Friday, November 11, 2022

FT8 basics that some HAMs still don't understand

 Not that I am an expert in FT8 communications but some basics are still not understood in the HAMradio FT8 community. I thought to just write them down here and hope someone will learn from it.

On the TX side:

 First of all I want you to understand that almost every transceiver has a transmit audiofilter. Dependent on your transceiver this audiofilter can be set at wide or small. But even on wide, it will not be wide enough for digimode covering a bandwidth of about 3000 Hz with maximum audio. To transmit with a constant maximum audio frequency you need to use "fake split" to set the transmit frequency to compensate in that way you always transmit at maximum of the audio transmit filter. Of course this only works if your radio is connected via CAT control to the software. The benefit is that you will not transmit distorted audio and harmonics (cleaner signal) and you will have equal power output all over the FT8 frequency spectrum. Of course I assume you understand how to setup the audio output to the transmitter, it should transmit with minimum ALC.

A beautiful signal from HA8BE on the 60m band. Wipes out most of the signals...

I've been posting about this before:

On the RX side:

 Second is the RX bandwidth. Of course, if you use an old radio, you will be limited to about 2500-2600Hz. But most HAMs these days are getting more sophisticated equipment, especially those that are interested in the digital communication modes like FT8. A very populair radio, for instance, is the Icom IC-7300 which is a SDR radio. It can listen to a bandwidth of 3600Hz. I know other more sophisticated SDR radios can listen to 4000Hz or even more. Still most of the FT8 QSOs going on are limited to 200-2600Hz. Why?  Really, is this my misjudgement? Are most FT8 users equipped with 20 year old transceivers? I don't really think so. Spread out! Use the whole bandwidth... 

20m on a random time. A lot of spectrum is free to use!

Deliberate QRM?

It is also wise to check the DXcluster and before you transmit. So many times I see stations transmitting at exact the same spot in the waterfall as a DX station they probabely do not hear. A empty spot in the waterfall does not always mean it is actually free to transmit. It can happen by accident of course. Most times you will be notified by others to QSY (change frequency).

Just an example

 Have you ever been listening to DXpeditions that transmit with F/H (Fox/Hound). This is a great invention. What I do not understand is sometimes stations are calling in the same period as the DX. I really don't understand? Why calling if you don't see the DX station at all? Do they think the DX stations wil mysteriously get out of the noise for them.....or magically change periods just for them? Strange things happen....come on....check if you are in the right period! Sometimes this happens by accident...though I have seen stations calling in the same period of the DX for over 30 minutes.

Well, have you seen anything annoying on FT8 (or other modes)? Have any tips for others? Please comment. Hopefully someone has learned from this post.


MadDogMcQ said...

Hi Bas! Another excellent post - hopefully many will benefit from taking your advice. I doubt though, that many will check on before transmitting. It's like asking car drivers to check twice before pulling out in front of a biker, lol.

Have a great weekend!

73, Tom, M7MCQ.

NN4DX said...

Hello Bas. I had a revelation one day about receive bandwidth when operating around 200 Hz. It hit me that some of the DX probably use older rigs so I started to move above 300 or just below 3000. What strikes me odd is that folks like to cluster in the middle of the pass band. Please spread out, please use split, and please adjust your ALC.

Also, turn off you rig announcements and/or you software announcements. They get transmitted over the air and are annoying besides being illegal. If you hear it with TX monitor then it is getting transmitted.

Great mode!


Hartmut Luedtke said...

Hi Bas, Thanks for your article. Here a few more tips:
Turn off the microphone compressor, clipper and also equalizer. Turn off all notch filters, contour filters, DNR (Digital Noise Reduction) and NB (Noise Blanker).
73 Ham, DB6LL

Anonymous said...

Thank you for the very helpful article. It's just ham. Not HAM. It is not acronym, just an old slang name. You wouldn't type AMATEUR would you?

PE4BAS, Bas said...

@Tom, it would be wise to check the DXcluster/Hamspots. But sometimes this also happens deliberately. Not shure you can compare it with what you wrote. Some stations just hate it when others can see/hear DX they can't.

@Don, thanks for your useful tips.

@Hartmut, thank you also for these tips. At the IC-7300 compressor etc. is automatic turned off in USB-D. However, NB/NR and other RX shaping things not. So indeed you have to pay attention!

@Anonymous, I continue to use HAM. Just ham is something I have on my bread or in my diner. It is my blog and I can write what I want ;-)

73, Bas