Apparent statement from QRO.....
> "We have designed the transmit/receive (T/R) switching so that
> the relays are momentarily "hot-shotted" with a large voltage spike
> to speed switching. Also, the same circuit that controls the cathode
> bias switching also controls the T/R switching. This means that
> whenever the T/R relays are in transmit, the correct linear operation
> cathode bias will be applied. The T/R and cathode bias relays are
> sequenced so that no "hot switching" can occur. A fast open frame mechanical
> relay
> switches nearly as fast as some vacuum relays."
Nearly only counts in horseshoes and hand-grenades, Dick!
Even the finest "hot-shotted" vacuum relays have a speed limit.
>
> Previously, I understood "hot switching" to mean that RF is applied to the
> tubes before the main relay has a chance to close. The tubes then transmit
> into thin air, causing arcing, pitting and burning of the T/R relay contacts.
Hot switching can occur on key-up, or unkey. If there is RF on either the
input or output relay contacts when power is applied OR removed is
hot switching.
The way I read it, QRO's sequencing circuit makes sure that the
> main T/R relay is closed before cutoff bias is removed from the tube, thus
> protecting the T/R relay contacts. True? However, since the 3ms provided by
> the FT-990 is not enough time for the T/R relay to close, won't the exciter
> RF be "hot switched" between the antenna and cathode input circuit? Does
> this present a danger to the relay contacts that switch the exciter RF? If
> so, is this still called "hot switching?"
You are keying from the wrong end here. The exciter is keyed with a
"hand-shake" circuit after the relays in the amp are CLOSED. That is why
you need such high speed relays to operate @ >20wpm CW.
Alpha and Ameritron use such schemes to do this. See Rich's web site to
see how he accomplishes the same thing.
>
> BTW, the guy asked if he could use the amp in QSK. Seems to me that even
> though they claim to have speeded up the open frame relay to be "nearly as
> fast as some vacuum relays" (5-8ms?), it still won't be fast enough for QSK.
> True?
Not if the horse is out of the barn before you close the door!
I won't even get into the dust and nicotene on the open-frame relay problem.
(((73)))
Phil, K5PC
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