'm thinking about automating the elevation angle only, and keeping the azimuth fixed along the north-south meridian. I'm also going to experiment with a light plastic covering over the opening to keep out rain, but pass through signal (?) Dave |
Also moving only in elevation lets you map the galaxy pretty well.
If you allow the elevation axis to point the horn at the ground, you
could also automatically do calibration every so often. That would
help you make a reliable map of the Milky Way.
Best regards
Glen
Glen I Langston, Ph. D.
Galactic Astronomy Program Director
National Science Foundation
304-456-3032
… On May 31, 2022, at 2:41 PM, dave290 ***@***.***> wrote:
This email originated from outside of the National Science Foundation. Do not click links or open attachments unless you recognize the sender and know the content is safe.
Hi All,
I was interested to discover if a very small horn can still get useful signal. A small version would be easy to weatherproof and possibly automate for rooftop operation. Without doing any math, I made a truncated horn (15 inch diagonal, 5 inch depth) and attached it to the standard F-gallon can (see attached pictures.)
I ran this using the RTL-SDR combined with the NOOELEC Sawbird and got signal levels which were quite good, even in comparison with a much larger horn that I typically use. The attached data file shows signal at galactic longitude=30 deg, galactic latitude=0 deg, averaged for 600 seconds. The background temperature is higher than when I run the larger horn (300 K compared to 180 K) but the overall peak intensity is similar (~35 K) with both horns.
For an automated version, I'm thinking about automating the elevation angle only, and keeping the azimuth fixed along the north-south meridian. I'm also going to experiment with a light plastic covering over the opening to keep out rain, but pass through signal (?)
Dave
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David (ZL4DK), I built a new feed for my parabolic grid antenna. It was simply a wire cut to 5.5cm (1/2 lambda) backed by an aluminum plate 300mm x 100mm placed 50mm from the feed. The wire was mounted parallel to the long axis of the plate. My LNA was attached to the back of the plate and connected to the feed via a 6" SMA cable. A 3' SMA cable connected the signal to a wideband amplifier, a 1.420 GHZ bandpass filter and an AirSpy SDA. I saw a persistent bump at 1421.3 GHz, not sure if that was the H1 band. Unfortunately, the quality of the signal seemed to be about the same as when I had the original 2.4 GHz feed attached. I did notice, however, that the signal seemed to be stronger when my new feed was oriented parallel to the long axis of the antenna (it is a partial parabola). I mounted the new feed with 1/2" pvc pipe and included a slide coupling so I could vary the distance of the feed to the dish. I think the original feed was at 33cm. Varying the new feed +/- 5cm from that point did not do anything to the signal. I'd appreciate any comments or suggestion to improve the feed. Thanks! Tom |
Hi Tom and all,
One important thing to consider is that when looking at the Milky Way disk
the signal is strong, but looking at the Milky Way north or south poles the
signal is weak.
The Key is checking the system temperature using the hot/cold test. If
below 300 you should be able to see the Galaxy well
Regards Glen
…On Sun, Jun 5, 2022 at 2:26 PM TomConsi ***@***.***> wrote:
David (ZL4DK),
I built a new feed for my parabolic grid antenna. It was simply a wire cut
to 5.5cm (1/2 lambda) backed by an aluminum plate 300mm x 100mm placed 50mm
from the feed. The wire was mounted parallel to the long axis of the plate.
My LNA was attached to the back of the plate and connected to the feed via
a 6" SMA cable. A 3' SMA cable connected the signal to a wideband
amplifier, a 1.420 GHZ bandpass filter and an AirSpy SDA.
I saw a persistent bump at 1421.3 GHz, not sure if that was the H1 band.
Unfortunately, the quality of the signal seemed to be about the same as
when I had the original 2.4 GHz feed attached. I did notice, however, that
the signal seemed to be stronger when my new feed was oriented parallel to
the long axis of the antenna (it is a partial parabola). I mounted the new
feed with 1/2" pvc pipe and included a slide coupling so I could vary the
distance of the feed to the dish. I think the original feed was at 33cm.
Varying the new feed +/- 5cm from that point did not do anything to the
signal.
I'd appreciate any comments or suggestion to improve the feed.
Thanks!
