FT8 Stress and RF Choke Sizing

We know how stressful it is for our devices while using the digital modes: Radio, amplifier, coaxial cables, connectors and antenna system must be well sized.  High stress defined by a high temperature rise and increased loss during transmission cycles.

The chain – coaxial cable, connectors, antenna switches, RF Choke / Balun and antenna must be of excellent quality and adequate for the power used!

As an example, if we use 1000 watts in intermittent mode such as SSB, the system will be busy (full power) for a variable time from 20% to 40% depending on whether we are doing a normal QSO or participating in a contest! So, at worst 60% of the time our system will not be busy and will have time to cool down.

With digital emissions, during transmit, the system will be busy at full power and consequently the stress of the system will be very high!

One of the devices in this chain that will first show its limitation is the RF Choke or the Balun that, although it seems well sized (for example 3kW PEP RF Choke), will immediately show its limits as it has been sized to handle 3000 watts with intermittent transmissions such as SSB and not with constant transmission systems such as with digital modes!

What to do?
Size all the components in the chain well: Transmitter – Antenna and if you intend to transmit in digital modes, do not use continuous power levels exceeding 20% of the maximum applicable peak power (PEP – Peak Envelope Power).

Our high power RF Choke, capable of meeting this high stress environment is shown in the photo.