The BIG and SMALL ANTENNA topic part 2


#109

see The big Antenna S11 catalog


#110

I actually use these specific antennas on a whole load of gateways, including outside ones (although I use heatshrink and amalgamating to seal them). They have worked fine outside for over two years with no deterioration.


The big Antenna S11 catalog
#111

Your comment is a little off-topic (doesn’t talk about S11), so I’ll have to delete it.

But to comment on it first: even though you can make these whip antennas work for outdoor gateways, you change its characteristic by adding more plastic to it. So it works, but it is not recommended. It’s much better to use a proper outdoor antenna with mounting brackets on an outdoor gateway.


#112

Just making the point about return loss values and their S11 relevance to distance.
As has been stated many times before - Placement away from other objects, high up and line of sight to node is far more important than the antenna itself (as long as it is not affected by exposure to elements)

  • 6dB return loss === 75% of power is output
  • 10dB return loss === 90% of power is output
  • 20dB return loss === 99% of power is output

Also, Field strength (The measurement that determines how your antenna “sings”) is not the same as power.
https://www.satelusa.com/blog/tech-note-radio-power-vs-distance/

Field strength is measured by the square root of power, so if you take the best and worst cases as above, the distance increase will only equate to about 15% e.g. from 500m to 575m.

= ( SquareRoot(100) - SquareRoot(75) ) * 100 / (SquareRoot(75)
= ( 10 - 8.66 ) * 100 / 8.66
=== 15% increase in distance

Here is a table linking the info
Return%20Loss%20to%20VWSR%20table


(LoRaTracker) #113

What you really need to know is how well an antenna actually radiates power (in the direction of choice).

You can build (or buy I guess) an antenna that performs just great on a fancy antenna gizmo but radiates badly.


#114

For those that are interesting in modelling antenna, download “mmanabasic.zip” from here
http://hamsoft.ca/pages/mmana-gal.php

There are loads of examples to play with in the examples folder, and you can immediately see the predicted effect of tweaking after you have pressed “start”. You can also view the polar plot in 2D or 3D (press 3D FF) and rotate your viewpoint.
You can also change the height of the antenna with respect to actual ground (Change the “add height” option in the tab “Calculate” ) and mess about with the “type of ground”

Once installed, do the following:

  1. Execute MMANABASIC_GAL (Should be in your list of programs)
  2. Press “File–>Open” and select this file “C:\MMANA-GAL_Basic\ANT\HF simple\Vertical\0.25GP with slope radials.maa”
  3. Press the tab for “Calculate” and press the button “start”
  4. Press the tab for “Far Field Plots” and you get this plot - notice the SWR and calculated Impedance

MMANA-GAL%20quarter

If you want to see how things change, change a 1/4 wave vertical to a 3/4 wave vertical. All you have to do is press the tab for “Geometry” and change the Z2 length from 5.233258 to 15.699774, and repeat steps 3 and 4

What you will notice is that a 3/4 wave vertical has a higher angle of radiation and a worse SWR (because the impedance isn’t near 50 ohms) as per this
MMANA-GAL%20three%20quarters


(Tony Smith) #115

Thanks @CurlyWurly for the link. The biggest takeaway from these plots; over real (resistive) soil the power transmitted horizontally or even below the horizontal is zero. So this antenna is fine on a node where the gateway is elevated, but not the reverse,


#116

Some practical tests today with the antennas I measured in The big Antenna S11 catalog. I used three identical GPS tracker devices running exactly the same code. The three trackers were always kept right next to each other while I was driving. The order of the three was changed a couple of times during the day. I believe we have a clear winner here, and this was also the one that won the S11 test.

Antenna
https://za.rs-online.com/web/p/telemetry-antennas/7934363/
Result
https://ttnmapper.org/special.php?node=ttntracker-v1_2-0001&date=2018-10-29&gateways=on

Antenna
https://za.rs-online.com/web/p/telemetry-antennas/0542563/
Result
https://ttnmapper.org/special.php?node=ttntracker-v1_2-0003&date=2018-10-29&gateways=on

Antenna
https://za.rs-online.com/web/p/wifi-antennas/8197398/
Result
https://ttnmapper.org/special.php?node=ttntracker-v1_2-0004&date=2018-10-29&gateways=on

Summary of results that can be seen in above TTN Mapper links (between 6h20 and 16h20):

Device Receiving gateways Furthest link Received packets
ttntracker-v1_2-0001 8 35km 2722
ttntracker-v1_2-0003 5 5.6km 157
ttntracker-v1_2-0004 5 4.3km 424

#117

@jpmeijers
If you don’t mind, please amend your thread to qualitatively summarise your findings in one place so that we can see why you say one is a clear winner (other than with S11 measurement)?
I’m thinking relative signal strengths between them when all the trackers are at a certain distance etc.It would be very helpful I think.

thanks
CW


(LoRaTracker) #118

+1

In one location, relativly clear of obstructions, put on one antenna, let the mapper run a bit. Record the RSSIs and SNRs of the received packets.

Change antenna, repeat.

Now you have a direct dB comparison of the actual real world antenna performance, its this we are really interested in.

The information provided by such a real world comparison is much more useful (to most users) than what you will get with an antenna tuning gizmo or theoretical plot.