Tom
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Hi Tom, Regards |
Tom, You may be interested in the loop feed about halfway down this page; |
Glenn & David, The zenith-looking plot was a slanted line running from about 500 (signal strength) at the low freq. end to about 600 at the high freq. end. There was no obvious H1 bump, such as seen in DSPIRA videos, using both short and long integration times. I pointed the antenna directly at the ground and the overall signal strength went DOWN (!) to about half the zenith level. There were also large bumps in the plot throughout the frequency range. The plot went back to its original shape when I pointed the antenna at zenith. With the antenna pointed at zenith, if I rotated the feed away from the center of the antenna the overall signal strength went down and then back up to the original level, like an AGC. Looking over all my past results I cannot say for sure if I have ever observed the H1 line with any version of my set-up. Needless to say this is frustrating because the DSPIRA videos and posts from others readily show the H1 line. I repeatedly used nsfintegrate100.grc to get a noise figure of my system but I found the program very inconsistent. It sometimes produced nothing after the procedure, the outputs that I have seen certainly did not resemble what is shown in the Memo 28. I am pretty much at my wits end with this. It seems that every element of my system is suspect. Please give me some suggestions as to how I can untangle this mess. I can email you plots of the results mentioned above if you give me an address. Thanks, Tom |
Hi Tom, my email address is Z***K(at)yahoo.com Regards |
Is there a way to do the "Hot" calibration without having to point the antenna directly at the ground. I find it extremely difficult to point my antenna below 0 elevation. Thanks, |
Hi Tom,
You should probably do the 50 Ohm test first, as that is easier.
That will show you whether you have sufficient gain. The signal should be
about 4 times higher with the 50h Ohm termination on, as compared to without it.
I’m afraid that the main problem will likely be interference entering antenna
via the horn support structures. I’ve sign the power level go DOWN
when pointing at the ground, if interference is dominating.
Zero degrees elevation is a problem as the interference will be worst. If there
are any hills in the area, pointing at those will be the same as pointing
at the ground, but your antenna beam is probably around 18 degrees, so
the hill would need to rise up 10 degrees to fill the beam.
Good luck!
Glen
… On Jul 11, 2022, at 11:31 AM, TomConsi ***@***.***> wrote:
Is there a way to do the "Hot" calibration without having to point the antenna directly at the ground. I find it extremely difficult to point my antenna below 0 elevation.
Can we just use a 50 ohm resistor to get the hot signal?
Thanks,
Tom
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Glen I have had a lot more success using SDR#+the IF WIndow Average plugin, compared to spectrometer_w_cal.grc running under Raspbian on a Raspberry Pi 4. I think it is because I cannot sufficiently point the antenna to ground to get a Hot calibration. Even a one meter antenna with its feed struts is a very bulky item and difficult to manipulate. SDR#+plugin uses the 50 ohm dummy load for its background calibration and does not need ground-pointing. What are the major difference between SDR#+plugin compared to spectrometer_w_cal.grc? From a signal processing point of view are they doing the same thing? Another contributor to my success is the addition of amplifiers to my signal train: I think the long-term way to go is to use a GNU Radio-based program running on a Raspberry Pi for its customizability and the potential for remote operation of the antenna. However, for simply seeing the H1 signal, and knowing that I can see it from my observing site, I find SDR#+plugin very useful. Cheers! Tom |
I have completed the building of the can, horn, LNA, and most of the cradle. I would like to test the LNA before I put the cover on. I read that the best coax cable to use for radio astronomy is 9913; however, this seems very expensive. Is 9913 what I should use or is there another type that is acceptable? Thank you. |
Hi WHRZG,
These are the parts I use to build a small radio telescope.
I also test new LNAs with them. The 1st cable is longer
than you need for an LNA test, will be needed for your telescope.
I’ve used this 3m = 10’ cable several times for the connection
between the LNA and the SDR. It’s currently $17 on Amazon
XRDS -RF 10ft SMA Male to SMA Female Coax Extension Cable,
50 Ohm KMR240 Low Loss SMA Coax Coaxial Cable with SMA:
https://www.amazon.com/dp/B08LMSZW73
I combine this with a short 15cm, 8in semi-rigid
cable inside the weather proof container. This is $7 on Amazon.
DHT Electronics 2pcs 150mm Antenna Extension Cable SMA Male to SMA Male Antennae
Adapter Semi Flexible 0.141” RG402
https://www.amazon.com/dp/B07CZ34MHZ
The 50 Ohm load will go directly on the input to the LNA.
These are $8 on Amazon.
Pack of 2 SMA Male Adapter 1W DC- 3.0GHz coaxial Terminator Termination
Loads 50 ohm RF Coax Adapter Connector
https://www.amazon.com/YOTENKO-coaxial-Terminator-Termination-Connector/dp/B07TQ5J5C2
Here are two guides to testing your LNA effective temperature:
https://github.com/WVURAIL/lightwork/blob/master/memos/LightWorkMemo028-r7-NoiseTemp.pdf
https://github.com/WVURAIL/lightwork/blob/master/memos/LightWork0030-r1-ATaleOfThreeLNAs.pdf
Good Luck!
