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KPA1500 Linearity

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K9MA

KPA1500 Linearity

I recently ran a two-tone test and measured CW power gain. (SN1078) It
doesn't look good. The two-tone waveform shows distinct "flat-topping",
and the power gain drops 25 percent from 1000 to 1500 Watts. My old
3-500Z amplifier is much better. Has anyone measured IMD or linearity,
or seen any test results?

While I'm primarily a CW operator, I'd be very reluctant to use the
amplifier on SSB.

73,

Scott K9MA

--
Scott K9MA

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Wes Stewart-2

Re: KPA1500 Linearity

I don't have a KPA1500 or enough power attenuators to test my KPA500, but I have
spent many dozens of hours looking at TX IMD on my two K3s.

I will simply say, if you haven't already, check the IMD of the bare K3 before
blaming the KPA1500. Garbage in, garbage out. That of course doesn't pardon the
KPA for dropping gain.

Wes N7WS

On 6/9/2018 2:21 PM, K9MA wrote:

> I recently ran a two-tone test and measured CW power gain. (SN1078) It doesn't
> look good. The two-tone waveform shows distinct "flat-topping", and the power
> gain drops 25 percent from 1000 to 1500 Watts. My old 3-500Z amplifier is
> much better. Has anyone measured IMD or linearity, or seen any test results?
>
> While I'm primarily a CW operator, I'd be very reluctant to use the amplifier
> on SSB.
>
> 73,
>
> Scott K9MA
>

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K9MA

Re: KPA1500 Linearity

I did look at the K3 output, and it's much, much better than the KPA1500 output. I also checked that the KPA1500 supply voltage was not dropping much: 53 V in standby, 52 V at 1500 W.

73,
Scott K9MA

----------

Scott Ellington

--- via iPad

> On Jun 9, 2018, at 7:26 PM, Wes Stewart <[hidden email]> wrote:
>
> I don't have a KPA1500 or enough power attenuators to test my KPA500, but I have spent many dozens of hours looking at TX IMD on my two K3s.
>
> I will simply say, if you haven't already, check the IMD of the bare K3 before blaming the KPA1500. Garbage in, garbage out. That of course doesn't pardon the KPA for dropping gain.
>
> Wes N7WS
>
>
>> On 6/9/2018 2:21 PM, K9MA wrote:
>> I recently ran a two-tone test and measured CW power gain. (SN1078) It doesn't look good. The two-tone waveform shows distinct "flat-topping", and the power gain drops 25 percent from 1000 to 1500 Watts. My old 3-500Z amplifier is much better. Has anyone measured IMD or linearity, or seen any test results?
>>
>> While I'm primarily a CW operator, I'd be very reluctant to use the amplifier on SSB.
>>
>> 73,
>>
>> Scott K9MA
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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wayne burdick

Re: KPA1500 Linearity

Administrator

In reply to this post by K9MA

Scott,

I’m not sure how you’re doing the test, but this is definitely not characteristic.

We test every amp for IMD, and we see an average of about -35 dBc (3rd order, ARRL method) across all bands. This is state of the art for an LDMOS deign running class AB. Other SS amps using similar designs have have similar performance.

Any amp’s gain levels off as it approaches peak power (ie, is slightly in compression). But it should not be flat-topping unless it’s over driven or is starved for supply current/voltage.

Finally, both the transceiver and amp will vary from band to band somewhat in IMD. You might for example see -40 dBc on one, but in the low 30’s on the other, on a given band. Again, this is typical of all such SS rigs/amps except those running class A or using closed-loop feedback (predistortion).

Please call Monday to discuss your test method with one of our technical staff.

73,
Wayne
N6KR

----
http://www.elecraft.com

> On Jun 9, 2018, at 2:21 PM, K9MA <[hidden email]> wrote:
>
> I recently ran a two-tone test and measured CW power gain. (SN1078) It doesn't look good. The two-tone waveform shows distinct "flat-topping", and the power gain drops 25 percent from 1000 to 1500 Watts. My old 3-500Z amplifier is much better. Has anyone measured IMD or linearity, or seen any test results?
>
> While I'm primarily a CW operator, I'd be very reluctant to use the amplifier on SSB.
>
> 73,
>
> Scott K9MA
>
> --
> Scott K9MA
>
> [hidden email]
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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Michael Blake

Re: KPA1500 Linearity

In reply to this post by K9MA

Scott, I don’t know if this helps much but several of the locals have constructed BLF-188 amps (singles and pairs) in the past two years. The W7, Israeli and Russian boards were used and they all suffered the same fate in various degrees. They would cease being very linear at about 75% of their CW output. Careful selection of bias and feedback levels would allow some improvement but in none of the cases were the devices even close to acceptable IMD wise at their data sheet output levels. The only one that am aware of that worked well was a W8 friend who is driving it (EB-104 water cooled Russian amplifier) with an Anan and used Pure Signal to effectively clean it up. On all of the others when the output came up to the target level you could immediately start seeing them in the opposite sideband.

