What is FT8?
FT8 is a digital mode forming part of the WSJT-X Suite, and was first released in mid-2017.
It enables QSO’s when the received signal level is as low as -24dB and each over takes 15 seconds or about 90 seconds for a full QSO.
There are many guides to its use on the web, the one I used being at https://www.physics.princeton.edu/pulsar/K1JT/FT8_Operating_Tips.pdf
160m experiments winter 2017-18
During Winter at near sunspot minimum in late November and early December 2017, and again in January and February 2018, I tried FT8 out on top band (160 m) using my horizontal delta loop as a single fat long wire, fed against my ground system through an auto ATU. Antenna modelling software shows me that the antenna is not particularly efficient at this frequency so I used 60W PEP, for some 7 sessions for short periods around 9 PM on weekdays.
A simple results table ordered by distance:
Winter night-time propagation on 160m is by skywave so some simple geometry on these results shows that the take-off angle from my antenna is roughly 15 to 20 degrees for the longest distances and 50 to 60 degrees for the shorter distances based on a reflective layer height of 300 to 400km.
FT8 QSO’s don’t (as at Spring 2018) provide antenna or power data so meaningful comparison of signal strengths isn’t practical. However my reports ranged between -20dB and +7dB and those I gave were between -24dB and +12dB
All great fun and using PSK Reporter one can see where your signal is being received, in my case as far away as JA (Japan) but unfortunately I wasn’t able to work them.
Brief trials on other bands have shown that with relatively low power (for HF!) and a simple antenna worldwide DX is fairly easy to do, even during this sunspot minimum period, e.g. I’ve worked China on 20m and Indonesia on 40m. I have been considering adding a linear amplifier to my system as I hope to have more operating time shortly, but with results like these that expense is on hold!
Your computer clock
An exact computer clock is essential, within +/- 1 second, needing changes to how the clock is managed.
Using Windows 10 I first tightened its Internet time checking interval to daily instead of weekly, and to a nearer time-server, by some registry changes I found on the web. Using a time checking website such as http://www.time.is these changes give me around +/-0.3 to 0.7 seconds accuracy, which seems OK but maybe not quite good enough.
For tighter timing I’ve recently been trying out Meinberg NTP, which gives the exact time.
I tried FT8 from a portable location in early April 2018, for a short period, using my FT817. Band conditions weren’t great (on SSB voice) and I found some technical issues:
- Despite setting up the software at home it at first didn’t work for CAT control when out portable. Found that the USB/RS232 dongle that I need to use didn’t retain its com port number from home but was allocated a different one!
- The weather included a cold fitful breeze, although it felt warm with the bright sun. I initially had few FT8 decodes and immediately suspected the laptop clock was being affected by the temperature changes.
- I plugged in a GPS module purchased on the web, running from USB, using BktTimeSync to discipline the laptop clock. Problem solved, but further experiments with software needed, not least about another com port number reallocation…
Reading the laptop screen is also less than easy in full sun, and my polarised sunglasses make it appear completely black.
More updates later!