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KPA500 Fuse blown

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Jim Brown-10

Re: KPA500 Power In Digital Modes

On Tue,11/11/2014 3:26 AM, Nick-VE3EY wrote:
> This happened with my KPA500 until I realized that my Microham double-six antenna switch is only rated to max 30MHz.

Nothing specific about this antenna switch -- getting any matrix switch
like that to have low SWR at 6M is quite tricky to do. I had a similar
problem with a different 2x6 switch on 6M -- rather high SWR. My
solution was to not run my SteppIR through that switch. Instead, I feed
it directly into one output of my KAT500. The matrix switch feeds a
different input of the KAT500.

I also found that other "stuff" I had in series with the path between
the KPA500 and the tuner was increasing to the SWR -- a not very good
power/SWR meter and a tapoff for a monitor scope. I also found a few
junk connectors connecting that stuff.

Bottom line -- when I cleaned up the signal path, SWR went from slightly
more than 2:1 down to 1.1:1.

73, Jim K9YC
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Eric Norris-2

Re: KPA500 Power In Digital Modes

In reply to this post by Jim Brown-10

As others have said, check your jumpers, and especially any barrel or elbow connectors you bought at a hamfest. They are junk. I learned the hard way that paying through the nose for good connectors, like Amphenol, is cheaper than buying a new 3CX800 tube, and saves hours of frustration. Save them for QRP--that's all they are good for.

73

Eric WD6DBM

Michael Eberle <[hidden email]> wrote:

>Yes, I suppose something may just need a slight adjustment. It just
>frustrates me when things don't work like I expect them to. I was
>always afraid to run JT65 at more than 80-100 watts until I saw this
>post. Started trying higher power while keeping a close eye on the
>temp. No faults on any band but 6M if it gets much over 200 watts (8
>watts drive). It seems to be running 450 watts easily on 160M.
>
>On 11/11/2014 5:44 AM, Eric Norris wrote:
>> Don't do it! If you can't get an answer here, contact Elecraft support. Your KPA500 will work great on 6m once you get this issue resolved. Mine runs at 600w on 6m meteor scatter using FSK441 30 seconds on, 30 seconds off, for hours on end, hitting 65C but soldiering on without complaint. That would leave my former dual 3-500Z amp squeaking from the freaking.
>>
>> 73
>>
>> Eric WD6DBM
>>
>> Michael Eberle <[hidden email]> wrote:
>>
>>> On 11/10/2014 5:56 PM, [hidden email] wrote:
>>>> On Mon, 10 Nov 2014 09:34:09 -0800, Jim Brown wrote:
>>>>
>>>>> During KPA500 beta, I was loaned one for a major RTTY contest weekend
>>>>> and told to run it "with all the lights lit." I did, and it worked fine.
>>>>> In the 3-4 years I've owned one, I regularly run it at full power in
>>>>> digital modes on all bands, 160-6M. When it gets warm, the fan speeds
>>>>> up, but it continues to put out full power. This includes digital modes
>>>>> like FSK441 and JT65A on 6M, and lots of RTTY on the HF bands.
>>>
>

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Rick WA6NHC

Re: KPA500 Power In Digital Modes

I would submit that if they're no good for QRO, they're no good for QRP as well (where every erg counts). Buy then use quality materials, it matters.

Rick, WA6NHC

iPad = small keypad = typos = sorry ;-)

> On Nov 11, 2014, at 12:02 PM, Eric Norris <[hidden email]> wrote:
>
> Save them for QRP--that's all they are good for.
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Jim Brown-10

Re: KPA500 Power In Digital Modes

In reply to this post by Joe Subich, W4TV-4

On Tue,11/11/2014 7:17 AM, Joe Subich, W4TV wrote:
> Your measurements are not of the conditions I describe. You are using
> *filtered and band limited pink noise* (slide #3 - EQ settings) not the
> specific digital signals I mention *and* your measurements are at PEP
> not average power (slide #2 - LP-100A set to peak).

Right -- my test conditions for SSB are MORE demanding than either PSK31
or JT65A, and were intended to approximate the response of the K3 (and
amp) to a speech signal. I also made one measurement of the K3 at high
power without compression. Occupied bandwidth was nearly identical to
the 10dB compression, so I did the rest with compression.

Did you miss the CW measurements, where the modulation was a shaped
square wave?

When I have time (I'm currently hot and heavy with antenna work), I
will, however, repeat these measurements with a PSK31 test signal, and
with JT65A. I don't expect the results to be a lot different.

