RFM69 Range issues

[evb]

@Yveaux, Do you have specific weblinks how to use the rtl-sdr module to debug radio range issues?
I'm searching and reading about it on the net, but till now not yet found a usable debug workflow.

@bjornhallberg are you progressing?

I've also still range issues for my nodes 25m away from my gateway. There are isolated brick walls, sunproof glass, concrete floors, etc between these nodes and the gateway, but when I read about ranges of more then 400m, free sight I suppose, I'm wondering of there are external factors playing a role here...
The nodes are communicating with the gateway, but I loose regularly messages and for door nodes that's a little unfortunate :-(

[canique]

@evb when doing range tests I also tested range through multiple buildings, so there was no clear line of sight. Distance was approximately 200 meters @ 13 dBm (max transmission power restricted due to regulations in the EU) with an external 5dbi antenna. That was the edge where TX was working.

For door nodes, ACKs and retransmissions are a must. I even use that in my temperature nodes.

[evb]

@canique The door nodes sketches have code to treat the acks and retransmission, but still sometimes, the messages are lost...

I thought first that it could be because the pro mini's are running on 1MHz and it was reported that MySensors lib didn't work well at this frequency.
But my door node at 3m away from the gateway, didn't miss yet one single message and the nodes are not freezing, the next time the message is getting through.
So maybe there is 'noise' around who is disturbing the radio communication, but how to detect that without professional expensive equipment?
Maybe via this RTL-SDR thing?

[canique]

@evb If it's intermittent, chances are high that it is noise. But the noise could also stem from the gateway itself. Just a theoretical example to illustrate what I mean: access to an SD card on the gateway => noise. Then it would appear that you randomly lose messages, although it coincides with an access to the SD card.

It's time intensive to spot stuff like this. You could setup a gateway that just scans the same frequency (in promiscous mode) and samples RSSI. You could log each detection of a transmission (when RSSI values go from say -100dBm to -70 dBm) and then check if something is being transmitted from your nodes at the time in question.

Or you could setup a second gateway right next to your first one and see if that one is receiving the message. If one of them is receiving the message, it's probably a gateway issue. If neither is receiving the message there could be another transmission ongoing or it's a node issue.

[boanjo]

I agree with @Yveaux that it's a good idea to fire up the RTL-SDR dongle if you have one. I've been using it quite extensively in the past when working with more plain OOK devices and it's a real eye-opener when you see the spectrum. A lot of noise and garbage where i live at least in the 433Mhz spectrum. In the 868MHz you "shouldn't" have that much (mainly your own devices) perhaps. I used mainly SDR# (SDRSHARP) which (IMHO) is the best option if you run windows. GQRX (linux) does the job too but is a bit harder i think. Move the RTL dongle around (close to GW etc) to see if the actual GW is radiating or if you pick up some other sources.

[evb]

Besides the 'how to' question, what are the models used?
I see the Airspy R2 at 219 euros or the Airspy Mini (dongle) at 138 euros, still quite expensive...
And I see a RTL-SDR kit with dipole antenna for 34.95 dollars or 40 to 50 euros in Europe.

[boanjo]

@evb Ah, sorry i ment to write which models i used too... No i have only tried the really cheap ones :)

Here are the ones i've used:

The mini is just crap if you compare it with the two bigger sized dongles so i didn't link to it. The two bigger ones work well so it's more up to you what kind of antenna connector you want (and price). See the links for more details
RTL-SDR.COM is ~28$
https://www.ebay.com/itm/272411458376

The middle DVB-T TV kit is ~11$
https://www.ebay.ca/itm/USB2-0-Digital-DVB-T-SDR-DAB-FM-TV-Tuner-Receiver-Stick-RTL2832U-FC0012-Z-/124383617220?oid=182403360614

The how part i actually not much harder than to hook it upp connect to the device, turn the frequency to the wanted range and view the energy mass on the center frequency (it's often good to set the decay a bit longer so the eye can capture the peaks). But if there are questions feel free to ask!

[evb]

Ok, the RTL-SDR.COM kit is ordered. So, now waiting for it :-)

[Tmaster]

The best antena that i tried on rfm69 is the dipole. Direct solder to the rfm69 board. One wire 0.8mm with 8.2cm long on Ant pin,and other in ground in oposite Direction,same size.thos for 868mhz.
I have the gate sensor at 50m outdoor and never seen a miss comunication.

