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KAT100 Power Calibration Problem

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JeremyJones

KAT100 Power Calibration Problem

I have just finished my KAT100, and am having an issue during the Power Calibration of R3 and R4. I am using a K2 with KAT2. I have a cable running from the Ant 1 jack of the KAT2 to the Ant 1 jack of the KAT100. The KAT100 RF In jack is connected to the Transmitter jack of the power sensor of my W2. The Load jack of the W2 sensor is connected to a 250W, 50 ohm dummy load. The K2 is set for 10W. The W2 is inline only to check the actual power out, due to the strange readings I was getting.

When I hit TUNE, I can only get a voltage range of 0.0 to 0.07 VDC at U5 pin 5 while adjusting R4. The table in the manual indicates that I need to set R4 so that I get 1.8V at U5 pin 5.

I have double checked the orientation of the diodes, everything checkout in the previous tests. T4 has the correct windings, and continuity between pads 1 and 4 is good.

What else should I be looking at.

Thanks for any help,
Jeremy
VA3ZTF

Don Wilhelm-4

Re: KAT100 Power Calibration Problem

Jeremy,

You did not mention it, so I have to ask - when connected as you
describe, did you first obtain a good null at U5 pin 3 (by adjusting
C31)? That is a necessary first step. If you did not get a voltage
measurement in the single digit millivolt range (less than 10
millivolts), then 'all bets are off' and you need to first resolve that
problem.

Be certain to follow the manual instructions - no power to the KAT100
and no control cable attached.

Once you have achieved that (nulling) balance point, you can proceed to
the next step. While observing the actual power output, set the K2
power for 10 watts as observed on your external wattmeter.
Once you have established that power level, then adjust R4 to produce
1.8 volts on U5 pin 5.

After obtaining that adjustment, reverse the RF IN and ANT1 connections
and adjust R3 (with the external wattmeter reading 10 watts) for 1.8
volts on U5 pin 3.

Then do 'the math' as indicated in the manual to further adjust R4.
After that 'job done'.

If you fail to find a balance point on C31, that problem must be
resolved before continuing with anything else (unless you want to do it
over and over again). Should you not obtain a good null, investigate
the winding of T1. It must be wound *exactly* as indicated by the
illustration in the manual including the direction of the turns. If the
direction of the turns is reversed, the alignment voltages will be
reversed - hence your low voltage at U5 pin 5.

73,
Don W3FPR

On 2/27/2014 8:11 PM, JeremyJones wrote:

> I have just finished my KAT100, and am having an issue during the Power
> Calibration of R3 and R4. I am using a K2 with KAT2. I have a cable
> running from the Ant 1 jack of the KAT2 to the Ant 1 jack of the KAT100.
> The KAT100 RF In jack is connected to the Transmitter jack of the power
> sensor of my W2. The Load jack of the W2 sensor is connected to a 250W, 50
> ohm dummy load. The K2 is set for 10W. The W2 is inline only to check the
> actual power out, due to the strange readings I was getting.
>
> When I hit TUNE, I can only get a voltage range of 0.0 to 0.07 VDC at U5 pin
> 5 while adjusting R4. The table in the manual indicates that I need to set
> R4 so that I get 1.8V at U5 pin 5.
>
> I have double checked the orientation of the diodes, everything checkout in
> the previous tests. T4 has the correct windings, and continuity between
> pads 1 and 4 is good.
>
> What else should I be looking at.
>
>

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JeremyJones

Re: KAT100 Power Calibration Problem

I was only able to get U5 pin3 down to 0.03VDC during the SWR Bridge Null test. Is that low enough? The manual says 0 volts or close to it.

Jeremy
VA3ZTF

Don Wilhelm-4 wrote

Jeremy,

You did not mention it, so I have to ask - when connected as you
describe, did you first obtain a good null at U5 pin 3 (by adjusting
C31)? That is a necessary first step. If you did not get a voltage
measurement in the single digit millivolt range (less than 10
millivolts), then 'all bets are off' and you need to first resolve that
problem.

JeremyJones

Re: KAT100 Power Calibration Problem

I just reread Dons post, and he says less than 10mV, so I guess I have some trouble shooting to do with that first,

Jeremy
VA3ZTF

Don Wilhelm-4

Re: KAT100 Power Calibration Problem

Jeremy,

Tune the capacitor very slowly and use a non-metallic tool. The null is
sharp and deep.
You must have a good 50 ohm dummy load connected.
You may want to take your external wattmeter out of line to do the nulling.
The actual voltage will depend on the power level, at 5 watts it should
be less than 10 mV, but you should be able to get it below 15 or 20 mV
if the power is 10 watts. If you are using 20 watts or more from the
KPA100, then your 30 mV is probably OK.

Ideally, the voltage should go to zero, but being practical, one may not
be able to adjust the capacitor in fine enough increments to achieve
that goal.

