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SWR

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Ken G Kopp

SWR

IMHO ....

There is far too much emphasis put on chasing "perfect" SWR readings.

Except in rare instances SWR's of 2:1 or less are OK in the real world, and
most would be hard-pressed to tell any difference.

I have a friend who recently spent several days fretting and climbing over
a reading of 1.7: 1.... (;-)

73

Ken - K0PP
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vk2rq

Re: SWR

The issue with running with an SWR of 2:1 is that many modern radios have fold back protection circuitry that will introduce non-linearity under such conditions and produce IMD products. For this reason it is usually better to avoid running into such mismatched loads.

73,
Matt VK2RQ

> On 12 Feb 2015, at 5:00 am, Ken G Kopp <[hidden email]> wrote:
>
> IMHO ....
>
> There is far too much emphasis put on chasing "perfect" SWR readings.
>
> Except in rare instances SWR's of 2:1 or less are OK in the real world, and
> most would be hard-pressed to tell any difference.
>
> I have a friend who recently spent several days fretting and climbing over
> a reading of 1.7: 1.... (;-)
>
> 73
>
> Ken - K0PP
> ______________________________________________________________
> 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
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Eric Swartz - WA6HHQ

Re: SWR

Administrator

While the K3 will reduce power around a 2:1 SWR to protect the PAs, since we control power with a long hold time via the uC and DSP and not with an analog ALC loop, that will not make TX IMD worse.

73,
Eric
elecraft.com
_..._

> On Feb 11, 2015, at 7:08 PM, Matt VK2RQ <[hidden email]> wrote:
>
> The issue with running with an SWR of 2:1 is that many modern radios have fold back protection circuitry that will introduce non-linearity under such conditions and produce IMD products. For this reason it is usually better to avoid running into such mismatched loads.
>
> 73,
> Matt VK2RQ
>
>> On 12 Feb 2015, at 5:00 am, Ken G Kopp <[hidden email]> wrote:
>>
>> IMHO ....
>>
>> There is far too much emphasis put on chasing "perfect" SWR readings.
>>
>> Except in rare instances SWR's of 2:1 or less are OK in the real world, and
>> most would be hard-pressed to tell any difference.
>>
>> I have a friend who recently spent several days fretting and climbing over
>> a reading of 1.7: 1.... (;-)
>>
>> 73
>>
>> Ken - K0PP
>> ______________________________________________________________
>> 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]
> ______________________________________________________________
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Guy Olinger K2AV

Re: SWR

Yup, folks (including me on a given day) still stuck with analog thinking
about what is really a digital radio. Hard thing to unlearn.

73, Guy K2AV

On Thu, Feb 12, 2015 at 10:11 AM, Eric Swartz - WA6HHQ, Elecraft <
[hidden email]> wrote:

> While the K3 will reduce power around a 2:1 SWR to protect the PAs, since
> we control power with a long hold time via the uC and DSP and not with an
> analog ALC loop, that will not make TX IMD worse.
>
> 73,
> Eric
> elecraft.com
> _..._
>
>
>
> > On Feb 11, 2015, at 7:08 PM, Matt VK2RQ <[hidden email]> wrote:
> >
> > The issue with running with an SWR of 2:1 is that many modern radios
> have fold back protection circuitry that will introduce non-linearity under
> such conditions and produce IMD products. For this reason it is usually
> better to avoid running into such mismatched loads.
> >
> > 73,
> > Matt VK2RQ
> >
> >> On 12 Feb 2015, at 5:00 am, Ken G Kopp <[hidden email]> wrote:
> >>
> >> IMHO ....
> >>
> >> There is far too much emphasis put on chasing "perfect" SWR readings.
> >>
> >> Except in rare instances SWR's of 2:1 or less are OK in the real world,
> and
> >> most would be hard-pressed to tell any difference.
> >>
> >> I have a friend who recently spent several days fretting and climbing
> over
> >> a reading of 1.7: 1.... (;-)
> >>
> >> 73
> >>
> >> Ken - K0PP
> >> ______________________________________________________________
> >> 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
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> > Post: mailto:[hidden email]
> >
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Wes (N7WS)

Re: SWR

It's still an analog PA.

