SWR POTY verbessern

  • ...

    Ich hab das hinter mir, irgendwo im Forum hab ich auch Bilder mit Wärmebildkamera gepostet, da kommt man ins schwitzen wenn mann die Kabel anschaut ...

    sehr interessant die Bilder. Während der N Stecker rechts relativ kühl ist, glüht der SMA links förmlich.

    0,5dB Verlust sind schnell erreicht, das sind schon 10% der Leistung.


    Bei N-Buchse im Poty muss man auf den Platz schauen, bei mir kommt sich der mit der Halterung in die Quere.


    vy 73, Kurt

  • wenn man bedenkt, dass hier aufwändig erzeugte HF verheizt wird ..

    Robert welche Leistung hast Du da zum Verbraten geschickt?


    Verschmorte Fernonst-Stecker können einem auch den Enstufen Transistor kosten ....

    Für 2.4 GHz sollte man auch solch schön anzuschauenden Bling-Kram auch wirklich nicht verwenden.

    Selbst für Messaufbau sind Adapter dieser Qualität für herrliche Überraschungen gut. Meist ist das Z schon weit weg von 50R.

    Übrigens habe ich hier letztlich für die 160m GP ein Pigtail gebaut aus Aircell7 welches noch seit paar Jahren im Lager lag.

    Kann man auf grund des Dielektrikums gleich in die Tonne, vermutlich der Wellenwiderstand schon sonstwo.

    Ich benutze hier zur Speisung auf 2.4GHz übrigens direkt bis ans Feed LCF14-50 mit N-Stecker. Für POTY könnt man N-Kuppler draufbaun und Adapter von N auf SMA.

    Ich vermute aber mal dass bei vielen Eigenbau-POTY auch billigbuchsen aus Fernost verwendet wurden.

  • Robert welche Leistung hast Du da zum Verbraten geschickt?

    ... das waren 50 Watt DATV Signal.

    Ich hatte zunächtst auch den SMA Stecker als Schwachpunkt gesehen, das Wärmebild zeigte dann aber dass das ganze Kabel bis zum Wattmeter Schrott ist.

    Man muss auch die Pigtails entsprechend dimensionieren, oder am Besten weg lassen.

    Hab jetzt nach der PA 25cm Huber SUHNER SUCOFLEX 104, dann Ecoflex-15 bis zum POTY. Jetzt bleibts kalt.


    Bild noch ohne Wetterschutz

  • 25cm Huber SUHNER SUCOFLEX 104

    :thumbup::thumbup::thumbup:


    Aber der N-Winkel auf dem Bild am Poty ....... schau mal alleine wie der konstruiert ist da im Knick. Säg den mal auf da hauts Dich um.

    Mach da mal lieber einen gescheiten rein, der sieht mir sehr nach LingLing aus.


    https://shop.spinner-group.com…ads/Spinner/299750-DS.pdf


    Sowas verwende ich hier wenns sein muss oder gleich gewinkelten Stecker aufs 1/4" drauf.

  • Um den N-Winkel komme ich nicht rum, sonst kriegt das Ecoflex die Kurve nicht :-)

    Interessant dabei ist, dass mit dem N-Winkel das VSWR geringfügig besser wurde ...


    Aber Du hast recht, da sollte noch was edleres rein.

  • Hi People,

    i like to focus back on the main theme: 'SWR verbessern...'

    I built 3 POTY-patches from the official assembly instruction and none of them (even with small variations) will match on 2400 MHz. I find a resonance about 80 MHz above the target - this results to 2480 MHz . My serious question: Are the original dimensions valid until now?

    My dimensions from the original publication:




    Thank you for a helpful comment.

    73, Herko DK3HU

  • Herko,

    are you using N Connectors with that ring on the backside?
    If yes, change them.

    I had massive problems with them and nothing worked. Also with too high resonances and no "double dip" - bending whatever didn´t help. I soldered 4 POTYS with different sizes and distances trying to fix it. After I kicked them to 08/15 Ns and viola spot on all POTYs i have build.

    The dimensions are ok in your picture.

    Greetings

    Sandor

  • show an image.


    the RF connector grounding especially. Oh yes, do not expect not to have to adjust a little, love especially if you change materials.


