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Re: KPA500 and SWR above 1.5:1

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Geoffrey Downs-3

Re: KPA500 and SWR above 1.5:1

The manual says the bargraph shows green ("normal") up to an SWR of 1.5:1,
yellow ("marginal") from 1.5:1 to 2.1:1 and red ("excessive") above that.
Does this mean no inhibition of output by the protection system (and no
need for it) up to 1.5:1 but progressive reduction of output above? If so,
will the amp operate without damage in the yellow zone and what %
reductions in output might be expected up to 2.1:1? Also in what conditions
of SWR does the intelligent 2.5db output reduction apply; and at what SWR
does output shut off altogether - ie the REFL HI fault condition.

Apologies if these questions have already been answered, in which case
perhaps someone could refer me to where. I have looked at the manual and
searched back on the reflector without success.

73 to all

Geoff
G3UCK

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Eric Swartz - WA6HHQ

Re: KPA500 and SWR above 1.5:1

Administrator

The KPA500 bases its SWR protection on reflected power level, not an
absolute SWR. The KPA500 is happy up to a 2:1 SWR at 500-W out. As long
as the actual reflected power is below that for a 2:1 SWR at 500W, it
will not reduce its power. This means you can operate into a higher than
2:1 SWR load at full amplifier gain if you reduce the amp's output power
slightly.

The amp "soft-faults" and reduces output power by about 2.5 dB by
switching in an input attenuator at the 500W 2:1 reflected power point,
and it flashes a red LED to alert you to this so you can adjust driver
power (or SWR via an external tuner) down a bit. Once this is corrected
below this threshold by the operator, the KPA500 automatically goes back
to full gain. It also does this for minor overdrive conditions.

Of course, for excessive SWR events (wrong antenna, open antenna etc),
and severe overdrive, the amp protects itself by immediately hard
faulting and going into bypass mode. After correcting the fault, just
push the operate/standby switch to get back on-line. While at Contest
University, our Italian representative surprised me by demonstrating
this feature to customers by pulling the coax from the dummy load while
the amp was transmitting. After I recovered from my surprise, I realized
the amp was perfectly happy and had protected itself as advertised :-)
But don't try this at home, as he also received a minor RF burn to help
him remember this event..

73, Eric WA6HHQ
www.elecraft.com
====

On 5/11/2011 9:24 AM, Geoffrey Downs wrote:

> The manual says the bargraph shows green ("normal") up to an SWR of 1.5:1,
> yellow ("marginal") from 1.5:1 to 2.1:1 and red ("excessive") above that.
> Does this mean no inhibition of output by the protection system (and no
> need for it) up to 1.5:1 but progressive reduction of output above? If so,
> will the amp operate without damage in the yellow zone and what %
> reductions in output might be expected up to 2.1:1? Also in what conditions
> of SWR does the intelligent 2.5db output reduction apply; and at what SWR
> does output shut off altogether - ie the REFL HI fault condition.
>
> 73 to all
>
> Geoff
> G3UCK

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Tony Estep

Re: KPA500 and SWR above 1.5:1

On Wed, May 11, 2011 at 1:10 PM, Eric Swartz - WA6HHQ, Elecraft <
[hidden email]> wrote:

> ...As long as the actual reflected power is below that for a 2:1 SWR at
> 500W...

Which is quite a bit (62.5 watts), so it's pretty tolerant.

Tony KT0NY
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Geoffrey Downs-3

Re: KPA500 and SWR above 1.5:1

In reply to this post by Eric Swartz - WA6HHQ

Thank you Eric. That is interesting and impressive. I will be seriously
considering a kit.

73

Geoff
G3UCK

----- Original Message -----
From: "Eric Swartz - WA6HHQ, Elecraft" <[hidden email]>
To: "Geoffrey Downs" <[hidden email]>
Cc: <[hidden email]>
Sent: Wednesday, May 11, 2011 7:10 PM
Subject: Re: [Elecraft] KPA500 and SWR above 1.5:1

> The KPA500 bases its SWR protection on reflected power level, not an
> absolute SWR. The KPA500 is happy up to a 2:1 SWR at 500-W out. As long as
> the actual reflected power is below that for a 2:1 SWR at 500W, it will
> not reduce its power. This means you can operate into a higher than 2:1
> SWR load at full amplifier gain if you reduce the amp's output power
> slightly.
>
> The amp "soft-faults" and reduces output power by about 2.5 dB by
> switching in an input attenuator at the 500W 2:1 reflected power point,
> and it flashes a red LED to alert you to this so you can adjust driver
> power (or SWR via an external tuner) down a bit. Once this is corrected
> below this threshold by the operator, the KPA500 automatically goes back
> to full gain. It also does this for minor overdrive conditions.
>
> Of course, for excessive SWR events (wrong antenna, open antenna etc), and
> severe overdrive, the amp protects itself by immediately hard faulting and
> going into bypass mode. After correcting the fault, just push the
> operate/standby switch to get back on-line. While at Contest University,
> our Italian representative surprised me by demonstrating this feature to
> customers by pulling the coax from the dummy load while the amp was
> transmitting. After I recovered from my surprise, I realized the amp was
> perfectly happy and had protected itself as advertised :-) But don't try
> this at home, as he also received a minor RF burn to help him remember
> this event..
>
> 73, Eric WA6HHQ
> www.elecraft.com
> ====
>
> On 5/11/2011 9:24 AM, Geoffrey Downs wrote:
>> The manual says the bargraph shows green ("normal") up to an SWR of
>> 1.5:1,
>> yellow ("marginal") from 1.5:1 to 2.1:1 and red ("excessive") above that.
>> Does this mean no inhibition of output by the protection system (and no
>> need for it) up to 1.5:1 but progressive reduction of output above? If
>> so,
>> will the amp operate without damage in the yellow zone and what %
>> reductions in output might be expected up to 2.1:1? Also in what
>> conditions
>> of SWR does the intelligent 2.5db output reduction apply; and at what SWR
>> does output shut off altogether - ie the REFL HI fault condition.
>>
>> 73 to all
>>
>> Geoff
>> G3UCK
>
>