Tune and Auto Tune

Tech Net Library

Tune and Auto Tune

HF Transceiver / SSB Operation

by Rick Medero s/v C_Language

Tuning Your SSB


Many models of HF transceivers have the auto tune feature (not to be confused with the autotuner box). This feature will invoke a tune operation on the first push of the TX button on the mic if the tune operation had not been done for the selected frequency. The tune operation can take some number of seconds to complete and while running, the audio into the mic may not be heard by receiving stations.

Rather than depending on the auto tune feature, it is better to force a tune prior to speaking by using the radio's tune button. Also forcing a tune operation prior to receiving will improve reception.

It is important to note that during a tune operation the transmitter emits power that can interfere with other receiving stations. The proper way to perform a tune operation is to first verify by listening for several seconds that the selected frequency has no traffic. If you find that the desired frequency is busy move to a legitimate frequency near the desired frequency and perform the tune after verifying that frequency is not busy. If the desired frequency is currently in use for a net, then you should assume it is busy.

Why does a transceiver need a good match and what is a "match"? To help you understand what the antenna tuner is doing, you can think of it like a transmission in a car. The function of a transmission is to match the speed and torque of the engine to the required speed and torque at the wheels to transfer maximum power from engine to the wheels. The antenna tuner matches the voltage and current at the transceiver to the voltage an current at the antenna to transfer maximum power. As you may have experienced with your car, when the transmission is not in the proper gear undesirable performance will result. When transmitting into a poorly matched antenna, most transceivers will reduce output power to protect the transmitter from damage. When an antenna is not matched well, much of the energy that should go out of the antenna is reflected back to the transmitter and is dissipated as heat. You may have heard some stations with portions of their speech missing, this can be caused when the transmitter sees too much reflected energy and momentarily reduces its output power.

Why does an HF transceiver need antenna tuning when a VHF does not? All transceivers require a good antenna match. The difference is that with a VHF radio the range of frequencies is narrow enough to allow a fixed antenna to be matched over the entire range. Also the frequency is high enough to allow a relatively small antenna that can be purchase for that specific application. With an HF transceiver the range of selectable frequencies is so wide that it is impractical to have an antenna that will present a good match without a device to tune the antenna. This if the function of the antenna tuner box.



Rick's site s/v C_Language