All of the data sheets that we saw at the time talked about CW/FM applications and none provided specs for SSB linear service.

These have been my observations of the BLF-188 amps.

Very 73 - Mike - K9JRI

> On Jun 9, 2018, at 9:08 PM, K9MA <[hidden email]> wrote:
>
> I did look at the K3 output, and it's much, much better than the KPA1500 output. I also checked that the KPA1500 supply voltage was not dropping much: 53 V in standby, 52 V at 1500 W.
>
> 73,
> Scott K9MA
>
> ----------
>
> Scott Ellington
>
> --- via iPad
>
>> On Jun 9, 2018, at 7:26 PM, Wes Stewart <[hidden email]> wrote:
>>
>> I don't have a KPA1500 or enough power attenuators to test my KPA500, but I have spent many dozens of hours looking at TX IMD on my two K3s.
>>
>> I will simply say, if you haven't already, check the IMD of the bare K3 before blaming the KPA1500. Garbage in, garbage out. That of course doesn't pardon the KPA for dropping gain.
>>
>> Wes N7WS
>>
>>
>>> On 6/9/2018 2:21 PM, K9MA wrote:
>>> I recently ran a two-tone test and measured CW power gain. (SN1078) It doesn't look good. The two-tone waveform shows distinct "flat-topping", and the power gain drops 25 percent from 1000 to 1500 Watts. My old 3-500Z amplifier is much better. Has anyone measured IMD or linearity, or seen any test results?
>>>
>>> While I'm primarily a CW operator, I'd be very reluctant to use the amplifier on SSB.
>>>
>>> 73,
>>>
>>> Scott K9MA
>>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>>
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>
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K9MA

Re: KPA1500 Linearity

In reply to this post by wayne burdick

Thanks, Wayne. I'm glad to hear this isn't typical.

I sent a report to tech support with all the details. I'll call later next week, as I'll be out of town with the KX2 until Thursday.

73,
Scott K9MA

----------

Scott Ellington

--- via iPad

> On Jun 9, 2018, at 8:28 PM, Wayne Burdick <[hidden email]> wrote:
>
> Scott,
>
> I’m not sure how you’re doing the test, but this is definitely not characteristic.
>
> We test every amp for IMD, and we see an average of about -35 dBc (3rd order, ARRL method) across all bands. This is state of the art for an LDMOS deign running class AB. Other SS amps using similar designs have have similar performance.
>
> Any amp’s gain levels off as it approaches peak power (ie, is slightly in compression). But it should not be flat-topping unless it’s over driven or is starved for supply current/voltage.
>
> Finally, both the transceiver and amp will vary from band to band somewhat in IMD. You might for example see -40 dBc on one, but in the low 30’s on the other, on a given band. Again, this is typical of all such SS rigs/amps except those running class A or using closed-loop feedback (predistortion).
>
> Please call Monday to discuss your test method with one of our technical staff.
>
> 73,
> Wayne
> N6KR
>
>
> ----
> http://www.elecraft.com
>
>> On Jun 9, 2018, at 2:21 PM, K9MA <[hidden email]> wrote:
>>
>> I recently ran a two-tone test and measured CW power gain. (SN1078) It doesn't look good. The two-tone waveform shows distinct "flat-topping", and the power gain drops 25 percent from 1000 to 1500 Watts. My old 3-500Z amplifier is much better. Has anyone measured IMD or linearity, or seen any test results?
>>
>> While I'm primarily a CW operator, I'd be very reluctant to use the amplifier on SSB.
>>
>> 73,
>>
>> Scott K9MA
>>
>> --
>> Scott K9MA
>>
>> [hidden email]
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]

Wes Stewart-2

Re: KPA1500 Linearity

In reply to this post by wayne burdick

Thank you for posting this. I have been saying it for years on these forums and
getting told that I didn't know what I was talking about. Now maybe the
naysayers will take note.

Wes N7WS

On 6/9/2018 6:28 PM, Wayne Burdick wrote:
> Finally, both the transceiver and amp will vary from band to band somewhat in IMD. You might for example see -40 dBc on one, but in the low 30’s on the other, on a given band. Again, this is typical of all such SS rigs/amps except those running class A or using closed-loop feedback (predistortion).
>

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Jim Brown-10

Re: KPA1500 Linearity

In reply to this post by K9MA

On 6/9/2018 2:21 PM, K9MA wrote:
> While I'm primarily a CW operator, I'd be very reluctant to use the
> amplifier on SSB.

