Collinear antenna ground plane and height question - Page 1
Forum section: electronics / rf-microwave

author: uer166
author_rank: Super Contributor
timestamp: January 01, 2024, 05:55:23 am
content: I have a goal of communicating between a base station and a handheld device ~2-3 miles apart (LoRa application). From what I've read I'd need >50ft height for the base station to talk to the handheld device sitting ~6ft up above ground for ~3mi LoS accounting for the fresnel zone. With this I have a few questions having little real-world RF experience yet:For a collinear antenna such ashttps://lora.rf-explorer.com/downloads/RFELA-3%205X9.pdf, what is the ground plane requirement? I would like to use a fiberglass of carbon fiber mast, neither which provide a counterpoise. There seems to be no pictures of the test setup they used to generate the radiation pattern. Would 4 wires at ~45 degrees down be sufficient? Would it need a real flat plane?Is the 50ft an over-estimate? I used an online calculator such ashttps://afar.net/fresnel-zone-calculator/Tx power will be 17dBm limited by the chipset, with -135dBm or so Rx sensitivity.If the height requirement seems reasonable, Any specific recommendations for a mast that would take <1hr to deploy in a desert environment with minimal help required (<3ppl)? I was looking at the likes ofhttps://www.dxengineering.com/parts/dxe-tfk46-hd

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: January 01, 2024, 12:06:17 pm
content: While primarily intended for amateur radio 2 way radio coverage type predictions, this web site produces coverage plots that can be tweaked for other uses. You have to register first, but it is free to use.https://www.ve2dbe.com/english1.htmlSJ

author: A.Z.
author_rank: Super Contributor
timestamp: January 01, 2024, 06:50:23 pm
content: my wild guess is that the 1m or coax coming with the antenna acts as a counterpoise, if so, just add a W2DU choke right after it, as for height, I think you'd better reason in terms of (fractions/multiples of) Lambda

author: uer166
author_rank: Super Contributor
timestamp: January 01, 2024, 09:45:24 pm
content: Quote from: Solder_Junkie on January 01, 2024, 12:06:17 pmNeat! I used that calculator, and am getting well in excess of 30mi coverage with 50ftThat is way longer than I need, why such a discrepancy vs. the Fresnel zone calculator?

author: uer166
author_rank: Super Contributor
timestamp: January 01, 2024, 10:24:51 pm
content: Even with both antennas at 1m, I'm getting well over 3mi coverage. Does that calculator only assume straight line LoS without taking into account Fresnel? This seems overly optimistic, but maybe in the real world it'll work anyway. If someone has experience using such a calculator with real world tests to confirm, would be good to know.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: January 01, 2024, 10:48:10 pm
content: With 2m (144 MHz) Yagi antennas at 10m above ground, one site about 500 ft above sea level, the other only about 6 ft, at 50 miles between us, 40 Watts of SSB at each site, the prediction is pretty close to what we experience on daily skeds.On a 20 mile path over hilly ground, again on 2m SSB, the actual results are similar to predictions.Don’t forget the reliability percentage figure, and that the results can be influenced by building clutter, wet foliage and warm air rising over urban areas, etc.SJ