If it is what it says, it will activate the relay in the SB-220 AFTER the drive is applied. This causes the driver's RF power to strike an arc across the 'standby' side of the relay, as the relay's contact lever breaks the standby-side circuit, and moves to the "transmit" side. Doesn't happen right away, takes a twentieth of a second or so.
For amplifiers that use barefoot drive, under 40 Watts PEP, this arc is too small to matter.
The more drive power, the larger this arc will be. It's a characteristic of the RF-sensing method in the first place. The relay won't start to change over until there is sufficient drive to activate it.
The ham radios the SB-220 was built to be used with get around this problem by keying the amplifier directly from the PTT circuit in the radio. Tends to give those relay contacts a "head start", before the transmitter circuits wake up and start pumping drive power.
A foot switch is a popluar way around the problem, but if you're "late" with the switch, you will pull an arc across the standby side of the relay. Some folks find it hard, but if the foot switch is pressed BEFORE you key the mike, and released AFTER you unkey, no arc problems. So long as the relay is in motion only when NO drive power is present, it lasts a lot longer.
Had a customer with a 4-by-3-500Z box. Insisted on using a foot switch. Trouble is, he's diabetic, and has limited feeling in his feet. His foot would slowly slip, and release the foot switch while he was keyed and talking with WAY too much drive power. He'd notice the wattmeter, and move his foot back to key the big box back up. All the while talking at the top of his voice.
The result is the the input-side relay on that box would last him about 16 to 18 months on average. Got pretty good at changing it out, whenever he would complain that his receive side was dropping out. Made me wish I had made that relay a plug-in type.
Offered to put a keying relay in his base radio, to key the big box with a patch cord, but he liked his foot switch just fine, thank you.
Never, NEVER try to install a relay in a radio by hooking one side of it to the mike's transmit pin. Here's one method, that senses the transmit-only 8 Volts in most base or mobile radios. Not that much to it. A 12-Volt DC relay, NPN transistor, resistors, diode, and bypass capacitors are all that's on it. Used to just string the parts across the lugs on a relay. The circuit board is less labor, and more robust.
Installing the Nomad Radio KeyBoard in the Galaxy Saturn Turbo
Still working on step-by-step instructions for other models and brands.
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