73, Jim K9YC
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James Rogers

Re: KPA500 Power In Digital Modes

In reply to this post by Michael Eberle

Then you have a problem. I regularly run my KPA500/KAT500 at full power
on every band, including 10M and 6M in all modes, CW, SSB, RTTY, FSK441
etc. As for the KAT500 faulting, I always run the KAT500 in manual
mode. It "knows" where to tune for my modes of operation and the
frequencies I operate (like the CW DX windows, RTTY frequencies etc). If
it doesn't then I hit the TUNE button.

73s Jim, W4ATK
On 11/11/2014 4:30 AM, Michael Eberle wrote:

> On 11/10/2014 5:56 PM, [hidden email] wrote:
>> On Mon, 10 Nov 2014 09:34:09 -0800, Jim Brown wrote:
>>
>>> During KPA500 beta, I was loaned one for a major RTTY contest weekend
>>> and told to run it "with all the lights lit." I did, and it worked
>>> fine.
>>> In the 3-4 years I've owned one, I regularly run it at full power in
>>> digital modes on all bands, 160-6M. When it gets warm, the fan speeds
>>> up, but it continues to put out full power. This includes digital modes
>>> like FSK441 and JT65A on 6M, and lots of RTTY on the HF bands.
> I cannot get my KPA500 to run more than about 200W on 6M without
> getting a PA DISS fault. Temp is not even up to 60C yet.
> Between that and the KAT500 coming 'untuned' and faulting in the
> middle of a QSO on 10M, I'm about ready to throw them both in the
> trash and go back to my tube amp.
>
> Mike
> KI0HA
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> .
>

Joe Subich, W4TV-4

Re: KPA500 Power In Digital Modes

In reply to this post by Jim Brown-10

Jim,

> Right -- my test conditions for SSB are MORE demanding than either
> PSK31 or JT65A, and were intended to approximate the response of the
> K3 (and amp) to a speech signal.

That SSB is *more* demanding than PSK31 is incorrect. SSB audio can
be compressed/clipped significantly without IMD if the compression is
done correctly. PSK31 on the other hand *can not* withstand *any*
compression without significant close-in IMD. See the work by W7AY
for that information. JT65A (and other JT modes) on the other hand
is a saturated single tone mode akin to FSK that has *no issue* with
compression and is, in fact, not compressible.

> When I have time (I'm currently hot and heavy with antenna work), I
> will, however, repeat these measurements with a PSK31 test signal,
> and with JT65A. I don't expect the results to be a lot different.

If you do the measurements correctly, they will be a LOT different.
JT65A will show little or no change in IMD from 25 to 100 W average
(and PEP) output on the K3 (or 100W to 600W average and PEP output
on the KPA-500. PSK31, however, will go to pot in a hand basket if
the average power output on the K3 goes above 30 watts or so or if
the average power output of the KPA500 goes above 150 watts or so.
If you are measuring *TRUE* peak power, those are equivalent to
100-110 W PEP from the K3 or 600W PEP on the KPA500 given the 6 dB
crest ratio in the PSK31 waveform.

JT65 and JT9 (all sub-modes) have a 0 dB crest factor, PSK31 has a
6 dB crest factor - other modern data modes have various crest factors
- you need to understand the crest factor of the input waveform.

> Did you miss the CW measurements, where the modulation was a shaped
> square wave?

No, I did not "miss" the CW measurements - they have no bearing on
the issues here.

73,

... Joe, W4TV

On 2014-11-11 4:07 PM, Jim Brown wrote:

> On Tue,11/11/2014 7:17 AM, Joe Subich, W4TV wrote:
>> Your measurements are not of the conditions I describe. You are using
>> *filtered and band limited pink noise* (slide #3 - EQ settings) not the
>> specific digital signals I mention *and* your measurements are at PEP
>> not average power (slide #2 - LP-100A set to peak).
>
> Right -- my test conditions for SSB are MORE demanding than either PSK31
> or JT65A, and were intended to approximate the response of the K3 (and
> amp) to a speech signal. I also made one measurement of the K3 at high
> power without compression. Occupied bandwidth was nearly identical to
> the 10dB compression, so I did the rest with compression.
>
> Did you miss the CW measurements, where the modulation was a shaped
> square wave?
>
> When I have time (I'm currently hot and heavy with antenna work), I
> will, however, repeat these measurements with a PSK31 test signal, and
> with JT65A. I don't expect the results to be a lot different.
>
> 73, Jim K9YC
> ______________________________________________________________
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>

mcduffie

Re: KPA500 Power In Digital Modes

In reply to this post by Jim Brown-10

> I would submit that if they're no good for QRO, they're no good for QRP as well (where every erg counts). Buy then use quality materials, it matters.

