Selfbuild X-Band Converter

  • Hello,


    today i tested my x-band lnb with my CAS 220 and my KTI mesh dish 3,65m.


    The SNR is nearly the same, at the mesh it is about 0,2 db better.


    Someone can tell me what SNR he got for:


    21.50°E SES 16 (GovSat 1) 7402 (1106) - 8,5 db


    and


    37.00°E Sicral 2 7501(1204) - 8,2 db



    it seems to be a bit low for me, my qth is northern germany.


    Someone can tell me where to find footprints for the X-band sats?


    Also i like to know if somebody builded a mechanical polarizer instead using a dielectrical plate and how the improvement is.


    And maybe something about a selfbuilded scalar ring.


    Thank you!




    • Offizieller Beitrag

    Nice work and welcome to the forum.


    I used the Excel sheet from here https://www.qsl.net/ct1dmk/mw_low.html to calculate the scalar rings for a PF feed. It worked well. There is also information on squeezed pipe polarisers. I use one but it is literally a squeezed pipe (using a vice).


    Have a look at qwer's posts in the X band data and GS sections for signal levels.


    Do you have the feed below the focus? If you don't have inclination adjustment, you may find to better to put to the side of the Ku feed.

    Bilder

    1.2m Prodelin 3122 az-el with one of:
    S: Helical feed, 0.8dB NF LNA, X: 1.2dB NF LNA, conical feed,
    Ku 12-18GHz: corrugated conical feed, 1.5dB NF LNA, Ku (Standard): SMW Q-PLL type C, Prodelin feed. Ku (Extended): 11.3GHz LO SMW & Prodelin Feed Ka: Gilat ex-ODU PLLs Gilat feeds, Ka 18-26.5GHz: Patriot feed, home made 4dB NF LNA, Ka DSN: Corrugated conical feed, home made 3dB NF Down-Converter

    1.5m IRTE, Polar mount with Octagon OSLO mod. C120, IRTE feed
    40km East of London, UK

  • Thank you for your quick reply and the link.


    Do you know how to calculate the polariser for 7,5 GHz instead of 8,4 GHz?


    Forgot to mention, i have a second motor on my dish for the elevation. so it should be in focus, at least when the are no extreme east or west positions.


    I put it intentionally under the ku-feed, to have the same azimuth degree.

    • Offizieller Beitrag

    You can scale the design to match the waveguide. It is explained a little more in this article: https://www.qsl.net/ct1dmk/cp_feed_dmk06.pdf

    Paul uhf-satcom makes polarisers for 8.4GHz and they do still work at 7.5GHz.


    I made my polariser by squeezing the 28mm pipe in a vice, a little at a time, to optimise the null from a signal which had the opposite polarisation. The best description of the operation of this type of polariser is in these 2 articles: W2IMU 10GHz Part 1 & 2 here https://www.microwavers.es/ind…oteca/category/16-antenas

    1.2m Prodelin 3122 az-el with one of:
    S: Helical feed, 0.8dB NF LNA, X: 1.2dB NF LNA, conical feed,
    Ku 12-18GHz: corrugated conical feed, 1.5dB NF LNA, Ku (Standard): SMW Q-PLL type C, Prodelin feed. Ku (Extended): 11.3GHz LO SMW & Prodelin Feed Ka: Gilat ex-ODU PLLs Gilat feeds, Ka 18-26.5GHz: Patriot feed, home made 4dB NF LNA, Ka DSN: Corrugated conical feed, home made 3dB NF Down-Converter

    1.5m IRTE, Polar mount with Octagon OSLO mod. C120, IRTE feed
    40km East of London, UK

    • Offizieller Beitrag

    I use a 34mm copper pipe instead of 28mm, maybe that is not so good...

    34/35mm is fine for the milsat band. Here is one of my early X band set-ups, based on 35mm pipe and a 76 to 35mm reducer as the feed. You might just be able to see the squeeze of the pipe, it does not need much to get the differential 90 degree shift. I now use 28mm which covers 7-9GHz reasonably well.


    I've added a picture of the PF feed using 35mm pipe. The scalar is based on Luis Excel sheet linked from post #2.

  • Now i got better SNR, i removed the two inline amps after the mixer output and replaced them by a better one with lower noise.


    The problem is, that i got about 70 Meters to the dish, so i need high signal-level. After about 50 Meter there is another inline amp at the moment.


