Reception distances at UHF – My 1000:1 rule.

I often get asked what range you can get in ‘typical conditions’ using LoRa. There is a simple answer;

“There is no such thing as typical conditions.”

On several occasions constructors have got in touch and said; “I am only getting 1KM, yet you are quoting hundreds of KM, what is wrong with my set-up?” The answer to that is also simple;

“There is probably nothing wrong”.

It is not commonly understood how much the range\distance of communications at UHF can vary. Of course most people expect a difference between an urban area and hilltop to hilltop, but the actual differences are often a surprise. Are the communications over flat or hilly terrain, in urban, rural or forest or perhaps ground to satellite or ground to high altitude balloon?

I was fortunate during the radio testing for the $50SAT project to be able to develop a real world rule of thumb. Whilst testing the Morse beacon (on 437Mhz) I wondered if cutting the transmit power between dits and dahs would make an audible difference, there was an advantage in doing so as it saved around 33% of the battery power.

So I set-up the $50SAT transmitter board running the Morse beacon in my garden and wandered away up the road with my Yaesu FT60 hand-held till the Morse beacon was only just audible above the background noise. This was at a distance of 1km. I live in an urban area and its relatively flat.

The very same $50SAT transmitter board was put into orbit in November 2013. Some months later I was walking into town (it was a nice day) and $50SAT passed at approx 1200km distance. I heard the Morse Beacon very clearly with my Yaesu FT60.

In an urban environment the limit of reception was 1km, yet with the exact same transmitter and receiver and clear line of sight, the reception distance was 1200km, probably more.

That is where my 1000:1 rule comes from.

Thus whilst you might get 400KM with LoRa from the ground to a high altitude balloon, do not be surprised if at ground level in a city you get 400M or less.

This difference is also why it is so difficult to compare reception at different locations. I might get 1KM in my locality, the same equipment might cover anywhere between 250M and 10KM+ elsewhere. The differences are a good reason to be clear about the conditions applying to a reception report, preferably with pictures of the area.

Small LoRa Receiver

LoRa Relay as Receiver

 

This is a Cute LoRa Receiver, at least I think its cute, for bench use that I built up to be sure I always had a LoRa receiver handy. This is one of the small relay boards built as a LoRa receiver. I added a serial connection for the PC and an audio uplink cable to allow payloads to be decoded by FLDIGI on the PC then heat shrinked it all up.

The receiver is small enough to attach direct to the N Type socket I have on my bench, its the feed from the antenna on the shed roof.

EMF Field 2016

EMF 2016 Badge

Had a great time at this event, lots of really interesting stuff and very well organised. We all had these badges, wonder if you could use it as a tracker ?

I was at EMF giving a talk on a previous project, $50SAT, you can see the presentation here on You Tube

$50SAT Presentation

EMF Field 2016

There is a small section on LoRa at the end. It would be very interesting to see someone try a LoRa device from low Earth orbit, and I have received some interest from a ‘Space Agency’. There might be issues at apogee with Doppler, but if not the digital communications ought to have far greater range than we had with the RFM22B on $50SAT. One day maybe.

Trees

LoRa Relay – Part 3

With the relay built and working we can turn our attention to getting it into an advantageous position, such as 60ft up a handy tree.  20

The relay is sized so that it fits with a battery neatly inside two rocket nose cones taped together. This is a neat streamlined package that we can pull up and down a tree with minimal risk of it getting caught. The beads are there so that when pulling the strings, there is no pressure on the relay itself. But how to get the relay up a tree ?

 

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Tree climbers do use crossbows for firing lines, but I figured that if I went over the local park with a crossbow, there would likely be unwelcome attention from the men and women in blue.

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Building the Relay Board

LoRa Relay – Part 2

A LoRa relay is a powerful tool in the search for a tracker. The concept is simple, the relay is put in an elevated position and listens for and re-transmits the LoRa packets.

Height above ground, particularly in relatively flat areas, can significantly improve signal reception and range. The relay PCB is small and light, taped to the end of a 10M telescopic pole it can improve signal reception by 6-10dB, this represents a double or more increase in range.

The relay board can be built to take a battery charger, so you can put the relay in a waterproof box and keep the battery charged with a small solar panel, current consumption of the relay is around 15mA average.1

 

Separate the PCB by scouring the line of small holes in the PCB centre with a sharp strong blade, and snap the PCB in two.

 

First solder the components that are fitted to the bottom side of the PCB, these will be out of sight underneath the Pro Mini when assembly is finished. These components are R1,R2,R3,R4,D1,D4, see picture below.

2

 

There are two 5pin angled headers to fit. The one on the top of the PCB (the side with the DRF1278F and the PCB lettering) fits in the row of holes nearest the non-antenna end of the PCB. This header is for the connection of the battery and another supply such as 5V from a RC receiver. See the picture right below with the top 5 pin header and the Polyfuse fitted.

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How to Search 500 Square Kilometres in 10 minutes

LoRa Relay – Part 1

Of all the LoRa programs I have written, the relay program is by far the most significant, the impact it can have on long range locating is monumental, and it’s a very simple program.6

At ground level a ‘lost’ tracker, be it a Radio Controlled (RC) model or high altitude balloon, could be just too far way to receive good signals. What can very significantly improve search range is increasing the altitude above ground of your receiver, even a 10M pole can make a big difference, especially in urban areas.

Its often not practical to put a large handheld LoRa receiver at height. A good location in an urban area for a receiver may well be on the roof of a house but how do you get all the kit up there ?

The simple answer is that you don’t have to, you put the relay ‘up there’ instead. The relay listens for packets coming from the ‘lost’ model or balloon and then retransmits them so you can pick them up on your normal LoRa receiver. The relay is small light, and self contained.

Using a bit of string and a weight, a small rubber ball is good a stone is not, its only a few minutes work to get a line over a house or tree and pull the relay up. If you carry a long extensible pole, also useful for rescuing models from trees, put the relay on that, the extra 10M or so of height can make a real difference.Part 1 - 2

With a low cost radio control plane or quadcopter, it’s possible to get the relay to 100M plus above ground very quickly. Take a look at the pictures, with a LoRa GPS tracker left running in my garden, once the plane was flown to about 100M I was able to pick up the trackers transmissions, and hence location, across 12kM+ of urban environment and countryside, C on the map below. In about ten minutes I had covered a search area of 500 square kilometres, imagine how long that would take to search at ground level !!!

Part 1 - 3

An alternative to using a RC model to get the relay to altitude is to use a kite, the relay is light enough.

The software for the relay is in the HAB programs folder on the dropbox, set the frequency and LoRa constants to match your normal tracker and receiver settings and turn it on. 

The next article will cover the building of the relay.