TX Antenna challenge

  • TX antenna challenge


    I did some interesting antenna test during the evening sun. The test does not meet scientific requirements, but still shows interesting results.

    As a comparison in the uplink, I have had the following antennas competed


    1. 3 Turn Helix in front of 1m prime focus dish
    2. 36 turn Helix (rhcp)
    3. 5 ½ turn Helix in front of 90cm Offset, but overhead the LNB ( o bit of center)


    The 3 turn with prime focus was definitely the winner. Around 7 dB less (not calibrated) I received the signal from the 90cm Offset with 5 ½ turn helix. Far away (only a bit over the noise) I could read the signal from the helix. The TX Power was 2 watt.


    I´ll practice some more tests the next days, with yagis and “beer can antenna” in front of the dish.


    Please note, during the transmission with the prime focus the Helix was not in front of the antenna anymore.

  • For situation 3, I have the same issue here and I think the induced offset is coming awfully close to the first null of a 90cm dish. So I am thinking about cutting a 40cm half circle out of the helix's reflector and try to reduce the offset.

  • Hi


    This can be a solution.

    The next day’s I´ll try a PCP log-per and the “beer can antenna” as feed system. Let´s see how the different between prime focus and offset will be in that case. Must be the same, I guess.

  • Another item to add to the "tx antenna challenge" :

    Successfull QSO with IZ2CPS (thanks Roby !) with -for transmission- a "double quad" antenna made from copper wire bent into an "8" figure, with copper-clad PCB (150 * 100 mm) as the reflector. No dish- just the double-quad as explained in Rothammel's antenna book. We had used this for a WLAN link spanning a few hundred meters years ago.

    Now (with relatively slow, but human-readable CW) and 900 mW from a BU-500 tx converter running "barefoot" same old antenna spanned almost 40 Mm (mega-meters). No dish (for transmit), just the tiny double-quad antenna. Makes a nice 'reference gain' antenna for comparisons with various other TX-antenna tests.


    Of course this little gadget (see attachment) is not sufficient for SSB, and I doubt the Chinese "8 Watt" (in reality 3..4 Watt) WLAN booster will make "dish-less" SSB QSOs possible. But I will see what the old homebrew 25 turn "WLAN DX helix" can do (without a dish, of course), and how it compares with a dual feed in a 40- or 60 cm offset dish. But that's another subject...





    Cheers,

    Wolf DL4YHF .