LoRa experiences? 2

[itsmoked]

Hi, I'm working on a product that should be 'connected'. It's a very low data rate kind of product that basically states something is working correctly with perhaps a few bytes of data thrown in. I assumed I was going to use LTE since I have a commercial M2M account with a provider but then I stumbled across some LoRa videos and looked into it further. Dang! Free connectivity. I can get into that! If there isn't a LoRa gateway around you can put your own up, so that's what I'm going to do.

I'd hate to miss out on any available wisdom. Have any of you done anything with LoRa?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[VEBill]

Not me, but...

On YouTube is Andreas Spiess ("the guy with the Swiss accent").

If I recall correctly, he's done quite a few excellent videos on this subject. Goes into tremendous detail, and shows the common errors that he makes along the way.

Perhaps that's the videos that you've seen.

Beware the different frequency bands. Again from memory, Asia 433 MHz, Europe 868 MHz, North America 915 MHz. Please double check.

I'm tempted to set-up a gateway for my area, but I've got too many other things to do.

Cheers.

 

[itsmoked]

Thanks VE.

He is indeed the one who woke me up to the subject. Heck, his videos are so good that for the first time I became a Patreon and am supporting him and his endeavors.

I've ordered most everything but an antenna to do this. I thought there was a good 'antenna store' somewhere but I'm not finding any. I'm considering a 'base station' style in 915MHz. Got any thoughts on if that's worth it verses some little junker antenna?

In Andreas' "War Driving" video he discovered that setting even crummy antenna'd nodes on the roof of his car considerably enhanced reception due to the ground plane thus provided. It just so happens that my chimney has a flat piece of heavy sheetmetal (6 x 3 feet) capping it (no longer a fireplace). So I was thinking of mounting the antenna in the center of that plane. Perhaps a magnetic base so-so antenna would do the job on that plane.

I recall that if you have a plane under an antenna you can slightly beam the radiation based on how you position the antenna on the finite sized plane. Is that true and if it is which way does that work? Does the beam sort of head in the direction of longest projection of the ground plane in front of the antenna? Or am I all wet?

I'm also toying with the idea of using wifi to link to the back-haul because then I could solar power the whole thing and just plop it down anywhere without wires of any kind. Thoughts?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[VEBill]

At higher frequencies, even 915 MHz, moving the RF hardware 'up the tower' (so to speak) resulting in extremely short RF cables means that the cable loss due to lengthy coaxial cables is essentially eliminated. As you're contemplating, the backhaul down to 'ItSmoked HQ' can be by baseband cable or (as you've mentioned) WiFi.

Having suffered through at least two nearby lightning strikes, a wireless link (and local solar power) would be better (safer, lightning-wise) than cable(s).

Antennas: You can achieve fairly high gain and omni-directionality with a high gain vertical monopole (typically a collinear array). They squeeze the gain along the horizon, assuming that's where everyone is located. You could make one if you wish, but ideally some test equipment would be used to confirm the tuning / match.

Beware cheap commercial antennas. Many are junk. Even the ones where the antenna makes sense may have extremely lossy cable. I have a Wifi Yagi that is in need of better coax.

I wouldn't bother using the ground plane to try to twist the gain pattern. There are better approaches.

A nominal ground plane is about +5% bigger than quarter wavelength. Many applications would be best with a ground plane that is not horizontal, but sloped down. This improves the match to 50-ohms and pulls the gain down a bit to hit the horizon. General rule of thumb.

If I were you, just get it working and optimise the antenna as Phase 2. Don't let the antenna distract you from the other 99% of the project.

 

[itsmoked]

Thanks for the education.

I think your last point is a great one.

I've also recognized the geographic limitations of my location making an omnidirectional pattern sort of pointless. The location has about a 150 foot near-cliff surrounding it around the back 180 degrees about a 2 blocks away. Seems I'd be wasting fully half the radiated power projecting against that hillside. Maybe there's a planer antenna that would roughly beam in one direction (the direction of most potential users). I'll give the antenna that's coming in the kit a try first.