This discussion reminds me of the problem Radio Shack introduced when they sold
some elbows that actually used a small diameter coil spring for a center
conductor going around the 90 degree bend. Think about that for a minute and
realize what happened when they were used on higher frequencies.

Gary
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Jim Brown-10

Re: KPA500 Power In Digital Modes

In reply to this post by Joe Subich, W4TV-4

On Tue,11/11/2014 2:33 PM, Joe Subich, W4TV wrote:
> PSK31 on the other hand *can not* withstand *any*
> compression without significant close-in IMD.

I don't know where you got the idea that I was suggesting compression
for PSK31. My testing with pink noise is intended to simulate speech,
and I tested with and without compression.

It's raining, which stops antenna work, so I set up PSK31 measurements
this afternoon. Here's a link to the data. Note that I used PSK-D mode
-- internally generated by the K3.

http://k9yc.com/P3SpectrumMeasurementsSlides.pdf

Note that, except at full power, PSK31 is significantly narrower than CW.

73, Jim K9YC

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KEN-3

Re: KPA500 Power In Digital Modes

In reply to this post by Joe Subich, W4TV-4

On Nov 10, 2014, at 7:30 PM, Joe Subich, W4TV wrote:

> Depending on the crest factor (peak to average ratio) of the mode
> in use, the average power from the KPA-5000 should be kept 6 to 10
> dB below the rated maximum (e.g., 60 to 150 watts) just as a 100W
> transceiver should be kept between 10 and 25 watts average.

Since the K3 turns off the final stage when below 13 watts, does that mean running 10 watts is a bad choice since that's running the lower power stage at near maximum?

From a cooling perspective alone, I have often wondered if it's better for a K3 to be run at 15w rather than 10.

Ken WA8JXM

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Joe Subich, W4TV-4

Re: KPA500 Power In Digital Modes

> Since the K3 turns off the final stage when below 13 watts, does
> that mean running 10 watts is a bad choice since that's running
> the lower power stage at near maximum?

As it relates to that part of the distortion caused by compression
or clipping in the amplifier chain (IF-> Low power amplifier -> PA),
running the K3 at 10 watts is probably worse than running it at 20
watts. I don't have specific data on the particular devices used
in the K3 but in general IMD is minimum around 80% of maximum rated
output.

73,

... Joe, W4TV

On 2014-11-19 6:50 AM, Ken wrote:

>
> On Nov 10, 2014, at 7:30 PM, Joe Subich, W4TV wrote:
>
>> Depending on the crest factor (peak to average ratio) of the mode
>> in use, the average power from the KPA-5000 should be kept 6 to 10
>> dB below the rated maximum (e.g., 60 to 150 watts) just as a 100W
>> transceiver should be kept between 10 and 25 watts average.
>
>
> Since the K3 turns off the final stage when below 13 watts, does that mean running 10 watts is a bad choice since that's running the lower power stage at near maximum?
>
> From a cooling perspective alone, I have often wondered if it's better for a K3 to be run at 15w rather than 10.
>
> Ken WA8JXM
>
>

Jim Brown-10

Re: KPA500 Power In Digital Modes

In reply to this post by KEN-3

On Wed,11/19/2014 3:50 AM, Ken wrote:
> On Nov 10, 2014, at 7:30 PM, Joe Subich, W4TV wrote:
>
>> >Depending on the crest factor (peak to average ratio) of the mode
>> >in use, the average power from the KPA-5000 should be kept 6 to 10
>> >dB below the rated maximum (e.g., 60 to 150 watts) just as a 100W
>> >transceiver should be kept between 10 and 25 watts average.

Joe made this statement assuming that the KPA500 produced FAR more
distortion than it actually does. A few days later, I showed
measurements with a K3 driving a KPA500 to 500W with PSK31 showing that
the distortion was EXTREMELY low. I had already published comparable
measurements for CW and SSB, with the same result.

P3SpectrumMeasurementsSlides.pdf

73, Jim K9YC

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Joe Subich, W4TV-4

Re: KPA500 Power In Digital Modes

> Joe made this statement assuming that the KPA500 produced FAR more
> distortion than it actually does. A few days later, I showed
> measurements with a K3 driving a KPA500 to 500W with PSK31 showing
> that the distortion was EXTREMELY low.

