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Carl Reade

Anyone doing hydrogen line observing?

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52 minutes ago, Coto said:

For the 1420 MHz bandpass filter, I've found this one: http://adsbfilter.blogspot.com/2015/06/hydrogen-line-1420-mhz-filter.html [20 EUR + 7 EUR shipping (total = 30.75 USD)]. I think it's a pretty good deal for its quality/price.

Now that I've taken care of the filtering, I'm curious as to which LNA would be more ideal for me: http://g8fek.com/uploads/9/4/4/3/94435411/sba13001700-box_a5.pdf or http://g8fek.com/uploads/9/4/4/3/94435411/sba12501450-sma_a5.pdf ? They seem to share similar characteristics (in terms of NF and Gain), but I'm not sure what's best if I'll be looking to pick up HI emissions only (1420 MHz) (and won't care about other frequencies unless I switch up the feed etc.). Both LNAs cost £145.00 + £9.50 Shipping (total = £154.5 = 173 EUR = 197 USD).

As for RAS, I don't think I'm getting anything from them any time soon. The $199 LNA (with NF=0.29db) might have been worth it if the shipping was not $45 (!) to Greece and their customer support was a bit more helpful.

Hi I have the 1300/1700 one. It incorporates the OH line band at 1.6Ghz. the other incorporates the amateur band at 23cm for moon bounce communication at 1.2Ghz. that's the only real difference.

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1 minute ago, Carl Reade said:

Hi I have the 1300/1700 one. It incorporates the OH line band at 1.6Ghz. the other incorporates the amateur band at 23cm for moon bounce communication at 1.2Ghz. that's the only real difference.

Oh, right, I had forgotten about the OH line-observation possibilities. Guess the 1300/1700 one will be my choice then!

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My next step on the project is to add a total power element to the scope. I have an old RA project from years ago which has a simple diode detector and a DC amplifier circuit. My plan is to bypass the dongle and connect the dish/ amp chain to this and and an ADC to measure the voltage and see what results I get.

I could be way off the method. If it works it will add a bit more capability.

Carl

 

IMG_20181122_094931.jpg

IMG_20181122_094907.jpg

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I didn't really understand what you're trying to do. What is a "total power element"? Are you trying to replace the SDR with a different type of receiver? What more kind of "capabilities" will you be able to achieve with the new type of receiver? The only thin I can think of is wave amplitude, phase and waveform detection, but I don't think that's what you're trying to achieve (no "oscilloscope"/"spectrum analyzer" mentioned).

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37 minutes ago, Coto said:

I didn't really understand what you're trying to do. What is a "total power element"? Are you trying to replace the SDR with a different type of receiver? What more kind of "capabilities" will you be able to achieve with the new type of receiver? The only thin I can think of is wave amplitude, phase and waveform detection, but I don't think that's what you're trying to achieve (no "oscilloscope"/"spectrum analyzer" mentioned).

Basically the same as what you do with a satellite meter and LNB.

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5 minutes ago, Carl Reade said:

Basically the same as what you do with a satellite meter and LNB.

Why would you want to do that? Capturing the data with an SDR offers a lot more benefits. Are you trying to do this for i.e. presenting the instrument to i.e. a school, where you can't really bring an SDR, a laptop etc. (so the dish and backend is more compact)?

Edited by Coto

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Could be useful when fine tuning the system/dish to  optimise it perhaps?  Integrating a continuum signal over a wide bandwidth 

Robin 

Edited by robin_astro

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2 hours ago, robin_astro said:

Could be useful when fine tuning the system/dish to  optimise it perhaps?  Integrating a continuum signal over a wide bandwidth 

Robin 

Yep nail on the head!

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6 hours ago, Coto said:

Why would you want to do that? Capturing the data with an SDR offers a lot more benefits. Are you trying to do this for i.e. presenting the instrument to i.e. a school, where you can't really bring an SDR, a laptop etc. (so the dish and backend is more compact)?

It is for the current setup which is not portable. It is a continuum addon. I should be able to work out beam width etc. I should be able to add a two way splitter and read continuum, spectrum at the same time using SDR Sharp and an ADC program. 

