K3 - qsk keying loop

[Phil Salas]

"Over the past decade I've used a slew of Ten-Tec and Yaesu xcvrs interfaced
to Ten-Tec, Alpha, and Acom amplifiers via plug 'n play keying loops with
uniformly excellent performance.  The lack of QRO QSK with the K3 may be a
big issue with some prospective K3 contesters."

I disagree that this is a problem.  The new TenTec Orion and Omni VII
transceivers have a minimum "amp-key to RF out" delay of 15ms.  The Kenwood
TS480 and TS2000 have a minimum delay of 10ms.  My Yaesu MKV has an
adjustable delay of 0-30ms (5ms default).  I measured the delay on my
IC-706MKIIG at 15ms, and on a IC-7000 at 10ms.  If you have a QSK amp, it
will switch at least within 10ms if it uses high speed signal relays,
probably around 3-6ms with vacuum relays, and maybe 1-2ms if it uses PIN
diodes.  Both the THP and SPE solid-state amps switch in 7-10ms using high
speed relays.  So all you have to do is to adjust your K3 delay to something
longer than the amplifier relay switching time. If you have any doubts, set
it to 10ms and you should be fine.

You can hear where the delay needs to be set by listening to your signal on
a second receiver.  I experimented with this using my Yaesu MKV and my
QSK-modified Ameritron ALS-600.  The relays in my modified ALS-600 switch in
3ms (measured with a 'scope).  But just for the heck of it, I listened to my
signal on a second receiver while I shortened the delay time on my MKV, and
I started hearing key clicks in the receiver right around 3ms (just like my
measurements had predicted).  So I just re-set my MKV to 5ms delay and
everything worked fine.  I had to set the delay on my MKV to 10ms when I was
testing the THP and SPE amps to stop the clicks.  

Phil - AD5X




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[Dick Green WC1M]

Pardon me for jumping in here. I don't have a K3 and don't have one on
order. I'm trying to make that decision. I've read a lot of good things
about the K3. Absence of a keying loop isn't one of them.

 

Although it's true that some modern QSK amps may appear to work fine without
a keying loop, bear in mind that both Acom and Ten-Tec recommend using them.
Elecraft should consider the recommendations of the amp manufacturers, not
what they *think* will work correctly. Even if Elecraft is right, why force
the owner of a $6,000+ amplifier to go against the manufacturer's stated
recommendation? If something goes wrong with the amp's T/R relay, causing an
expensive ship/repair/ship drama, will Elecraft indemnify the owner?
Probably not. I sure wouldn't want to get in the middle of that
finger-pointing exercise.

 

Alpha 87A owners can relax: Alpha specifically discourages use of the 87A
keying loop. That's not surprising, because the keying loop logic in that
amp doesn't work correctly. It's not a problem because the PIN diodes switch
almost instantaneously and there are no mechanical contacts to burn. You can
drive that amp all day with the PTT output line. And that's what Alpha tells
you to do.

 

Let's look a little closer. The typical Jennings and Kilovac type vacuum
relays used in QSK amps have rated switching times in the  6-8ms range. In
some designs, the relay is triggered with a burst of high voltage which
reduces the switching time to as little as 2ms. So, theoretically, there's
no danger of hot switching if the transceiver has a delay between PTT and
the start of the RF envelope of, say, 15 ms. But the problem is that you may
not know what else the amp is doing besides closing its vacuum relay. For
example, the Acom 2000a has a rather complex T/R switching sequence that
involves several relays, and the timing may be longer if the amp has to
retune. My point is that you can never be sure exactly what timing
constraints a QSK amp may impose, so it's best to follow the manufacturer's
recommendation and let the amp decide when it's safe to apply RF. In other
words, use a keying loop if the manufacturer says to.

 

In theory, relying on the transceiver to delay RF can reduce the maximum QSK
speed (i.e., compromise the ability to hear between code elements.) But
that's only true if the transceiver's delay can be reduced to less than the
amp's switching time. If the delay isn't adjustable, then the excess delay
will be present whether a keying loop is used or not. The best setup is a
keying loop with a fully configurable PTT delay. At any rate, I can't attest
to the effect of an extra 10ms or so of receiver muting at high speeds. The
QSK experts will have to comment on that.

