FT8: What's That Sound?

While I ever so slowly ease back into spring tower and antenna work, the technical articles are slow in coming. They will return! But for now I have another article about operating, and in particular about operating FT8. This is timely since 6 meters is intermittently open to South America and sporadic E season is a few weeks away.

Have you ever worn headphones while operating digital modes? Few do since there is usually nothing worth listening to. The software does all the work. About the only time I do it is when I want to quickly check 50.313 MHz for activity. When nothing is heard I flip back to HF and conventional modes.

Another good reason to listen is to monitor your own signal. Is the audio distorted? Is there power line hum? Is the microphone live? Almost all of us use SSB on our transceivers to operate digital modes, and our signals are subject to the same problems that are common on phone. I expect that rig technology will evolve to improve digital mode operation, but for now we must be careful since the SSB set-up is different for phone and digital.

Since SSB bugaboos have been discussed from time to time on the blog, I will only briefly mention a few items: disconnect the mic, disable the speech processor and keep the average power well below the CW or PEP peak power capability of your transmitter and amplifier.

Now let's move on to several items that seem to be increasingly common on the digital frequencies.

I hear voices

The FTdx5000 I use for digital modes has the front mic jack live at all times. The buffer amplifiers for the mic jack and rear audio input jack are mixed and there is no possibility to disable one or the other. Many rigs are similar. It is critical to unplug the microphone on the majority of rigs when digital modes are used. The computer software should be the only audio source.

Yet many forget. I do it occasionally since it is so easy to forget. Put on your headphones and listen to any busy FT8 channel and you will often hear background shack noises and conversations. Most hams realize their mistake and correct it. Unfortunately there are a few who never do and woe to those who tell them! Unless the signal is local and strong you may have difficulty identifying the guilty party.

You have mail!

Most of us use Microsoft Windows on our shack computers. Windows handles peripheral equipment with a great deal of flexibility so that it is responsive to the behaviour of most people. It deals with audio devices and sound cards being attached and detached, along with their various driver and configuration requirements. That doesn't always work for hams and others with very particular requirements for their audio devices.

Windows has a designated default sound card. It is typically on the motherboard, and uses the front or rear audio jacks. When there is more than one sound card, on the motherboard or added by the user, the default can be changed, and the change can cause problems. The default sound card is the one that Windows uses for notifications. These include the "bong" sound when you do something wrong, the chime or voice announcement when an email arrives, among many others standard applications. 

In most installations your digital software uses the default sound card. When Windows notifications occur during a transmission they will be transmitted. That's not good! There are ways to prevent it by delving into Windows settings or with additional hardware.

Since I don't have multiple sound cards on my current shack PC, my solution is to disable all Windows audible notifications. It works for me, though others may not like doing that. An alternative is to have two or more sound cards and use a non-default sound card for the rig interface. Many recent generation rigs include a sound card in their USB interfaces so you don't have to go out and buy one. If your rig has it, use it.

Courtesy tone

Modern transceivers have a plethora of features that almost nobody uses. One that should never be used on HF is the courtesy tone. This is the feature that transmits "beep!" when you release the PTT. It was popularized decades ago on VHF/UHF repeaters to make explicit when a transmission was over. The use of squelch on FM can make the end of a transmission difficult to deduce without it. On SSB it is not necessary and, in my opinion, it sounds ridiculous.

When you switch to digital modes, of course using the SSB mode of the rig, the courtesy tone feature is applied if enabled. In most instances it does not cause QRM because everyone's transmissions are synchronized. However, it is still poor operating practice and locals in particular will have no difficulty identifying the culprit. Don't use the courtesy tone feature and this won't happen to you on FT8.

Text to speech

We have some wonderful tools at our disposal to improve our results at gathering DXCC countries, grid squares, states and many other awards. The ability to passively monitor all activity on an FT8 channel can be exploited to further those aims. There are software applications that will monitor the messages decoded by WSJT-X, look up the call signs in local and remote databases, and issue notifications when a station is needed for one of those awards.

Many times I've heard these announcement on FT8 channels, and in one case from two stations at the same time. Not only does this interfere with others, it also halves the periods that you are monitoring since the transmissions exclude the possibility of listening during those periods. Unless you can route the notifications over a different audio path than that for the received audio, turn off those features.

Voice announcement features of modern transceivers can also be a concern. Features that are so useful to blind hams have found use in many shacks. With the features enabled, the rig will audibly announce the frequency, mode and other data. Depending on how the audio is routed between the rig and PC, these announcements can inadvertently be transmitted when using digital modes. 

Every rig is different and I don't have or use these features, so I cannot offer a recommendation other than to turn them off when you don't need them. For audio routed to the PC on digital modes, you might not even notice that it is happening unless you check for it.

Sound card shuffle

Among its many peculiarities, Windows is notorious for reordering, renaming, reconfiguring and renumbering peripheral devices during periodic updates and sometimes over a PC restart. It isn't noticed by most people since it doesn't affect their use of the PC. It is difficult to predict when it is likely to occur. You must be observant.

As mentioned earlier, Windows usually does it to transparently deal with what it believes are potential trouble points. With our particular computer interface needs in the shack, we need to prevent or recover from what Windows chooses to do.

With digital modes pay particular attention to sound card names and ordering. With many sound cards, it is a good idea to check the default and sound card assignments after Windows updates. There are security products that can disturb your configuration and those settings will need attention as well.

Monitor your transmissions

Almost all of the aforementioned problems can be discovered by monitoring the transmitted audio. Use the rig's monitor feature from time to time to ensure that the transmitted audio is clean and uncluttered by extraneous audio sources. This is especially important after you've made configuration changes on your rig, PC or software applications. It isn't something that needs to done all the time so it shouldn't be a burden.

It is sad to say that few hams pay attention to their transmitted signals, be it to check for distortion, key clicks or inappropriately routed audio. In some cases it is necessary to listen on a separate receiver since not all potential problems can be heard using the rig's monitor feature. Alternatively, ask a friend to listen and let you know if anything is amiss.