Carl Reade

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.

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

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

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

Bargain!

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.

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

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.

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.

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.

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.

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.

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

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.

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.

Yep nail on the head!

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

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