lopy/lopy4 - LORA on 433MHz

[g0hww]

I notice that the LoPy4 claims the following operable frequency ranges for LORA:

LoRa Operating Frequencies

– 868 MHz (Europe) at +14dBm maximum
– 915 MHz (North and South America, Australia and New Zealand) at +20dBm maximum
– 433 MHz (Europe) at +10dBm maximum
– 470 – 510 MHz (China) at +14dBm maximum

but that the 'normal' LoPys claim:

Operating Frequencies

– 868 MHz (Europe) at +14dBm maximum
– 915 MHz (North and South America, Australia and New Zealand) at +20dBm maximum

As a licenced radio amateur, I'm interested in the potential use of these devices in our 70cm band, with covers 430-440 MHz here in the UK. Others, notably the one and only Travis Goodspeed have already been dabbling with this with other hardware and I'd like to have a go with some LoPys.

Can we confirm that the blurb on the web-page is correct and that the LoPy4 LORA radio is really frequency agile between 868MHz and 433MHz and also confirm whether or not the same is true of the 'normal' LoPy?

I guess I can test my pair of 'normal' LoPys myself to see if they will tune in the 433MHz band, but if I can get conformation that if I preorder/buy new LoPy4s they will be capable of operation on both 868 and 433 MHz (not concurrently, but in a frequency agile, software controlled fashion) then I'll be ordering a pair imminently.

Cheers,

Darren, G0HWW

[colinza]

@jmarcelino Aha! This is excellent, thanks for pointing me in the right direction.

[bmarkus]

Darren,

the issue is, that 125kHz bandwidth is not allowed on 70cm in IARU REGION 1. While the SX127x supports lower bandwidth modes, you need TXCO instead of normal XTAL.

73... Béla, HA5DI

[jmarcelino]

@colinza
Sorry, corrected the URL now.

For Band 2 (430-440 mhz) you don't need to to any changes.

[colinza]

@jmarcelino That repo I think is private? Can't seem to access it.

As a radio ham I have access to 430-440 mhz here, so I'd love to be able to lock it down to around 434mhz and do some experiments

[jmarcelino]

@sympatron
Band 3 is not supported but you can enable it by removing the validation check from the code:

https://github.com/pycom/pycom-micropython-sigfox/blob/master/esp32/mods/modlora.c#L1136

Some of us did this to capture the LoRa satellite transmission at the Things Conference event but that was a pretty strong signal to start with.

The problem is the RF path has been tuned (via matching network) for 433Mhz so Band 3 (137-175Mhz) will see some significant attenuation and shouldn't be be officially supported.

[Sympatron]

@jmarcelino Does this mean that Band 3 is or will be supported via the 433MHz port?

[jmarcelino]

@colinza

There is no manual switching involved the module will automatically use the 433 port for any low frequencies (LF) in the listed ranges:

[colinza]

@seb Okay so we can switch in software, but where is the software? Can't find that API documented... Board is using v1.8.6-798-gebbcca48-dirty that it came with

[seb]

The original LoPy modules cannot operate on the 433MHz band unfortunately. The new LoPy4 on the other hand uses the Semtech SX1276 Transceiver which is capable of using both bands via two separate antenna ports (a 433 one and a 868/915 one). You will be able to switch between bands in software.