I tried spring antenna and same dipole with an coax cable and didn't work at that range. And a mono-pole without ground plane(wire) have more lost packets( i just try communicate directly,dont have any signal scanner).

[evb]

Did receive yesterday my RTL-SDR.COM USB stick :-)

A first measure of the spectrum around the 868MHz band from my fix desktop computer with the Airspy SDR# software recommended on the RTL-SDR.COM website.

You see clearly the lines in the waterfall blue section when a node sends something.
With my limited knowledge about radio signals and use of this Airspy SDR# Studio software, I think that the spectrum around my house is relatively quiet?

Yet another printscreen with the SDR Console version software

Will install the software now on my laptop to be able to go near the nodes and gateway.
To be continued.

Already a question, my RFM69HW are working in the 868Mhz band, yet I see movement at 867.970 MHz and 868.020 MHz. At the center 868 MHz, I see no movement.
Someone with more knowledge about this, can explain this? I would expect a signal at 868 MHz...

[mfalkvidd]

@evb that's how frequency shift keying works. 867.970 is a "0" and 868.020 is a "1" (in the default MySensors configuration, which uses 50kHz deviation).

[skywatch]

A better SDR would be the airspy R2. It puts the others to shame. (even the mini).

They are cheaper from itead in China than a local supplier (as with some other things).

It showed me that quite a few neighbours use 868MHz for garage door openers.

[mfalkvidd]

@skywatch why would the rtlsdr be insufficient for this task?

[evb]

@skywatch Yes, it should be better for his price of 219 euros ;-)
I bought now the rtlsdr for 29 euros directly from the RTLSDR site from their Chinese store.
My purpose was to see if there was much noise or not in my environment.

[skywatch]

@mfalkvidd It all depends on range and signal to noise ratio. The longer the range the better the receiver SNR nedds to be for the same signal to be received - This thread is about 'Range Issues' so therefore it matters.

You might run into problems if your SDR is less sensitive than your chosen tx/rx pair.

[skywatch]

@evb From itead it is 139.84 euros. see here https://www.itead.cc/airspy.html

If you can wait until December they usually have a sale on with about 30% discount. That is how I got them for less than £90 GBP....

[mfalkvidd]

@skywatch that's incorrect. The reason sdr is discussed in this thread is because yveaux said

if you have a cheap sdr lying around you could use that to verify transmission frequencies and signal levels to some extent

[evb]

@skywatch Based on your answers, I see that you seemingly have knowledge in this matter.
I have range issues and just wanted to see if this is due to external environmental factors (neighbors using the same frequency, etc)
And to spend more than 200 euros for something that I will use maybe one time, that was way too much.
(Purchase price manufacturer 140 euros + 10 euros shipping + import taxes because more than 22 euros + customs clearance = 219 euros). I live in Europe where they specialize in taxes :-(

I know you usually get what you paid for, so I don't expect extraordinary performance either...

[boanjo]

@evb Yes, i agree your 868MHz doesn't look that busy and shouldn't be the root cause. Have you been able to establish the specific sensor that you have range issues with (i.e. how it look in the spectrum analyzer)? This is a bit easier when working with "dumb" sensors that sends repeatedly every minute or so. Might be a good idea to add a frequent send (just temporarily while troubleshooting this).

[skywatch]

@evb said in RFM69 Range issues:

@skywatch Based on your answers, I see that you seemingly have knowledge in this matter.

Yup! - 40+ years as a licenced radio amateur along with years working on aircraft radar receivers, air-to-air missile seeker heads, underwater systems and satcomms. We had some great equipment at work!

My point is that if the sdr has a noise floor of say -70dBm and the RFM has a noise floor of -80dBm then the RFM can still 'see' interfereing signals that the sdr doesn't, You can see the signal to noise ration in sdr# by looking at the blue bar to the right of the main spectrum display. To get your sdr set to the optimum level you need to adjust the gain to maximise this figure, then you are operating in the optimal domain for SNR and hence what you can see'hear.

When you say 'range issues' what sort of range are we talking about and in what conditions? Have you tried small movements of the radio module as often that can make a difference.