Antenna for Simple Device in Oil Drum

[flywire]

I’m looking at putting a simple RFM95W 915 / ESP32 device in a rural mailbox (oil drum - metal cylinder with round surface to the top) 1.2 m above ground 5 km away. Around mailbox end is a little challenged for sight distance from the other end high on a hill.

@TijnOnlijn

The almost best results I had so far were with relatively thick solid copper wire.

Measurements in table at end of UCA_Board/Antenna/UCA_Antenna_tuto.pdf at master · FabienFerrero/UCA_Board · GitHub show good performance from simple antennas.

I’m concerned about distance, metal container, ground-plane and damage/vandalism to obvious device. Any advice on how to get a good signal with a simple antenna?

[LoRaTracker]

@flywire

I’m looking at putting a simple RFM95W 915 / ESP32 device in a rural mailbox (oil drum - metal cylinder with round surface to the top) 1.2 m above ground 5 km away. Around mailbox end is a little challenged for sight distance from the other end high on a hill.

How high is the TTN Gateway antenna ?

[flywire]

60+ m

[LoRaTracker]

A simple rule with antennas is the higher the better.

Another is keep antenna cable runs as short as possible.

(and yes that can be a contradiction)

The oil drum will act like a ground plane, which helps.

Whether your link works over a ‘challenged’ line of sight rather depends, UHF comms is heavily dependant on line of sight. At short range you can get reception, when there is no line of sight, due to reflections.

[flywire]

Can you explain the oil drum acting like a ground plane? I’m thinking of a short copper wire directly into the RFM95W module. I understand with this configuration the length of the antenna is taken from the top of the pcb. What would be inside the drum and what outside?

Worst case I’m sure there would be good (through one tree) line of sight within 6 m in height (length of a pvc pipe) at the mail box which is probably achievable - flagpole hey? Maybe with a funny cap.

Btw - easily get 15 km from inside building on hill to inside another building on the flat with a handheld 0.5W Handheld UHF radio claimed to have 4 km range yet can’t get anything 200 m off the edge of the hill in the shadow.

[BoRRoZ]

@flywire

Maybe with a funny cap.

yes, excellent plan

[flywire]

@BoRRoZ

excellent plan

That’s worst case. I want to explore simple options more.

[BoRRoZ]

I would go for your lovely idea of a pole with a funny cap
And maybe this one in top ?

Very simple homemade outdoor 868Mhz antenna (groundplane)

Hamradio is all about experimenting, so why not build another antenna ? One of the most common antenna’s is the ground plane antenna which is basicly a 1/4 lambda driver element and 3 or 4 reflector elements (creating a artificial ground). It’s a simple antenna to build with a good bandwidth, it doesn’t have any gain over a dipole because it’s dipole. Ok for the record it has a +2.15dBi gain (so you 3$ ebay 5 dBi antenna only has a 2.85dB gain over a dipole) More info at : Electronic…

[flywire]

Yeah, that’s the worst case funny cap I had in mind, possibly as a solid base plane over pvc pole cap. Maybe even just as a flat circle base plane.

Now, how does the short copper wire get a reasonable chance? Inside or outside the drum and where in respect to the drum as ground plane?

[BoRRoZ]

is the drum horizontal or vertical placed, what are the exact measurents, what material.
Can you for example drill a little hole to place an SMA (or N type) connector ?

many questions, but it also a complicated, not easy to test yourself, problem

[lex_ph2lb]

You could also use a simple stock antenna and mount it like this (using a cable gland to make a water tight seal ) :

That way you can add the antenna on top and seal it nicely.

The sameway I build my Inside-out-antenna :

http://www.ph2lb.nl/blog/index.php?page=lora-inside-out-antenna

[flywire]

The 20l drum is like the one below but laying on it’s side sitting on a post. No worries about drilling a hole into it. Some people seem to have the urge to drive over them!

A SMA connector means the copper wire won’t be directly soldered to the RFM95W module.

I’m still not clear on how “The Ground Plane Antenna” section in the more info document works (something about impedance) but it seems if it is directly connected to the RFM95W module then it needs to be above the drum. An esp32 will be under the module and there will be a usb power bank there too. I’d probably prefer to attach a 100 mm pvc cube (electrical junction box) to the top of the drum, even if I need to put a new flat ground plane disk in the junction box.

[BoRRoZ]

very interesting project… keep us informed !

[flywire]

I agree although a couple of points:

1. My first rule is simple so I don’t want to use an sma connector if I don’t need it.
2. I suspect a short pvc tube wouldn’t draw much curiosity so less likely to be interfered with.
3. Surely a copper wire inside the pvc tube above the drum would make a rubber antenna redundant.
4. Still wondering exactly where the ground plane would be if the antenna wire above the drum is soldered directly to the RFM95W module inside the drum?