The BIG and SMALL ANTENNA topic part 1

End Devices (Nodes) Hardware
28

interesting ! let us know the results :sunglasses:

29

I bought the last one listed but I won’t be able to do tests for a couple months. Please keep us in touch with your findings! :grinning:

30

It arrived. Looks really good and professional. Will Try to put it on the roof today. The cable in picture is not included.

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31

Hello,

I have a Cisco LoRaWAN gateway with me here.

You can attach two antennas to this gateway.
At the moment I only have one antenna for this gateway.
I’m wondering if a second omnidirectional antenna will have a big influence on the reach of the gateway.

Thanks in advance.

32

This will in most cases drastically lower the reception quality. Two omnidirectional antenna’s both receive the same broadcast from a node, but with a slight phase delay because they are placed some space apart from each other. If you connect these two antenna’s to the same radio, both signals are added and, because of the phase delay, partly cancel each other out.

The (publicly available) Cisco documentation is very brief, but I would suspect that both RF ports lead to the same radio front-end. This is probably for use with high-gain directional antennas.

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33

That Cisco gateway seemingly uses two SX1301. Could it be they have two completely separated radio paths?
Furthermore, they support two separate bands: 868MHz and 915MHz. Maybe they expect the user to use a different antenna for each?
I really wish the datasheet was more complete, or that I had one of those gateways to tear apart.

34

The SX1301 is a baseband processor, not a radio and it has no RF interface. It communicates to the SX1257 radios through a digital interface.

Indeed, a block diagram and some more information would be handy. I know some people at Cisco, maybe I’ll hear with them :slight_smile: .

35

I know, and this is why it’s weird. Why would you even need two SX1301, if you’re not effectively making two separate concentrators?
I’ll try and get in contact with them through my work, we’ll see if we can get anything out of it.

36

The Mtech Conduit also has the option of two SX1301’s, afaik to offer dual-band operation with the full amount of demodulators per band.

37

yeah :sweat_smile:

38

A Pitenna instead of a cantenna?

39

Here’s mine measured using a pocketVNA.
Mine is a 58 cm length with advertised gain of 5 dBi. Bought it from Taobao.
S11 plot is very good and VSWR is close to 1.0 at 868 MHz and 915 MHz. The 915 MHz is shifted a little towards 935 MHz though. On the Smith Chart plot, 50 Ohm impedance is spot on for 868 MHz and slightly at 935 MHz.

I actually bought the 1.2 m length with 10 dBi gain version. But, as I used a forwarding warehouse in China, the warehouse rejected them as the maximum length limit for shipping was 1.2 m and with the box and packaging it was 1.3 m! Had to send them back to the seller. But, seller was nice to do a refund. So ended up with these instead. Got it for RMB90 only and comes with the 2 clamps. The black antenna fixture I bought separately but unfortunately the hole was too small for the antenna to go in, so have to use the supplied clamp instead. The N-type connector to SMA cable was bought from them too at RMB15 for 1 meter length. Basically whatever you guys are paying on Aliexpress, it’s the same amount in Taobao but in RMB. Those guys really make a huge mark up.

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40

It looks pretty good for 868. It’d be even better if that VSWR were to be bang-on 868MHz, but it’s damn close.
For the Smith abacus, you forgot to put the marker on the right frequency :frowning_face:

Any chance you can get the gain tested? Last time I did something like that, it required two identical antennas and an anechoic chamber, among other things…

If someone had told me a few years ago I’d be looking at RF antenna impedance diagram for fun, I would have thrown them out of the room :rofl:.

41

you probably speak chinese ? nice tool that pocketVNA :sunglasses:

42

I can speak very little Chinese, like buying food and ask for direction. I used Google translate all the time and re-read the translation (the pin ying of course) so it makes sense before I hit the enter button!

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43

For the Smith abacus, you forgot to put the marker on the right frequency
I forgot about that but I did a trace along the path it is as what I have mentioned.

Any chance you can get the gain tested? Last time I did something like that, it required two identical antennas and an anechoic chamber, among other things…
Unfortunately I don’t have access to an anechoic chamber.

The USB VNA really helps because I used to purchase lots of antenna and to test them I usually put them on top of the roof to get as much of LOS as possible. It also means climbing up and down the roof to test. Surprisingly majority of these antennas are craps and totally out of tune. So, the VNA really helps to filter out bad antenna before even testing them outside. :slight_smile:

44

I did a search on that site … but :fearful:

45

You should always search using Chinese words instead of English. That way you get what you really want. Those results with English are usually used as a bait for people out of China I guess (just look at the price, it’s high even for Taobao standard). Here’s a modified search of yours in Chinese. I basically translate the phrase “antenna glass” into Chinese and add 868MHz at the back. Once you see something you like but want to see more of these, mouse over them, there’s an option of “find similar”. It’s sort of like an art. Unless you are searching for rock band T-shirts, very less likely your English phrase search is useful!

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47

will this Aomway 915MHZ 933MHZ 3dBi 50ohm T Type Spring Spiral Antenna SMA RP-SMA For rxReceiver. I am testing simple dragino + arduino on 915+ mHz indoor. I am a total newby to all this. Here is the link. https://www.banggood.com/Aomway-915MHZ-933MHZ-3dBi-50ohm-T-Type-Spring-Spiral-Antenna-SMA-RP-SMA-For-rxReceiver-p-1126186.html

48

only for receiving (possibly it is not 'matched) … not the best choice