[AMPS] Hot Switching

[measures]

>
>
> 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.
>>
And, if the go signal for amplifier relay closure is delayed even a few 
mS, hotswitching can occur no matter how speedy the relays are.  .  

>> 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.

An Unkey hotswitch would seem unlikely because transceivers ordinarily 
stop making RF before the unkey relay signal is sent to the RL control 
circuit in the amplifier.  
>
> >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?

Hopefully.  Another consideration is to make sure the relays open quickly 
so that they are ready for remake.  .  
- The easiest way to obviate the remake hotswitching problem is to make 
sure that the vacuum relay opens quickly enough to be ready for the next 
dit or syllable.  This is accomplished by putting roughly 2x the coil R 
in series with the diode that damps the reverse v spike across the relay 
coil when the relay opens.  

>>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? 

A RJ-1A or HC-1 vacuum ant. relay closes in c. 1.8mS with the speedup 
circuit on my Website.  .  The Matsushita RSD RF reed relay closes in 
1mS, so it is fast enough right out of the box.    My guess is that a 3mS 
radio could not cause a hotswitch..  

>>  This 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.
>
My  solution to Not hotswitching is blazing speed.  The total P cost is 
c. 8w of DC power lost - but only during make.  .

>> 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.
>

amen, Phil -- Why is he using the blazing open-frame relay when a 6uS 
opto and a 3A npn switch to make a silent ECBS cost under $2.?.  

later

-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


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