CW is 100% Amplitude Modulation of a carrier by a rectangular wave, so
the transitions are rich in harmonics that are heard as clicks, and they
WILL excite IM in a non-linear path.

73, Jim K9YC

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Paul Baldock

Re: KPA1500 Linearity

In reply to this post by K9MA

What you report of compression near the maximum
power is certainly true of the amplifiers like
the SPE-1.5K that use a single device, but I
would have thought this would not be true of the
KPA1500 that uses 2 devices. This is the reason I
returned my SPE and ordered the KPA. Hopefully
the compression is less than 1dB.

Has anybody else measured it?

- Paul - KW7Y

At 02:21 PM 6/9/2018, you wrote:

>I recently ran a two-tone test and measured CW
>power gain. (SN1078)Â It doesn't look
>good.Â The two-tone waveform shows distinct
>"flat-topping", and the power gain drops 25
>percent from 1000 to 1500 Watts.Â My old 3-500Z
>amplifier is much better.Â Has anyone measured
>IMD or linearity, or seen any test results?
>While I'm primarily a CW operator, I'd be very
>reluctant to use the amplifier on SSB. 73, Scott
>K9MA -- Scott K9MA [hidden email]
>______________________________________________________________
>Elecraft mailing list Home:
>http://mailman.qth.net/mailman/listinfo/elecraft
>Help: http://mailman.qth.net/mmfaq.htm Post:
>mailto:[hidden email] This list hosted
>by: http://www.qsl.net Please help support this
>email list: http://www.qsl.net/donate.html
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K9MA

Re: KPA1500 Linearity

The gain compression I measured, between 1000 and 1500 W on 40 meters, was 1.4 dB. I used the K3 and KPA1500 power meters. Factory calibration of the KPA1500.

Scott K9MA

----------

Scott Ellington

--- via iPad

> On Jun 14, 2018, at 2:51 PM, Paul Baldock <[hidden email]> wrote:
>
> What you report of compression near the maximum power is certainly true of the amplifiers like the SPE-1.5K that use a single device, but I would have thought this would not be true of the KPA1500 that uses 2 devices. This is the reason I returned my SPE and ordered the KPA. Hopefully the compression is less than 1dB.
>
> Has anybody else measured it?
>
> - Paul - KW7Y
>
>
>
> At 02:21 PM 6/9/2018, you wrote:
>> I recently ran a two-tone test and measured CW power gain. (SN1078)Â It doesn't look good.Â The two-tone waveform shows distinct "flat-topping", and the power gain drops 25 percent from 1000 to 1500 Watts.Â My old 3-500Z amplifier is much better.Â Has anyone measured IMD or linearity, or seen any test results? While I'm primarily a CW operator, I'd be very reluctant to use the amplifier on SSB. 73, Scott K9MA -- Scott K9MA [hidden email] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email]
>
> ______________________________________________________________
> Elecraft mailing list
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>
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Paul Baldock

Re: KPA1500 Linearity

I received my KPA-1500 yesterday (#244) and did some linearity tests today

14.2MHz, Dummy Load, ATU Bypassed. Using KPA-1500
internal Power Meter. Continuous carrier.

10W drive, Gain = 15.6dB 180W
15W drive, Gain = 15.8dB
20W drive, Gain = 15.9dB
25W drive, Gain = 16.0dB 1.0KW
30W drive, Gain = 15.9dB
35W drive, Gain = 15.7dB
40W drive, Gain = 15.6dB
43W drive, Gain = 15.4dB 1.5KW
45W drive, Gain = 15.4dB 1.57KW

Based on this it look like about .6dB compression
at 1.5KW. I think that's pretty good for an SS Amp.

I also measured the gain on all the bands at
1.5KW out. Drive varied from 31W on 80M to 47W on
15M. or 16.8dB to 15.0dB. That amount of variation is rather disappointing.

I also noted that the internal power meter is
pretty inaccurate at low levels. For Example at
50W on 20M it reads 43W. Its pretty close above
300W and right on at 1.5KW where its calibrated.

I would be interested to see any data that others have collected.

