Icom IC-7300 Hot-

switch Mitigation

The Issue

The Icom IC-7300 was released with a flaw in its external amplifier keying circuit apparently caused by an incorrect timing parameter

programmed into the SEND relay logic. The SEND jack on the rear of the transceiver is used to key an external linear amplifier on and

off in synchrony with the IC-7300 RF output as mitigated by the Menu/Set/Function TX Delay parameter. That parameter sets the time

the RF output is delayed from the time the transmitter is keyed on until RF output begins. (The TX Delay parameter sets the time the

RF output is delayed from the time the transmitter is keyed on, which is not what is addressed in this article; the TX Delay functions

nominally as expected. This article is concerned with the RF output continuing beyond the time the transmitter is keyed off, termed an

RF-tail, causing hot-switching of external linear amplifier.)

Unfortunately, there is no similar user adjustable menu setting for controlling the delay time from when the transmitter ceases RF output

and the SEND jack commands an external amplifier off. Because the IC-7300 continues to output RF energy while an external amplifier

is in the process of switching off, the amplifier's TR/RX relay is subject to hot-switching and the concomitant possibility of arcing at the

relay contact points, or worse yet, welding together of those points resulting in the amplifier taken out of service.

This RF-tail issue has been extensively addressed for years by Amateur operators on both the IC-7300 discussion group, and

QRZ.COM Forum. Below is finally a possible hardware solution to the hot-switching issue originally suggested by Frank Johnson

(G0GSR)

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Complete description of the fix in in the groups.io ic7300 forum files.

/g/ic-7300/files/ic7300_rf_tail_fix.pdf

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73,

Dave, w6de

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