The CW key line is shown but is not important to understand the timing as it follows the HSEND line very closely and obviously has is not applicable to any mode other than CW.Īmplifiers are generally controlled via the Send Control jack which is a bare relay contact but may also be controlled via the HSEND output driving an external buffer device. The HSEND line is both an input and output but when it is low the radio is in transmit mode and when it is high the radio is in receive mode.
The drawing below shows the basic timing external to the radio.
The amplifier (or any other devices that may be switched in or out) must be in the circuit BEFORE any RF begins and must not be switched out of the circuit until the RF has totally ceased and then need to be switched out quickly. The timing of this switching is important if we expect relays to not be damaged and if we want our transmitted signals to be spectrally clean. Since almost everyone uses the same antenna for both transmitting and receiving, an external amplifier must be switched in and out of the circuit when going from transmit to receive. The following measurements were made on some Icom radios and an Elecraft K2/100 but all radios have the same issues.
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