- Paul KW7Y

At 02:26 PM 6/14/2018, K9MA wrote:

>The gain compression I measured, between 1000
>and 1500 W on 40 meters, was 1.4 dB. I used the
>K3 and KPA1500 power meters. Factory calibration of the KPA1500.
>
>Scott K9MA
>
>----------
>
>Scott Ellington
>
> --- via iPad
>
> > On Jun 14, 2018, at 2:51 PM, Paul Baldock <[hidden email]> wrote:
> >
> > What you report of compression near the
> maximum power is certainly true of the
> amplifiers like the SPE-1.5K that use a single
> device, but I would have thought this would not
> be true of the KPA1500 that uses 2 devices.
> This is the reason I returned my SPE and
> ordered the KPA. Hopefully the compression is less than 1dB.
> >
> > Has anybody else measured it?
> >
> > - Paul - KW7Y
> >
> >
> >
> > At 02:21 PM 6/9/2018, you wrote:
> >> I recently ran a two-tone test and measured
> CW power gain. (SN1078)Ã It doesn't look
> good.Ã The two-tone waveform shows distinct
> "flat-topping", and the power gain drops 25
> percent from 1000 to 1500 Watts.Ã My old
> 3-500Z amplifier is much better.Ã Has anyone
> measured IMD or linearity, or seen any test
> results? While I'm primarily a CW operator, I'd
> be very reluctant to use the amplifier on SSB.
> 73, Scott K9MA -- Scott K9MA
> [hidden email]
> ______________________________________________________________
> Elecraft mailing list Home:
> http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm Post:
> mailto:[hidden email] This list
> hosted by: http://www.qsl.net Please help
> support this email list:
> http://www.qsl.net/donate.html Message delivered to [hidden email]
> >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> > Message delivered to [hidden email]

K9MA

Re: KPA1500 Linearity

I'll have to make some more measurements, but Paul's seem to have much less gain compression than mine. (0.6 vs 1.4 dB from 1 kW to 1.5 kW) That's also closer to the specs for a pair of BLF88XR's.

73,
Scott K9MA

------

Scott Ellington

--- via iPad

> On Jun 15, 2018, at 11:24 PM, Paul Baldock <[hidden email]> wrote:
>
> I received my KPA-1500 yesterday (#244) and did some linearity tests today
>
> 14.2MHz, Dummy Load, ATU Bypassed. Using KPA-1500 internal Power Meter. Continuous carrier.
>
> 10W drive, Gain = 15.6dB 180W
> 15W drive, Gain = 15.8dB
> 20W drive, Gain = 15.9dB
> 25W drive, Gain = 16.0dB 1.0KW
> 30W drive, Gain = 15.9dB
> 35W drive, Gain = 15.7dB
> 40W drive, Gain = 15.6dB
> 43W drive, Gain = 15.4dB 1.5KW
> 45W drive, Gain = 15.4dB 1.57KW
>
> Based on this it look like about .6dB compression at 1.5KW. I think that's pretty good for an SS Amp.
>
> I also measured the gain on all the bands at 1.5KW out. Drive varied from 31W on 80M to 47W on 15M. or 16.8dB to 15.0dB. That amount of variation is rather disappointing.
>
> I also noted that the internal power meter is pretty inaccurate at low levels. For Example at 50W on 20M it reads 43W. Its pretty close above 300W and right on at 1.5KW where its calibrated.
>
> I would be interested to see any data that others have collected.
>
> - Paul KW7Y
>
>
> At 02:26 PM 6/14/2018, K9MA wrote:
>> The gain compression I measured, between 1000 and 1500 W on 40 meters, was 1.4 dB. I used the K3 and KPA1500 power meters. Factory calibration of the KPA1500.
>>
>> Scott K9MA
>>
>> ----------
>>
>> Scott Ellington
>>
>> --- via iPad
>>
>> > On Jun 14, 2018, at 2:51 PM, Paul Baldock <[hidden email]> wrote:
>> >
>> > What you report of compression near the maximum power is certainly true of the amplifiers like the SPE-1.5K that use a single device, but I would have thought this would not be true of the KPA1500 that uses 2 devices. This is the reason I returned my SPE and ordered the KPA. Hopefully the compression is less than 1dB.
>> >
>> > Has anybody else measured it?
>> >
>> > - Paul - KW7Y
>> >
>> >
>> >
>> > At 02:21 PM 6/9/2018, you wrote:
>> >> I recently ran a two-tone test and measured CW power gain. (SN1078)Â It doesn't look good.Â The two-tone waveform shows distinct "flat-topping", and the power gain drops 25 percent from 1000 to 1500 Watts.Â My old 3-500Z amplifier is much better.Â Has anyone measured IMD or linearity, or seen any test results? While I'm primarily a CW operator, I'd be very reluctant to use the amplifier on SSB. 73, Scott K9MA -- Scott K9MA [hidden email] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email]
>> >
>> > ______________________________________________________________
>> > Elecraft mailing list
>> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> > Help: http://mailman.qth.net/mmfaq.htm
>> > Post: mailto:[hidden email]
>> >
>> > This list hosted by: http://www.qsl.net
>> > Please help support this email list: http://www.qsl.net/donate.html
>> > Message delivered to [hidden email]