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What is wrong with my K2 #6705 ??

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Fred Bennett N9TA-2

What is wrong with my K2 #6705 ??

Hi Folks

I stayed home from work today to do a little work with #6705.
At first I had NO output on 12 meters....FIXED...just WAY out
of adjustment on C44 & C46 (Very touchy until in the ballpark on
C44).

Here's the remaining problem....low output across the bands:
All readings taken with digital wattmeter into 50 ohm dummy.
80 5.37
40 7.61
30 7.09
20 7.38
17 7.72
15 7.67
12 4.27
10 3.48

CAL/CUR has been set to 3.5 amps (Should be WAY high enough)

Here's the interesting part....during these TX tests the BUILT IN power
reading shows in excess of 10 watts (meter pegged) while the outboard
meter shows MUCH less. I've double checked the component placement,
soldering, and Taken out and measured the values of R67, R68, D9, R66,
R69....and confirmed that C77 is a .001 cap. Everything looks ok in the
"RF Output Detector" section. I've noticed however, that when I first
go into TX mode the output spikes and cuts back very rapidly....it seems
that #6705 "thinks" it's putting out WAY more power than it really is.
The question why???

Any help would be much appreciated!! 73..de..Fred N9TA

On a whim, I measured the DC resistance of my dummy load (old oil filled
MFJ paint can). It reads 63.7 ohm.....could this small a mismatch give me a
false power reading??
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Don Wilhelm-4

Re: What is wrong with my K2 #6705 ??

Fred,

That dummy load is way off at DC, so who knows what the actual value is
at RF. It could be the only source of your problem.

Specifically, *any* deviation from 50 ohms pure resistive will cause the
basic K2 to indicate (and control) power incorrectly.
That dependency is removed when the KAT2 or KPA100 or KAT100 are added
because those options contain true wattmeters.

I don't have any assistance to offer other than to say find a known good
dummy load. Ridge Equipment has a 50 ohm dummy load flat to 1.5 GHz for
$11.99, but you will likely need an adapter for the input - they sell
those for $5. See https://www.ridgeequipment.com/store/dummyloads.html

The base K2 has only a diode detector to measure the RF output, so it
can only measure the voltage. Using the 10 watt level as an example,
with a 50 ohm load, the K2 measures 22.3 volts of RF and declares that
the power is 10 watts (and it actually is). If the load is instead 63
ohms, and you request 10 watts, the K2 will control the power until the
RF voltage reaches 22.3 volts, but the actual power being developed is
only 7.9 watts.

Your dummy load likely has some reactance as well as resistance, so who
knows what the actual impedance is at the various frequencies.

73,
Don W3FPR

Fred Bennett N9TA wrote:

> Hi Folks
>
> I stayed home from work today to do a little work with #6705.
> At first I had NO output on 12 meters....FIXED...just WAY out
> of adjustment on C44 & C46 (Very touchy until in the ballpark on
> C44).
>
> Here's the remaining problem....low output across the bands:
> All readings taken with digital wattmeter into 50 ohm dummy.
> 80 5.37
> 40 7.61
> 30 7.09
> 20 7.38
> 17 7.72
> 15 7.67
> 12 4.27
> 10 3.48
>
> CAL/CUR has been set to 3.5 amps (Should be WAY high enough)
>
> Here's the interesting part....during these TX tests the BUILT IN power
> reading shows in excess of 10 watts (meter pegged) while the outboard
> meter shows MUCH less. I've double checked the component placement,
> soldering, and Taken out and measured the values of R67, R68, D9, R66,
> R69....and confirmed that C77 is a .001 cap. Everything looks ok in the
> "RF Output Detector" section. I've noticed however, that when I first
> go into TX mode the output spikes and cuts back very rapidly....it seems
> that #6705 "thinks" it's putting out WAY more power than it really is.
> The question why???
>
> Any help would be much appreciated!! 73..de..Fred N9TA
>
> On a whim, I measured the DC resistance of my dummy load (old oil filled
> MFJ paint can). It reads 63.7 ohm.....could this small a mismatch give me a
> false power reading??
>
>

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Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Fred Bennett N9TA-2

Re: What is wrong with my K2 #6705 ??

Don

We're thinking alike I think. I've started with the assembly of the KAT2
option.
I've still got the KAT2, Batt, SSB, KIO2, and 160M options to build. I'm
hoping the installation of the KAT2 will "fix" my problem.

Fred

Don Wilhelm wrote:

