Ian
Interesting comments on hot switching, some remarks:
>It depends on the combination of the transceiver, the amp and
> the voice.
I have not seen any hot-switching problems using commercial ham
amps, but I have only operated Alpha, QRO and the AL-1500 with
QSK installed. The "export" only amps usually don't have QSK and
I notice now it's becoming a $200 option on some models.
>To repeat: there must be *no* mechanical relays - and no other time
>delays -
I measured the wiper travel time on several Dow-key relays using
a counter and 10 kHz source that could handle a dead short. I had
shorts on the NC/NO ports and the counter would only see the
10 kHz when the wiper was in motion. The average time from start
to close was around 12-14 milliseconds depending on the bounce
from the contact cleaning slide action. I was not able to improve that
time much even increasing the coil DC to over twice. Maybe 2 or 3
milliseconds was all. Dow-key RF relays in amps no longer work
with modern radios even with speed up circuits.
>only simple answer I can think of is to use a contest logging program
>with a built-in DVK facility and a hard-wired PTT output - the
program
>will have a user-configurable delay between PTT and the start of
audio
>output (same for CW keying also).
Not sure one is available. The problem is Logging software can insert
the PTT signal before the DVK pulse when the F key is hit but it needs
to know when the DVK voice message is over so it can release PTT.
Speaking for TRLog which has CW and paddle PTT control, no PTT
signal is available for a DVK. The DVK boards I use turn on and off
PTT
with the message. My suggestion was to have TRLog insert PTT for 20
miliseconds then remove it. By then the DVK PTT signal would hold the
amp relay until the end of the message.
73 Rich KL7RA
>Jim Reid wrote:
>>Ok, is it possible to hot switch the amp when
>>using the SSB mode? I don't think so, unless you
>>"switch" right in the middle of a loud vowel sound?
>>Correct?
>
>It depends on the combination of the transceiver, the amp and the
voice.
>
>Basically it's a race against time between the transceiver and the
amp.
>The amp gets its PTT from the transceiver, and it then has to change
the
>relays over before the RF arrives.
>
>Rich's solution is to make the relays switch much faster, and that
>usually buys you enough time. Rich is correct to say that even if you
>only use semi-breakin, something still needs to be done because you
>always get arcing on the first key-down. The only difference for full
>(between-the-dots) breakin is that the arcing happens much more
often.
>
>Rich uses fast vacuum relays, and speeds them up even more by forcing
>current through them from a high-voltage supply. There's also an
>excellent relay speed-up circuit by K1KP that runs off the normal
supply
>rail and achieves much the same as the high-voltage method. There's a
>description on W6XX's site, and also in my RadCom column a few months
>ago.
>
>If your setup is already nearly OK, then either of these circuits can
>move your amp well ahead in the race against the transceiver, and
often
>can completely cure the relay arcing.
>
>However, the amp cannot even start to switch until it gets the PTT
>signal from the transceiver. If the transceiver wastes too much
valuable
>time in getting the PTT signal out to the amp, there will be problems
>that even the fastest amp can't handle. If the PTT output involves a
>relay inside the transceiver, much time is wasted and then it's
>impossible to give the amp enough time to switch... in extreme cases
the
>RF output has started before the PTT relay closes, so your amp
doesn't
>have a chance!
>
>If the transceiver has a solid-state PTT switching output, that's the
>fast one, so *use it*. You may also need to build a transistor
interface
>into the amp, so that it doesn't overload the small switching
>transistors that most rig manufacturers seem to use. This should be p
art
>of any amplifier upgrade.
>
>Many transceivers with a slow PTT output can be easily modified to
pick
>up the key and/or mic contact closure, and send it instantly to the
>rear-panel PTT output. A new solid-state switch (open collector) is
>connected directly in parallel with the existing one, so that either
>will command the amp.
>
>To repeat: there must be *no* mechanical relays - and no other time
>delays - in the entire path between your morse key and the circuit
that
>switches the RF relays in your amp.
>
>But VOX is a problem, because there's no way to speed-up the reaction
of
>the VOX circuit itself. If you're using a DVK for contesting, with
lots
>of compression, you may be hitting the amp with almost full power in
the
>first few milliseconds - which is almost as bad as the CW situation.
The
>only simple answer I can think of is to use a contest logging program
>with a built-in DVK facility and a hard-wired PTT output - the
program
>will have a user-configurable delay between PTT and the start of
audio
>output (same for CW keying also). FSK data can be bad too, but again
>most PC software can key the rig and then delay the start of the AFSK
>output.
>
>[Hmmm... I seem to be writing the outline for a talk that I'm
scheduled
>to give next year! If it's useful, carry on reading...]
>
>There are other solutions too. A good solution for CW-only operators
is
>to use an amp that allows you to plug the key directly into it. The
amp
>has a sequenced key-out line that does to the transceiver's normal
>morse-key input. Then the amp has full control, and doesn't key the
>transceiver until it's good and ready. But that doesn't solve any of
the
>problems on phone or other modes.
>
>Another solution is to use a transceiver that has a separate control
>input, so you can press the key or the PTT and key the amp, but the
>transceiver won't actually deliver RF until the control line goes
low.
>The transceiver keys the amp in the normal way, but there is no RF
drive
>until the amp sends a 'ready' signal back through this control line.
>
>Recent Yaesu rigs have this on the band-data output, mainly for use
with
>their own solid-state amp. But then my FT-990 messes everything up,
by
>delaying the PTT output by several milliseconds, and then delaying
the
>RF by a *further* 10 milliseconds from the time the control line goes
>low. In total, that's enough to ruin it for fast QSK - with
>semi-breakin, the first dot will be cut in half; and with
full-breakin,
>*every* dot will be cut in half. (Question: are the FT1000 series any
>better?)
>
>[Well, that's been useful for me, to get my thoughts together for the
>talk. I hope it's been useful for AMPs too.]
>
>--
>73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
> Editor, 'The VHF/UHF DX Book'
>http://www.ifwtech.co.uk/g3sek
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