TTN Gateways lost range and RSSI after nearby lightning strike


(Amora) #1

Hello.

I am from México. I need your help to fix my gateways.

I have five TTN 915 MHz Gateway´s running firmware v1.0.5. They are in different sites of my city.

To increase the GW range, I put outside two of them, with the next installations:

  • TTN GWs into an IP65 ABS box placed on the top of a 6m metal pole.
  • Original GW antenna.
  • Power over an 8m STP Cat5e Ethernet cable with the TP-LINK TL-POE200 Kit.
  • The PoE kit is supply by a 127 VCA 90 J surge suppressor.
  • A TP-LINK TL-WA855RE Wi-Fi range extender isolates the GW from the Internet home router.
  • No ground system.

IMG_2439

Next the installation, the GWs range was about 2 km with RSSI around -70 from fixed nodes.

After a rain with nearby lightning strike, the GWs range dropped to about 100m with RSSI around -105 from fixed nodes.

I changed the GW installation to an internal place to avoid more damage. They didn’t recovery their original range an RSSI values.

I installed another TTN GW outside. I tried to protect it at the most:

  • TTN GW into an IP65 metal box placed on the roof of a house.
  • 824-960 MHz 6 dBi Omni antenna from Altelix, mounted on the top of a 5m metal pole over the roof.
  • A 20ft RPSMA M / N M 400FR-Series coaxial cable between the antenna and the GW.
  • Antenna lightning protection: N-Male to N-Female Bulkhead 0-6.4 GHz Gas Tube Lightning Protector with a 600V gas tube.
  • GW lightning protection: RP-SMA Male to RP-SMA Female Bulkhead RFID & WiFi Lightning Protector 0-6.4 GHz with a 90V gas tube.
  • Ethernet cable surge protector: TRIPP-LITE SUPRESOR RJ45 (DNET1).
  • Home Internet router protection: A TP-LINK TL-WA855RE Wi-Fi range extender isolates the GW from the Internet home router.
  • Supply protection: TTN GW AC adapter protected with a 127 VAC surge suppressor (90 J).
  • Ground system:
    • Earth electrode: three conductive interconnected rods driven into the ground.
    • 20m 8 AWG cable from the rods to an aluminum bar near the GW.
    • Single point ground near the GW (aluminum bar).
    • Metal pole, GW metal box, RJ45 suppressor, lightning protectors and Ethernet cable directly connected to the single point ground.

IMG_2403

IMG_2415

IMG_2432

This TTN GW resisted the first rain, but with the next storm, the RSSI dropped to around -105. After the last storm, the RSSI changed to around -125 with a 20m maximum range.

I want to fix my TTN GWs.

The public documentation I have is the TTN GW schematic diagram (ttn_gateway_V2.3.1.pdf file) from:

https://github.com/TheThingsProducts/gateway/blob/develop/hardware/TTN_Gateway_V2.3.1.pdf

the Microchip GW schematic diagram at the LoRa Technology Gateway User’s Guide (40001827A.pdf file) from:

and the Semtech PicoCell Gateway V1.0 Prod Folder for North America reference design schematic diagram (SX1308P915GW_Picocell_GTW_e381v02c_sch.pdf file) from:

https://www.semtech.com/products/wireless-rf/lora-gateways/SX1308

I see two differences between the Microchip design and the Semtech design:

a) At the RF antenna part, the Semtech design has a ESD protection device (TVS D801 diode LXES15AAA1-153) and the Microchip don’t.

b) Instead LC passive components likes Semtech design, Microchip design uses the ceramic low pass filter U10 (0915LP15B026E).

Microchip RF antenna part.
Microchip_GW_sch

Semtech RF antenna part
Semtech_GW_ref_des

I removed the shielding of the LG9271 TTN GW RF module (mPCIe Smart Gateway card from Microchip/Occammd) and noted that the antenna section is similar than the Microchip LoRa Gateway design (with a ceramic filter and without a ESD protection device).

IMG_2448

Finally, my questions are if the TTN GW LG9271 RF card is damaged because it doesn’t have the TVS diode as the Semtech reference design, what components do you recommend to change? (taking the Microchip LoRa Gateway schematic diagram as the LG9271 schematic diagram); and do you recommend to connect a ESD protection device likes the TVS diode LXES15AAA1-153 in all my TTN GW’s to avoid they lost range an RSSI by nearby lightning strike? or do you have a better solution?

Thanks.


(S56g) #2

Hi amora
my 0.01$ : use of DC shorted antennae helps. J-pole or closed dipole are way better to protect front-end circuits. We are using a homemade J-poles and so far no problem (“colinears” and “ground-planes” were principal culprits for two fried gateways). We don’t have them installed enough time to draw conclusions but gateways stayed in production this summer.
Tom


#3

I would bypass the first filter and see if that works. As as protection I would add a BAV99, because I have those, but they would probably interfere with the transmit signal.


#4

You can mount TVS diode direct to U.FL connector pin and GND (open metal from shield).


#5

I have the same experience but hadn’t had time for a closer inspection. Thanks for sharing you’re findings.


(Amora) #6

mvdswaluw.

I bypassed first the ceramic low pass filter U10, second the RF switch U8 and third the LNA U9.

Only with the LNA bypassed (SPF5043Z circuit), the TTN GW recoveried 30 RSSI values from a fixed node, from -85 RSSI without bypass to -55 RSSI with bypass. A no damaged TTN GW always received -35 RSSI. I thing the LNA is damaged. I’ll change it in the next weeks.

image

As a protection, I´ll probe the next TVS diodes: LXES15AAA1-153 (Murata), CG0603MLU-05E (Bourns), SP0502BXTG (Littelfuse) and ESD7951ST5G (ON Semiconductors).

Regards.


(Amora) #7

lex_ph2lb.

The first TTN GW I placed on the outside did not suffer damage with lightning discharges for 3 months. I’m not an expert on the subject, but I think it was because the antenna was close to a wall that absorbed the discharges electromagnetic induction.

IMG_2274

My hypothesis is that GW TTNs are not designed for external location, of the whole equipment or just the antenna, so sooner or later those GW installed on the outside will lose range and RSSI values.

Greetings.


(Amora) #8

x893-00

For surge and ESD I will solder TVS diodes in all my TTN GWs, in the U.FL connector track. For lightning & surge I will connect a 90 V gas discharge tube near the antenna (external GWs).

imagenproct2

imagenproct1

Thank you.


#9

Thank you for your setup information and photo. It indeed may explane a few things.

I had contact with my gateway supplier and he confirmed that that sometimes could happen. I’m having a few SMA attenuator PCB’s laying around I want to use for the TVS diodes and add them inline with the antenna (near the gateway). The 90V gas discharge tube is also on my shopping list next to a new RF board for my gateway.


(Helioz) #10

Just another perspective on signal degradation:
I have previously encountered moisture ingress in coax/connector/antenna as the cause of similar issues. Once moisture has penetrated deep into coax (capillary action) the best solution is to replace the cable.
I use DC4 squeezed into all exposed connections and then seal the connector with silicone tape.


#11

That’s indeed a common problem. But being a hamradio operator for years special vulcanizing tape is part of every antenna installation. :slight_smile:

Edit : like the products you point out in you’re post (couldn’t see them on my mobile).

But just to be sure I replaced the coax and the antenne when I found out about the signal drop. But with the same result leaving no other option the to replace the RF board :-1:


(Helioz) #12

@lex_ph2lb fine business.

DE
VK3ERW