Doubt about the Lora Antenna kit



  • I bough the LoRa antenna kit at one of the PyCom distributors, Exptech. When I tried it, it had a surprising bad performance. Looking at the RF current profile along the antenna, it was similar to a lambda/4 antenna. And is is too short for a lambda/2 antenna, assuming a typical design. So either I received a non-genuine device, sold a such, or the device description is wrong.
    The difference matters, since a lambda/4 antenna requires a conductive base to be assembled for good performance. This surface adds the other half of a lambda/2 antenna. None of the PyCom cases work as such. The intended lambda/2 antennas are way less critical.



  • @jcaron I have two antennas which perform more robust. One, which looks similar, but is 22 cm long (18 cm up from the hinge). That one shows a nice current profile, peak in the middel of the "active" section and going down to almost zero towards bot sides. The other is a home-brew ground plane antenna, along a recipe from the ttn forum, which also work pretty well. Both are not very sensitive to touching the xxPy and moving.
    Compared to these the PyCom antenna performs between 6dB and 16 dB, depending on placement and touching. I have my xxPY built into a aluminium box with the antenna connector at the shorter side. The PyCom antenna shows some current at the connector, which explains the sensitivity to touching.
    Picture: GP antenna on FiPy in a box, built from a SMA connector an 1.5 mm wire. Tip wire it 82mm, the radial are 86 mm.
    0_1526903721654_GP antenna on FiPy.jpg



  • @robert-hh
    For that I'd have to tear down (cut?) into the brass section, the cable just goes inside. Not something I can do immediately I'm afraid.

    @jcaron
    I don't personally know who makes them and in any case wouldn't be allowed to say



  • @robert-hh The one I have at hand looks exactly the same, but there seems to be about 0.5 cm difference in length (mine is shorter).

    Have to admit I haven't measured anything in terms of antenna performance, just trusted the antenna to work as intended. We've had a lot of performance issues, but it's an indoor deployment and we assumed the issue came from there... Would be interesting to find out if changing the antenna would have made a big difference.

    @jmarcelino do you know the original manufacturer and reference? They actually look like Pulse Larsen W1038 antennas, which are 1/4 wavelength dipole... for 2.4 GHz.



  • @jmarcelino Can you tell where the shield of the cable is connected?



  • @robert-hh
    That's a good point and I don't know if the antenna is really lambda/2

    I tore one down and what I see is a brass 70mm sleeve balun, brass skirt and ~ 87mm tail with a small twist on it. So it looks more like quarter wave to me.

    0_1526898398588_IMG_0129.jpg



  • @jcaron Seems to be the same size:
    0_1526896665116_Antenna.jpg



  • @robert-hh You should probably post a picture of the antenna with a ruler or some other size reference next to it so it could be compared to the intended antenna.

    Those we got directly from Pycom are a bit over 19 cm end-to-end, a bit over 16 cm from the hinge axis to the tip.


 

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