I have a Dragino LPS8 Gateway. In my first setup my gateway was installed in a closet with the small antenna. I live in an urban area, 3d and last floor of my house. All the houses in the are are 3d floor high.
I had approximately a coverage of 400m around the gateway, a normal coverage for my setup.
For now what I have seen, it improves the coverage up to 1.3km around me. That’s the good point.
But in an area of 400m around my coverage is really poor.
So does it comes from the antenna? Or my setup?
Higher gain antenna should really be avoided as the way they work is they focus the energy towards the horizon if you are lucky and choose the right one, or towards a down angle or up into sky if you choose wrong. (Ok if broadcasting from a hill or high mast/tower or talking to planes!) In doing this they create nulls and peaks closer in which get worse as the gain increases! Also they can be very poor immediately above and below, if mounted high enough depending in building construction you can often find that signal level is very poor in the immediate surrounding area. There is a reason why the emergency services often use simple stumpy 2 or 3 dbi ants!
Note 1.3km is ok ish in a dense urban environment but usually look for 2-3.5km depending on absorbers, building clutter and mitigating reflection assist. Is external ant on very good ultra low loss cable or simple RG58 type? That can loose you a lot of range if not compensated withTx Pwr, and that doesn’t help loss of sensitivity.
Depending on the variant of 240 cable used 8m will be loosing you about 2,2db @915Mhz, good but not brilliant, add in say 0.5-0.7db loss for the 4 connectors and you are down 2.7+db. I would tend to keep that to <4 or maybe 5m. To put that loss in context it is roughly the same as stepping down 1 SF in terms of LoRa coding gain wrt range - i.e. @SF 10 a node will look more like SF9, at SF8 it would have range more like SF7…
My knowledge in RF and antennas is closed to zero so sorry il my question are stupid…
Can I assume that my internal antenna is a 0dBi?
If I use a 3dBi antenna and my loss in cables and connectors is 2.7dB can I that there is no gain to use an external antenna? Or my coverage must be better because the antenna is higher and less obstacles between the device and the gateway?
You said that I am better to use a 3dBi antenna rather than a 6dBi because of the 6dBi antenna will focus toward the horizon. But I guess that there is an optimal hight to choose for my 3dBi antenna. How can I choose this height?
And if you know a good website who explain antenna for dummies
The simplest practical antenna, a 1/4wave vertical or dipole has a gain of 2.1dBi and this is assumed to be used when the power limits are set, normally 14dBm.
So if for instance you fitted a 6dBi antenna direct to the gateway (no losses) then you would be exceeding the legal power limit by 6-2.1 = 3.9dBm, assuming the transmitter was set to 14dBm.
If you had the antenna on cables with a loss of 2.7dB, you would be exceeding the power limit by 6-2.1-2.7 = 1.2dBm.
The position of the antenna can be more important than the gain. If you use the internal antenna inside a building you will get a coverage of a few 100m. The signal will be significantly attenuated by walls and windows.
If you put the gateway with its internal antenna on the roof of a building the coverage will increase.
If you cannot install the gateway outside, put the gateway under the roof and install an antenna outside on a pole. It is a good solution if the gain of the antenna compensates the loss of the cable and the plugs. The position and the radiation diagram of the antenna is more important than the gain.
Using 14dBm ERP and SF7 the maximum distance can be more than 300km. You need 6dB more to double the distance. So even if you have only 8dBm ERP you can already achieve 150km. Gain is not as important as it seems.
What is important? The antenna of your gateway should “see” the node because at 868 MHz we have a quasi optical propagation with some reflections.
I am trying to find a better antenna than my actual antenna.
Actually I have the following radiation diagram:
As I said the coverage is not optimum when I closed to the gateway.
I am looking to the 5.8dBi Rak antenna, easy for me to buy and it looks like to have a good radiation diagram:
Yes, reread my post above and avoid using higher gain ants! As stated the higher gain does not come through some magical amplification but rather by focussing existing available RF energy. In doing so they induce greater and greater notching of pattern which bets more pronounced as headline gain of ant increases. This can best be seen by the dips at approx 230deg and 190deg in the 1st plot you just posted… where do you think your shorter range coverage will be serviced from when ant installed. Stick to a 2-3.5 dbi ant with closer to isotopic radiation pattern.
Yes I understand what you say, but when I look at the Dragino antenna which have a gain of 3dBi and I am not convinced of the better coverage I will have. And it’s the same thing for the 3dBi RAK antenna. That’s why I was looking at the 5.8dBi antenna.
Below it’s the 3dBi RAK antenna. It looks worth than my actual antenna…
What you say is a manual action and it’s to stay legal. There is nothing automatic in my gateway.
Maybe I am wrong I am a newbie in RF and antennas…
That’s why you’d have to make the manual adjustment (to the TX level tables) if you use a higher gain antenna. And that adjustment would remove the benefit of the higher gain antenna, making the whole exercise pointless.
Additional antenna gain which raises the ERP above 14dBm, in most countries, requires that you reduce the transmit power which then results in no advantage to distant nodes receiving packets.
In addition to not improving performance for distance nodes a high gain antenna can make close in reception worse …
OK so what are the pro to change my origin antenna for a new one? Except the fact that it will be waterproof?
I can keep my indoor antenna and put it on my roof…