    (sorry for google German but I don't speak German and this is the German section)

  • Hello Herko,


    AFIK the dimensons are unchanged. I also experienced this phenomenon. I solved it by inserting a few pieces of dielectric material (I took parts of the plexiglas of an old CD cover) between the reflector and the "antenna". Thus I could bring the resonance of the TWO peaks left and right from 2.400 MHz and I could significantly improve the returnloss of these both resonances. A test via the QO-100 transponder showed, that my signal was al least 1dB better after this procedure. Thus the readings of the analyser were prooven in reality ;-)


    1dB is not much and you can think if it's worth the effort, but also the SWR was now in an acceptable range and I hope my 2,4GHz final will be happy ;-)


    73 de Johannes

  • Hi OMs,

    thanks for your comments so far. I will send some pictures tomorrow. I use an SMA Jacket that is mounted by 2 screws, carefully aligned in length not to protude the reflector pane. I also did a lot of alignment, bending any possible edges and also soldering some drops of tin on different locations. As johannes stated, it is possible to put some things inside the resonant area, let it be dielectric or metal , but this is not the way i would prefer, because the circular characteristic is affected. On Remco's plots i see a clear resonance in the desired range, i get these characteristic RL, but this is abt. 80 MHz too high :-((

    Best regards

    Herko

  • Hello,

    here are the pictures. Possibly the soldering is not so sober, but i am sure this is not the main cause of my problems. Meanwhile i talked to other experienced OMs and they noticed the same problems with a too high resonance.



    Thanks for your comments!

    Regards Herko

  • Hi Herko,


    as far as I see, you used a lot of solder for the reflector. The produced meniscus influences the resonance significantly.

    I had the same effect, removed the patch, used a file to remove the meniscus to get a right angle as good as possible and reinstalled the patch again.

    Try to use solder as less as possible. For a second POTY I used SMT solder paste, which gaves perfect results.


    73, Thorsten

  • Thorsten, may be,

    but first check the hole around the inner conducter.

    I miss it on the picture.

    Or not visible.


    The inner conductor must go through a 3mm hole through the reflector to the radiator.


    Herko, can you make a picture from this point with an other angle?



  • So

    So apologize for the English, but they differ in at least 3 places from the recommended design. The reflector is not as recommended. The material is not as recommended and the plug is not as recommended. I don't know about the patch thickness, but that also has a little effect. All of these deviations are perfectly acceptable, but can change the resonance slightly. The most critical is the distance of 3 mm and it is very difficult to correct it over the entire area - but this is not necessary because you can adjust it.




    The POTY design at 2.4 GHz is necessarily a very narrow band to create circular polarization from a single feed on a patch with a large wavelength tube that forms a short in the middle where it shouldn't be by right. To keep the design simple, I only used one feed and not two with phases of how it should be done.




    Voting is easy and necessary to get a good circle response. All you have to do is bend the corners slightly inwards or outwards, depending on the resonance you set. Only a little should be enough. This is one of the reasons why I have recommended soft copper and non-springy brass. Non-resilient brass is fine too, but higher loss. I doubt it is important with normal power inputs.

    apologies for the English but these differ from the recommended design in at least 3 places. The reflector is not as recommended. The material is not as recommended and the connector is not as recommended. I don't know about the patch thickness but that also has a small effect. All of these deviations are perfectly acceptable but may change the resonance slightly. The most critical is the 3mm spacing and it's very hard to get it correct over the whole area - but you don't need to as you can tune it.


    The POTY design is necessarily very narrow band at 2.4 GHz in order to create circular polarization from a single feed, on a patch with a large in terms of wavelength bit of pipe forming a short circuit in the middle where by rights it should not be. To keep the design simple I used just one feed and not two with phasing like it should be done.


    Tuning is simple and needed to get good circular response. All you need to do is slightly bend the corners in or out depending which resonance you are tuning. Just a little should be enough. This is one of the reasons I recommended soft copper and not springy brass. Non springy brass is also fine but higher loss. I doubt it matters at normal power inputs.

  • Oh yes,

    thank you for the numerous comments.

    Let me state:


    0) Why do you apologize for writing in english ? - Brexit is not so far in the past ;-) ;-)


    1) The hole for the connector can not be seen but it is 4mm in diameter. There is no dielectric material around the pin and this is the way Remco recommends.

    2) The reflector is the 3rd attempt in hope to get a better result. No1 and No.2 has been round and had a diameter of 105 mm -> same problem fres is too high.

    3) The spacing between reflector and front-panel is exactly 3mm. I used two spacers especially manufactured for this purpose. By bending the distance of the edges, you obtain a variation of +- 10 MHz . Also the the right angle between the tube and the antenna is exactly 90 degrees.

    4) The thickness of the material is 1 mm as recommended. But surely it is made of brass and can not be bent as desired.


    So, my hope was that someone perhaps could correct the diameters by simulation. I am not able to calculate these parameters. As i stated earlier and i am not the only one who watched the deviation when building this antenna.


    73, Herko

  • It's a German thread. Anyway, yes, I am well aware of the limitations of the simulation as I had only access to the student version of CST. My copper version works fine. If it's consistently 80 MHz high I would suggest scaling the patch by 2% and see what happens. Make sure you look at it on a Smith chart though as you can't tell what's really happening otherwise.

  • I have made 5-6 POTY, almost all of which are on the high resonant frequency 60-80mhz... Curved edges do not improve much, effective amplification is the insertion of the dielectric sheet