K3 and Expert 1K-FA

[W4GRJ]

I agree on the protective response time of the Expert being very fast, I
have accidently hit it with 100w a couple times ..... it alarms and shuts
down with no apparent harm done.....the absolutely best amplifier I have
ever used.

Jack
W4GRJ


-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Paul Christensen
Sent: Wednesday, April 21, 2010 10:10 AM
To: [hidden email]
Subject: Re: [Elecraft] K3 and Expert 1K-FA

> So, please do not advise someone with a solid state amp to disconnect
> their ALC- unless you want to assume the cost of repairs.

Overall, I agree with that assessment.  However, I do no not make use of the

K3's ALC line with my SPE solid-state amp.  In looking at the SPE's
protection circuitry, a fault buss is created that applies a high level of
bias to the power MOSFETs when any of about 6-7 different fault conditions
occur.  The response time is exceptionally fast to the point where if I
deliberately blast the SPE with full power from the K3 without ALC connected

(don't try this at home - I'm a risk taker but did so only after reviewing
the circuit), the SPE detects the presence of high input power and applies
enough MOSFET bias to keep output power below about 1100 watts.  How
instantaneous?  I have not measured the response time but it does respond
well to the leading-edge power spike from another well-known transceiver.
Today, a solid-state amp should be smart enough to know when it's being
overdriven.

Also, an unknown with the SPE amp is what happens to amplifier linearity
when the bias protection circuitry begins to engage to keep power from
exceeding 1KW?  But the same question must be asked of any transceiver that
interfaces to an amp while using an ALC line.  I like to think that when an
amp and transceiver come from a common manufacturer, the ALC circuitry is
probably optimized since the designer knows exactly what's needed at the ALC

"meet me" point between the amp and transceiver.

Paul, W9AC

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[Mel]

I agree with Doug but from another prospective.  Look at the energy budget for portable work.  Less total "consumed" power is good.

Mel, K6KBE

--- On Wed, 4/21/10, Doug Turnbull <[hidden email]> wrote:

From: Doug Turnbull <[hidden email]>
Subject: Re: [Elecraft] attenuator in amp was Re:  K3 and Expert 1K-FA
To: "'Doug Faunt N6TQS [phone]'" <[hidden email]>, [hidden email]
Cc: [hidden email]
Date: Wednesday, April 21, 2010, 2:08 PM


Dear OMs,
    I can not understand why one would want to run the K3 at 100 W rather
than 20/30/50 Watts.   Why drive the K3 harder when driving it more lightly
should improve reliability and possibly improve linearity.   The waste of
energy is also undesirable; the fifty watts out that is discarded probably
costs 100 Watts of energy.  The idea of adding an attenuator for 50 Watts of
energy sounds mad to me and environmentally unfriendly as well.

          73 Doug EI2CN



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[K6LMP]

think of it as insurance to protect against a short circuit between the headphones....


Lew K6LMP


On Apr 21, 2010, at 2:31 PM, Mel Farrer wrote:

> I agree with Doug but from another prospective.  
          [I assume you meant "perspective"]

> Look at the energy budget for portable work.  Less total "consumed" power is good.
>
> Mel, K6KBE
>
> --- On Wed, 4/21/10, Doug Turnbull <[hidden email]> wrote:
>
> From: Doug Turnbull <[hidden email]>
> Subject: Re: [Elecraft] attenuator in amp was Re:  K3 and Expert 1K-FA
> To: "'Doug Faunt N6TQS [phone]'" <[hidden email]>, [hidden email]
> Cc: [hidden email]
> Date: Wednesday, April 21, 2010, 2:08 PM
>
>
> Dear OMs,
>     I can not understand why one would want to run the K3 at 100 W rather
> than 20/30/50 Watts.   Why drive the K3 harder when driving it more lightly
> should improve reliability and possibly improve linearity.   The waste of
> energy is also undesirable; the fifty watts out that is discarded probably
> costs 100 Watts of energy.  The idea of adding an attenuator for 50 Watts of
> energy sounds mad to me and environmentally unfriendly as well.
>
>           73 Doug EI2CN

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[W8JI]

<<    I can not understand why one would want to run the K3
at 100 W rather
than 20/30/50 Watts.   Why drive the K3 harder when driving
it more lightly
should improve reliability and possibly improve linearity.
The waste of
energy is also undesirable; the fifty watts out that is
discarded probably
costs 100 Watts of energy.  The idea of adding an attenuator
for 50 Watts of
energy sounds mad to me and environmentally unfriendly as
well.>>

Doug,

The primary reason is safety, and the secondary reason is a
cleaner signal.

