Hi,
We bought a full wave LoRa antenna (see picture) for our pycom device and we have tested it and it seems to be getting worse RSSI values than the normal small pycom antenna. At about 500m the pycom antenna gets around -77dbm and the full wave antenna gets around -100dbm which is about the same as a tiny internal antenna that we have so we are wondering what could be causing this?
Many different things can cause it apart from poor electrical connections. If youâre in a built up area where your testing it could just be the way the signals bouncing off buildings. Have you tried moving the antenna around to different locations?
I have tried a few different locations. Urban, suburban and in a remote location with not much interference.
The remote location is the one I need it for and that is the one that I did the test from 500m away. My concern is more that the pycom antenna in almost the same location works better. The small pycom antenna I have had ranges of around 5km and the large antenna that I would expect to be better only got to 1-2km.
My reason for getting the full wave antenna was that it could become a solution if we needed a bit more range but if it has less range than the half wave pycom antenna then there isnât much point.
I am having similar issues with this external half wave antenna. Could be the cable but I have 2 cables and both have the same result. I also have 2 of the full wave antennas so it seems unlikely to be a faulty antenna.
Thank you for your help
It does sound very odd.
Assuming the antennaâs were set up correctly it should be much better.
Iâm not sure if thereâs any radio operators on the forum that could help but if not it might be work giving the team at Core-Electronics a call.
Shaun
Ok might give core a call. What could cause them not to be set up correctly?
They are vertical, connected with a 1m RP-SMA(female) cable then a 100mm SMA(male)-u.fl cable. The settings on the pycom are optimized for range.
It could be as simple as grounding and installation. Antennaâs seam simple but theyâre actually very complicated pieces of equipment. The physical whip antenna is actually only half of the antenna.
Thereâs a short description of grounding here:
https://www.electronics-notes.com/articles/antennas-propagation/grounding-earthing/antenna-ground-plane-theory-design.php
Radio Frequency can be sneaky stuff, and a perfectly tuned antenna will not necessarily âmatchâ your transmitter thus causing âstanding wavesâ which can reduce the efficiency of your setup, or even worse, destroy the transmitter. Is your operating frequency 433MHz in which case the antenna should be about 70cm long, or 865MHz and therefore 35cm long?? Your antenna is quoted as being 500mm and therefore may not be suited to your transmitter. Antennas are always designed to a frequency, and a LoRa antenna may be for any of the available frequencies.
I have been planning (on and offf) a simple SWR meter for higher frequencies for Diyode magazine, but was not sure if there would be sufficient interest.It would require high sensitivity or a greater transmitting power than LoRa uses. Please, forum, is there a need for simple cheap LoRa test gear?
Bob Harper VK4WG (i.e. Radio Amateur)
PS: Sorry, I misread the question and now see you had said 500m, not 500mm which I wrongly assumed was the antenna length. This antenna type is designed for free space and should NOT require a groundplane, and in fact it should be mounted clear of anf groundplane by a metre or so.
Brief Commissioning procedureâŠ
-check that the antenna is designed for the same frequency (band) as you are using. (OR multi-band)
-check for any damage including that the cable hasnât been pulled off the antenna! (internally)
-check that the plug and sockets match each other and are clean of debris. (and dry)
-mount vertically above any metallic obstacles or groundplanes.
-if possible, use the internal SWR protection to test the quality f the match. (I do not know what your transmitter chip can/will allow you to do and how easy it might be to access the function.)
-if mounting where exposed to the elements, use a non-corrosive sealant to protect from the weather.
I donât see any mention of the impedance of the devices or the cable between them. These must be matched, or you will get no power transfer.
OK, understood, but to clarify⊠The expected impedance is nominally 50Ω for the cable and connectors but be aware that 75Ω can be another common impedance. The RF doesnât suddenly stop if impedance isnât matched, but there will be losses. Thatâs where SWR comes into the argument. For example if your transmitter is 50Ω but your antenna is 25Ω or 100Ω the SWR will be 2:1 and half your power will be absorbed by your transmitter possibly causing it to overheat and destroy the final transistors. NOT always, but in extreme circumstances at least. An SWR of 2:1 is to be avoided but is not that drastic, yet! We aim for less than 1.5:1, and OCD types want 1:1 which is like 0 or infinity, not quite achievable!
So you get power transfer, but not all of it!
The antenna best comparison would be to a âStandard Dipoleâ or other standard antenna. Then all other antennas can be assessed against that one standard.
âdBiâ is a mathematical comparison over an Isotropic Source, (hence the âiâ) which is a fictional antenna sharing the RF energy equally in all directions, over the surface of sphere centered on our antenna.
A full wave antenna should have a gain of about 3dB over a half wave dipole, which has gain over an Isotropic source. But 6dBi gain sounds more like advertising/marketing than engineering.
PS: I wrote about this in Diyode if you have access to past issues.
