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Carl Reade

Anyone doing hydrogen line observing?

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2 hours ago, Coto said:

@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?

Hi you won't be disappointed with the LNA.

Ok there are a lot of connectors so I will start from the feed.

Assuming you are using an N type probe at the feed. (Female)

SMA male to N male adapter (LNA input), SMA male to F female (LNA output) then F male to coax (2 meter of coax to get to rear of dish) then F male, then line amp, back to back F male, then line amp, then F male to coax (15 meters), then F male to DC inserter.

(I placed the two line amps inside the mounting pole for convenience only the LNA is connected directly t the dish feed)

Carl

 

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Thanks Carl,

Please confirm I've picked everything correctly:

1 hour ago, Carl Reade said:

 Assuming you are using an N type probe at the feed. (Female)

I haven't built the feed yet, but I'm looking forward to getting two connectors of this: https://www.ebay.com/itm/N-type-female-jack-RF-COAX-connector-4-hole-panel-mount-with-solder-cup-chassis/152049939697?hash=item2366e1f4f1:g:TnYAAOSw-RRXC0pi:rk:3:pf:0

 

1 hour ago, Carl Reade said:

SMA male to N male adapter (LNA input)

https://www.ebay.com/itm/SMA-Male-to-N-Type-Male-Jumper-Plug-RF-Adapter-Router-Link-Cable-Connector/191853422040?hash=item2cab5ae5d8:g:bkUAAOSw0JpV3SO1:rk:1:pf:0

 

1 hour ago, Carl Reade said:

SMA male to F female (LNA output)

https://www.ebay.com/itm/F-Female-Jack-to-SMA-Male-Plug-Straight-RF-Coax-Coaxial-Connector-Adapter-IN/283052461595?hash=item41e73dce1b:g:HuQAAOSw3mdZcbz1 (This one seems to match the name but not the looks (looking at the in-line amps they seem to both be female?))

 

1 hour ago, Carl Reade said:

then F male to coax (2 meter of coax to get to rear of dish) then F male

https://www.ebay.com/itm/LOT-RF-Antenna-CATV-TV-FM-F-Male-to-PAL-Male-Jack-Plug-Coax-Connector-Adapter/112928596636?hash=item1a4b11a29c:m:m781-_KV5_k6eh4pjef2J7w:rk:4:pf:0 (I already have coaxial cable, so I'll just get 2pcs of the F male connectors (how many ohms is this rated for and what kind of coax cable should I use?))

 

1 hour ago, Carl Reade said:

back to back F male

Isn't the previous thing ^ back-to-back F male too?


Looks like I'll need to calculate how many F males I'll need...

1 hour ago, Carl Reade said:

then F male to DC inserter.

I'll use SMA since my Bias Tee (aka The HackRF Killer) has an SMA port. Should be able to power the LNA and the 2 in-line amps by itself, right? Specifications of the bias tee can be found here: https://www.ebay.com/itm/RF-Divider-Biaser-Bias-Tee-10MHz-6GHz-for-HAM-radio-RTL-SDR-LNA-Amplifier-50VDC/113170701206?epid=21021845279&hash=item1a597fdb96:g:9Q0AAOSwvmxbWqtq

Edit: Can I power the entire chain using the LNA's power supply clips, or will that only power the first-stage LNA?

 

Thanks!

Edited by Coto

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2 hours ago, Coto said:

Thanks Carl,

Please confirm I've picked everything correctly:

I haven't built the feed yet, but I'm looking forward to getting two connectors of this: https://www.ebay.com/itm/N-type-female-jack-RF-COAX-connector-4-hole-panel-mount-with-solder-cup-chassis/152049939697?hash=item2366e1f4f1:g:TnYAAOSw-RRXC0pi:rk:3:pf:0

 

https://www.ebay.com/itm/SMA-Male-to-N-Type-Male-Jumper-Plug-RF-Adapter-Router-Link-Cable-Connector/191853422040?hash=item2cab5ae5d8:g:bkUAAOSw0JpV3SO1:rk:1:pf:0

 

https://www.ebay.com/itm/F-Female-Jack-to-SMA-Male-Plug-Straight-RF-Coax-Coaxial-Connector-Adapter-IN/283052461595?hash=item41e73dce1b:g:HuQAAOSw3mdZcbz1 (This one seems to match the name but not the looks (looking at the in-line amps they seem to both be female?))

 

https://www.ebay.com/itm/LOT-RF-Antenna-CATV-TV-FM-F-Male-to-PAL-Male-Jack-Plug-Coax-Connector-Adapter/112928596636?hash=item1a4b11a29c:m:m781-_KV5_k6eh4pjef2J7w:rk:4:pf:0 (I already have coaxial cable, so I'll just get 2pcs of the F male connectors (how many ohms is this rated for and what kind of coax cable should I use?))