While the K3 does not have overshoot, many rigs do. This
compounds the drive problem, and it compounds the overshoot
problem.
For example my IC706 overshoots to about 140 watts  whether
the output power is set at 50 watts or at 100 watts.  If I
have an amp that drives at 40 watts and the radio overshoots
to 140, that is disaster. If I have an amp that drives at 80
watts and the rig overshoots to 140,  it might not blow up
and the broadband "pulse" generated by leading edge
overdrive will be a whole lot less level and even less
duration.

The 3 dB attenuator is a **very** good idea, because nothing
can fix or reduce these problems except a pad. External ALC
won't work.

73 Tom







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[Bob Cunnings NW8L]

On Wed, Apr 21, 2010 at 3:14 PM, Eric Swartz - WA6HHQ, Elecraft
<[hidden email]> wrote:
> You will need the mod.

Ah. Will the ALC connection be prescribed as mandatory for the K3/KPA500 system?

Bob NW8L
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[P.B. Christensen]

>    I can not understand why one would want to run the K3 at 100 W rather
> than 20/30/50 Watts.   Why drive the K3 harder when driving it more
> lightly
> should improve reliability and possibly improve linearity.   The waste of
> energy is also undesirable; the fifty watts out that is discarded probably
> costs 100 Watts of energy.

For the same concerns, I think an auto-switched pad engaged during an input
fault is a good idea.  In the case of the SPE amp, I would not like to have
30-watts dissipating as heat in the front end of the amp.  The 3dB pad does
improve return loss into the amp input by the same amount.  But, the
effective gain factor of the amp is then reduced by 3dB.

The pad may assist with improving linearity from the driving transceiver,
but improving linearity can be accomplished with better efficiency if the
transceiver has an internal ATU with an auto-tune function that can be
programmed to limit the transceiver's power during the tune function.

Paul, W9AC

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[W8JI]

30-watts dissipating as heat in the front end of the amp.
The 3dB pad does
improve return loss into the amp input by the same amount.
But, the
effective gain factor of the amp is then reduced by 3dB.>>>

A 3dB pad gives 6 dB return loss. For example if load SWR is
2:1 (5.5dB RL) and we add a 3 dB pad, return loss is 9.5 dB
(1.4:1 SWR).

A 3 dB 50 ohm pad with an open circuited output looks like
150 ohms. You can make a 3:1 SWR test fixture by opening and
shorting the output.



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[P.B. Christensen]

Yes, that's right, 3 dB per trip to and from the load.  Not 3 dB in total as
I indicated.

Paul, W9AC

----- Original Message -----
From: "Tom W8JI" <[hidden email]>
To: "Paul Christensen" <[hidden email]>; <[hidden email]>
Sent: Wednesday, April 21, 2010 7:05 PM
Subject: Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA

> 30-watts dissipating as heat in the front end of the amp. The 3dB pad does
> improve return loss into the amp input by the same amount. But, the
> effective gain factor of the amp is then reduced by 3dB.>>>
>
> A 3dB pad gives 6 dB return loss. For example if load SWR is 2:1 (5.5dB
> RL) and we add a 3 dB pad, return loss is 9.5 dB (1.4:1 SWR).
>
> A 3 dB 50 ohm pad with an open circuited output looks like 150 ohms. You
> can make a 3:1 SWR test fixture by opening and shorting the output.
>
>
>
>

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[P.B. Christensen]

> A 3dB pad gives 6 dB return loss. For example if load SWR is 2:1 (5.5dB
> RL) and we add a 3 dB pad, return loss is 9.5 dB (1.4:1 SWR).

