> The new Alphas were not the first to offer sequenced keying.
> The 77 series of Alpha amps all featured "reverse keying."
> This technology has been around since the first high speed vacuum relays
> hit the market. The modern pin diode schemes are incredible! No moving
parts,
> and no noise.
I'm not sure about the 77-series, but my Alpha PA-70V accommodates
high-speed VOX in its "Break-In" mode. The amp remains keyed and the output
network is coupled back into a small tuned RF amplifier using a FET which is
then routed to the amp's back panel BNC connector. This works surprisingly
well, and I do not hear the effect of IP3/IP2 distortion on large incoming
signals, although I suspect the RF amp exhibits nowhere near the front-end
overload characteristics as do today's top-end transceivers. Still, the
best approach seems to take advantage of modern high-speed vacuum relay
keying circuits like Rich's or through the use of high-power PIN diodes.
BTW, I just received my Alpha 87A with AlphaMax and the new firmware seems
to automatically correct tuning into variable loads quite well. Last
weekend, I deliberately mistuned my Force12 Sigma and the Alpha was right
there making its necessary adjustments and tuned to a degree that was every
close to manual optimization. This feature is great here in Florida where
the daily rains constantly force you to retune as the antenna dries out.
-Paul, W9AC
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