I found the following presentation on the FT8 data mode that might be of interest to members:
http://blog.radarc.org/wp-content/uploads/2018/02/SEMDXA-FT8-Presentation-2017-11-09noVideos.pptx
I found the following presentation on the FT8 data mode that might be of interest to members:
http://blog.radarc.org/wp-content/uploads/2018/02/SEMDXA-FT8-Presentation-2017-11-09noVideos.pptx
I found this great presentation about data modes from W6AER.
http://w6aer.com/downloads/Digital_Modes_W6AER_NCDXC.pdf
I was on 20m working EU and DX stations using FT8 this afternoon. Just after 16:00, I noticed all signals faded quite markedly and within a minute or two. It was sufficiciently ominous for me to check on http://dx.qsl.net/propagation/index.html and http://www.swpc.noaa.gov/products/goes-x-ray-flux. A couple of minutes later, I saw an X class flare reported. That explained the HF fadeout. About 5 minutes later I saw it was rated as X8.2, only a little weaker than the X9 flare we had on the 6th September. It will be interesting to see if the CME was Earth directed, and if so, how much aurora we’ll get for VHF propogation fun.
David M0DHO
This evening I came across a terrible signal on 15m FT8. The audio from a Cuban station sounded distorted. I won’t name and shame the station. The audio fundamental was about 600Hz, and the waterfall showed strong signals at 1200Hz and 1800Hz matching the 2nd and 3rd harmonic of the audio signal. This caused significant QRM across a significant part of the FT8 segment. Almost certainly the station was overdriving the audio, either causing distortion from their soundcard, and/or distortion in the rig’s modulation chain.
There are several things you can and should do to avoid this, especially when using significant power and/or gain antennas:
Best regards,
David M0DHO
I’ve been trying JT65 andf JT9 for about 5 weeks now. I thought I’d give FT8 a try. This is a new data mode designed by Joe Taylor, K1JT, and Steven Franke, K9AN. You can find more information at http://www.arrl.org/news/ft8-mode-is-latest-bright-shiny-object-in-amateur-radio-digital-world.
One of the strengths of JT65 and JT9 is that they are very sensitive, JT9 being slightly more so than JT65. However, each transmit or receive period is a minute. So it takes at least 4 minutes to complete a QSO. In many cases, the signal to noise ratio of stations is well above the minimum for a successful decode. So FT8 was designed for that, using 15 second periods rather than 1 minute. So one big advantage is that in many cases you can complete a QSO 4x faster with FT8 than JT65 or JT9.
Unfortunately, there’s a downside. Some JT65 and JT9 decoders, such as those in JTDX, are very good at decoding multiple replies to your CQ, even those on the same frequency (to the nearest Hz). It does this through multiple decoding passes where decoded stong signals are then deducted from the recorded data to expose weaker signals beneath. However, the same does not currently appear to be the case with the FT8 decoder in WSJT-X 1.8.0-rc1. So while you can see a reply on the waterfall, you often get no decode. This is particularly the case if your signal is strong at long distance and attracts multiple replies. Even with single replies, often decode fails despite a visible trace on the waterfall.
For working DX on 80m, I’ve found JT65 and JT9 is much better than FT8, being able to decode signals only just faintly visible on the waterfall. So which data mode you should use depends on what you are trying to achieve. For faster QSOs with decent strength signals where multiple repies are not the norm, then FT8 is a better choice. But for working DX with marginal signals, where your patience might be better rewarded, JT65 and JT9 might be better.
David M0DHO
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