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I have been away from Amateur radio for years, but I finished work recently so can come back to the interest, I did do 70cms AM TV back many years ago, have a W&D 50MHz IF board sat on the shelf but none of the original gear. There is a small amount of ATV activity in my area as I have found, but articles in Radcom on the QO-100 sat has piqued my interest,
I have now got a MiniTiouner-express managed to pick up a 1m Sat dish 2nd hand and can receive pictures and sound via the downlink. So that is one side sorted, now to the expensive and more technical side.
I have played with the gnu radio software and a Hackrf one I have, I am using the example from gnu-radio to send DVB-S2 signals and can do this in a very controlled manor with SR5000K, SR2000K and SR500K. all is OK streaming a video in a simple loop.
But if I put the system into my spectrum analyzer an old HP 853A then I notice it is not a clean transmission. The flowgraph and GUI sink look very clean as does the main carrier on the HP but there are side spurs less than 20 dB down on carrier. I am not sure if this is because of the 8 bit A2D converter or some other restriction. I know from other articles that the Hackrf prefers to have a sample rate over 8MHz to stop aliasing, possibly only on RX as I believe it is down to the A2D. But can not try it by independently change the sample rate without changing the modulation in gnuradio.
So to my initial questions has anyone tried with Hackrf one and have they been successful or is the unit just not good enough? Does the 12 bit A2D of the Pluto or Lime solve the issue, or is the flowgraph I am using outdated?
Also is there any software package that I can try using a computer to drive the unit direct rather than using a Rasp PI and other extras for it. I have a few HP thin clients that can run Ubuntu and Debian. They only draw 10 to 16 Watts power and are small units so can be put into an enclosure.
It must be better to ask then try and figure out on my own.
I think the hackRF has been used successfully. What I see in your images appears to be a failure of the filtering. It might be worth posting the flowgraph so we can look at it. Perhaps you need more taps or there is some other problem.
I am afraid with Gnuradio, despite all the attempts to make it easy to use, you do still need to understand a bit of DSP theory to hack it. I did some experiments with it back in 2014 https://flic.kr/p/o9qbBS This was DVB-T but you can see similar effects and I saw the same with DVB-S. I think I cured this but it was five years ago and I don't recall.
I have just finished reading the CQ-DATVcompendium that gives me a slightly better insight. Charles the Mini-Tiouner-express is working well.
OK a flow graph first. This is virtually straight out of GRC examples, but I set the SR rate to be 1M and set the FEC to be 1/2, I was hoping to figure a variable to set all the rate blocks at the same time but could not figure it. Roll off is 0.2 default the FFT filter is as default and the sample rate is symbol_rate x 2.
Charles, I will happily show ignorance here, when I got the Hackrf I went through the tutorials for the hackrf one in which there are 11 but they seemed to stop and never continue, even bought a book called Practical signal processing by Mark Owen, but to be honest found some of the maths and explanations to be above my capabilities without guidance.
I believe you are saying I have to add signals to the signal, so that would be after the FFT filter and before the source. I am guessing here?
I think I need to go back through the examples and learn a bit more, thanks for your assistance.
Does anyone on the forum give lessons?
I notice you have the bandwidth in the sink set to 6 MHz, try reducing that to 1.5 MHz (for example). I don't own a hack-rf but that might narrow the analogue tx filters in the hack-rf.
If you are going add an interpolator you need to do it between the FFT RRC filter and the sink.
If you interpolate x2 you will have to increase the sink sample rate by x2 as well to maintain the same symbol rate.
The DATV-Express hardware has fixed 5 MHz LPF filters after the DACs and I have to do a lot of interpolation of the signal I am transmitting to move the alias frequencies into the band reject part of the filter. Lime and Pluto have programmable filters. I am not sure what the case is as far as the hack-rf is concerned. In the Express HW when I don't have enough interpolation I get exactly the same looking spectrum that you are seeing.
It looks like it does prefer the sample rate to be over 8 MHz, preferably 10 MHz or above to remove the spurious aliases.So I added a resampler with a variable called 'resample'
Now this bit worked but not sure if there is a better way. I wanted to keep the Sample rate going to the Hackrf at 10Mhz or better so the formular for the resample variable is 'int(round(5e6/symbol_rate))'. So for various Sample Rates the resample value changes changes
125K is 40 so sample rate to sink becomes 10 MHz
250K is 20 so sample rate to sink becomes 10 MHz
500K is 10 so sample rate to sink becomes 10 MHz
1Meg is 5 so sample rate to sink becomes 10 MHz
2 Meg is 6 so sample rate to sink becomes 12 MHz
66K is 76 so sample rate to sink becomes 10.032 MHz
333K is 15 so sample rate to sink becomes 9.99 MHz
All seem to work giving a picture and good D numbers in RX
Lastly a couple of traces from the Spectrum Analyzer. This is a SR250K rate with 200 KHz per division: and lastly the same with a 10 MHz per division showing the 60DB to the base. Now I have to understand video rates better for each SR. Back to reading the compendium again.
All this is to understand and get it to work before I go out and buy more equipment that to be honest I may not be able to work from my location.
But being able to provide a cleaner signal for me was very important, there are still issues with the Hackrf in that it does not shut down properly after being in TX mode. So a command line call to Hackrf_info sorts that.
So at least if I can use the Hackrf one a few MHz band-pass filter will clean up any out of band spurs.
I have been making a 23 cms yagi as per a spreadsheet from DL6WU, again as a test to see if I can receive the GB3FT repeater. Just a short one 14 element, but it is a starting point. I think I am just out of the coverage area.
Any way playing next with Video streaming from another linux box.
Again thanks both for your help, I need guidance to point me in the correct direction most of the time.