Glen
… On Aug 22, 2022, at 1:38 PM, whrzg ***@***.***> wrote:
I have completed the building of the can, horn, LNA, and most of the cradle. I would like to test the LNA before I put the cover on. I read that the best coax cable to use for radio astronomy is 9913; however, this seems very expensive. Is 9913 what I should use or is there another type that is acceptable? Thank you.
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Thank you very much Glen!
Bill
… On Aug 23, 2022, at 8:03 AM, Glen Langston ***@***.***> wrote:
Hi WHRZG,
These are the parts I use to build a small radio telescope.
I also test new LNAs with them. The 1st cable is longer
than you need for an LNA test, will be needed for your telescope.
I’ve used this 3m = 10’ cable several times for the connection
between the LNA and the SDR. It’s currently $17 on Amazon
XRDS -RF 10ft SMA Male to SMA Female Coax Extension Cable,
50 Ohm KMR240 Low Loss SMA Coax Coaxial Cable with SMA:
https://www.amazon.com/dp/B08LMSZW73
I combine this with a short 15cm, 8in semi-rigid
cable inside the weather proof container. This is $7 on Amazon.
DHT Electronics 2pcs 150mm Antenna Extension Cable SMA Male to SMA Male Antennae
Adapter Semi Flexible 0.141” RG402
https://www.amazon.com/dp/B07CZ34MHZ
The 50 Ohm load will go directly on the input to the LNA.
These are $8 on Amazon.
Pack of 2 SMA Male Adapter 1W DC- 3.0GHz coaxial Terminator Termination
Loads 50 ohm RF Coax Adapter Connector
https://www.amazon.com/YOTENKO-coaxial-Terminator-Termination-Connector/dp/B07TQ5J5C2
Here are two guides to testing your LNA effective temperature:
https://github.com/WVURAIL/lightwork/blob/master/memos/LightWorkMemo028-r7-NoiseTemp.pdf
https://github.com/WVURAIL/lightwork/blob/master/memos/LightWork0030-r1-ATaleOfThreeLNAs.pdf
Good Luck!
Glen
> On Aug 22, 2022, at 1:38 PM, whrzg ***@***.***> wrote:
>
>
> I have completed the building of the can, horn, LNA, and most of the cradle. I would like to test the LNA before I put the cover on. I read that the best coax cable to use for radio astronomy is 9913; however, this seems very expensive. Is 9913 what I should use or is there another type that is acceptable? Thank you.
>
> —
> Reply to this email directly, view it on GitHub, or unsubscribe.
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Hi Tom,
Your system design sounds fine, but I’m wondering if your signal is dominated by interference in and out of band. The main advantage a horn has is very low susceptibility to interference.
It sounds like the software is running, which is very good, as that is often a big stumbling block.
The first test I would do is to run the 50OHm load test to make sure the amplifier gains and cables are all good. See:
https://github.com/WVURAIL/lightwork/blob/master/memos/LightWorkMemo028-r7-NoiseTemp.pdf
I’ve put together a video set for building the simplest possible horn that works pretty well.
Since you have all the hardware already the extra cost of the pail is only about $25. Then
you can compare these results to see how much RFI your environment has.
Here’s how to build a small horn telescope in a few hours.
https://www.youtube.com/playlist?list=PLFMYhHhJW1VDYESTcHJIiwNbRQXWpFlyF
Glen
… On Jul 7, 2022, at 3:09 PM, TomConsi ***@***.***> wrote:
Glenn & David,
I have built an RF Ham Design 1m mesh antenna with their "Radio Astronomy" helix feed (1400 - 1427MHz). The antenna is directly connected to a GPIO LNA filtered for the hydrogen line, that feeds an AirSpy SDR. I power the LNA with an external supply, I do not use the AirSpy bias Tee. I also have a DC block between the SDR and the LNA. I am running spectrometer_w_cal.grc on a Raspberry Pi with 8GB ram and the Raspbian operating system. I pointed the antenna at zenith at a time of day (11:50am EDT) when a wisp of the Milky Way was crossing zenith. I used 400ms for short averaging and 10s for long averaging. I did not calibrate the system. Here is what I observed:
The zenith-looking plot was a slanted line running from about 500 (signal strength) at the low freq. end to about 600 at the high freq. end. There was no obvious H1 bump, such as seen in DSPIRA videos, using both short and long integration times.
I pointed the antenna directly at the ground and the overall signal strength went DOWN (!) to about half the zenith level. There were also large bumps in the plot throughout the frequency range. The plot went back to its original shape when I pointed the antenna at zenith.
With the antenna pointed at zenith, if I rotated the feed away from the center of the antenna the overall signal strength went down and then back up to the original level, like an AGC.
