Carl Reade

Hi Dave as I'm sure you've read I use a Nooelec dongle which is the cheapest probably on the market. It has no screening and no txco however it does work and has proved very reliable so anything else will be an improvement 😂 I would probably go for the RSP1 or duo for the reasons you stated. My biggest nark is the lack of software that can display sub dB readings, increments of 0.2 dB for astro work. Spectravue can do it but is tied to the RF Space SDR 14. Hopefully the software will get better. Carl

Yes I understand S parameters however placing a metal rod straight through a wave guide no longer makes it a wave guide. You will have a lot of loss and the pattern will be totally random to the design. Yes it will produce a result but nowhere near what it should be. The mathematical design of the feed and choke does not allow for a large metal conductor through it.

How are you doing the tests with and without the rod?

Congratulations!! You have cracked it!! Now it's tweaking time. Regarding the filter it looks like you didn't need it as there isn't much interference. There is some loss in them but if I was fitting it, it would be between the Tee and SDR. The dish, I would cover it with small mesh like fencing material to make it efficient and useable. I would still remove the metal rod through th feed and replace with a different method. It maybe working but not fully as designed. At 400Mhz your looking at lots of interference. You would be going into multiple Yagi territory and not a dish as it would need to be huge to be useful. PS the ladder was a bad idea?

It would be fine as a line amp. He would be better off with the G8FEK amp.

Hi you will get there keep at it. A noise figure of 2.8 is not good at all. The H line with a decent setup only comes up around 2 dB above the noise. You would need 1 dB or less at the feed. A 3m dish will be excellent for the job. With your LNA on the dish you should easily pick it up.

Yes he's linking the DC to the amp chain. Here's a simple test, with just the feedhorn and LNA point it at the Sun and away from the sun and look at the live readings while you do it. Use very little intergration as you want to be as live as possible. You should see a rise in overall noise when pointed at the sun. At the side of your LNA is a small pin with a lug. This is for external DC. The pin is positive and the lug is negitve. It's designed to solder the wires onto.

I don't think there is a tidy way round it bar giving the main LNA its own twin lead feed which people do.

I still think your wave guide is no longer a wave guide. If the main LNA isn't powered there will be nothing. At the moment for testing I would power the LNA separate using its power lug at the side careful of the positive, negative. I would remove the line amp for the moment just use the bias tee direct to the main LNA.

Trust me you will never see a feed horn with a metal pole through it. The can is mathematically sized along with the rod for the desired frequency putting a rod through it makes its whole dynamic has changed and effectively no use. The efficiency of the dish is irrelevant and usually worked out at 60% 70% efficiency. Measure the input to the line amp with a volt meter and see if there is voltage.

Hi first things first, you have just placed a large metal pole straight through your feed horn you cannot do that. The horn needs held to the dish from the outside. You will need to fill the hole back in. I would remove the line LNA or check the main LNA is getting 12v with a volt meter. I don't know if the line LNA allows power pass? I can see the H line live without much averaging. Try using SDR sharp I never got anything out of GNU radio. Peak hold should give you an indication of the readout has changed.

You will probably need to do a bit of detective work to see what it is. With antenna, without antenna etc. But I suspect it's probably the PC causing it so maybe hard to get rid of. Try ferrite rings as well on the USB lead.

Never had any issues with 5m and used 10m powered for astro cameras all worked fine. Ferrite rings also good to add. Yes metal boxes where you can.

I get that at different points sometimes. I would suspect it's either PC or SDR generated RFI. It's recommended the SDR is a good 5 meters from the PC. PCs put out all sorts of RFI.

Hi sorry link didn't post, http://parac.eu/projectmk4.htm

Hi radio skyline probably not much use unless your measuring total power. Have a look at this site this is where I learned a lot and what I use CFRAD can pull out the H line with the smallest of signals and can be graphed in all sorts of ways. Carl

Its likely to be in there you would just need the data extracted from it. If you were recording with CFRAD program you could extract it.

Hi heres info from a previous post, Ok best advice i would say is, Get the biggest dish you can! You will likely have to make the dish feed yourself either the the one on this thread or the can type (measurements online). Next is a good low noise amplifier (LNA). Around 30db gain and the lowest noise figure you can get. This noise figure will be the benchmark for the system. You will need probably two 20db satellite line amplifiers these are cheap and work fine. You will need filters in line as well to keep out interference. You can get these on the LNA4ALL site. You will need a power supply 12V and a DC inserter to power the amplifiers. You will need a receiver, a SDR dongle is fine A computer and software. Once you have a working scope then you can improve it as you go along. Carl For the first stage LNA I used one from www.g8fek.com. Then a satellite line amplifier and a filter I had already. LNA4ALL do H line filters. Requirement for filters depends on your RF environment.

Hi I'm assuming Adam thinks your using wideband amps which will amplify all frequencies hence the need to place a filter between them as they could get saturated with unwanted signals. The reason I place my filter last is because anything that is picked up in the system chain ie the coax or line amps is filtered out before it gets to the SDR. Don't forget your front end LNA is already filtered for the H line it's not wideband. So adding a filter at the SDR just gives you added protection from signals picked up from the line amplifier or coax. If your not getting interference from nearby out of band signals you may not even need it. There are no set rules. Don't over think it. Front end filtered LNA amplifies the signal you want, next the line amp compensates for cable loss then filter (if needed) gets rid of any unwanted signals then SDR.

Well I think it's Been well thought out as a title. It does cover all now. I really cannot understand the objections. If your using your mark 1 eyeball through glass or mirrors or both then it's visual. The moment you add electronics to that chain it's electronically enhanced and viewing. At the end of the day your view is either enhanced with electronics or it's not. If you want to make a visual report do it in visual if you want to show a picture do it here. Or you could take up radio astronomy we are down at the bottom ???

Think it's all down to mass produced cheap dongles and it was added to get rid of the spike don't think it has any other effects. The more expensive high end SDRs wouldn't have it.

Now that is the bandwidth you should be using. Yes far too narrow. I think the spike is the DC spike inherent in SDRs. As I use SDR# program it can be removed using the "correct IQ" option. Not sure if GNU has that somewhere.

Ah good you found the cause. You seem to have an interference free spectrum then which is welcome.

Hi it looks like a very narrowband signal. You should expect the H line to be around 1420.4Ghz and more of a "hump" in the spectrum. I have seen this method work but to bring out the H line but it needed the data processed over a period of time using the CFRAD program and then graphed in Excel. I could not get the program your using to work right on my PC for some reason. I would think both designs of feed horn will work fine. You should do a sun test and direct it at the sun to see if the noise rises.

Hi you should get a result without a line amp but I would use one to compensate for mismatch, cable loss and connectors etc. Ref the painting there is no reason you can't paint over the connector plate and nuts as long as they are making an electric connection to the tube.