73,
Don W3FPR

On 2/28/2014 4:32 PM, JeremyJones wrote:

> I just reread Dons post, and he says less than 10mV, so I guess I have some
> trouble shooting to do with that first,
>
> Jeremy
> VA3ZTF
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/KAT100-Power-Calibration-Problem-tp7584832p7584865.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
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JeremyJones

Re: KAT100 Power Calibration Problem

I've taken the watt meter out of the loop, and have the K2 set for 10W. Double checked the windings and solder on T1, and it still won't go below 30mV. I definitely have C31 at the low spot as the voltage climbs on either side. I still can't get anywhere the voltage needed at U5 pin 5 for the power calibration.

Jeremy
VA3ZTF

Don Wilhelm-4 wrote

Jeremy,

Tune the capacitor very slowly and use a non-metallic tool. The null is
sharp and deep.
You must have a good 50 ohm dummy load connected.
You may want to take your external wattmeter out of line to do the nulling.
The actual voltage will depend on the power level, at 5 watts it should
be less than 10 mV, but you should be able to get it below 15 or 20 mV
if the power is 10 watts. If you are using 20 watts or more from the
KPA100, then your 30 mV is probably OK.

Ideally, the voltage should go to zero, but being practical, one may not
be able to adjust the capacitor in fine enough increments to achieve
that goal.

73,
Don W3FPR

On 2/28/2014 4:32 PM, JeremyJones wrote:
> I just reread Dons post, and he says less than 10mV, so I guess I have some
> trouble shooting to do with that first,
>
> Jeremy
> VA3ZTF
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/KAT100-Power-Calibration-Problem-tp7584832p7584865.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> 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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Don Wilhelm-4

Re: KAT100 Power Calibration Problem

Jeremy,

How much power are you sending through that wattmeter? If it is 20
watts or more, it may just be that 30 mV is OK.

73,
Don W3FPR

On 2/28/2014 9:55 PM, JeremyJones wrote:

> I've taken the watt meter out of the loop, and have the K2 set for 10W.
> Double checked the windings and solder on T1, and it still won't go below
> 30mV. I definitely have C31 at the low spot as the voltage climbs on either
> side. I still can't get anywhere the voltage needed at U5 pin 5 for the
> power calibration.
>
> Jeremy
> VA3ZTF
>
>
> Don Wilhelm-4 wrote
>> Jeremy,
>>
>> Tune the capacitor very slowly and use a non-metallic tool. The null is
>> sharp and deep.
>> You must have a good 50 ohm dummy load connected.
>> You may want to take your external wattmeter out of line to do the
>> nulling.
>> The actual voltage will depend on the power level, at 5 watts it should
>> be less than 10 mV, but you should be able to get it below 15 or 20 mV
>> if the power is 10 watts. If you are using 20 watts or more from the
>> KPA100, then your 30 mV is probably OK.
>>
>> Ideally, the voltage should go to zero, but being practical, one may not
>> be able to adjust the capacitor in fine enough increments to achieve
>> that goal.
>>
>> 73,
>> Don W3FPR
>>
>> On 2/28/2014 4:32 PM, JeremyJones wrote:
>>> I just reread Dons post, and he says less than 10mV, so I guess I have
>>> some
>>> trouble shooting to do with that first,
>>>
>>> Jeremy
>>> VA3ZTF
>>>
>>>
>>>
>>> --
>>> View this message in context:
>>> http://elecraft.365791.n2.nabble.com/KAT100-Power-Calibration-Problem-tp7584832p7584865.html
>>> Sent from the Elecraft mailing list archive at Nabble.com.
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:
>> Elecraft@.qth
>>> 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:
>> Elecraft@.qth
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>> Please help support this email list: http://www.qsl.net/donate.html
>
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/KAT100-Power-Calibration-Problem-tp7584832p7584881.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
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JeremyJones

Re: KAT100 Power Calibration Problem

I'm only running 10W through it.

I've just gone through the complete instruction manual to ensure I haven't missed anything. Everything checks out. I've just finished the SWR Bridge Null test and am down to 0.018VDC.

Jeremy
VA3ZTF

Don Wilhelm-4 wrote

Jeremy,

How much power are you sending through that wattmeter? If it is 20
watts or more, it may just be that 30 mV is OK.

73,
Don W3FPR

JeremyJones

Re: KAT100 Power Calibration Problem

Correction, 0.018 was at 5W. 10W still gives 0.036VDC

Jeremy

JeremyJones wrote

I'm only running 10W through it.

I've just gone through the complete instruction manual to ensure I haven't missed anything. Everything checks out. I've just finished the SWR Bridge Null test and am down to 0.018VDC.

Jeremy
VA3ZTF

JeremyJones

Re: KAT100 Power Calibration Problem

Checked my dummy load with an MFJ-259 and it is 50 ohms resistive, no capacitive. Rechecked all soldering with a lighted magnifying glass and cleaned up a couple of joints. Rewound T1 just to be sure it wasn't shorted in the windings.

Still the same results of 0.035VDC on pin 3 of U5.

Jeremy
VA3ZTF

Don wrote

Jeremy,

Check the soldering on all the relays, inductors and capacitors - particularly the relays.
If the relays are not well soldered, there can be an inductor or capacitor in the path that will prevent you from getting a good null.
Another thing that will prevent a null is an inductive or capacitive reactance in your dummy load.
You might want to check that with an antenna analyzer to be certain it is a pure resistance.

73,
Don W3FPR