{"id":2926,"date":"2024-03-18T13:45:02","date_gmt":"2024-03-18T13:45:02","guid":{"rendered":"https:\/\/m0aws.co.uk\/?p=2926"},"modified":"2024-03-22T14:19:52","modified_gmt":"2024-03-22T14:19:52","slug":"868mhz-ground-plane-vertical-antenna","status":"publish","type":"post","link":"https:\/\/m0aws.co.uk\/?p=2926","title":{"rendered":"868Mhz Ground Plane Vertical Antenna"},"content":{"rendered":"\n

In my quest to improve my Meshtastic<\/a> signal range using home-brew antennas I’ve finally put together a neat little ground plane vertical antenna for the 868Mhz ISM band.<\/p>\n\n\n\n

The design follows the normal ground plane simplicity using 4 radials and a vertical radiating element albeit on a tiny scale. The radiating element is 82mm long and the radials are each 92mm long.<\/p>\n\n\n\n

\"M0AWS<\/a>
M0AWS 868Mhz Ground Plane Vertical Antenna<\/figcaption><\/figure>\n\n\n\n

Initially I modelled the antenna at a height of 3m above the ground with the radials tilted downwards at 45 degrees. I took this approach as this is how I have built ground plane verticals for the 70cm band in the past and so I thought I’d try the same approach on the 868Mhz ISM band. (I later found this to be detrimental to tuning!)<\/p>\n\n\n\n

The 3D far field plot for the antenna shows it has a very nice, relatively high gain lobe at just 2 degrees elevation with a number of lower gain lobes higher up.<\/p>\n\n\n\n

\"M0AWS<\/a>
M0AWS 868Mhz Ground Plane Vertical Antenna 3D Far Field Plot<\/figcaption><\/figure>\n\n\n\n

Looking at the 2D far field plot you can get a better understanding of the radiation pattern and gain figures at various angles. At 2 degrees there is 6.7dBi gain with the next major lobe being at 8 degrees with 4.36dBi gain, far more than I imagined I’d see for such a simple antenna.<\/p>\n\n\n\n

\"M0AWS<\/a>
M0AWS 868Mhz Ground Plane Vertical Antenna 2D Far Field Plot<\/figcaption><\/figure>\n\n\n\n

Putting the antenna together was easy enough with particular attention being paid to the measurements of both the radials and radiating element. I soldered some lugs to the ends of the 2.5mm diameter solid core wire radials to enable easy attachment to the N Type chassis socket that I decided to use as the base for the antenna. This worked out well and provided a good solid mechanical and electrical connection for the 4 radials.<\/p>\n\n\n\n

For the radiating element I used an N Type plug with the vertical 2.5mm solid core wire element soldered to the inner centre pin of the male connector. I also slid a small piece of insulation down the wire to stop it from shorting against the metal outer of the plug and then pushed in a tight rubber plug to stop water ingress.<\/p>\n\n\n\n

\"M0AWS
M0AWS 868Mhz Ground Plane Antenna Close Up<\/figcaption><\/figure>\n\n\n\n

Connecting my VNA I found the antenna was mostly resonant at 790Mhz with an SWR of 2.5:1. I knew this would be the case and that the wires would need a little trimming. <\/p>\n\n\n\n

Trimming the wires a couple of times in 1mm nibbles<\/em> I got the point of resonance up to 868Mhz but, the antenna was still exhibiting a lot of reactance that was keeping the SWR above 2:1. Trimming the radials reduced this slightly but, I could not get an SWR much lower than 1.95:1.<\/p>\n\n\n\n

Scratching my head I decided to try moving the radials back up so that they were horizontal rather than at 45 degrees downwards, this had the immediate effect of the SWR dropping to 1.1:1. <\/p>\n\n\n\n

\"M0AWS
M0AWS A rather fuzzy photo of the 868Mhz SWR curve for the GP Antenna<\/figcaption><\/figure>\n\n\n\n

The SWR stays below 1.2:1 from 868Mhz to 871Mhz which is plenty wide enough for the Meshtastic devices. Why there is so much reactance when the radials are bent down at 45 degrees I am not sure, but it was easy enough to resolve.<\/p>\n\n\n\n

\"M0AWS<\/a>
M0AWS 868Mhz Ground Plane Antenna<\/figcaption><\/figure>\n\n\n\n

The finished antenna is tiny but, seems to work well. Signals from my other nodes are up by 6-9dB according to the SNR reports in the Meshtastic app. I now need to make a couple more of these for my other nodes and then hope to hear some other nodes locally once they appear on air.<\/p>\n\n\n\n

Remodelling the antenna in EzNEC with the radials as shown above the gain at 2 degrees is now 5.5dBi, down 1.2dBi but, the overall radiation pattern is identical to the original. <\/p>\n\n\n\n

Total cost of the build is about \u00a31 and an hour of my time tinkering with it, bargain!<\/p>\n\n\n\n

\"M0AWS-4
M0AWS-4 Meshtastic Node 868Mhz Antenna Deployment<\/figcaption><\/figure>\n\n\n\n

More soon …<\/p>\n","protected":false},"excerpt":{"rendered":"

In my quest to improve my Meshtastic signal range using home-brew antennas I’ve finally put together a neat little ground plane vertical antenna for the 868Mhz ISM band. The design follows the normal ground plane simplicity using 4 radials and a vertical radiating element albeit on a tiny scale. The radiating element is 82mm long … <\/p>\n

Continue reading “868Mhz Ground Plane Vertical Antenna”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[276,6,28,45,4,271,285,65,275,272,186,134,227,232,233,17],"tags":[],"class_list":["post-2926","post","type-post","status-publish","format-standard","hentry","category-868mhz","category-antenna","category-antenna-modelling","category-eznec","category-ham-radio","category-heltec","category-heltecesp32v3","category-home-brew","category-ism","category-meshtastic","category-nodes","category-projects","category-swr","category-vna","category-vna-3g","category-weak-signals"],"_links":{"self":[{"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/2926","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2926"}],"version-history":[{"count":26,"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/2926\/revisions"}],"predecessor-version":[{"id":2966,"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/2926\/revisions\/2966"}],"wp:attachment":[{"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2926"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2926"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2926"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}