Tom,

The 6 dB R/L from the 3 dB pad is definitely correct but you lost me on the
2:1 SWR and corresponding R/L figure above.  I calculate a 2:1 VSWR as a 9.3
dB R/L and a 1.4:1 SWR at 15.56 dB R/L.  What am I not taking into
consideration?

Paul, W9AC

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[n7ws]

The actual return loss improvement is twice the attenuation, but I know Paul knows that.


--- On Wed, 4/21/10, Paul Christensen <[hidden email]> wrote:

> For the same concerns, I think an auto-switched pad engaged
> during an input
> fault is a good idea.  In the case of the SPE amp, I
> would not like to have
> 30-watts dissipating as heat in the front end of the
> amp.  The 3dB pad does
> improve return loss into the amp input by the same
> amount.  But, the
> effective gain factor of the amp is then reduced by 3dB.
>
> The pad may assist with improving linearity from the
> driving transceiver,
> but improving linearity can be accomplished with better
> efficiency if the
> transceiver has an internal ATU with an auto-tune function
> that can be
> programmed to limit the transceiver's power during the tune
> function.
>
> Paul, W9AC

     
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[Guy, K2AV]

This thread started off with a K3 owner driving an Expert 1K-FA with
the power control set to 100 watts.  That K3 owner can just set the
power knob to 30 watts and move on. Based upon the performance of the
current firmware in a K3, can't any K3 owner driving any amp can just
set the power control to the proper drive, and forget the ALC?  ALC
doesn't fix leading spikes anyway, so what's it good for?

All my amps have ALC circuits but I haven't hooked them up in years.

73, Guy.
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[W8JI]

----- Original Message -----
From: "Paul Christensen" <[hidden email]>
To: <[hidden email]>
Sent: Wednesday, April 21, 2010 7:43 PM
Subject: Re: [Elecraft] attenuator in amp was Re: K3 and
Expert 1K-FA


> A 3dB pad gives 6 dB return loss. For example if load SWR
> is 2:1 (5.5dB
> RL) and we add a 3 dB pad, return loss is 9.5 dB (1.4:1
> SWR).

My bad dyslexia Paul.

A 3dB pad gives 6 dB return loss. For example if load SWR is
2:1 (9.5dB
RL) and we add a 3 dB pad, return loss is 15.5 dB (1.4:1
SWR).

That should make more sense!

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[Bob Naumann W5OV]

" When repairing the THP amps for failed MOSFETs, how do you know with
certainty the ALC line was disconnected by the customer"?

The customers tell us.

73,

Bob W5OV




-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Paul Christensen
Sent: Wednesday, April 21, 2010 10:14 AM
To: [hidden email]
Subject: Re: [Elecraft] K3 and Expert 1K-FA

> Do people blast the inputs of their SS amps with 200w or 400w? You bet
> they
> do. They fry the FETs immediately too.

And that can occur whether or not an ALC line is used between the
transceiver and amp since ALC is a feedback function and the response time
back to the transceiver, and the response time of the transceiver, is not
instantaneous.

> We see them on a fairly frequent
> basis and we have gotten adept at swapping out FETs quickly - at
> significant
> expense to the owner of the amp. In the vast majority of cases, they had
> ALC
> disconnected and made a mistake when switching antenna outputs from these
> high-power transceivers.

When repairing the THP amps for failed MOSFETs, how do you know with
certainty the ALC line was disconnected by the customer?  Also, what is the
typical ALC response time of the THP amplifiers?

I think it would be an interesting exercise to set up multiple transceivers
across vendors, together with multiple solid-state amps across vendors, and
measure the total ALC loop time period.

Paul, W9AC

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[P.B. Christensen]

> set the power control to the proper drive, and forget the ALC?  ALC
> doesn't fix leading spikes anyway, so what's it good for?

