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K2/HF Packer Amp incompatability?

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VK7JB

K2/HF Packer Amp incompatability?

Hi Pat and group,

FWIW, I have just built an HF Packer Amp and have exactly the same problem with
marked audio distortion on SSB when driving it with my FT 817nd. Maybe the
problem isn't the K2?

I have discovered others with the same problem, but no-one with a solution to
this Amp's non-linear behaviour on SSB. I was waiting to finish building my K2
to try the amp with the K2, but I suspect now that the problem is with Amp. I
initially thought it was RF feedback and that the mic cord was the likely
culprit. But no amount of wrapping any of the connector cables through ferrite
toroids has has any influence. Audio is distorted on peaks in SSB and only when
the Amp is on and running into an antenna. Distortion is much less running the
Amp into a dummy load and absent running the amp in bypass. Reducing the input
power makes no difference to the audio quality. I've tried running the Amp and
the rig from separate power supplies and/or gel cells : makes no discernable
difference. I've never had any trouble with RF feedback before, running 600W
from my AL 811 into the same antenna system.

If you find any clues to a solution, please let me know. Glad I bought the
KPA100 for my K2!

73,

John
VK7JB

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Don Wilhelm-4

Re: K2/HF Packer Amp incompatability?

That sounds like the amp is not running linear. First make sure the
bias is set correctly.
Then do a test in CW mode -
Put a small amount of drive to the amp (measure it), and measure the
output. Compute the gain.
Increase the drive by a small amount, and again compute the gain.
Continue in small steps until you have reached the maximum output of the
amp.
The gain should be the same if the amplifier is really linear.

If the input impedance of the amplifier is changing with drive level,
that can be cured with an attenuator at the input - the driver will then
see a more constant impedance.

73,
Don W3FPR

On 9/14/2010 9:57 AM, [hidden email] wrote:

> Hi Pat and group,
>
> FWIW, I have just built an HF Packer Amp and have exactly the same problem with
> marked audio distortion on SSB when driving it with my FT 817nd. Maybe the
> problem isn't the K2?
>
> I have discovered others with the same problem, but no-one with a solution to
> this Amp's non-linear behaviour on SSB. I was waiting to finish building my K2
> to try the amp with the K2, but I suspect now that the problem is with Amp. I
> initially thought it was RF feedback and that the mic cord was the likely
> culprit. But no amount of wrapping any of the connector cables through ferrite
> toroids has has any influence. Audio is distorted on peaks in SSB and only when
> the Amp is on and running into an antenna. Distortion is much less running the
> Amp into a dummy load and absent running the amp in bypass. Reducing the input
> power makes no difference to the audio quality. I've tried running the Amp and
> the rig from separate power supplies and/or gel cells : makes no discernable
> difference. I've never had any trouble with RF feedback before, running 600W
> from my AL 811 into the same antenna system.
>
> If you find any clues to a solution, please let me know. Glad I bought the
> KPA100 for my K2!
>
> 73,
>
> John
> VK7JB
>
>
> ------------------------------------------------------------
> This email was sent from Netspace Webmail: http://www.netspace.net.au
>
> ______________________________________________________________
> 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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Joe Subich, W4TV-4

Re: K2/HF Packer Amp incompatability?

> If the input impedance of the amplifier is changing with drive level,
> that can be cured with an attenuator at the input - the driver will
> then see a more constant impedance.

The schematic in the HF Packer amplifier manual shows different input
attenuators for the K3 (3 db), FT-817 (4 dB) and "other" (5 dB). It
also appears that the design lacks any NFB to stabilize gain across the
operating range.

The construction manual (with schematics) for the HF Packer is here:
<http://site.hfprojectsyahoo.com/yahoo_site_admin/assets/docs/HFPackerAmp3.227113959.pdf>
(Google is your friend <G>.)

73,

... Joe, W4TV

On 9/14/2010 10:48 AM, Don Wilhelm wrote:

