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KAT2 Bridge null adjustment

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EMD

KAT2 Bridge null adjustment

Hello,

When I adjust C55 I initially get a high current message that last for a second, followed by a fluctuating power indication. The lowest I can adjust c55 down to is 1.7 volts.

So what have I missed. Thanks in advance.

73,
Ed ke7hga

Don Wilhelm-4

Re: KAT2 Bridge null adjustment

Ed,

The most common cause is T1 connected incorrectly or having
insufficiently stripped and tinned leads, so check that first.
The HiCur message may indicate a bad or incorrectly oriented diode.
Check all the components in the wattmeter area for good soldering and
correct values T1, D1, D2, C54, C55, R3, R4, C50, C51, R1, R2, C52, and C53.

Check for continuity from the center conductor of the input cable to the
center of the selected BNC antenna jack - you should find a very low
resistance (quite close to zero). Also check for a short from the
center conductor to ground.

A relay that is not operating properly (due to an unsoldered pin) can
also cause that behavior.

If that does not correct things, I can tell you how to bypass the L-C
board and test the wattmeter section alone.

73,
Don W3FPR

On 8/13/2011 2:03 PM, EMD wrote:

> Hello,
>
> When I adjust C55 I initially get a high current message that last for a
> second, followed by a fluctuating power indication. The lowest I can adjust
> c55 down to is 1.7 volts.
>
> So what have I missed. Thanks in advance.
>
> 73,
> Ed ke7hga
>

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EMD

Re: KAT2 Bridge null adjustment

Thanks Don I will start looking into those areas.

73,
Ed ke7hga

EMD

Re: KAT2 Bridge null adjustment

Don

I was using a cable to connect my Dummy load to the tuner. So I decided to see if maybe the connection could be bad so I connected the tuner directly to the #1 antenna jack and that was it. Now I have a steady power ready of 3.0 volts.

Thanks again.

73,
Ed ke7hga

EMD

Re: KAT2 Bridge null adjustment

In reply to this post by Don Wilhelm-4

Don,

I just realized that I had done the Bridge null adjustment with R6 installed. So should I remove it and start over?

73,
Ed ke7hga

Don Wilhelm-4

Re: KAT2 Bridge null adjustment

Ed,

No, R6 will not influence the bridge null. You are instructed to leave
it out until you check the voltage at U4 pin 1, during receive - it
should be zero - but you can also check that with R6 in. The zero
voltage in receive is the important one to the rest of the K2. If you
do detect voltage during receive, then remove R6 until you can find the
problem, otherwise leave it in.
The check for voltage in transmit is to be sure things are working right
in the wattmeter output, but that can also be checked with R6 installed.

73,
Don W3FPR

On 8/13/2011 5:06 PM, EMD wrote:

> Don,
>
> I just realized that I had done the Bridge null adjustment with R6
> installed. So should I remove it and start over?
>
> 73,
> Ed ke7hga
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/KAT2-Bridge-null-adjustment-tp6683608p6683878.html
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> ______________________________________________________________
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EMD

Re: KAT2 Bridge null adjustment

Okay Don thanks again. I did not indicate any voltage during receive. I think I'm going to wait until I get some sort of watt meter before I continue. But I'm off to work so that will have to wait until next month.

73,
Ed ke7hga

Don Wilhelm-4

Re: KAT2 Bridge null adjustment

Ed,

Do I recall that you have the Elecraft DL1? If so, you have the perfect
item for calibrating the power - in fact, better than most wattmeters.
Just measure the DC voltage at the diode and calculate the power - set
the forward voltage pot so the K2 indicates that same power, and job done.

73,
Don W3FPR

On 8/13/2011 7:01 PM, EMD wrote:
> Okay Don thanks again. I did not indicate any voltage during receive. I
> think I'm going to wait until I get some sort of watt meter before I
> continue. But I'm off to work so that will have to wait until next month.
>
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EMD

Re: KAT2 Bridge null adjustment

Thanks Don,

I will give that a try. Should I use the RF probe that I made or just use the DMM probes?

