Author Topic: Suggestions for an antenna in a box  (Read 179 times)

sheikhumar

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Suggestions for an antenna in a box
« on: February 18, 2019, 03:20:54 AM »
I am trying to build a Moteino node (RFM69HCW 433Mhz) that transmits to a gateway Moteino situated in the centre of the area that I need to cover (~50-60 metres radius mostly open area with 2 walls in between). The node can be at any point in this radius at any point in time and can be facing any direction. I am using a 173mm simple wire antenna (wavelength/4). Thing is I cannot keep the antenna vertical as suggested by almost everyone due to the height of the box that I am using (pictured below) so I have wrapped the wire around the sides of the box. The gateway does not have this constraint and I can keep the antenna vertical.

Will this approach decrease the range of the Moteino? I could alternatively make a hole in the box's lid and pass the antenna through that hole but I need the enclosure to be waterproof as much as possible so I am trying to avoid any unnecessary holes. Also will the wrapped wire have more/less range than a helical antenna?

Another thing, the antenna keeps breaking up from the Moteino due to flexing and I am afraid that soldering again and again might break the ANT connection on the Moteino. Can I use 2 wires as one Antenna, one small one which will be kept vertical attached to ANT and another one soldered to the shorter one, so there is less chance of the shorter one breaking? I read that I could use a Coaxial cable too, which one would be better?

Kylix

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Re: Suggestions for an antenna in a box
« Reply #1 on: February 18, 2019, 03:54:49 AM »
Felix also wraps the antenna for the SwitchMote:



The RSSI will decrease by doing it but ... you'll have to find yourself if the payload still reaches the Gateway (I'd say you won't have any problem with the whip wire though).

Otherwise, you could solder an u.FL connector on the moteino board:


and then attach an external SMA/RP-SMA antenna through a pigtail like this

« Last Edit: February 18, 2019, 04:00:46 AM by Kylix »

Felix

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Re: Suggestions for an antenna in a box
« Reply #2 on: February 18, 2019, 09:18:23 AM »
You can solder the ANT wire directly to the radio module ANT pin on the bottom, for a stronger connection. Or apply some hot glue around it...
You can always use different antennas for different applications and constraints. For very small places there are ceramic antennas - typically "small antenna" = "small horn" = "small performance" but you can get by if you only use it around the hours. Each antenna has its pros and cons. Too much to talk about here.
Wrapping the antenna will obviously have an effect on its effectiveness. I would only recommend where necessary, like the SwitchMote photos Kylix linked above, sometimes there's no better way.

HeneryH

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Re: Suggestions for an antenna in a box
« Reply #3 on: February 18, 2019, 10:02:18 PM »
I thought I read that wrapping into a helix would theortically not have any negative impact but in my actual experience it does.  I must have my theory incorrect.  It has been many many years since my EE studies and I haven't had practical in it since then.