Arguably, ALC helps to function as a time-averaging RF level control that
can protect against ongoing over-drive but not necessarily peak power busts.
What I don't like about traditional ALC are the unknown side-effects (e.g.,
non-linearity) that can occur as a result of level-setting and timing
differences between the transmitter and amp.  Dynamic monitoring for amp SSB
non-linearity can be accomplished with reasonably good accuracy using a
scope in trapezoid mode.   However, once transceivers began introducing
delay as result of DSP, it's become nearly impossible to use the trapezoid
method to look at system linearity of both the transceiver and amp, and the
corresponding ALC effect.   Other methods for measurement are probably
beyond the cost and effort at most stations.

Since the input Z of most solid-state amps is well-controlled at 50-ohms,
that the input Z should not appreciably change as output Z changes, then
can't we simply use a feed-forward ALC system instead of feedback ALC?   A
fast RF voltage peak detector can be bridged across the amp's input Z.  When
the RF voltage exceeds ~ 70.7Vpk, correction bias is applied to the
solid-state PA. Simultaneously, a 3dB pad could then be inserted at the amp
input until average input power drops below 50W.   With the exception of the
pad, the SPE amp works like this -- only it has a fault summing network that
looks at half a dozen other parameters, all of which instantly apply MOSFET
bias through the summing network to cut-off RF, and place the amp in bypass
when any one of the non-ALC faults occur.

Paul, W9AC
 

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[W8JI]

<<<Since the input Z of most solid-state amps is
well-controlled at 50-ohms,
that the input Z should not appreciably change as output Z
changes, then
can't we simply use a feed-forward ALC system instead of
feedback ALC?   A
fast RF voltage peak detector can be bridged across the
amp's input Z.  When
the RF voltage exceeds ~ 70.7Vpk, correction bias is applied
to the
solid-state PA. Simultaneously, a 3dB pad could then be
inserted at the amp
input until average input power drops below 50W.   >>>

We can protect the amp if we can change bias or switch a pad
a lot faster than the rise time of the envelope, but that
does not help the bandwidth. It could actually make the
bandwidth problem worse, and is unlikely to make it better.

The ideal solution would be to have a system that remembers
the ALC required, and starts the transmitter with just a bit
less than the expected voltage and makes slow or small
adjustments or corrections from there.

Better yet, why are most radios made the way they are? Put
the SSB ALC entirely in the audio system. For example we
could split-frequency process the audio with far more
effective results and less intermodulation or harmonic
distortion  than any type of RF clipping or compression. The
VOMAX did that, although not nearly as well as we could do
with a DSP system, in the 70's or 80's. We should be doing
all the gain control and processing at audio.

Trying to fix transmitter issues at the amplifier by
wrapping the amp back into the transmitter controls just
doesn't seem logical. RF clipping or limiting, unless it is
gain reduction with a PIN diode attenuator, doesn't make
much sense to me.

73 Tom

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[Guy, K2AV]

I get that in general given all the various TRX out there.

But for the K3, the digital functions in firmware do a far better job
of signal management before the signal is ever analog, much less RF,
which can include pre-compensating for issues in the analog circuits.
Much of the talk seems to assume that level control can only take
place in analog circuits with their limited portfolio of tricks.  The
digital effects all of those, and others not possible in analog,
accomplishing it all before DAC.

While over time some number of K3 TX level issues have been reported
and fixed by Elecraft, none of those have been solved by analog
circuit changes, all done in firmware.

It seems that the STRATEGY of using a feedback voltage from the
amplifier is obsolete.  The Expert amp has a very quick protection
circuit that kicks in before damage can occur.  If the protection
function of AGC feedback voltage is handled well by the amplifier
using other means, there is nothing to be done by AGC using a TRX like
a K3.