> Fred,
>
> That dummy load is way off at DC, so who knows what the actual value
> is at RF. It could be the only source of your problem.
>
> Specifically, *any* deviation from 50 ohms pure resistive will cause
> the basic K2 to indicate (and control) power incorrectly.
> That dependency is removed when the KAT2 or KPA100 or KAT100 are added
> because those options contain true wattmeters.
>
> I don't have any assistance to offer other than to say find a known
> good dummy load. Ridge Equipment has a 50 ohm dummy load flat to 1.5
> GHz for $11.99, but you will likely need an adapter for the input -
> they sell those for $5. See
> https://www.ridgeequipment.com/store/dummyloads.html
>
> The base K2 has only a diode detector to measure the RF output, so it
> can only measure the voltage. Using the 10 watt level as an example,
> with a 50 ohm load, the K2 measures 22.3 volts of RF and declares that
> the power is 10 watts (and it actually is). If the load is instead 63
> ohms, and you request 10 watts, the K2 will control the power until
> the RF voltage reaches 22.3 volts, but the actual power being
> developed is only 7.9 watts.
>
> Your dummy load likely has some reactance as well as resistance, so
> who knows what the actual impedance is at the various frequencies.
>
> 73,
> Don W3FPR
>
> Fred Bennett N9TA wrote:
>> Hi Folks
>>
>> I stayed home from work today to do a little work with #6705.
>> At first I had NO output on 12 meters....FIXED...just WAY out
>> of adjustment on C44 & C46 (Very touchy until in the ballpark on
>> C44).
>>
>> Here's the remaining problem....low output across the bands:
>> All readings taken with digital wattmeter into 50 ohm dummy.
>> 80 5.37 40 7.61
>> 30 7.09
>> 20 7.38
>> 17 7.72
>> 15 7.67
>> 12 4.27
>> 10 3.48
>>
>> CAL/CUR has been set to 3.5 amps (Should be WAY high enough)
>>
>> Here's the interesting part....during these TX tests the BUILT IN power
>> reading shows in excess of 10 watts (meter pegged) while the outboard
>> meter shows MUCH less. I've double checked the component placement,
>> soldering, and Taken out and measured the values of R67, R68, D9, R66,
>> R69....and confirmed that C77 is a .001 cap. Everything looks ok in the
>> "RF Output Detector" section. I've noticed however, that when I first
>> go into TX mode the output spikes and cuts back very rapidly....it seems
>> that #6705 "thinks" it's putting out WAY more power than it really is.
>> The question why???
>>
>> Any help would be much appreciated!! 73..de..Fred N9TA
>>
>> On a whim, I measured the DC resistance of my dummy load (old oil filled
>> MFJ paint can). It reads 63.7 ohm.....could this small a mismatch
>> give me a
>> false power reading??
>>
>

Don Wilhelm-4

Re: What is wrong with my K2 #6705 ??

Fred,

You will still need an accurate dummy load to set the balance on the
KAT2 correctly. If the dummy load is not accurate, the power
calibration will be off as well.

The Elecraft DL2 is a great dummy load.

73,
Don W3FPR

Fred Bennett N9TA wrote:

> Don
>
> We're thinking alike I think. I've started with the assembly of the KAT2
> option.
> I've still got the KAT2, Batt, SSB, KIO2, and 160M options to build. I'm
> hoping the installation of the KAT2 will "fix" my problem.
>
> Fred
>
>
> Don Wilhelm wrote:
>
>> Fred,
>>
>> That dummy load is way off at DC, so who knows what the actual value
>> is at RF. It could be the only source of your problem.
>>
>> Specifically, *any* deviation from 50 ohms pure resistive will cause
>> the basic K2 to indicate (and control) power incorrectly.
>> That dependency is removed when the KAT2 or KPA100 or KAT100 are added
>> because those options contain true wattmeters.
>>
>> I don't have any assistance to offer other than to say find a known
>> good dummy load. Ridge Equipment has a 50 ohm dummy load flat to 1.5
>> GHz for $11.99, but you will likely need an adapter for the input -
>> they sell those for $5. See
>> https://www.ridgeequipment.com/store/dummyloads.html
>>
>> The base K2 has only a diode detector to measure the RF output, so it
>> can only measure the voltage. Using the 10 watt level as an example,
>> with a 50 ohm load, the K2 measures 22.3 volts of RF and declares that
>> the power is 10 watts (and it actually is). If the load is instead 63
>> ohms, and you request 10 watts, the K2 will control the power until
>> the RF voltage reaches 22.3 volts, but the actual power being
>> developed is only 7.9 watts.
>>
>> Your dummy load likely has some reactance as well as resistance, so
>> who knows what the actual impedance is at the various frequencies.
>>
>> 73,
>> Don W3FPR
>>
>> Fred Bennett N9TA wrote:
>>
>>> Hi Folks
>>>
>>> I stayed home from work today to do a little work with #6705.
>>> At first I had NO output on 12 meters....FIXED...just WAY out
>>> of adjustment on C44 & C46 (Very touchy until in the ballpark on
>>> C44).
>>>
>>> Here's the remaining problem....low output across the bands:
>>> All readings taken with digital wattmeter into 50 ohm dummy.
>>> 80 5.37 40 7.61
>>> 30 7.09
>>> 20 7.38
>>> 17 7.72
>>> 15 7.67
>>> 12 4.27
>>> 10 3.48
>>>
>>> CAL/CUR has been set to 3.5 amps (Should be WAY high enough)
>>>
>>> Here's the interesting part....during these TX tests the BUILT IN power
>>> reading shows in excess of 10 watts (meter pegged) while the outboard
>>> meter shows MUCH less. I've double checked the component placement,
>>> soldering, and Taken out and measured the values of R67, R68, D9, R66,
>>> R69....and confirmed that C77 is a .001 cap. Everything looks ok in the
>>> "RF Output Detector" section. I've noticed however, that when I first
>>> go into TX mode the output spikes and cuts back very rapidly....it seems
>>> that #6705 "thinks" it's putting out WAY more power than it really is.
>>> The question why???
>>>
>>> Any help would be much appreciated!! 73..de..Fred N9TA
>>>
>>> On a whim, I measured the DC resistance of my dummy load (old oil filled
>>> MFJ paint can). It reads 63.7 ohm.....could this small a mismatch
>>> give me a
>>> false power reading??
>>>
>