 

Isn't the previous thing ^ back-to-back F male too?


Looks like I'll need to calculate how many F males I'll need...

I'll use SMA since my Bias Tee (aka The HackRF Killer) has an SMA port. Should be able to power the LNA and the 2 in-line amps by itself, right? Specifications of the bias tee can be found here: https://www.ebay.com/itm/RF-Divider-Biaser-Bias-Tee-10MHz-6GHz-for-HAM-radio-RTL-SDR-LNA-Amplifier-50VDC/113170701206?epid=21021845279&hash=item1a597fdb96:g:9Q0AAOSwvmxbWqtq

Edit: Can I power the entire chain using the LNA's power supply clips, or will that only power the first-stage LNA?

 

Thanks!

All correct bar f connector male and back to back. 

Here is an f connector (male) and a back to back. (Pictures)

The coax is 75 Ohm either RG6 or better WF100.

Ref the LNA, the outer lugs will only power it. The line amps need power via the coax. I cannot see the current rating of the bias tee to know wether it will run all three amplifiers.

 

pwd_ba122.jpg

f-connector.jpg

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Sorry, I'm a bit confused. I've figured out how to connect the copper wire probe (antenna) to the N-type connector, the N-type connector to the LNA (via the SMA Male to N-Type Male), the LNA to the bandpass filter (via an SMA male to male), but I'm not sure how to connect the bandpass filter (SMA male end) to the in-line amplifiers (and them to the SDR). I think my misunderstanding has to do with F Type vs PAL Type difference and what the ports of the in-line amplifiers are.

 

Also, based on the SETI dimensions, I made this feed design: Screen_Shot_2018-12-11_at_9.04.07_PM.png

 

I am expecting the final product to look like this:

425144134f204b6130a777a5822732d7.png

 

Do the dimensions look good? How close to the listed dimensions do you think it actually needs to be? I've found an aluminium tube* with a 15cm diameter, but I'm not sure if it's too small.

 

*What should the feed be made out of? Will any aluminium do?

Thanks!

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Personally I would not place the filter at the LNA as it is already filtered. 

I am not sure what current or voltage they can take if your powering up the coax as it will be inline.

I would place the filter next to the SDR as last in the chain and therefore no volts or current to worry about as it's on the RF Side of the bias T.

As the filter is SMA male you need to convert them to F type to connect to the coax. So you will need two SMA female to F female then F connectors on the coax will screw on at each end of it. 

As the line amps are already female F. You just need F connectors on the coax to connect them.

Ref the feed horn not critical as long as your talking within a few mm here and there. Any aluminium will do as long as it is robust enough and not flexing in the wind.

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I'll look for those connectors you mentioned, thanks!

Now, you'll notice I have added two copper wire probes on my diagram ^. This is for receiving signal from both polarization "angles" (both horizontal & vertical polarization). With a single probe, I'd lose a lot of signal and sensitivity. To combine the two signals, I have two ways:

1) Get two LNAs and then combine the signals together, or

2) Get an SMA Splitter (will this work? https://www.ebay.com/itm/SMA-Maschio-a-due-SMA-femmina-Triple-T-RF-Adattatore-connettore-3-vie-Split-L7H7/253248470740?hash=item3af6c8fed4:g:TvQAAOSw~QRaAtRx:rk:7:pf:0 ) and combine the two signals together, and then forward the combined signal into the LNA.

 

I'll favor the second one because it is cheaper (I'll just need a splitter and a tiny SMA extender). Will this work?

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Signals from natural sources are generally randomly polarised I assume your looking for circular polarization which will require the two probes to be matched and phased.

Or use a helix feed.

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1 hour ago, Carl Reade said:

Signals from natural sources are generally randomly polarised I assume your looking for circular polarization which will require the two probes to be matched and phased.

 Or use a helix feed.

 

Yes, they are randomly polarized, but if I only have a single vertical probe, and the incoming wave has a 45 deg polarization "angle", the probe will only absorb 50% strength. With an additional probe placed 90 degrees (horizontally placed), that becomes a total power of 50%+50% = 100%, so I don't lose any signal strength due to polarization angle.

Edited by Coto

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36 minutes ago, Coto said:

 

Yes, they are randomly polarized, but if I only have a single vertical probe, and the incoming wave has a 45 deg polarization "angle", the probe will only absorb 50% strength. With an additional probe placed 90 degrees (horizontally placed), that becomes a total power of 50%+50% = 100%, so I don't lose any signal strength due to polarization angle.

