superkuh,
Thanks so much for your reply. We'll take a look over the next few days.
We have a SAW filter with 65MHz width centered at 1.42 GHz surrounded by two LNA's (from Nooelec). We'll check the signal at 470 MHz to see if this is the case but we had hoped that this filter in-line would clean up the signal.
We can add another bandpass filter to the setup as you suggest, but should we filter out the signal directly from the antenna before heading into the first LNA?so instead of<ant> -- <LNA> -- <SAW> -- <LNA> -- <coax> -- <SDR>we should have:<ant> -- <filter> -- <LNA> -- <SAW> -- <LNA> -- <coax> -- <SDR>
I didn't think this signal was interference with human produced radio signals because when we turned the antenna away from the sun by 90 degrees (in both dimensions) the signal disappeared, and when the antenna was pointed straight up at the sun the signal was strongest. So does this imply that instead of making a proper Yagi antenna, we instead made a Yagi antenna that has stronger absorption at 90 degrees off axis?
I also saw your discussion on http://superkuh.com/ and realized that we didn't shield our components. I know in the "final" version we would, but just trying to get first light I thought we might skip it. Is this where the noise is coming in from?
We'll give this a try and let you know.
Thank you,
Eric
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Regards,
Raydel
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Hi Eric,
There has been a lot of good advice given already, so there is no need to get into that again. Just as something in addition, you may want to have a look at a series of articles dealing with the observation of hydrogen with small antennas and simple setups at our website:
https://astropeiler.de/beobachtungen-der-21-cm-linie-mit-einfachen-mitteln
Best regards
Wolfgang
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If you are asking about HI, than the answer is little to none. For an HI emission the Hydrogen atom must be at ground state for 10,000,000 years (on average). To be at ground state for that period, the temperature is typically under 20K.
Tom Crowley
Sent from Mail for Windows 10
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Hi Eric,
Those are terrestrial signals. Under certain conditions if the transmitters are very powerful and nearby they can get into the system, even using SAW, and in many other cases, they are just entering the system if the LNA is not shielded of even through the coax or some connector.
On Hydrogen profiling, you need a massive amount of Hydrogen to get the spectral line, so using such kind of antenna and pointing to the Sun, there will be more Solar Continuum (Solar RF noise) than actual Solar Hydrogen. You need a lot of Hydrogen, like the whole Galaxy arm to be able to get spectral monitoring.
I bet others, which are really experts can explain better.
Regards,
Raydel
On 30/06/2020 04:06, Eric Ross wrote:
> superkuh, > > Thanks so much for your reply. We'll take a look over the next few > days. > > We have a SAW filter with 65MHz width centered at 1.42 GHz surrounded > by two LNA's (from Nooelec). We'll check the signal at 470 MHz to see > if this is the case but we had hoped that this filter in-line would > clean up the signal. > > We can add another bandpass filter to the setup as you suggest, but > should we filter out the signal directly from the antenna before > heading into the first LNA? so instead of <ant> -- <LNA> -- <SAW> -- > <LNA> -- <coax> -- <SDR> we should have: <ant> -- <filter> -- <LNA> > -- <SAW> -- <LNA> -- <coax> -- <SDR> > > I didn't think this signal was interference with human produced radio > signals because when we turned the antenna away from the sun by 90 > degrees (in both dimensions) the signal disappeared, and when the > antenna was pointed straight up at the sun the signal was strongest. > So does this imply that instead of making a proper Yagi antenna, we > instead made a Yagi antenna that has stronger absorption at 90 > degrees off axis? > > I also saw your discussion on http://superkuh.com/ > <http://superkuh.com/rtlsdr.html> and realized that we didn't shield > our components. I know in the "final" version we would, but just > trying to get first light I thought we might skip it. Is this where > the noise is coming in from? > > We'll give this a try and let you know. > > Thank you, > > Eric > > On Monday, June 29, 2020 at 7:11:18 PM UTC-4, superkuh wrote: > > To me this looks like the third harmonic of 470 MHz DMR mobile radio > basestation/handsets. So they're not real signals at 1420 MHz but > they are real at ~470 Mhz. Try looking around down there to see if > you see the same thing. If it is then a high pass filter >1GHz would > help. > > -- -- You received this message because you are subscribed to the > Google Groups "Society of Amateur Radio Astronomers" group. To post > to this group, send email to sara...@googlegroups.com To > unsubscribe from this group, send email to > sara-list-...@googlegroups.com For more options, visit this > group at http://groups.google.com/group/sara-list?hl=en --- You > received this message because you are subscribed to the Google Groups > "Society of Amateur Radio Astronomers" group. To unsubscribe from > this group and stop receiving emails from it, send an email to > sara...@googlegroups.com > <mailto:...@googlegroups.com>. To view this > discussion on the web visit > https://groups.google.com/d/msgid/sara-list/7ea5fd14-32b0-4de1-888e-9260a0943101o%40googlegroups.com > <https://groups.google.com/d/msgid/sara-list/7ea5fd14-32b0-4de1-888e-9260a0943101o%40googlegroups.com?utm_medium=email&utm_source=footer>.
