The amateur radio corner


(Jcavera) #1

I had made this to a thread that will probably be buried, and so it's worth mentioning again: Get involved with your local amateur radio group! We are actually using radio, after all. And there are several benefits to be gained from collaboration...

  • You can learn about software defined radio. If nothing else, it's a very useful debugging tool. Kind of like a Wireshark for RF.
  • Hams run repeaters. Repeaters are on towers. And they often have internet access for control purposes. If you ask nicely, they may let you co-locate a gateway.
  • In many parts of the world, amateur radio frequency allocations bumps up against the ISM bands used by LoRa. It's nice to play nice.
  • Bring LoRa to hams. They already experiment with half-a-dozen different digital modes and our tools and techniques could bring some positive cross-over.

Just my two cents. Sorry if it's been discussed before.


The BARGAIN basement part 2
#2

there are allready ham's active with lora/ttn as far as I know.

maybe you can change the topic title in : THE AMATEUR RADIO CORNER for example
so ham's can find each other here on TTN


#3

Sounds good. I must say I really do value their knowledge and think they're a valuable contribution to ttn, but also that I have difficulties in understanding their explanations. It is really a specialism.


(Jcavera) #4

Good suggestion -- done!


(Jcavera) #5

Well, I'm a ham (N9EVY) and so I'll try to keep any explanations simple and on-point! :slight_smile:


#6

Well that's great! Most RF topics here are about gateway antenna's. Nodes often use simple flexible wires that aren't even straight. I think there's much to win in an explanation how the ideal node antenna would look like. Material, dimension, ground plane (or area) and such. For instance I usually use 1,5mm thick massive copper rod. 86 mm in length while I think in theory it should be 82mm but the 86 seems to perform better.

Do you have an opinion about it?


(Jcavera) #7

Indeed I do! First note this: Antennas are voodoo. Pure and simple. If you get better amplification by swinging a dead cat three times under a full moon, then by god, ship every unit with a dead cat. That said, there are a few general principles:

  • 1/(2^n) wave antennas are better than other oddball ratios. Full wave are generally best.
  • Vertical antennas are omni-directional, but that just means that they suck equally in every direction.
  • Ground planes are great and bigger is generally better. A square mile sheet of copper should do it.

And something that applies to your case:

  • The antenna is not the antenna. The antenna is the antenna plus everything leading up to it that isn't completely shielded, minus the parts that are inadvertently shielded, plus an unknown (and unknowable) factor based on god's will and the signs of the zodiac.

Seriously, antennas are voodoo. If you want repeatability, then L-com makes some fine antennas that almost always conform to spec. Except when they don't. But then you can return 'em. For tiny, do-it-yourself nodes, I'm (so far) having okay results with quarter-wave-ish, 18 awg wire pointing more-or-less straight up.

Now for the "optimum" case. Note that this is theoretical (doable) optimum and actual optimum may involve the aforementioned voodoo rituals and dead cats. Circular hunk of solid copper as a ground plane, one-wavelength in diameter, with everything below that shielded and sunk to earth ground. From that, a full-wave vertical, as straight as possible, and preferably superconducting, or at least solid copper.


#8

I'll have a good thought about that :slight_smile:

As far as I understood 1/2 wl would not be better than 1/4th. But would a single full wavelength wire work better though? Even when it's not tied to a cat (for simplicity I ignore the color and temperature of the cat here)


(Jcavera) #9

As far as full, half, quarter, eighth, etc. waves: In theory, you get slightly better results from longer to shorter (full better than half, half better than quarter, and so on). But that difference may be tiny. Other things that you can do that would make more of a difference are better shielding leading up to the antenna and a better ground plane.

Oh, and calicos seem to work better than marmalade cats. Or so I've been told.


(Jcavera) #10

Oh, and get an SWR meter! Good impedance matching between the feed (everything before the antenna) and the antenna itself is probably the best thing that you can do! If SWR is high, you can take wire cutters and clip the antenna, or add a variable loading coil (antenna tuner) to make it a better match!

[edit because SWR meters need more explanation] The goal of any antenna is to convince a bunch of unruly electrons that they should be making photons instead of heat. To measure that tendency, an SWR meter is used to measure the "standing wave reflection". This gives you a basic indication as to how well the antenna is managing power. A ratio of 1:1 means that (almost) all of the electrons are managing to make a nice radio wave. Higher ratios means that some part of the signal is lost to waste heat.

So in practice, you put an SWR meter in between the antenna feed line and the antenna itself and then adjust accordingly. Note that SWR meters have connectors designed for larger antennas and so won't really give meaningful results if you're just soldering a wire to a PCB.


#11

Would it be an idea if radio amateurs would tune the gateways in their neighborhood? No need that everyone got such a meter himself and besides, i guess when you exactly know how to use might be useful too.


(Jcavera) #12

That would be a good idea. And it'd be particularly simple if the gateway in question is co-located with a ham repeater (see above). That way, when routine maintenance and tuning is done, it could just be done on everything at once.


#13

most radio amateurs don't have the right equipment to 'tune' at these high frequencies, also many antenna's and lora transmitters can't be 'tuned imho


(Jcavera) #14

True in that UHF and EHF SWR meters are much more rare than their HF/VHF counterparts. But they can be had for a couple hundred bucks. And if a ham is running a 1.2 Ghz repeater, they'll almost certainly have one. As far as tuning... true to a point. But if you're using a vertical hunk of wire as an impromptu antenna, you can tune it by lopping off bits with a wire cutter. (important safety tip: do not lop off bits while transmitting)


#15

and that's only one side of the story.. you will need a separate RF generator with a variable RF output because the signal level of a lora transmitter (like rn2483) is to low (and to short) to meassure SWR unless you own very expensive equipment off course :wink:


#16

Given the amount of energy LoRaWAN uses I don't think there will be much of a health risk.


(Jcavera) #17

Very true! I hadn't thought about the power requirement! Yeah, most diagnostic tools need more than +30 dBm to work with. And unfortunately, LoRa tops out at +30 (here in the US anyways -- can't speak for other places).


#18

Glad there is a ham radio corner on TTN !

My callsign is ON3ZOE and active since several years on HF mainly in digital modes, especially wspr and PSK (in QRP). These operating modes are the reason why I am interested in loraWAN : getting data over UHF bands in smallband and below the noise.
Most of the ham operators I know in Belgium are involved in WirelessThings or WirelessBelgium, who own UHF/VHF repeaters with lora gateways and Wifi dishes on it. Our gateway (RPi and IMST ic880A on Mikrotik board) is located on such a high premise and connected to their backend.

If any other hams are active on this TTN forum I'd be glad to hear from them - I already met Lex PH2LB http://www.ph2lb.nl/blog/index.php?page=lora who is very responsive when antennas are discussed. On our side we know some more about Software Defined Radio.

73s de on3zoe.


#19

received yesterday by mistake, any of you dutch radio amateurs interested ? pm me :sunglasses:


#20

Like OM Wim ON3ZOE all ready wrote in the post above, I'm also a amateur radio operator / ham / OM which is active on this forum. I have done a few things with antenna experiments and helped a few people with my hands-on ham radio operating practice and / or idea's about the RF part of TTN / LoRaWAN.

IMHO hams (amateur radio operators) can contribute to the TTN / LoRaWAN because most of them like to experiment, have hands-on experience and build RF related stuff. Although most of them prefer working with lower frequencies (often the HF frequencies < 30Mhz) there are still a lot of hams experimenting with higher frequencies like 70cm (430Mhz), 23cm (1230Mhz), 13cm (2300Mhz), up to 3cm (+10Ghz).

73 de Lex PH2LB