It's not that simple. If that were the case all feed horns would be designed that way. They need to be properly  phased or you will end up with not even 50% at all hence circular polarization covers both horizontal and vertical equally.

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These are just three designs similar to my idea (I could probably find more if I looked deeper):

1) http://www.millitech.com/MMW-Antenna-DualPolHorn.htm


2)

800px-LNB_dissassembled.JPG

 

3)

b374182465d931755dac2d970714db07.png

 

Originally, the recommendation came from a professional radio astronomer (who's "specialty" is wave polarization). While he isn't a feed/antenna expert, I ended up finding this design being used in other feed horns online (like the above), so I got more confidence in this design.

Just to be clear, I'm not looking to detect circular polarization, only horizontal, vertical and the "angles in-between".

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The first one doesn't give what you connect it to?

The second is a satellite LNB which all have two probes but only one used at a time when the satellite box switches between horizontal or vertical.

The last I haven't seen.

I still think phasing is involved for it to work correctly. 

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Okay, I referred to the professional and you're right - phasing will indeed be a problem, causing weird polarization effects etc., so I'll have to "abandon" the idea of combining the two signals in series (unless you have some other way of combining them without getting an extra LNA, filter, SDR etc.).

Now I'm waiting for everything to arrive so I can get started :)

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38 minutes ago, Coto said:

Okay, I referred to the professional and you're right - phasing will indeed be a problem, causing weird polarization effects etc., so I'll have to "abandon" the idea of combining the two signals in series (unless you have some other way of combining them without getting an extra LNA, filter, SDR etc.).

Now I'm waiting for everything to arrive so I can get started 

I would go with a single probe first get up and running then all improvement can be added later. I will be looking to see if I can improve mine.

While you waiting on the bits you could practice with the software your going to use. I found it a learning curve as well but it's half the system ?

From SETI site,


Construction details of the quarter-wavelength coaxial probe, which serves as the interface between the cylindrical waveguide feedhorn and the feedline (or antenna-mounted low-noise amplifier). The flange-type coaxial connector is mounted through the side of the cylindrical waveguide at the specified dimension, and receives a type N coaxial connector or adapter. For circular polarization, two such probes may be mounted 90 degrees apart on the feedhorn, and their outputs combined 90 degrees out of phase electrically by using a phase-quadrature hybrid coupler.

 

Click on thumbnail to 
Edited by Carl Reade

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Just got the dish!

image0.jpg

It's an offset dish.

- Major (horizontal) diameter: 160cm

- Minor (vertical) diameter: 150cm (therefore collecting_area = pi*(150/2)^2 = 17,671.4 sq. cm = 1.76 sq. m)

- The widest hole size is 5 cm (measured at the very left/right edges of the dish). Getting closer to the center that length decreases to maybe around 3 cm.

What would the dish's maximum collecting frequency be? c (m/s) / 0.05 (m) = 5 995 849 160 Hz = about 6 GHz?

The dish came in a bit dusty (grabbing it and looking at your hand will make you think you just grabbed white chalk!), but not a problem considering I only paid €50 for it! Looking forward to cleaning it with some water and cloth.

 

What do you think of the smoothness of the reflecting surface? Each bar looks like a cylinder bent into the shape of a parabola. Hopefully the smoothness won't affect the antenna's gain significantly.

image0.jpg

 

image0.jpg

 

Now I'm just trying to see how I can attach the arm feed to the dish (it didn't come with the dish ?, so I'll need to build one from scratch).

One last question: I see the holes are (up to) 5cm wide, but why are the holes not "filled" on the other axis? Does this indicate that only signals with the "right" polarization angle will be reflected?

Thanks!

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Hi what was the dish advertised as? It looks like a centre pole fed type.

The bars will probably act as a polarised filter.

I would be concerned about the spacing. To be efficient 1/10 of a wavelength or less is used. The other thing is the feed will pickup ground noise when pointing upwards.

 

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I measured the dish myself and it's 160x150cm. It wasn't really "advertised", just given away by a ham amateur, so I came to the conclusion that it is an offset (why would a slightly elliptical beam be preferred?).

I guess no reason to think of using two probes at the feed then since only one polarization will be reflected with this dish.
I've heard the 1/10th of λ before (on forums etc.) but is there an actual "reliable" citation for this (like cv.nrao.edu or an Antenna Theory book or something)?

When the feed is "exposed" to ground noise, radiation in the L-Band (and below) will be reflected off the dish. Higher frequencies will not be reflected off the dish, but if they do end up in the feed, they'll be at a higher frequency (and I've got bandpass filters for that).

Worst case scenario I cover up the dish with aluminum foil or something..?

