Wave jamming

[schnapsy]

My Nmea4wifi is from 2019 and has always worked very well.
During the summer, I encountered problems.
Indeed, to connect my autopilot to OpenCPN, I added TCP mode to the already installed UDP mode.

This Wifi/UDP/TCP mode worked very well for about 7-8 minutes (the flashes were regular) then shut down; and then, every 10 seconds, a simple nmea sentence was sent (with a brief flash).
I read and reread the forum.

So I disconnected each connection one after the other, the breakdown recurred regularly, after around 7/8 minutes.
I also did a hard reset then a web reset, without success, still this malfunction.

So I bought a new multiplexer in September, configured it exactly the same way and the failure happened again.

And I finally understood, I'm an idiot!
From the beginning, I had "forgotten" to check the "entry" box in TCP mode on OpenCPN and therefore, inevitably, after a while, the system blocked.
So everything is settled, but...

BUT BUT,

Whether on the boat or at home, the new Nmea4wifi multiplexer jams the FM radio as soon as it is plugged in. This is not the case for the multiplexer purchased in 2019.
So I wonder.

Why does this new model interfere with FM and does this not then risk jamming AIS - VHF transmissions/receptions ?
What can be done to avoid this interference (apart from replacing the old multiplexer)?

[Luis Sa]

Hello Schanpsy,

Sorry for this late answer. As you probably know all multiplexer use a switching voltage regulator to bring the 12V voltage from the service battery down to 5V. Everything works from 5V directly (namely the 485 driver) or from 3V3 (reduced from the 5V through a linear AMS1117 regulator). The ESP modules, for example work from this 3V3 power supply.

Switching regulators reduce the power that we take from the battery but may introduce RF interference. In the beginning (6 years ago) I used switching regulators that I could buy in the internet. From 2020 I started to design and build "my own" switching regulators. I was obliged to make changes in the design to cope with chip shortage. So your old multiplexer possibly uses a different frequency that does not interacts so much with FM as the one on the new multiplexer.

Before I advance I note that what I wrote so far is not completely valid for the NMEA3WIFI as this one needs to use 12V.

I am convinced that interference with VHF and AIS is not likely to appear. In my own experience and other users that help me in the development, this interference did not show up. Also note that FM radios almost work with a small copper wire working as an antenna. On the other hand VHF radios use very specific tunned antennas that are mounted very high in the mast.

One solution could be to power the multiplexer through the USB socket. You could build an external linear regulator to bring the 12V down to 5V. That could be just the 7805 regulator mounted in a small heat sink. From the 5V taken at the 7805 you would connect a USB cable (could be just a power cable without the data wires).

Final note - I assuming that the interference that you got comes from the switching regulator. I would need to confirm that. The ESP32 module also requires a current supply with many spikes when it uses WIFI. The interference coud also come from this.

Hope these observations are useful.

Regards, Luis

[schnapsy]

Thank you Luis for this detailed response.
In the meantime, I will continue to use my Nmea4Wifi from 2019 which works very well (contrary to what I thought).
If I understood correctly, the new multiplexer that I bought by mistake brings nothing more than the one from 2019.

[Luis Sa]

Hello,

Yes. You can run present firmware in the old hardware.

It could be useful if you could temporarily feed power from a cheap 9V battery to see if the FM interference exists. The idea was to check if the interference comes through the common 12V service battery.

Regards, Luis

[schnapsy]

No problem.
I am currently not at home.
But as soon as possible, I will do the test and tell you the result here.