Saturday 28 October 2017

More UHF APRS Testing

I tried the E32-TTL 1 watt 70cm LORA module a bit further away from home, again using APRS software to send the position to the internet.
The location I tried first was some high ground just off the A65 to the west of Settle (grid reference somewhere around SD786669) on the narrow road above the Austwick TV mast. This has a good take off towards the west.
Instead of the mobile antenna I put a short antenna directly on top of the module and taped the thing to a mop handle so it could be as high as possible while operating. This also gets rid of any coax cable loss.

 Video camera also fixed to mop handle

 View to the west from near Settle

 But did it work? Yes it did, at a distance of 37.7 miles (60.7km), with more than one transmission being received as I moved around the parking area.
I tried another two locations further south, which weren't on high ground, but received nothing. These were at the Lancaster (Forton) M6 motorway service area and just outside the boundary of the Charnock Richard M6 motorway service area.

My next experiment was to compare the performance of the LORA module against normal 1200 baud packet radio using an FM mobile transceiver.
Using the same antenna as in my last blog post (it's a small Moonraker dual bander, about 40cm long, on a mag mount), I transmitted APRS beacon messages from my Yaesu FT-8900 on its 20 watt setting. The frequency was the same as I had used for the LORA test.

See the results of the LORA test below

Result? A lot worse than the 1 watt LORA transmissions. Because the car APRS tracker has no logging function, I could only guess where any failed transmissions were from. I know that it beacons every 110 seconds so I've put red Xs in rough locations of where it should have worked but didn't.
The blue O shows where it actually worked but no location was sent (my tracker is programmed to send some other information every few beacons instead of the location). I had stopped the car there, which would have helped as I wouldn't have been passing through any multipath dead spots while transmitting.
So with 13dB (20x) more power on the same frequency, traditional packet radio is still worse than LORA when used mobile. Even if you compared VHF packet with UHF LORA, I don't think 20 watts VHF (to a 0dB gain antenna like the Moonraker) would get much further than 1 watt UHF.

And here is Dales Radio's Ingleton antenna (103.0 MHz), covering the area further west of Settle, with Settle itself on 104.9 MHz.

Thursday 19 October 2017

433 MHz LORA

Experimenting with a couple of 1 watt 410 - 441MHz LORA based modems.
The part number is E32-TTL-1W (there are also 100mW versions available).

Manufacturer's website and data sheet

Only about £12 each on the usual sites

With most electronic equipment shipped from overseas, the specifications are usually quite 'optimistic' so I wasn't really expecting 1 watt from them. Especially as the 100mW version looks exactly the same. But they really do put out around 1 watt.

They fit nicely inside a Choc Box once you cut out the bit which is supposed to go through the terminal block. The cable is a USB to TTL serial adaptor, they were less than £1 each.
The power is supplied from the USB cable (red wire), with the current on transmit 670mA (I couldn't actually measure this using a USB tester, maybe the quick variation in transmit power confused it).
Although they draw quite a high current from the USB port, I had no trouble using them on a PC USB3 port and my phone's USB-C connector (through an On The Go cable).

Programming software. These settings are for the highest power output and slowest transmission rate (greatest range). There are 65536 addresses available, but #FFFF can be used as a broadcast address.

Only 1 MHz channel steps are available, and the transmission is 125 KHz wide, centrered on the MHz.

How far do they go? LORA is supposed to work with very weak signals at the lowest transmission rates. I connected one modem to the car antenna and the other to the base antenna on my chimney. The data I transmitted came from an Android App on my phone APRSDroid and was received by APRSIS32 in Windows.
To these applications and the APRS internet servers, it looked just like I was using packet radio TNCs and the normal APRS frequency (in the UK) of 144.800 MHz.

Transmitting at least once every 2 minutes, I drove to a point over 8km away. At this distance there was no line of sight. It even worked in Dalton town centre, behind a hill. Over the route there were only 2 locations where the signal was lost, see the Xs on the map below
These locations are at the back of a hill, I would have expected it to be worse in the town centre than there but at least I know where to test in future.
Range would have probably been well over 8km if I'd carried on further east along the A590.
These are good results for 1 watt, probably as good as 10 watts on VHF APRS using normal 1200 baud packet radio.

This would be interesting as a weak signal mode when propagation is good on UHF. Using terminal software you can just type and they transmit, much like PSK31 but with error correction.