73, Guy

On Wed, Apr 21, 2010 at 8:54 PM, Paul Christensen <[hidden email]> wrote:

>> set the power control to the proper drive, and forget the ALC?  ALC
>> doesn't fix leading spikes anyway, so what's it good for?
>
> Arguably, ALC helps to function as a time-averaging RF level control that
> can protect against ongoing over-drive but not necessarily peak power busts.
> What I don't like about traditional ALC are the unknown side-effects (e.g.,
> non-linearity) that can occur as a result of level-setting and timing
> differences between the transmitter and amp.  Dynamic monitoring for amp SSB
> non-linearity can be accomplished with reasonably good accuracy using a
> scope in trapezoid mode.   However, once transceivers began introducing
> delay as result of DSP, it's become nearly impossible to use the trapezoid
> method to look at system linearity of both the transceiver and amp, and the
> corresponding ALC effect.   Other methods for measurement are probably
> beyond the cost and effort at most stations.
>
> Since the input Z of most solid-state amps is well-controlled at 50-ohms,
> that the input Z should not appreciably change as output Z changes, then
> can't we simply use a feed-forward ALC system instead of feedback ALC?   A
> fast RF voltage peak detector can be bridged across the amp's input Z.  When
> the RF voltage exceeds ~ 70.7Vpk, correction bias is applied to the
> solid-state PA. Simultaneously, a 3dB pad could then be inserted at the amp
> input until average input power drops below 50W.   With the exception of the
> pad, the SPE amp works like this -- only it has a fault summing network that
> looks at half a dozen other parameters, all of which instantly apply MOSFET
> bias through the summing network to cut-off RF, and place the amp in bypass
> when any one of the non-ALC faults occur.
>
> Paul, W9AC

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[n7ws]

Couldn't agree more.  Especially the split-band processing part :-)

http://k6mhe.com/n7ws/S_PROC.pdf

BTW, arguably one of the best sounding SSB rigs around, the TS870 does use split-band speech clipping done in DSP.  I bought mine new in 1998 and it's a "late" S/N.

Wes  N7WS

--- On Wed, 4/21/10, Tom W8JI <[hidden email]> wrote:

> Better yet, why are most radios made the way they are? Put
> the SSB ALC entirely in the audio system. For example we
> could split-frequency process the audio with far more
> effective results and less intermodulation or harmonic
> distortion  than any type of RF clipping or
> compression. The VOMAX did that, although not nearly as well as we could do with a DSP system, in the 70's or 80's. We should be doing
> all the gain control and processing at audio.
>
> Trying to fix transmitter issues at the amplifier by
> wrapping the amp back into the transmitter controls just
> doesn't seem logical. RF clipping or limiting, unless it is
> gain reduction with a PIN diode attenuator, doesn't make
> much sense to me.
>

     
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[Arie Kleingeld PA3A-2]

Great wisdom this list brings.
Yoda

73
Arie PA3A

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[Phil Salas]

"Without an attenuator to "match levels", people are gambling
with or without the ALC connected.  73 Tom"

I agree.  I was surprised to see that my IC-706MKII put out a full power
spike regardless of where the output power was set (even set at 5-weatts
output, the first-dit spike was 100+ watts).  I measuered the drive required
for my ALS-600 and built an attenuator that is switched in-line when I turn
on the amplifier.   This way I can always leave my transceiver set to full
power and not worry about overdriving the amp, either with a first-dit spike
or forgetting to reduce drive when I put the amp in-line (info in the
"Articles" section at www.ad5x.com).

The K3 has solved the overshoot problem, but not the "forgetting to turn
down drive" problem for me.  The attenuator takes care of that.  I use my K3
A-output for barefoot operation, and the B-output going to the
ALS-600/MFJ-998 combo.  I do this since the amp and tuner are not designed
for 6 meters, and don't look good on 6-meters even when bypassed.  So the
A-output with the K3 ATU is used on 160-6 meters for barefoot operation, and
the B-output with K3 ATU bypassed is used for 160-10 meters with the
ALS-600/MFJ-998.  I connect A-barefoot or B-amplified outputs to the
appropriate antenna with a 6x6 remote antenna switch (MFJ-4726).  Yes, the
K3 remembers power settings on a per-band basis, but not on an A/B basis
(yet).

Phil - AD5X

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[W4GRJ]

When I turn SUB Rcv'r on I get a USE AUX message, can't find in the
manual...can someone explain.

Tnx,
Jack
W4GRJ


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