FT8 - Transmitting

 

Background

Following on from a post earlier this year, where I discussed reception of FT8 signals, I finally got around to transmitting on this mode in the last few days.

As a quick reminder, FT8 is a digital mode for sending messages by radio and is particularly good at getting "through the noise". For those not familiar, everything we do produces Radio Frequency (RF) emissions. Many devices are shielded to reduce this, some are better than others and some have no shielding at all.

As a result, that generates a lot of junk/background radio emissions which can make it difficult to get a strong signal through. FT8 is intentionally designed to work in conditions that would be far from optimum for other modes.

It is mostly used on (High Frequency) HF bands. Again, for those who are unfamiliar, these are the "long distance" bands and are affected by various factors from time of day, solar weather and other conditions. FT8 can be used on VHF and UHF bands - which are "line of sight" only but are rarely, it appears, used on these. 

HF Propagation

Lets start with a short description of HF and Propagation.

HF radio operates, strictly speaking between 3 and 30mhz. That said, lower frequencies are often included but 3 - 30mhz is the standard accepted definition.

There is a LOT of utilisation of this range of frequencies, some for amateurs, some for long distance air-traffic control (for example, Oceanic flights maintain comms with ATC through HF radio) and many other users.

Amateurs have a number of bands they can use in this range. The table below shows the "name" of the band, for example 80 metres. This relates to the wavelength required to operate on the band and the frequency range contained within the band.

Each band has it's own characteristics, strengths and weaknesses. These can change over the course of a day and part of the benefit of using FT8 is being able to see this. 

Some bands work well during the day and are then "dead" during the night and vice-versa.

Knowing which band to use and when, to achieve the contact you want, is important and comes with practice and understanding the fundamental principles involved.

A quick note on propagation. In short, HF signals "bounce" off the ionosphere at different altitudes ("layers") and then return to earth. This is how these signals can cross oceans and continents - they are not dependent on line of sight - unlike VHF and UHF.

The image below gives an idea as to the way this works and it should be noted that signals can bounce up and down more than once so can get around the world with the right equipment.

Setup

This post is not intended to be a user-guide but a bare-bones outline of FT8 and what is required, so i won't be going into every detail - others have covered this far better than I can and there are always plenty of willing helpers in the amateur radio community.

Radio

I run quite an old radio which doesn't natively interface with a computer - essential for this mode.

My radio is an Icom IC706 (MK1) which is capable of transmitting on all the HF bands (as well as 2m VHF).

This radio can output upto 100 watts on HF but most people limit themselves to a max of around 30watts when running FT8. For those not in the amateur radio community - you always use the minimum power required to do the job.

That said, my current licence only allows me to operate at 10 watts on these bands and that is more than sufficient for me, for now. 

Antenna

I'm not very well setup for HF. Really i should have an outdoor antenna - of which there are many different types with a range of pros and cons. It's academic for me at present as I've no desire to install something outdoors for this due to the difficulty of doing so at my address. That may change at some point, but for now, I'm not a big HF user so am quite satisfied with what my little indoor antenna can do.

I use one of these which is ok for the job. I would certainly get better results using another antenna but for now, this does me.

Computer Interface

The radio requires two distinct "connections" - one of which to ensure sound flows to and from the computer and one to allow the computer to control the radio for tuning, transmitting and so on.

Sound is generated by the computer which is the digital signal converted to analogue then transmitted (or received) by the radio. 

For example, if I'm transmitting a signal, the computer will create the sound required to transmit and do so automatically.

If I'm receiving, that sound needs to be fed from the radio to the computer and decoded.

To do this, I need an interface, something which will handle these tasks. 

I use an XGG Comms Digimode4 (below). This includes a built-in soundcard and chipset for controlling the radio.

Setup is simple - just plugin to the ports on the radio and the USB into the computer.

Having its own dedicated soundcard means i can still use my computer as normal for other audio input and output.

Computer

With an appropriate radio and interface in place, the next step is to install and configure the requisite software.

I use the following to run FT8, theoretically, you could get away with just the first but the second and third make the experience far more visual and intuitive.

WSJT-X

This is the main receive and transmit application for a variety of digital modes (FT8 is one of many). This application controls the radio, tuning to the relevant frequencies, generating the audio for transmit and decoding any signals received.

Gridtracker

Gridtracker is used to show signals sent and received on a map, call log and provides other information, for example, band conditions (below). I will talk more about this when we get to "results".

PSKReporter

Strictly speaking, this is not required for FT8 but is an incredibly useful tool. In short, every signal sent or received by anyone using WSJTX can be uploaded to the site automatically.

This allows us to see how far our signals are reaching and how far we are receiving from. As we have already discussed, there are many factors which will affect where we can transmit to and receive from. Learning about factors which impact HF propagation, transmit and receive are things which can occupy some for a lifetime!

Results

FT8 is a two-way mode of communication. Sure, you can use it receive only to see where your signals are coming from. 

When transmitting though, even if you don't get a response to your call, you can get useful information.

Below is a screenshot from PSKReporter showing where my transmissions have been received in the previous 24 hours.

Colours indicate different bands I've transmitted on.

What can we determine from this? 

Firstly, Europe is well covered. Not checked but think I've been received in all countries in Europe, parts of the Middle East, Russia and the US.

Looking at the furthest east and west we can determine an initial range for transmissions. 

From the West, USA we have Louisiana at 4,504 miles and a town in Russia, north of China, at 3,315 miles - so a current demonstrable range of around 8,000 miles - likely to be more on a "good" day and less on a bad day - dependent on band conditions and other factors.

Reception is always likely to be stronger than transmit and in this case, this is no exception. In the last 24 hours I have received signals from Japan to the west coast of the USA and in the southern hemisphere, from Indonesia and other parts of Asia to South America.

Conclusion

Even with a fairly limited antenna setup, it is possible to send and receive signals at a great distance. As a tool, this is useful for seeing what bands are "open" (available to use) for other purposes. FT8 is one of many data modes and allows for two-way communications across the globe. 

Whilst we have many other means of sending comms (internet, telephony, etc), this is different as it is possible for a person at home to bounce signals more or less into space, having them reach a distant person with the right equipment. 

Amateur radio is a hobby geared up to individual learning and, sharing this data is often used for academic research but in short, to those asking "why?" I guess the answer is - because we can!