 

A keying loop is also very desirable for preventing hot switching of antenna
relays. A TX ENA or TX INH port can be used to suppress RF before and during
any switching. It's possible to use PTT to prevent switching from taking
place, but it's not as foolproof as suppressing RF -- there are timing
windows where hot switching can occur. Also, if you use PC-based software to
do your switching, it's a heck of a lot more difficult to detect when PTT
has been closed than it is to raise TX INH. My point  is that many contest
stations, including mine, have switching systems based on the
commonly-available keying loops found on popular rigs. Why force us to give
up or modify those hard-won systems?

 

This leads me to the key question: Why not implement a standard feature that
the amateur community has come to rely on? After all, you wouldn't want to
get a reputation of ignoring such things, like a certain other US-based
manufacturer of amateur transceivers :-)

 

I think it's unfortunate that Elecraft has made the decision to omit a
keying loop. They may not have realized that the K3 is going to appeal to a
whole different breed of users than the K2, including contesters who have a
wide variety of equipment, station configurations and very demanding
requirements. Lack of this feature is going to complicate my buying
decision, for sure. But I'm always willing to resort to a mod if I have to
(Warranty? What warranty?) Is there a point in the circuit where it would be
possible to safely implement a TX INH or TX ENA function? If so, my
soldering iron is heating up. ? If not, I hope K3 will reconsider a keying
loop for the next major rev.

 

73, Dick WC1M

 

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[Don Rasmussen]

[Elecraft] Re: K3 - qsk keying loop
Dick Green WC1M wc1m at msn.com

Hi Dick,

Happily, the K3 is modular. Would I be incorrect to
assume that a hardware solution could be engineered to
perform this specific purpose, and reasonably
inexpensively?

All it would really take would be for Eric and Wayne
to buy into the idea of it's importance. I don't see
them sticking their jaw out about this issue simply
out of principle (like some others made a mistake of
doing in the past?)

Part of Elecraft's larger difficulty at this time
involves the fact that they have created a transceiver
that will appeal to a wide variety of interests.

Contesters, CW ragchewers (me), AM, FM, Digital, ESSB,
SWL, even transverter fanatics.

They have released a very fine base model K3, which I
feel will be accepted very well, however they still
have to get the subreceiver integrated into the
firmware and release that bit of hardware and I expect
that is bigger on the list of to do's than the keying
loop - just my guess.

There are also other larger issues behind that like AM
and FM support (advertised), maybe some transverter
issues, and variable roofing filters.

There is a lot in competition for these guys attention
and it will be interesting to find out how the voting
is done with respect to everyone that wants everything
in their own diverse interest.

As a part time contester, given the fact that there
are acceptable methods of getting the switching done,
I'd like to see some features that are not there at
all added, before making something that is already
there a little better.

And I understand that a true contester would fight me
to the grave over this one issue, but we both pay our
money and take the best we can get.

As a general operator, I've been pushing hard to get
some kind of single press band switching in the
firmware, which is pretty meaningless to a contester
that is allowing the program in his computer program
to do all that.

Anyway, I know the radio was primarily focused towards
contesting from the beginning and maybe it would have
been icing on the cake to have the switching done a
backwards compatible way on top of all the other good
stuff, but most likely at the expense of some other
things that would not have made it into the radio.
Some things are still waiting (like ESSB or AM) to be
fully implemented.

Darn I wish I had an amp to be concerned about, and it
won't ever happen at this QTH, but the guys still have
a transceiver that you have your eyes on and I have on
order already so I suppose that's fair enough for now.


;-)

de wb8yqj

[Elecraft] Re: K3 - qsk keying loop
Dick Green WC1M wc1m at msn.com
Wed Nov 28 18:24:57 EST 2007

Previous message: [Elecraft] K3 SSB Bandwidth at this

Pardon me for jumping in here. I don't have a K3 and
don't have one on
order. I'm trying to make that decision. I've read a
lot of good things
about the K3. Absence of a keying loop isn't one of
them.

 

Although it's true that some modern QSK amps may
appear to work fine without
a keying loop, bear in mind that both Acom and Ten-Tec
recommend using them.
Elecraft should consider the recommendations of the
amp manufacturers, not
what they *think* will work correctly. Even if
Elecraft is right, why force
the owner of a $6,000+ amplifier to go against the
manufacturer's stated
recommendation? If something goes wrong with the amp's
T/R relay, causing an
expensive ship/repair/ship drama, will Elecraft
indemnify the owner?
Probably not. I sure wouldn't want to get in the
middle of that
finger-pointing exercise.


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