Carl Reade

1 hour ago, Coto said:

It's based on 5V? Why did he say max 20V? And what do you think I should do? The only other bias-tee I have is this, but I'm not sure if it'll do or not: 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

Is the electronics chain I mentioned correct? Someone suggested the coax is probably 75 Ohms and it'll be a mismatch with the SMA cables.

I can't see where 20v mentioned? Adam based his system on LNA4ALL which are fed with 5v (or can take 9v)

Your bias tee doesn't mention what current it can supply so cant answer. You need one that can supply the current for the LNA and line amp.

Yes sat coax is 75 Ohm but the lowest loss at these frequencies and with the gain involved the mismatch is negligible.

1 hour ago, Coto said:

Carl, what's the specifications of your bias tee? Adam's Bandpass Filter [http://adsbfilter.blogspot.com/2015/06/hydrogen-line-1420-mhz-filter.html] (which I'm planning to use as a bias tee) seems to only be able to pass 150mA through the cable, yet, the LNA + in-line amps take up about 500mA. Am I misinterpreting Adam's words?

Also, does your RTL-SDR get oversaturated by the high gain the LNA + 2x in-line Amplifiers output? Right now I'm trying to find the right cables to connect everything together. I would use a shielded 5-meter SMA to SMA extension cable but I've only got an unshielded SMA to SMA cable (I didn't know unshielded cables act as an antenna!). So here's my solution to avoid ordering a shielded SMA to SMA cable (which I've only found on ebay) and hold the build for another month or so:

Is it a good idea to have the second In-line Amp after the long 5m cable? I'm mainly using it due to connectivity capabilities, cause I can't think of any other way of connecting the antenna to the SDR which is far away.

*Are your in-line amps also F-Type?

 

Thanks,

Coto

Hi forget Adams design as it's based on 5 Volts. Your LNA and line amps require 12 Volts.

The bias tee is rated at 65 V at 1 Amp so can run all.

All coax cables are shielded or they are an antenna including SMA.

So you use satellite coax from the LNA through the the line amps the whole way back to the bias tee. Then from the bias tee to the filter then the dongle you can use SMA 5 cm tails. That way the filter is not at the power side of the bias tee.

Looks pretty good paint should be fine.

On 01/03/2019 at 00:16, Coto said:

How come the antenna probe connector's ground plate must be in contact with the feed, but it doesn't matter if the dish is also in contact? Antenna grounding is one of thing I really don't understand - why must the feed be in contact at all?

Probably need to look at wave guides and transmission lines.

The feed is a wave guide or think of it as a filter and you want that filtered frequency maintained within the coax.

The fed doesn't need to be in contact with the dish as most satellite LNBs are held in plastic to the dish.

The attaching of the feed horns and materials is probably more a strength and convenience issue.

Again it's an antenna theory subject which others may know better.

Here's a useful gif.

52 minutes ago, Coto said:

Didn't know that, thanks. Is it OK that the feed is also in contact with the dish? A threaded rod (1-meter long screw) holds the feed into place which is held by the dish using 4 nuts in total (2 for the feed, 2 for the dish) end. Is that OK, or should I somehow isolate the feed-screw area with another material where electrical contact is made?

Feed should be fine with contact. I've seen many feed horns attached this way.

4 hours ago, Coto said:

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?

Yes it absolutely needs grounded to the structure is the short answer. Regarding material doesn't really matter. Weathering is probably more important.

Thanks guys doesn't look good then. Seen the Starzonia one bit too spicy price wise.

Hi all would the 50 ed be suitable to use with the Attic infinity for wide field, any drawbacks?

I'm thinking this instead of adaptors and lenses.

Cheers Carl

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

6 minutes ago, Coto said:

Yup! Costed me only 4 EUR.

Bargain!

3 hours ago, Coto said:

Feed arrived:

(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.

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.

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.

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. 

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.

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.

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.

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.

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

Here's a handy SDR Sharp plugin for RA called IF averager. This about an hour ago. 

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.

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?

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.

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.

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.