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I wonder if  any geostationary satellites put out signals near the radio astronomy bands (intentionally or otherwise) which could be useful as beacons, avoiding the need to track a target while trying to optimise a setup. A quick google found this reference to L band downlinks used for satphones for example.

http://www.satsig.com/cgi-bin/yabb2611/YaBB.pl?num=1506439429

Robin

 

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13 hours ago, robin_astro said:

I wonder if  any geostationary satellites put out signals near the radio astronomy bands (intentionally or otherwise) which could be useful as beacons, avoiding the need to track a target while trying to optimise a setup. A quick google found this reference to L band downlinks used for satphones for example.

http://www.satsig.com/cgi-bin/yabb2611/YaBB.pl?num=1506439429

Robin interesting idea if I get a chance I will have a hunt with the spectrum analyser.

 

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@Carl Reade I'm trying to build a 1420 MHz Can Feed. Do you know the dimensions of the copper wire probe? A tutorial suggests I cut the length to 1/4 * λ = 1/4 * 21cm = approx. 5.25 centimeters. But it doesn't say anything about the thickness (diameter) of the copper wire. Does it not matter what diameter the copper wire has? Does thinner or thicker mean better, or what is exactly should I look for?

Also, do you know of a way to estimate the operating frequency range of the probe if it's cut for 1420 MHz?

Edited by Coto

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3 hours ago, Coto said:

@Carl Reade I'm trying to build a 1420 MHz Can Feed. Do you know the dimensions of the copper wire probe? A tutorial suggests I cut the length to 1/4 * λ = 1/4 * 21cm = approx. 5.25 centimeters. But it doesn't say anything about the thickness (diameter) of the copper wire. Does it not matter what diameter the copper wire has? Does thinner or thicker mean better, or what is exactly should I look for?

Also, do you know of a way to estimate the operating frequency range of the probe if it's cut for 1420 MHz?

Hi the rule for antennas,

The thicker it is the more broadband it is.

Unfortunately I don't have test gear to test the operation bandwidth but all antennas will pick up out of cut band to some degree but be most effective at their cut frequency.

Here's a pic of the SETI specs.

 

probe.gif

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36 minutes ago, Carl Reade said:

The thicker it is the more broadband it is.

So, should I just pick the thickest copper wire I have laying around, or is there a limit to what an N-type connector can "handle"? Also, what frequency range should I expect from a 1/8" thick copper wire probe?

Edited by Coto

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7 minutes ago, Coto said:

So, should I just pick the thickest copper wire I have laying around, or is there a limit to what an N-type connector can "handle"? Also, what frequency range should I expect from a 1/8" thick copper wire probe?

No thinner will be better for a specific frequency. Why would you want broadband for H line as you are filtering specifically for it?

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I see. So, is the ‘1/8”’ mark a thickness maximum they’d recommend? If I’ve got very thin copper wire (d<<1/8”), should I use that instead? (I’m guessing no cause then I risk the frequency range being too narrow which may or may not cut Doppler-shifted emissions - we don’t have any wire-thickness vs freq. range graphs to be sure so I would just go with SETI league’s recommendation.)

Edited by Coto

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On 21/11/2018 at 18:17, Coto said:

AS, I don't think I'm ge

Recommendation for an useful radio-astronomy book where i can find all necessary informations relating to the construction of an antenna that can read signals from non-organic hydrogen!!!

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9 hours ago, Coto said:

I see. So, is the ‘1/8”’ mark a thickness maximum they’d recommend? If I’ve got very thin copper wire (d<<1/8”), should I use that instead? (I’m guessing no cause then I risk the frequency range being too narrow which may or may not cut Doppler-shifted emissions - we don’t have any wire-thickness vs freq. range graphs to be sure so I would just go with SETI league’s recommendation.)

I suspect they just chose 1/8" tube because it slipped nicely over the end of the N connector pin making a robust construction.

Robin

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18 hours ago, Coto said:

 A tutorial suggests I cut the length to 1/4 * λ = 1/4 * 21cm = approx. 5.25 centimeters.

Are you planning to tune the antenna by trimming the length?  If not, 5.25cm will not give the correct resonant frequency. It will be too long. What you need is the electrical length to be 1/4 wavelength which will be shorter than this, depending on a number of factors.  Unless you are planning on tuning to resonance I would advise constructing a feed to the exact specification and dimensions of a known design.

