FT8 / Technical Articles

FT8: Low Signal or Low Power?

It is always interesting to speak on controversial topics, and FT8 sure has had its fair share of controversy. There is one complaint in particular that keeps reappearing: How much power can be used while transmitting in FT8?

FT8 is, in fact, a weak signal mode, not a low power mode. It is always recommended to use minimum output power to make a QSO. As I have pointed out in the past, as hams we are bound by CFR TITLE 47 Part 97.313: “An amateur station must use the minimum transmitter power necessary to carry out the desired communications.”

Communication modes such as FT8, FT4, JT9, JT65, QRA64, ISCAT, and MSK144 are all designed for making reliable and confirmed QSOs under extreme weak-signal conditions. From Gary Hinson, ZL2iFB’s FT8 Operating Guide at physics.princeton.edu:

Although FT8 is a weak signal mode, not a QRP mode per se, please keep your transmit power down. Be nice! Generally on HF, if a path is open, just a few watts will do. Put your amplifier on standby. Turn down the wick to QRP levels. Try it! If you don’t get any responses at all, try 10 watts, maybe 20 or 30. If you find that you routinely “need” 100 watts or more, that is a strong hint that your feeder and antenna system are inefficient. Check for corrosion and loose connectors. Try making a simple halfwave dipole as a comparison antenna. You will find that you can receive better if your antenna is in good shape, and reception is kinda useful for DXing.

The perfect transmission is about more than just power. Your radio might hear better or worse than other radios. You may be working with a compromised antenna system. You could have a wide variety of items causing noises that stunt your signal down to practically nothing. Or maybe just the sun isn’t very cooperative on the current day, causing the bands to be mostly closed.

Also from the FT8 Operating Guide:

There are situations where QRO, up to your license limit, is both appropriate and necessary, for instance CQing on a closed band, hoping to catch DX as the band opens, or calling someone weak (below, say,

-20 dB). Occasionally, we experience one-way propagation as if there is a giant diode in the ionosphere: DX stations are loud but cannot hear us. Maybe they have high QRM on their end. Maybe there is a tilt in the ionosphere.

Let’s take a look at what power is or can be. A more precise term would be ERP (effective radiated power). This is a measure of the flux in the direction of the opening (azimuth and elevation), which is a combination of power delivered to the antenna with its antenna pattern. As an example, the ERP of a 100 watt transmitter through a transmission line with -3 dB loss and an antenna gain of 11 dBI in the ionospherically determined path’s azimuth and elevation angles would be a bit over 600 watts.

Remember, more power will get the other station to hear you; however, it doesn’t help you receive more or better stations. The antenna and line gain and loss apply to both transmit and receive, though.

One more time for those in the way back–FT8 is a weak signal mode, NOT a low power mode. So when you’re on the air, play fair and responsibly.

Questions? Share them in the comments below or email me at KE8FMJ@arrl.net.

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