Pycom antennas work -really- well. I canât quite tell what model full wave antenna is in the photo, though it does appear different compared to the one we stock (which is shown below).
Test results aside, weâve done practical side by side testing with the Laird RG191 and were well impressed by the range/snr using the above antenna. The effective range more than doubled when mounted (compared to the duck antennas) at the same elevation. We get regular hits from across different regions in Newcastle, well outside of Adamstown.
With all of that said, Iâve never found myself needing a full wave with a LoPy4. From my experiments, is very easy to get 15-25KMs (line of sight) using the Pycom duck antenna.
TTN have a phone app that makes field diagnostics very easy. You get access to traffic logs and can see useful information, RSSI, gateways, SF, etc. I often refer to it as âa multimeter for LoRaWANâ in workshops.
Something more-offline would be nice though!
Hi Graham, thanks for your support.
We have just returned from the field where we have been testing the LoRa/Pycom œ wave antennas that we purchased from you. For our application it
would appear that the âPycom LoRa & Sigfox Antenna Kit SKU: CE04928â
may be beneficial in a number of areas.
The only issue with using this antenna could be protecting it from the elements and wildlife. It would be much appreciated if you could help with a couple of
questions:
With reference to the description of this antenna on your site (
https://core-electronics.com.au/pycom-lora-sigfox-antenna-kit.html ) it refers to the item as External Antenna. Does this have an IP rating, if
not do you believe it could handle continuous exposure to the elements in North Queensland?
We are also looking at the possibility of giving it extra mechanical protection by way of plastic tubing that completely surrounds the antenna. Do you know if this would have a negative effect on the antenna signal for LoRa?
If you can help with any of this it would be greatly appreciated.
Thanks
Bob,
Iâd vote for an analyser, I have lots of âlittle antennaeâ around and none are marked with their frequency. Also Iâm dubious of the specs of some of them.
BTW, 915Mhz is the Australian LoRa band.
Edward,
Iâd be real suspicious of the adapter and cable. At 915 losses go up astronomically.
Dave
I recognise that 915MHz is Australian LoRa allocation, but as an Amateur Radio Operator I have other nearby options, 420-450MHz being the most popular Band in which Hams use almost every possible means of comms from Morse Code to Amateur Television and Space communications via AR Satellites.
So if you want to step up your hobby please consider an Amateur radio Licence. Many Engineers of my vintage are Amateur radio Operators.
Re: your own âRadomeâ or plastic cover, Telecom whiten plastic conduit is often used by amateurs to weather protect a vertical antenna, and avoid âCockatoo Strikesâ as they love chewing up antennas.
Re: âAntennalyserâ for LoRa⊠It is a viable project and there are several commercial options but at a significant price. Home brewed Antennalyser at 915MHz would most likely consist of a curently used IC as the signal source, or a re-purposed old technology mobile phone or Arduino catIII shield!
The Guts of the unit is the Complex Impedance Bridge, which requires a little engineering to produce a predictable result, best achieved on a PCB with smd components. I have a useable design nearing completion.
The final part is a controller, datalogger, calculation engine and suitable display option.
Arduino/R-Pi fams will have more experience than I in graphic displays and touch screens so âTogether we are greater than the sum of our parts.â or âIt takes many specialists to make a siomple car!â
Aspiring engineers and programmers might like to put their hands up!
Follow on⊠The reason a full wave antenna has a better coverage is to do with the âAngle of Radiationâ (meaning that because it doesnât need a ground itâs best radiation is horizontal.) and itâs âBelly Gainâ (meaning that more vertical height causes the signal to be flatter and therefore stronger around itâs âBellyâ!
Also, Re: the Radome, there may be a slight loss in radiation but that depends on the material in the radome. PVC should not make a huge difference nor cause dlielectric losses, or change the tuning significantly⊠Make sure yo glue a Conduit end cap on the top, and leave the bottom open to drain any condensation from the radome.
The pictured Core antenna has itâs own radome of course and it doesnât need another one.
Bob,
FYI, Iâve just come across the nanoVNA.
have a look at https://www.rtl-sdr.com/reviews-of-the-nanovna-an-ultra-low-cost-50-vector-network-analyzer/comment-page-1/.
Dave
Thanks Dave, A VNA was at one time a $10,000 wish I could win Lotto kind of exercise. Now there are ICs to generate RF even over 18GHz, RF detectors to measure RF to those frequencies, and PCB manufacturers that can supply ceramic backed PCBs to keep things stable. However my eyesight isnât very SMD friendly nowadays.
So I had a quick look at the VNA you mentioned and like the idea of having one. I will certainly read the website more seriously when Iâve sent this, and see if it stacks up.
It canât be expected to be HP quality, but hobby quality is all weâre looking for.
The article I was thinking of was for an audio or LowRF frequency as an idea of how they work, and the programming to get answers from the data collected. âItâs only complex math!!!â B-)
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