On 2/12/2015 2:48 PM, Guy Olinger K2AV wrote:
> Yup, folks (including me on a given day) still stuck with analog thinking
> about what is really a digital radio. Hard thing to unlearn.
>
> 73, Guy K2AV
>
>

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Don Wilhelm-4

Re: SWR

Wes,

That is true, but the control of the drive to that analog PA is
different than that implemented in transceiver that use analog open loop
ALC and SWR power reduction. The K3 (and K2 and KX3) do ALC differently
than other transceivers. You may find similar systems in commercial
transceivers, but I don't think the same methods are employed in any
other amateur transceiver.

73,
Don W3FPR

On 2/12/2015 9:58 PM, Wes (N7WS) wrote:

> It's still an analog PA.
>
>
>
> On 2/12/2015 2:48 PM, Guy Olinger K2AV wrote:
>> Yup, folks (including me on a given day) still stuck with analog
>> thinking
>> about what is really a digital radio. Hard thing to unlearn.
>>
>> 73, Guy K2AV

Wes (N7WS)

Re: SWR

I realize all of that. But it's still an analog PA. What is an analog open
loop ALC?

On 2/12/2015 8:59 PM, Don Wilhelm wrote:

> Wes,
>
> That is true, but the control of the drive to that analog PA is different than
> that implemented in transceiver that use analog open loop ALC and SWR power
> reduction. The K3 (and K2 and KX3) do ALC differently than other
> transceivers. You may find similar systems in commercial transceivers, but I
> don't think the same methods are employed in any other amateur transceiver.
>
> 73,
> Don W3FPR
>

Don Wilhelm-5

Re: SWR

Wes,

An analog open loop ALC is one in which the drive is reduced in response
to an overload condition (high SWR, power level that exceeds the maximum
set level). The response is applied only after the offending condition
occurs - that is an open loop system.
With the K3, KX3 and K2 power control system being a closed loop system,
that condition does not exist. The overshoot possibility is detected
early and the power is reduced accordingly without PA overshoot and the
PA going into a distortion region.

If you have any understanding about closed loop control systems, you
will then understand 'damping' conditions. Underdamped systems will
oscillate near the 'set point' while overdamped systems will never come
up to the set point. Critically damped systems will quickly settle to
the set point and maintain the proper condition (power level,
temperature, you 'name it' condition). In the case in point, the power
level is the 'set point' that is considered. An open loop system is
totally undamped and will only respond 'after the fact' to conditions
that exceed certain thresholds. Closed loop systems approach those
thresholds with actions that will result in critical damping of the
response mechanism.

73,
Don W3FPR

On 2/12/2015 11:05 PM, Wes (N7WS) wrote:

> I realize all of that. But it's still an analog PA. What is an
> analog open loop ALC?
>
> On 2/12/2015 8:59 PM, Don Wilhelm wrote:
>> Wes,
>>
>> That is true, but the control of the drive to that analog PA is
>> different than that implemented in transceiver that use analog open
>> loop ALC and SWR power reduction. The K3 (and K2 and KX3) do ALC
>> differently than other transceivers. You may find similar systems in
>> commercial transceivers, but I don't think the same methods are
>> employed in any other amateur transceiver.
>>
>> 73,
>> Don W3FPR

Wes (N7WS)

Re: SWR

I guess it's semantics. If an undesired output event causes a corrective action
to be taken in a previous stage isn't this a closed loop? I believe it is, even
if it's a "man-in-the-loop" system, i.e. I see on the oscilloscope that I'm flat
topping so I turn the audio gain down to correct it.

On 2/12/2015 9:59 PM, Don Wilhelm wrote:

> Wes,
>
> An analog open loop ALC is one in which the drive is reduced in response to an
> overload condition (high SWR, power level that exceeds the maximum set
> level). The response is applied only after the offending condition occurs -
> that is an open loop system.
> With the K3, KX3 and K2 power control system being a closed loop system, that
> condition does not exist. The overshoot possibility is detected early and the
> power is reduced accordingly without PA overshoot and the PA going into a
> distortion region.
>
> If you have any understanding about closed loop control systems, you will then
> understand 'damping' conditions. Underdamped systems will oscillate near the
> 'set point' while overdamped systems will never come up to the set point.
> Critically damped systems will quickly settle to the set point and maintain
> the proper condition (power level, temperature, you 'name it' condition). In
> the case in point, the power level is the 'set point' that is considered. An
> open loop system is totally undamped and will only respond 'after the fact' to
> conditions that exceed certain thresholds. Closed loop systems approach those
> thresholds with actions that will result in critical damping of the response
> mechanism.
>
> 73,
> Don W3FPR
>