[K2] Low power output

[Petr, OK1RP/M0SIS]

Hi folks,

my colleque got as birthday gift from family the K2. All seems ok, receiver
works excellent.
The only issue he found is the low power output thru all bands. He can not
get 15W but something
below 10W... He mentioned in last email that preview owner had installed
KPA100 option which
has been removed probably before selling.
Is there something related to KPA100 which could be modified and need to be
now set back to get
15W from his K2 please?

Thanks,



-----
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"Apple & Elecraft freak"
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[Don Wilhelm]

Petr,

The specification for the K2 is for 10 watts or greater.  Most will go
to 12 watts on 40 and 30 meters with an adequate power supply voltage
while few can achieve 15 watts on all bands.

There is nothing specific to the KPA100 option that would cause low
power output from the base K2.
However, there are a few things to check.

First check the value of R98 on the bottom of the board.  The normal
value is 270 ohms, but after the addition of the KPA100, some
experienced power oscillation due to the added RF Gain, and that value
may have been increased to damp the oscillation.

Then check to make certain T4 was not wound for "greater efficiency at 5
watts" with a 2:2:1:1 ratio instead of the normal 2:3:1:1 ratio - count
the number of white turns on T4.  That 'more efficient' T4 is actually
less efficient above 5 watts and should never be used with the KSB2
option or the KPA100.

If there is also HiCur as well as low power then the problem is either
with T4 or the Low Pass Filter.

Make certain the power supply leads are tight and large enough to keep
the voltage drop low - a power source with at least 13.8 volts should be
used and the voltage should not drop below 12.5 during transmit.  15
watts is not possible with a lower voltage, and the output on 12 and 10
meters may be less.  10 watts or more meets specification.

If those checks do not provide the answer, then he will have to do the
"Transmit Signal Tracing" in Appendix A of the manual to identify the
first stage with less than the expected RF voltage output.

73,
Don W3FPR

On 9/4/2019 6:47 AM, Petr, OK1RP/M0SIS wrote:

> Hi folks,
>
> my colleque got as birthday gift from family the K2. All seems ok, receiver
> works excellent.
> The only issue he found is the low power output thru all bands. He can not
> get 15W but something
> below 10W... He mentioned in last email that preview owner had installed
> KPA100 option which
> has been removed probably before selling.
> Is there something related to KPA100 which could be modified and need to be
> now set back to get
> 15W from his K2 please?
>

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[Petr, OK1RP/M0SIS]

Hi Don,

many thanks for all kind help and ideas.
I will try to call him in order to explain all of these steps to be checked.
Most important is to double check what the real power is from his K2 as
I do not know if he measured the output power correctly with his external equipment.

Again Don thanks for your kind help and time!

btw: if you remember our son's K1 is still waiting on the shelf to be finished the
alignment...:)

best 73 - Petr, OK1RP



On Wed, Sep 4, 2019, at 4:29 PM, Don Wilhelm wrote:

> Petr,
>
> The specification for the K2 is for 10 watts or greater.  Most will go
> to 12 watts on 40 and 30 meters with an adequate power supply voltage
> while few can achieve 15 watts on all bands.
>
> There is nothing specific to the KPA100 option that would cause low
> power output from the base K2.
> However, there are a few things to check.
>
> First check the value of R98 on the bottom of the board.  The normal
> value is 270 ohms, but after the addition of the KPA100, some
> experienced power oscillation due to the added RF Gain, and that value
> may have been increased to damp the oscillation.
>
> Then check to make certain T4 was not wound for "greater efficiency at 5
> watts" with a 2:2:1:1 ratio instead of the normal 2:3:1:1 ratio - count
> the number of white turns on T4.  That 'more efficient' T4 is actually
> less efficient above 5 watts and should never be used with the KSB2
> option or the KPA100.
>
> If there is also HiCur as well as low power then the problem is either
> with T4 or the Low Pass Filter.
>
> Make certain the power supply leads are tight and large enough to keep
> the voltage drop low - a power source with at least 13.8 volts should be
> used and the voltage should not drop below 12.5 during transmit.  15
> watts is not possible with a lower voltage, and the output on 12 and 10
> meters may be less.  10 watts or more meets specification.
>
> If those checks do not provide the answer, then he will have to do the
> "Transmit Signal Tracing" in Appendix A of the manual to identify the
> first stage with less than the expected RF voltage output.
>
> 73,
> Don W3FPR
>
> On 9/4/2019 6:47 AM, Petr, OK1RP/M0SIS wrote:
> > Hi folks,
> >
> > my colleque got as birthday gift from family the K2. All seems ok, receiver
> > works excellent.
> > The only issue he found is the low power output thru all bands. He can not
> > get 15W but something
> > below 10W... He mentioned in last email that preview owner had installed
> > KPA100 option which
> > has been removed probably before selling.
> > Is there something related to KPA100 which could be modified and need to be
> > now set back to get
> > 15W from his K2 please?
> >
>

--
73 - Petr, OK1RP
--
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