#119

Just watch out to be consistent with your RSSI and SNR values. These are all indicators which are uncalibrated. Specifically the RSSI should actually be calibrated on a per gateway bases, but everyone uses the scaling factor provided in the TTN gateway conf file:

This is one of the reasons the main TTN Mapper map doesn’t plot colours anymore, but just a single colour indicating a YES or a NO to show if there is coverage or not. When you can’t trust the signal strength values, the next best is to use packet (or bit) error rate. That’s why the links posted by me above is valuable. It clearly indicates the packet error rates along a road.


(LoRaTracker) #120

Of course, but whilst the exact value of signal strength is somewhat unknown, as far as I am aware the reporting is relativly linear, so there is no need to trust the actual values.

Thus if the signal strength being reported from location A by gateway X varies say 2dBm (on average) between two antennas, since the only thing that has changed in the test is the antenna, then there is a 2dBm performance difference between the two antennas.


#121

Thanks JP for providing more info (and the app!).

Just a thought about the above, as LoraTracker says, it is easy enough to mitigate this - one can get the relative signal strengths from your 3 trackers with respect to a particular gateway . This compensates for the problems you’ve highlighted and should accurately reveal the relative “real world” performance of antenna choice (from same device type/location/time/SF etc). Unfortunately, whilst the “furthest link” is good for a qualative analysis (what I did ask for), I should have asked for a quantative analysis, so we can try to calculate dB figures.
My thought all along has been that people will be surprised to see how antenna choice makes little difference in the end (because proper math analysis says so).
Obviously, the caveat here is that the antenna are designed for 866Mhz use (and not fake nor WiFi)

unfortunately, the “furthest link” info you have given doesn’t prove much - because the gap between 5km and 35 km is too large - it coudl be that a gateway 30 KM away receive all 3 signals etc.

Also, I’m guessing that that the TTN mapper app doesn’t need to carry this “single gateway measuring of antenna” (well, why should it really - please prove me wrong?) as it’s purpose is for averaging general coverage from a gateway with respect to multiple nodes and displaying the agregated info as a heat map? - and this is perhaps the wrinkle here - we are awkwardly asking for more detailed info, that the App is not really designed to display info about?

I think both LoraTracker and I are meaning to ask for “relative antenna performance info” which is perhaps something that the TTN app is not really designed for? (why should your app do this - it’s purpose is to aggregate info from differing nodes and antennae to usefully display coverage info).

Great App BTW - serves its purpose well !


(Ud Lo Ra) #122

@azazeal: do you mean the one I posted just above? If so, did you check performance? Thanks.


#123

Anecdotally yes and I find its performance fine for my use (also consistent which is more important to me!).

Example deployment using that antenna: https://ttnmapper.org/colour-radar/?gateway=985DADFFFE51357D&type=radar&hideothers=on


(Jac Kersing) #124

Is it deployed outside? If so, how did you make sure the connection is watertight?


#125

There’s a n-type to sma cable (the ntype connects to a bulkhead at the bottom of an enclosure and is sealed with amalgamating tape). This runs up to a small 3D printed ASA mount adapter for the antenna (the gateway enclosure is on a metal plate for pole/wall mounting and the antenna sits on a 90degree top bit), the antenna friction fits into the adapter and the whole joint is sealed with heat shrink. The SMA connection comes into the bottom of the adapter and is sealed with amalgamating tape. I then tested the result on a vector analyser. For me I need discrete units and these antennas served that well. The mast sites are already in use for other equipment so sitting a procom onmi top of mast isn’t going to happen — and I don’t like high gain collinear antennas for lorawan), a ground plane monopole would work as well, but would just mean yet another thing for the installers to put up (it’s easier giving a box that is ready to go and telling them just crimp a rj45 connection, I also have low loss because the cable is shorter but still a nice shielded one). The onmi antenna is therefore half way up a pole which means it’s characteristics will be effected by the nearby metal anyway.


(Ud Lo Ra) #126

@azazeal: well, bought one and let’s see, thanks.

Different topic: this is what I found inside one of those 20cm whip antennas, noname nobrand:
IMG_2218

It is not what I saw in other pictures of this thread. Apologies for the ruler :slight_smile:

EDIT: the question is: is this for 868 or some multifrequency antenna adapted to? thanks. It works, but barely more, if any, than shorter versions.


#127

Ik denk dat dit een 2.4GHz WiFi antenne is met een goede gain. Onbruikbaar voor LoRa.

Hij lijkt erg veel op deze wifi antenne https://www.aliexpress.com/item/1pc-NEW-Tenda-6DB-2-4GHz-5GHz-Dual-Band-Wireless-Wifi-Antenna-RP-SMA-Male-19CM/32831127961.html


(Ud Lo Ra) #128

Thanks @costo, Google Translate helped me and this confirmed my doubts. Another one I have performs better.
I also finally tried the longer antenna linked above; it performs well, but apparently not better than my badly-home-made GPA. However, I have to do some more extensive analysis.
With GPA and using a node with the 20cm antenna, my indoor single channel gateway accidentally arrived up to 6.2 km, although this is not the norm and likely not omnidirectional (depending on walls).