    My question is, when i put a lna (with about 1db noise) directly after the mixer output and then directly after the LNA an inline amp with maybe 7 db noise, does the high noise factor then matter?


    Or is it better to take also a lna with 1db noise after the first one?


    Also i am thinking about to put a second lna directly after the x-band lna before the mixer.


    I got one, but i dont know the gain and the noise factor of it and the needed voltage, maybe someone can tell me?


    • Offizieller Beitrag

    The most important amplifier is the first one. The overall noise figure is established in the early stages. Draw a block diagram pf the system with the gains and noise figures of each stage. Then enter into a cascade noise figure calculator like this one: https://www.everythingrf.com/r…se-figure-gain-calculator. Then you can play with the architecture by moving blocks in the system and re-entering into the calculator. That will let you see how changes to each stage affect the overall performance. If you have a lot of attenuation (i.e. long IF cable) you will need reasonable gain before it. Normal LNBs have 50-60dB gain.


    What is the architecture of your whole system? If your post-mixer amplifier NF alone make a big difference, it suggests you need more gain before the mixer. However, if you do the cascade noise calculation what's needed will become clear.


    I got one, but i dont know the gain and the noise factor of it and the needed voltage, maybe someone can tell me?

    At a guess, judging by it's age (The Avantek name disappeared ~20 years ago), it's probably around 3-5dB NF. Amplifiers of that age were often designed for 15V but it's hard to be sure. I'd test it on 5V and increase the voltage until the gain did not change.

    1.2m Prodelin 3122 az-el with one of:
    S: Helical feed, 0.8dB NF LNA, X: 1.2dB NF LNA, conical feed,
    Ku 12-18GHz: corrugated conical feed, 1.5dB NF LNA, Ku (Standard): SMW Q-PLL type C, Prodelin feed. Ku (Extended): 11.3GHz LO SMW & Prodelin Feed Ka: Gilat ex-ODU PLLs Gilat feeds, Ka 18-26.5GHz: Patriot feed, home made 4dB NF LNA, Ka DSN: Corrugated conical feed, home made 3dB NF Down-Converter

    1.5m IRTE, Polar mount with Octagon OSLO mod. C120, IRTE feed
    40km East of London, UK

  • At a guess, judging by it's age (The Avantek name disappeared ~20 years ago), it's probably around 3-5dB NF. Amplifiers of that age were often designed for 15V but it's hard to be sure. I'd test it on 5V and increase the voltage until the gain did not change.


    ok, when it is 3-5db NF and i put it before the mixer it is better than putting a lna with 1 db after the mixer?

    because mixer and lof got higher nf???

    • Offizieller Beitrag

    If you put all the parameters of each stage into the calculator and try different configurations, that will tell you what is best. We really need the full block diagram of your system to understand how to optimise it.


    Attached are pages from a 1987 Avantek catalogue which show similar numbered amplifiers. They are packaged differently to yours but it suggests yours may have an NF <3dB.

  • Thank you for the pages, i tried different configurations with the calculator. at the weekend i will try them out and will see how good the improvement is.


    Does it matter if the circulation plate is at the front of the feedhorn or does it have to be some mm deeper in it?


    Also, does it matter how for away the plate is from the lnb antenna-pin?

    • Offizieller Beitrag

    Does it matter if the circulation plate is at the front of the feedhorn or does it have to be some mm deeper in it??

    I'd put it 20-30mm, or so, in to keep clear of the phase centre of the feed.


    Also, does it matter how for away the plate is from the lnb antenna-pin?

    I'd keep it a wavelength or 2 away.

    1.2m Prodelin 3122 az-el with one of:
    S: Helical feed, 0.8dB NF LNA, X: 1.2dB NF LNA, conical feed,
    Ku 12-18GHz: corrugated conical feed, 1.5dB NF LNA, Ku (Standard): SMW Q-PLL type C, Prodelin feed. Ku (Extended): 11.3GHz LO SMW & Prodelin Feed Ka: Gilat ex-ODU PLLs Gilat feeds, Ka 18-26.5GHz: Patriot feed, home made 4dB NF LNA, Ka DSN: Corrugated conical feed, home made 3dB NF Down-Converter

    1.5m IRTE, Polar mount with Octagon OSLO mod. C120, IRTE feed
    40km East of London, UK

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