> That sounds like the amp is not running linear. First make sure the
> bias is set correctly.
> Then do a test in CW mode -
> Put a small amount of drive to the amp (measure it), and measure the
> output. Compute the gain.
> Increase the drive by a small amount, and again compute the gain.
> Continue in small steps until you have reached the maximum output of the
> amp.
> The gain should be the same if the amplifier is really linear.
>
> If the input impedance of the amplifier is changing with drive level,
> that can be cured with an attenuator at the input - the driver will then
> see a more constant impedance.
>
> 73,
> Don W3FPR
>
>
> On 9/14/2010 9:57 AM, [hidden email] wrote:
>> Hi Pat and group,
>>
>> FWIW, I have just built an HF Packer Amp and have exactly the same problem with
>> marked audio distortion on SSB when driving it with my FT 817nd. Maybe the
>> problem isn't the K2?
>>
>> I have discovered others with the same problem, but no-one with a solution to
>> this Amp's non-linear behaviour on SSB. I was waiting to finish building my K2
>> to try the amp with the K2, but I suspect now that the problem is with Amp. I
>> initially thought it was RF feedback and that the mic cord was the likely
>> culprit. But no amount of wrapping any of the connector cables through ferrite
>> toroids has has any influence. Audio is distorted on peaks in SSB and only when
>> the Amp is on and running into an antenna. Distortion is much less running the
>> Amp into a dummy load and absent running the amp in bypass. Reducing the input
>> power makes no difference to the audio quality. I've tried running the Amp and
>> the rig from separate power supplies and/or gel cells : makes no discernable
>> difference. I've never had any trouble with RF feedback before, running 600W
>> from my AL 811 into the same antenna system.
>>
>> If you find any clues to a solution, please let me know. Glad I bought the
>> KPA100 for my K2!
>>
>> 73,
>>
>> John
>> VK7JB
>>
>>
>> ------------------------------------------------------------
>> This email was sent from Netspace Webmail: http://www.netspace.net.au
>>
>> ______________________________________________________________
>> 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
>>
> ______________________________________________________________
> 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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> Please help support this email list: http://www.qsl.net/donate.html
>

Geoffrey Mackenzie-Kennedy

Re: K2/HF Packer Amp incompatability?

In reply to this post by Don Wilhelm-4

Don,

Shortly after I sent my comment earlier today I received an email telling me
that the HF Packer amp was intended to be used for CW (Class C?) not SSB,
and that a modification was necessary for its use as a linear amplifier for
SSB - presumably at least a change in the amplifier's standing current by
changing its bias.

However Pat said that the K2/ HF Packer signal was distorted whereas the
IC-703/ HF Packer signal was not distorted. This suggests that the HF Packer
amplifer he tested is biased for linear operation, and is not running in
Class C.

Nevertheless as you suggest the results of a gain vs drive level test would
remove any uncertainty.

73,
Geoff
GM4ESD

Don Wilhelm wrote on Tuesday, September 14, 2010 3:48 PM

Pat Byers

Re: K2/HF Packer Amp incompatability?

Hi Don and Geoffrey,

The manual doesn't discuss biasing the amp for Class C, just for
linear operation. This is a 2nd Gen amp with only a single-turn pot
for bias adjustment which makes the adjustment tricky but doable (3rd
Gen has a ten-turn pot) but I'm pretty sure I set the bias correctly
for linear operation. I'll recheck it next time I get a chance to put
the amp on the bench.

I should also mention that although I started with a 2W drive level
(measured by an external Watt meter into a 50 Ohm load before I
connected the K2 to the amp) I experimented with other drive levels
both above and below the 2W setting while the K2 was connected to the
amp. My crude listening tests didn't detect any difference in output
quality at different drive levels. I should also mention that the
K2`s SWR meter didn`t indicate an abnormal match between the radio and the amp.

I recognize that I need to make more definitive measurements and
that`s why I plan to run a sine wave into the mike input of the K2
and observe the amp`s output with an oscilloscope. House renos
prevent me from doing that at the moment.

If there is a solution to this problem, hopefully it will be as
simple as adding attenuation between the K2 and the input to the amp.

Again, thanks for all the help.

Pat VE3EUR

At 11:58 AM 14/09/2010, Geoffrey Mackenzie-Kennedy wrote:

>Don,
>
>Shortly after I sent my comment earlier today I received an email telling me
>that the HF Packer amp was intended to be used for CW (Class C?) not SSB,
>and that a modification was necessary for its use as a linear amplifier for
>SSB - presumably at least a change in the amplifier's standing current by
>changing its bias.
>
>However Pat said that the K2/ HF Packer signal was distorted whereas the
>IC-703/ HF Packer signal was not distorted. This suggests that the HF Packer
>amplifer he tested is biased for linear operation, and is not running in
>Class C.
>
>Nevertheless as you suggest the results of a gain vs drive level test would
>remove any uncertainty.
>
>73,
>Geoff
>GM4ESD
>
>
>Don Wilhelm wrote on Tuesday, September 14, 2010 3:48 PM
>
>
> > That sounds like the amp is not running linear. First make sure the
> > bias is set correctly.
> > Then do a test in CW mode -
> > Put a small amount of drive to the amp (measure it), and measure the
> > output. Compute the gain.
> > Increase the drive by a small amount, and again compute the gain.
> > Continue in small steps until you have reached the maximum output of the
> > amp.
> > The gain should be the same if the amplifier is really linear.
> >
> > If the input impedance of the amplifier is changing with drive level,
> > that can be cured with an attenuator at the input - the driver will then
> > see a more constant impedance.
> >
> > 73,
> > Don W3FPR
>
>
>
>
>______________________________________________________________
>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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>Please help support this email list: http://www.qsl.net/donate.html