I have one specific location I'm trying to reach, a fellow EEs across town. He's 26 feet below me but about 1000 ft from him there's a geographical 1~2 meter hump I'm hoping won't stymie this whole thing.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[VEBill]

Optimising antenna gain pattern is something I'm familiar with. As you probably know, it's not always about maximum gain. For example, some aircraft installations would be best with the mythical isotropic antenna to provide zero gain and complete spherical coverage (to allow the aircraft to manoeuvre).

Perhaps you'd want a vertical element with a simple reflector. Either a 2-element Yagi (no directors) or a flat plate reflector. These would approximate (roughly) a cardioid pattern with a null aimed at your cliff and modest gain towards the front.

The YouTube videos hint that the LoRa range is incredible, so perhaps any old antenna would be fine.

PS: If you're making an antenna, a vertical dipole is often (much) easier to build than a ground plane. Less material and slimmer. Even the pattern can be slightly better aligned to the horizon (just a bit).

 

[itsmoked]

Now this is starting to sound like fun. Do you know of any web resources that show antenna styles and roughly what kind of patterns they project?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MacGyverS2000]

This might help, Keith:

Near the right-hand side you can see how multi-element antennas affect the pattern... pretty much everything out there is some form/combination of what's shown above.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[VEBill]

Actually, the complete range of antenna concepts and designs is mind-bogglingly vast.

Here's just an example, the Quadrifilar Helix. Provides circular polarization and wide coverage.

There are plenty more...

 

[VEBill]

The ARRL and the RSGB both publish quite a few antenna reference books. They're nicely focused on both the basic theory and the hands-on practical.

For your purposes, look for the ones covering the practicalities of V/UHF antennas. But even the general antenna books (e.g. covering HF antennas) still provide very useful background information applicable to any antenna application.

Unfortunately, these ARRL & RSGB books are often annoyingly expensive and annoyingly softcover.

 

[itsmoked]

Yes! This should be fun..
Thanks Dan! Just what I was looking for.

V; I love those two books, ARRL and RSGB, in the general handbook versions. I have 20 year old copies of both and am OK with the floppy covers.

I didn't know they had "antenna books". I'll hunt them down. I'm working in 915Mhz so long UHF sort VHF as you say.

Crazy helical you show there. With regards to light if one circularly polarizes light the receiving end should look for circularly polarized light and of course the same with microwaves as they use that to separate the up/down links of close geosynchronous satellites. Which begs the question: Is it OK to use a base-station antenna that's circularly polarized if the entire field of radios are all dipoles?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[IRstuff]

I would think that you'd lose 50% signal, on average

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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[VEBill]

I mentioned the Quadrifilar Helix as just an example that is arguably outside the posted 'Table 6-2' menu. It wasn't intended to be necessarily applicable to this application. The intended point is that the total range of antenna concepts and designs is vast, beyond the array of options presented in Table 6-2.

Yes. The downside of combining linear polarization with circular polarization (CP) is the -3dB cross-polarization penalty (linear to circular). An advantage of linear-to-circular is the elimination of the approximately -30dB dips when linear antennas are cross-polarized, while allowing simple whips at one end. This resistance to one source of fade can be very useful in certain applications (it's not uncommon with hobbyist drones, video links to ground).

One shouldn't think in terms of linear "50%" because it can be misleading (even if arguably accurate) when applied to communications links. -50% sounds so serious, but it's "only" -3dB which is quite often completely trivial. Another example is arranging a +30dB signal margin, which may be considered to be perfectly reasonable and comfortable. Thinking of such a margin in terms of a linear 1000x can lead to misunderstandings. But it is fair to use linear comparisons for RF heating applications where it really is linear.

--

Here's a picture of Apollo 9 CM pilot Dave Scott admiring quite a lovely antenna (NASA March 1969). ;-)

 

[itsmoked]

Ohhh, a nice little helical with a ground plane.
Thanks V for the helical/linear info.

For a little light reading I ordered three antenna books. One was like $3 as a Kindle book!

I got:

and

Now I need a LoRa transmitter that sends GPS coordinates so I can map coverage and generally test the system.


I also need to find someone who can run any antennas I build thru a directional coupling feeding it a swept frequency and displaying the reflection to see if I'm hitting the mark.

Keith Cress
kcress -

http://www.flaminsystems.com