Looking over all my past results I cannot say for sure if I have ever observed the H1 line with any version of my set-up. Needless to say this is frustrating because the DSPIRA videos and posts from others readily show the H1 line.
I repeatedly used nsfintegrate100.grc to get a noise figure of my system but I found the program very inconsistent. It sometimes produced nothing after the procedure, the outputs that I have seen certainly did not resemble what is shown in the Memo 28.
I am pretty much at my wits end with this. It seems that every element of my system is suspect. Please give me some suggestions as to how I can untangle this mess.
I can email you plots of the results mentioned above if you give me an address.
Thanks,
Tom
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Glen
Do you think the bump I am seeing at 421.3 ghz is the H1 line? There doesn’t seem to be much directionality in the signal. I think my satellite grid antenna is the weak link in the system. Is there anyway to test the antenna?
Regards
Tom
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________________________________
From: Glen Langston ***@***.***>
Sent: Sunday, June 5, 2022 6:44:14 PM
To: WVURAIL/dspira-lessons ***@***.***>
Cc: Consi, Tom ***@***.***>; Comment ***@***.***>
Subject: Re: [WVURAIL/dspira-lessons] dspira-lessons/forum/antennas/ (#3)
Hi Tom and all,
One important thing to consider is that when looking at the Milky Way disk
the signal is strong, but looking at the Milky Way north or south poles the
signal is weak.
The Key is checking the system temperature using the hot/cold test. If
below 300 you should be able to see the Galaxy well
Regards Glen
On Sun, Jun 5, 2022 at 2:26 PM TomConsi ***@***.***> wrote:
David (ZL4DK),
I built a new feed for my parabolic grid antenna. It was simply a wire cut
to 5.5cm (1/2 lambda) backed by an aluminum plate 300mm x 100mm placed 50mm
from the feed. The wire was mounted parallel to the long axis of the plate.
My LNA was attached to the back of the plate and connected to the feed via
a 6" SMA cable. A 3' SMA cable connected the signal to a wideband
amplifier, a 1.420 GHZ bandpass filter and an AirSpy SDA.
I saw a persistent bump at 1421.3 GHz, not sure if that was the H1 band.
Unfortunately, the quality of the signal seemed to be about the same as
when I had the original 2.4 GHz feed attached. I did notice, however, that
the signal seemed to be stronger when my new feed was oriented parallel to
the long axis of the antenna (it is a partial parabola). I mounted the new
feed with 1/2" pvc pipe and included a slide coupling so I could vary the
distance of the feed to the dish. I think the original feed was at 33cm.
Varying the new feed +/- 5cm from that point did not do anything to the
signal.
I'd appreciate any comments or suggestion to improve the feed.
Thanks!
Tom
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Hi Tom, |
Hi Tom and ZL4DK,
While I agree you might be able to detect the Sun with radio telescopes, my experience is that
it is not easy. With a 3 foot diameter radio telescope working at 1420. MHz the Sun adds about 4 Kelvin
to the 100 to 200 Kelvin system temperature. So only 2 to 4 % intensity variation. Gain variations
this large occur over a few hours with most amplifier SDR combinations, so the On-Off the sun observations
must be done fairly quickly and also must keep the telescope “elevation” about the same.
Good Luck!
Glen
From: ZL4DK ***@***.***>
Sent: Tuesday, October 11, 2022 5:57 AM
To: WVURAIL/dspira-lessons ***@***.***>
Cc: Langston, Glen ***@***.***>; Comment ***@***.***>
Subject: [EXTERNAL] - Re: [WVURAIL/dspira-lessons] dspira-lessons/forum/antennas/ (#3)
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Hi Tom,
you should easily be able to detect the sun with your setup. During the day point your antenna towards the sun and the whole spectrum should rise significantly. You should be able to compare this with the signal level you receive when pointing away from the sun.
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Good Afternoon |
These are still missing, would be great to have access to them. |
Thanks John,
Very sorry for the delay. I've actually been working very hard on documentation.
This year's Green Bank Observatory have created videos of their assembly of a new
horn radio telescope.
Will try to get this done next week.
Best regards
Glen
…________________________________
From: John Scherer ***@***.***>
Sent: Wednesday, July 24, 2024 4:40 PM
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Cc: Langston, Glen ***@***.***>; Comment ***@***.***>
Subject: [EXTERNAL] - Re: [WVURAIL/dspira-lessons] dspira-lessons/forum/antennas/ (#3)
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These are still missing, would be great to have access to them.
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Awesome, thanks Glen. Question for you, would it be possible to do Interferometry with the SDR's in different physical locations? |
Antennas Forum – Digital Signal Processing in Radio Astronomy - Lessons Portal
Lots of lessons
https://wvurail.org//dspira-lessons/forum/antennas/
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