Posts by DB1CC

    Hi,
    i am using Adalm Pluto over LAN. RF Side works perfect with SG-Labs Amp on a 5 turn Helical, but i have
    problems with my modulation. I am using a Headphone/Mic from Heil on the (normally fine) built-in Soundcard
    on my Desktop-PC. Level ist very low from mic, so i used +30dB preamp setting in Soundcard and have to level up more than 90% of Mic level at SDR Console to get a reliable SSB signal, but Modulations is absolutely worse.
    If i use the SDR Consoles internal test Tone, all looks ok. I have clean spectrum on RF with double tones wich are generated within SDR Console, (measured after PA with my HP Scpec, so i think the problem must be in Audio/Sound
    (or between my ears ;-)
    Also i got hi freq. audio distortions wich are not noticable if i monitor the audio via the soundcard itself.
    Any ideas?


    What type of audio interfaces / microphones are mostly used here i the community?


    Thanks in advance!


    BTW: all mods on Pluto done, & pwr supplys are clean and no RF strays in power lines / Mic / Reference freq. cables measurable....

    Hi Wilhelm,
    currently the Helix is mounted outside on the dish, so a cannot measure it, but f i remember it correct, the vane was about 10x12mm, made of a part of the same material like the shielding boxes from Schubert. Distance was about 2mm from the wire,
    but you must try size and distance, because it controls directly the matching. Also the used material changes vane size and distance.
    I screwed it to the reflector and bent it until i got perfect match. This is easy if you have a vector network analyser. I used the cheap one shown, but my big HP give similar results.
    Interesting was, that my helix shows much less loss on RX LNB as a POTY and i got good readable signals with this TX Helix with only about 200mW over QO100 using my 1m Dish. This is why i prefer Helix antennas....


    Helix Antennas are broadband by design, so an thick wire is not really needed. To be mechanically stable, it is better to use a plastic holder to support the wire. This example of my helix is built using 1mm Wire, supported by printed PETG holders and is very broadband as you can see. Impedance matching is done by a metal vane wich can be easily bent to get perfect match. Five windings give you good circular polarisation and high gain. Combined with the LNB in the middle of the Reflector, LNB loss is very low (about 0.5 to 1 dB)
    because of very low shadowing the LNB by the thin wire.