Robin

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3 hours ago, robin_astro said:

Are you planning to tune the antenna by trimming the length?  If not, 5.25cm will not give the correct resonant frequency. It will be too long. What you need is the electrical length to be 1/4 wavelength which will be shorter than this, depending on a number of factors.  Unless you are planning on tuning to resonance I would advise constructing a feed to the exact specification and dimensions of a known design.

 Robin

This is the design I found (from simple_ra documentation) :

Screen_Shot_2018-11-25_at_12.52.11_AM.pn 

I will be tuning to the frequency using an RTL-SDR (not trimming the wire and all that odd stuff). Would you say this feed design is reliable enough for me? If so, what would you say its frequency range would be? ±50 MHz?

Also, I'm not sure what you mean by "electrical length". I find some info online, but how should I translate all this to my own design? I would just follow this guide ^. I've never heard of "electrical length", all they mention is a length I should cut the copper wire to and use it as a probe.

Thanks!

Edited by Coto

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22 minutes ago, Coto said:

 

Also, I'm not sure what you mean by "electrical length".

 

https://en.wikipedia.org/wiki/Electrical_length

the probe needs to be 1/4 wavelength long but this is not the same distance as in free space 

The correction factor depends on several factors which are difficult to predict accurately, hence the need to trim the antenna element to length or use the figure established  for a given design. For example the particular Seti feed design posted has a probe length of 4.6cm compared with your calculated free air 1/4 wavelength of 5.25cm

From wikipedia

The electrical length of an antenna element is, in general, different from its physical length[better source needed] [4] [5][6] For example, increasing the diameter of the conductor, or the presence of nearby metal objects, will decrease the velocity of the waves in the element, increasing the electrical length.[7][8]

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Firstly, I'm not following the SETI design because that is a choke feed and it seems harder to build than the one provided by the simple_ra documentation. And I've kind of got the hang of what electrical length is, but my question still remains: what length should I cut the copper to? 

26 minutes ago, robin_astro said:

the probe needs to be 1/4 wavelength long but this is not the same distance as in free space 

I guess 1/4 * λ, but I don't understand what you mean by "the same distance as in free space". What does "free space" mean? And why should I care about all this? Isn't my goal to just cut the copper to the proper length? Are you trying to explain that electrical length is affected by the diameter of the copper wire probe? If so, I still don't have enough experience to come up with "ideal" copper diameter lengths, so, shouldn't I just go with 1/8 inches (since that has been done before and is the safest option)?

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45 minutes ago, Coto said:

Firstly, I'm not following the SETI design because that is a choke feed and it seems harder to build than the one provided by the simple_ra documentation. And I've kind of got the hang of what electrical length is, but my question still remains: what length should I cut the copper to? 

I guess 1/4 * λ, but I don't understand what you mean by "the same distance as in free space". What does "free space" mean? And why should I care about all this? Isn't my goal to just cut the copper to the proper length? Are you trying to explain that electrical length is affected by the diameter of the copper wire probe? If so, I still don't have enough experience to come up with "ideal" copper diameter lengths, so, shouldn't I just go with 1/8 inches (since that has been done before and is the safest option)?

Antenna theory is a complicated subject and all antennas are a compromise none are perfect. Basically your attempting to get a 50 ohm match from antenna to feed line to receiver. Two sizes I have come across is 4.8 cm and 4.6 cm length and 7mm thickness.

The SETI choke is an add-on to improve S/N so not absolutely necessary but an improvement you could add later.

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@Carl Reade LNA arrived, all looks good. Still waiting on a few more things.

I just ordered this in-line amp (I ordered 2pcs): https://www.ebay.com/itm/Satellite-20dB-In-line-Amplifier-950-2150MHZ-Signal-Booster-For-Antenna-AE/382605486101?hash=item5915106815:m:mU717aqYcmk_Qtp-xdJxoQw:rk:1:pf:0

What connectors did you use to connect the LNA's SMA port to the in-line amp's RG-6 connector? I couldn't find a way that allows me to do apply a single connector (I assume you used more than one?).

Also, for the feed, which connector did you use? N-type or something? And how did you connect it to the LNA?

Edited by Coto

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