"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."
Lou, this is the issue with the stupid 7300? xcvr.? ?It keeps putting out RF....AFTER? it opens the key line....and amp switching back to RX.....which then hot switches the TR relays in the amp.??
The alpha amps will not RLS their TR relays, until NO RF appears on the input.? ?The alpha amps have a simple RF sense circuit on their input (which also reads the freq, if it's the 9500 auto tune).
The W7RY? qsk board does the same thing.....( RF sense on input).? ?IF u say run a 1.5 kw cxr on the alpha....and reach over and pull out the key line from the back of the xcvr ( or pull out from the back of the alpha amp)...then amp will still put out 1.5 kw...... until the ptt /footswitch is released..... or if you let go of the hand key.? And if it's a 7300...with it's .....'RF tail', the alpha will not UN key it's TR relay/pin diodes on older alpha amps like the 87A...until the RF tail has finally gone.??
This is also an issue when using high swr shut down circuits, like in the array solutions powermaster wattmeter.? With the high swr threshold exceeded, you have 3 x ways to shut down the amp asap.?
(1)? open off keyline ( doesn't work on alpha amps)
(2) apply a few volts of DC? to the xcvr's ALC input? ( this method works superb)
(3) open off the xcvr's? .....'TX inhibit lead'? ?This method is the fastest if using the array solutions power master wattmeter.
The AS meter uses a SPDT fast relay to achieve any if the 3 x configs above.? ?Takes 4 msecs to get the COM contact to physically move from the NC contact over to the NO contact....(for? #2...applying a few volts to the alc jack of xcvr).??
However, when simply opening of the normally grnded? TX inhibit lead, the COM only has to move .0001" away from the NC contact, in order to open off the TX inhibit lead..... =? < 1 msec.?
