Posts by DG8ABG

    Robert, Bill,

    might be if it has not the better - wrote just to make shure !

    - i do not own the 13cm tansverter but

    my 23cm sg-lab has got that split (28mhz frq shift) option on both SMAs with a bridge inside (jumper 1)

    just have a look at sg-lab homepage "23cm transverter"


    " I am feeding the LNB with 13V, supposed to be vertical polarisation…

    Anyway, I'll keep searching how I can improve this…"

    Please beware:

    Feeding the LNB with +13V does not ensure vertical polarisation alone.

    If you feed +13V but mechanically rotate 90 Degrees you still get horizontal polarization !!

    Personally i first stumbeled about DC-feed problems cause my homebrew bias-T

    had not enought bandwith and was blocking everything above 500MHz - check your IF path aswell

    73 Marcus

    Made some pictures of one of my probes as described above to make things more clear -

    Its by far the best tool i ever build for rf measurements in circuit - its a simple cheap and all passive 20dB probe

    wondering why it has never been described so far !!!!

    if you add a ground clamp/spring at the tip to get gnd connection you can do absolute power probing anywhere in your circuit - but it also works without ground spring -

    resistors in this case .2 times 910 ohms parallel in 0402 ( 0603 also ok) and cap 0402 100nF


    If you have acces to a spectrum analyzer you can build yourself a simple probe / sniffer

    up to ghz

    solder a 450 ohm smd or better 2 times 910ohms parallel at the end of a short piece of

    semi rigid coax cable followed by 100nF cap to decouple dc :


    this will represent a voltage devider with 50 input of yout spectrum analyzer with 10:1 ratio, thus

    doing 20dB attenuation --

    with this probe you can check input / output level of your amplifier (relative measurement ) check if the stages still have gain and reasonable dB and you can locate the stage easily

    regards marcus

    Me again

    regarding my last post have a look at this video its great :

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    its about difference about balanced and doherty amplifier to make things more clear


    Sorry to write in german : getting complex -maybe someone can translate

    Nochmal kurz zum Thema UMTS Vertsärker:

    Bezug ist das Bild vom Verstärker ganz oben auf dieser Seite oder?

    Was sich meines Erachtens erkennen lässt, sieht die Endstufe aus als wär es ein Verstärker nach dem

    Doherty Prinzip, d.H eine Transistor in class a oder A/B für den Träger, der andere in class C gebiast um die Spitzenleistung zu verstärken ( wird bei UMTS Anwendungen gern gemacht um Wirkungsgrad zu erhöhen/ Ksten zu sparen,... ) -

    Infos u.a. hier :…pedias/doherty-amplifiers oder auch der Artikel von OM Konrad Hupfer DJ1EE zum Doherty Verstärker für 2m.

    Problem für die Anwendung bei anderen Frequenzen: nicht nur die Impedanzen für Leistungsanpassung ändern sich über der Fequenz

    sondern auch die 90Grad Phasenleitungen für die zweite Stufe (im Bild die jeweils längere Leitung an Eingang /Ausgang der Endstufen Transistoren) müssen eine andere Länge bekommen (kürzer werden ) damit das wieder sauber arbeitet -

    denke das wird einen nicht unerheblichen Beitrag zur reduzierten Ausgangsleistung liefern. Evtl könnte man auch mal einen der beiden Endstufentransistoren (der mit der höheren Gatevorspannung) alleine betreiben und auf max Leistung optimieren und dann weiter schauen.

    Das nur kurz dazu - Frage ist wie viel Leistung da am Ende raus kommen soll, ob die 70W bei 2,4Ghz reichen oder das Ziel ist den Verstärker bei der Frequenz voll auszufahren, dazu wie oben angesprochen denke ich muss man mehr modifizieren und Aufwand treiben.


    Just an idea - Have you measured just driver power over frequency to figure out if the diminished power comes from lack of driver power @ 2400mhz or from the final stage itself ? Driver seems to be similar to the MW7IC2725N as used in the F6BVA Amplifier so might be ok to use up to 2.4gigs



    Yes i use the same Filter in front of my EDUP EP-AB003 used as a driver stage ( removed input switch and connected SMA input via cable direct to splitting point at input of the Amps) wich gives 17dB Gain - assuming the Amp is liner no worries

    but if not - to filter in front of the antenna after a real PA you wont use it - it only takes 20dBm !!

    Zitat von Remco

    ik4idy Yes, that is known. There are + and - 20 kHz noise skirts , measured/received by many. And .. from what I have been told, a fix is underway.

    Thought i have not seen a spectrum plot of the beacon : Maybe it's a problem with the loop filter bandwith of the mixing pll - Might be that it is using a pfd frequency of 20khz ? This often leads to spurs of pfd freq or noise ears in the vicinity of the loop bandwith - Analog Devices has a good software tool calle ADIsimPLL to design loop filters for PLLs

    Anyway great job of the hole Amsat team so far and great many thanks for hanging on -