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Feed arrived:

image0.jpg

(Yes, it's huge, and I still have to add the choke ring.. I hope SETI-League is right!) - time to drill some holes and install the copper probe.

P.S.: In some feed designs I've seen Gold being used for the probes. Why is that? Isn't copper more conductive?

Edited by Coto

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3 hours ago, Coto said:

Feed arrived:

image0.jpg

(Yes, it's huge, and I still have to add the choke ring.. I hope SETI-League is right!) - time to drill some holes and install the copper probe.

P.S.: In some feed designs I've seen Gold being used for the probes. Why is that? Isn't copper more conductive?

Is it flue piping?

Gold is resistant to corrosion and tarnishing, probably why it's used.

 

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Just found this thread having been reading up on 1420MHz Hydrogen line imaging (I'm a radio amateur and professional software developer).   Great amount of info here...many thanks to everyone :)

I have noticed that some people are adding Satellite boosters after the pre-amp?  Normally the pre-amp should provide enough gain to overcome any feeder losses down to the receiver and also alleviate receiver sensitivity issues, so I'm not sure why they are required?   Also the boosters seem to be 75ohm which means a mismatch and consequent signal loss unless there is some matching being implemented? I'm sure there is a good reason just can't understand it at the moment.   A lot of good work going into this though.

I'm looking into doing the same but extending to 2 dishes with interferometry, although finding a location for them (I'm in South Devon) may be problematic (back garden, I've been strongly informed, isn't appropriate.....).

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15 hours ago, RobB said:

Just found this thread having been reading up on 1420MHz Hydrogen line imaging (I'm a radio amateur and professional software developer).   Great amount of info here...many thanks to everyone :)

I have noticed that some people are adding Satellite boosters after the pre-amp?  Normally the pre-amp should provide enough gain to overcome any feeder losses down to the receiver and also alleviate receiver sensitivity issues, so I'm not sure why they are required?   Also the boosters seem to be 75ohm which means a mismatch and consequent signal loss unless there is some matching being implemented? I'm sure there is a good reason just can't understand it at the moment.   A lot of good work going into this though.

I'm looking into doing the same but extending to 2 dishes with interferometry, although finding a location for them (I'm in South Devon) may be problematic (back garden, I've been strongly informed, isn't appropriate.....).

Hi that's a good question I did study most of the different designs that are out there for my own scope and generally they are used so I followed suit.

My thoughts are that they are purely for the various losses involved in the chain as the HI line is so weak and every fraction of a dB counts from the initial LNA and noise figure there.

I have around 14 or more various connectors/adaptors in play due to diffent premade filters and bias tee etc. I had to work with what I had.

So you have SMA, SMB, F type, F type barrels, N type all in one chain. Then also the losses involved with the filter and via tee. Which when added up is quite a bit for weak signal stuff.

Yes on the mismatch the main LNA is 50 Ohm as is the filter however the line amps, coax and SDR are 75 Ohm

So indeed there is a mismatch but I believe the lower loss in the 75 Ohm coax outweighs the mismatch involved.

One line amp is probably sufficient.

The chain of course would be a lot simpler if an all in one downconverted receiver was used.

I'm no expert and lack the test gear I would like so those are my thoughts on it.

A radio and astronomy seem to go hand in hand?

I don't have the space to use two dishes unfortunately, great to get more input on the subject.

Regards Carl

 

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Hello, my name is Carlos, I live in Argentina, I use the Google translator to write, sorry for the mistakes, I am happy to follow the thread of their projects and they are very interesting, I am also setting up a radio telescope and I am looking for information, so Thank you for the opportunity.

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On 12/01/2019 at 21:36, RobB said:

I have noticed that some people are adding Satellite boosters after the pre-amp?  Normally the pre-amp should provide enough gain to overcome any feeder losses down to the receiver and also alleviate receiver sensitivity issues, so I'm not sure why they are required?   

This is just speculation as I dont have the figures but I suspect these USB sticks are deliberately designed with low gain to avoid problems with overloading so are pretty deaf (They have an unfiltered front end and are just designed to receive strong signals from commerical stations eg TV in the presence of other strong signals.) The additional pre-amp plus filtering just turns them into a typical weak signal receiver configuration to give a measurable output . The second pre-amp could possibly be relocated to the other end of the feeder without affecting performance.

Cheers

Robin

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So I am currently trying to find an engineer to craft the feed for me, so everything should be ready soon.

Question: Should the antenna probe N-Type connector plate (GND?) be in contact with the metallic structure of the feed, or should I isolate it with some tape or something? Does it matter at all?

Another question is, how conductive must the feed material be?

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