Jim, is misconstruing what I wrote. I specifically said "*average*
power from the KPA-500 should be kept 6-10 dB below the maximum".
Jim made his measurements at PEP which *includes* the crest factor
(PEP = average power X Crest factor or alternately Average Power =
PEP/Crest Factor). If his measurements were made at average power,
the results would have been considerably different.

With most PSK, MFSK, PACTOR, etc. modes, it is important that the
average power output be kept low enough that none of the amplifier
stages is driven into saturation on the peaks which can be anywhere
from 3 dB to 13 dB greater than average depending on the digital
modulation. Note: FSK, JT65 and JT9 modes are "saturated" - their
crest factor is 1 (0 dB). Like CW, for those modes, PEP = average
power.

73,

... Joe, W4TV

On 2014-11-19 11:49 AM, Jim Brown wrote:

> On Wed,11/19/2014 3:50 AM, Ken wrote:
>> On Nov 10, 2014, at 7:30 PM, Joe Subich, W4TV wrote:
>>
>>> >Depending on the crest factor (peak to average ratio) of the mode
>>> >in use, the average power from the KPA-5000 should be kept 6 to 10
>>> >dB below the rated maximum (e.g., 60 to 150 watts) just as a 100W
>>> >transceiver should be kept between 10 and 25 watts average.
>
> Joe made this statement assuming that the KPA500 produced FAR more
> distortion than it actually does. A few days later, I showed
> measurements with a K3 driving a KPA500 to 500W with PSK31 showing that
> the distortion was EXTREMELY low. I had already published comparable
> measurements for CW and SSB, with the same result.
>
> P3SpectrumMeasurementsSlides.pdf
>
> 73, Jim K9YC
>
>
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Jim Brown-10

Re: KPA500 Power In Digital Modes

On Wed,11/19/2014 11:45 AM, Joe Subich, W4TV wrote:

>> Joe made this statement assuming that the KPA500 produced FAR more
>> distortion than it actually does. A few days later, I showed
>> measurements with a K3 driving a KPA500 to 500W with PSK31 showing
>> that the distortion was EXTREMELY low.
>
> Jim, is misconstruing what I wrote. I specifically said "*average*
> power from the KPA-500 should be kept 6-10 dB below the maximum".
> Jim made his measurements at PEP which *includes* the crest factor
> (PEP = average power X Crest factor or alternately Average Power =
> PEP/Crest Factor). If his measurements were made at average power,
> the results would have been considerably different.

Joe, you must misunderstand my measurements. They are ACCUMULATED peaks
for a fairly long measuring period, so they show transient clicks and
other forms of distortion far better than an averaged measurement.
Indeed, I showed measurements of the KPA500 running at 500W out that
have very low distortion (as indicated by occupied bandwidth). Yes,
bandwidth (and distortion) increases at bit if the KPA500 is driven harder.

As to peak and average power -- the measurements are of Peak Envelope
Power, which for CW, RTTY, PSK31, and the WSJT modes is keydown power,
and for all but CW, is the same as the Average Power. The average power
is less on CW because of the spaces between elements.

Crest Factor is relevant only on SSB. For normal speech, crest factors
range between 10 and 20 dB. We often use compression to reduce that
Crest Factor, and the K3 sounds very good when it is set for about 10 dB
of compression on peaks. I haven't measured the resulting Crest factors,
but long experience in pro audio suggests values of 6-10 dB would be the
result.

The KPA500 is quite well protected against conditions of overload. It
will add resistive attenuation if overdriven by as little as a dB and/or
into a poorly matched load, and will Fault if overdriven by a lot. Thus,
it is probably not possible to drive a KPA500 deep into saturation. This
is true regardless of the type of modulation in use (CW is modulation by
a square wave). The highest power measurements I made of the KPA500 were
at the level which more drive would have caused that resistive
attenuation to be added.

Indeed, the only way to reduce the Crest Factor with a KPA500 is to
apply more compression to the driving signal.

Note also that I showed measurements of the K3 driving a very good legal
limit tube amp to its rated power, and the waveforms were nearly
identical. That tube amp, a Titan 425, has no protection circuitry, only
a red LED indicating excessive grid current.

So -- the ONLY way in which my measurements show "better" numbers than
an averaged measurement is that they use peak power as a reference, and
applies ONLY to the SSB measurements.

73, Jim K9YC

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