73,
Ed ke7hga

Don Wilhelm-4

Re: KAT2 Bridge null adjustment

Ed,

With the Elecraft DL1, just use the DMM probes.
If you do not have the DL1, connect the RF Probe across the dummy load
(use a Tee adapter if you do not have direct access to the dummy load
terminals) - but keep the power to 5 watts or less to keep from zapping
the diode in the RF probe.

You can also use an oscilloscope (with a 10X probe) to measure the peak
to peak RF voltage across the dummy load. In that case, the calculation
formula is Power = (Vp-p) squared and divided by 400. Derivation left
to the student.

73,
Don W3FPR

On 8/13/2011 7:53 PM, EMD wrote:

> Thanks Don,
>
> I will give that a try. Should I use the RF probe that I made or just use
> the DMM probes?
>
> 73,
> Ed ke7hga
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/KAT2-Bridge-null-adjustment-tp6683608p6684038.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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>

Don Wilhelm-4

Re: KAT2 Bridge null adjustment

In reply to this post by EMD

Ed,

I would also recommend doing the power calibration on 40 meters - it is
a good compromise. There \is some variation in the response of the
diodes with respect to frequency, and also, if you are using an
oscilloscope to measure the RF voltage, the bandwidth of the 'scope can
cause some "confusion" - if your 'scope (and probe) is rated at 35 MHz,
the vertical response will be down 3 dB at 35 MHz. The use of a 'scope
rated at 35 MHz can be used for RF voltage measurements at 7 MHz, but
using it at 14 MHz, expect that the RF voltage shown by the scope will
be less than the actual RF voltage. Do not even think of using a hunk
of coax attached to the 'scope to measure RF voltages with any accuracy
- a 10X probe is mandatory to keep the 'scope from loading the device to
be measured (in this case, the transmitter output).

73,
Don W3FPR

On 8/13/2011 7:53 PM, EMD wrote:

EMD

Re: KAT2 Bridge null adjustment

In reply to this post by Don Wilhelm-4

Don,

When I use the DMM and measure the Voltage across I am only getting 6.0 volts. When I plug that into P=V*V/R I get .72volts. I have also noticed that when I push TUNE I sometime see a fluctuating power indication and other times I see 2.4f 0.0r. So what should I be looking at to adjust R1. Sorry to be so dense but this has me confused. Also when I select TUNE the S meter fluctuates with the power display.

73,
Ed ke7hga

Don Wilhelm-4

Re: KAT2 Bridge null adjustment

Ed,

Not enough information, so I am forced to make assumptions.
Are you using the RF probe to measure the RF voltage across the dummy
load? If so, 6 volts yields 0.72 watts as you stated, but if you have
the Elecraft DL1 and measure 6 volts, the power is 1.49 watts.

Adjust R1 to agree with the external power reading.

If you continue to see extreme fluctuation in the power displayed by the
K2, you may want to change the value of R98 on the bottom of the RF
board. See http://www.elecraft.com/Apps/Power_Control_Mod.html for the
"rest of the story".

73,
Don W3FPR

On 8/13/2011 9:30 PM, EMD wrote:

> Don,
>
> When I use the DMM and measure the Voltage across I am only getting 6.0
> volts. When I plug that into P=V*V/R I get .72volts. I have also noticed
> that when I push TUNE I sometime see a fluctuating power indication and
> other times I see 2.4f 0.0r. So what should I be looking at to adjust R1.
> Sorry to be so dense but this has me confused. Also when I select TUNE the
> S meter fluctuates with the power display.
>
> 73,
> Ed ke7hga
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/KAT2-Bridge-null-adjustment-tp6683608p6684158.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
>

EMD

Re: KAT2 Bridge null adjustment

Sorry Don,

I was using the DMM leads and not the RF probe to read the voltage on the DL1 measuring 6 volts.

Thanks again Don,

Ed