I still don’t understand the coax collinear by theoryĢ. But up- or down tilting the antenna gave worse results in the field test showing the main lobe is horizontal.ġ. Phasing errors can lead to an elevated main lobe. Another worry was the radiation pattern in the vertical plane. while measuring i could not change the VSWR by moving or touching the feedline so it is well decoupled. Most designs use a copper quarter wave tube (probably to fit it into a tube). I think the radials do a good job and contribute to the good VSWR. By that time i was in doubt if the antenna would work at all as designed but was delighted by the field tests which confirmed the extra gain to be expected. I then cut the top halve wave by one or two cm until it was on 868 MHz (the amount can be seen on the picture, taken after modification). But it resonated still too low in frequency (820 MHz). So i started cutting the whip: surprisingly with hardly any change! Lacking time (and about to give up on yet another coco disaster) i removed the whole top end which showed a big improvement. Also the bottom end had the core of the feedline connected to the radials, which in retrospect doesn’t seem to be very clever… When measuring VSWR the resonance was nowhere (600Mhz or so). I don’t recall the sources (there are so many) but it was with top shorted and with quarter wave whip added. I did measure the VSWR but did not take a picture. Results will be shared I’m back home again… Still promising and about what to be expected of this configuration! This weekend the gateway and the antenna will move to the rooftop. Long whip avagage RSSI -108 dBm (26 packets)Ĭollinear avagage RSSI -98 dBm (16 packets) Short whip avagage RSSI -113 dBm (13 packets) Long whip avagage RSSI -115 dBm (20 packets)Ĭollinear avagage RSSI -110 dBm (14 packets) Short whip avagage RSSI -118 dBm (11 packets) For each antenna the average of the RSSI values was calculated, resulting in:ĭistance to gateway Eindhoven airport: 7.2 km RSSI values varied +/- 4 dB without touching anything. At home the results were analyzed from the datafile Node-Red creates. I left the tracker running for a few minutes to have a number of observations). I used 3 types of antenna’s: Small whip, large whip and collinear. My LoPy LoRa tracker was used as signal source. Later that day i did some more tests at 530m from my gateway and 7.2km from the gateway at Eindhoven airport (FFFEB827EB75534E). I used a N-connector pigtail cable (so the blue part is a little piece of RG174 coax). Tuned it a little more by cutting the top halve wave with a cm or so. Only after removing the complete quarterwave top end, the SWR got right. While measuring the SWR with a N1201SA antenna tester it was impossible to tune the SWR by cutting the whip. However, while building i didn’t put the bottom part together in the way it was planned. Realizing this could well end in a frustration (i did some collinears for ADSB with mixed results) i started off with what i thought was a proper design.
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