Eric, just a comment… the real experience is that of spending the time doing things with your daughters as involved parent and children. That is absolutely priceless! Way to go!
Larry
Pahrump, nv
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Yeah, I raised 2 boys… it takes even less to get them bored, lol. But, perhaps there is an intermediate objective that can be more easily accomplished? Ask the on list experts what would your system and the kids really do pretty easily. Anything to show some real success? I bet there is. Then to keep them interested, move up to harder stuff. Have them doing some of the math and figuring out things as well. Plotting data, STEM kinda things… But at their pace..
Me, I am at the place where your children are, lol, and I am nearly 79 years old. Still fun!
Larry
Pahrump, NV
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Eric,
The 475MHz DMR signals ARE ALLOWED to transmit a small bit of third harmonic near 1420MHz. FCC specs are per transmitter service & classification. A 100W transmitter may specify 60dB below the carrier. This would be 100uW at 1420MHz area. If it is close by, 100uW could be a pretty strong signal, even coming in the side of a your dish . If the transmitter is legal you are stuck with it.
A cleaner pattern on your antenna could reduce interference a lot, as long as you are looking well above the horizon. If your dish feed has a choke ring on it, you could move the choke ring towards the dish will narrow the pattern and under illuminate the dish. This would lose a little gain on the dish but lower interferece by a lot.
Bruce Randall
From: sara...@googlegroups.com [mailto:sara...@googlegroups.com] On Behalf Of Eric Ross
Sent: Monday, July 20, 2020 8:30 PM
To: Society of Amateur Radio Astronomers
Subject: [SARA] Re: Helping my 13 and 15 yr old daughters with home-built 21-cm telescope first-light spectra of the sun (below): is our spectra correct?
Thanks for this advice. We did see a massive clear signal at roughly 475 MHz as you suggested. We changed our location slightly, insulated the components, and re-ran multiple 5-minute scans and subtracted out a noise floor. I attached the spectra we obtained below.
On Monday, June 29, 2020 at 7:11:18 PM UTC-4, superkuh wrote:
To me this looks like the third harmonic of 470 MHz DMR mobile radio basestation/handsets. So they're not real signals at 1420 MHz but they are real at ~470 Mhz. Try looking around down there to see if you see the same thing. If it is then a high pass filter >1GHz would help.
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Good morning, Eric!
Glad you and yours are working though the telescope issues together. Solving problems is the fun part, lol. It is great to hear that your children are enthused about this! I was a manager at Boeing when I was a working cuss, and had at one time 220 scientist, engineers and technicians working for me. I always implored the different supervisors to consider that when they were interviewing applicants for open positions, to consider women engineers. Why? Well, women have a different perspective on how to solve problems and some solutions are ingenious, at times. Have your girls Learn all the math and engineering they can. Working on space programs is FUN. I barely know anything about RA but I do know about space, lol.
Headed out for a Nat Parks tour? Well, given the covid 19 problems right now finding accommodations is going to be tough, especially here in the west. Las Vegas is virtually locked down, no hotels no restaurants, etc. Or at least severely reduced in number. My wife and I are on self-imposed exile, lol, because we are, ahem, ancient, and both of us have heart issues, diabetes and some others, like me, had pneumonia a long while ago. I ring all the alarm bells. My big daily event is going out to the driveway to snag the newspaper. Otherwise I stay indoors and isolated. Us old folks are truly in a world of hurt with this disease. 80% of us who get it, pass away from it.
As to visiting a National Park near us? Well, the only thing actually close is Death Valley and truly I do not recommend that for people not from the area and used to dealing with the heat. Last week or so ago the temp over there probably at, Bad Water, was 128 degrees F. That is only 6 degrees from the highest recorded temperature ever on the entire planet. And with humidity levels at or near 1% or so, staying hydrated is a true necessity. When I was racing my Sunbeam I took it to El Mirage dry lake, in Southern CA. to be inspected and on the way home the truck temp external temp read 127 degrees. Summers are bad times here unless you are travelling on a tour bus and I would not get on one of those petri dishes with who knows what is on board with you. Not trying to discourage you but just be aware that things are and can get difficult during travel. Not sure where you would be coming from, but consider everything before heading out.
If I can assist in any way, feel free to ask. There is always a chance I might be able to help.
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