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Problem with KAT2?

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Kevin Cozens-2

Problem with KAT2?

Greetings, all.

For some time I've suspected my K2 of being partially deaf (ie. not as
sensitive as it should be). I bought an XG3 a while ago and finally sat down
to check my K2.

I set up the K2 following the XG3 manual. Volume control set to was slightly
before 12 o'clock so I had maximum volume possible before there was audible
distortion heard in the speaker, I used a 400Hz filter as I don't have a
500Hz one set up, and I removed the KAT2. I took measurements at the speaker
terminals with the speaker disconnect as the volume was quite loud with the
speaker connected. On 40m, S+N was 532mV and N was 19.2mV for a receive
sensitivity of -135.7dBm (approximately).

I installed the KAT2, tuned in to a dummy load on ANT1 that measured 51ohms
on an ohmmeter, and set the KAT2 to calS mode. I ran the test again without
changing any controls from the first test. The speaker volume was only 55mV,
about 1/10th what it was without the KAT2. Calculated senstivity was around
-128dBm.

Sensitivity seems a bit lower with the KAT2. Perhaps I should have upped the
volume setting but I thought I should try and do a more direct comparison to
the bare K2.

Center conductor of ANT1 to KAT2 output is only 1 ohm so there is nothing
obviously wrong at DC levels. I don't like the 10 fold drop in speaker
volume with the KAT2 installed with all other things being equal. Is this
considered "normal" or is this an indication of a problem in my KAT2? Any
thoughts what to look for if this 10 fold drop in output is not normal?

--
Cheers!

Kevin.

http://www.ve3syb.ca/ |"Nerds make the shiny things that distract
Owner of Elecraft K2 #2172 | the mouth-breathers, and that's why we're
| powerful!"
#include <disclaimer/favourite> | --Chris Hardwick
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Don Wilhelm-4

Re: Problem with KAT2?

Kevin,

There is one possibility that your 51 ohm load (measured at DC) is not a
good 51 ohm pure resistance at the frequency you were measuring. Borrow
an antenna analyzer and test your load at the frequency of operation.

If that load does measure as a 51 ohm pure resistance (X value equals
zero or very low), then you have a KAT2 problem, but if it is not a pure
resistance, then your results will be misleading because the generator
was not looking into its output impedance and the voltages and currents
being fed into the K2 will be not as expected.

That does not say that your KAT2 is not causing a problem, it *only*
says your test results may be inconclusive.

73,
Don W3FPR

On 7/10/2013 9:41 PM, Kevin Cozens wrote:

> Greetings, all.
>
> For some time I've suspected my K2 of being partially deaf (ie. not as
> sensitive as it should be). I bought an XG3 a while ago and finally
> sat down to check my K2.
>
> I set up the K2 following the XG3 manual. Volume control set to was
> slightly before 12 o'clock so I had maximum volume possible before
> there was audible distortion heard in the speaker, I used a 400Hz
> filter as I don't have a 500Hz one set up, and I removed the KAT2. I
> took measurements at the speaker terminals with the speaker disconnect
> as the volume was quite loud with the speaker connected. On 40m, S+N
> was 532mV and N was 19.2mV for a receive sensitivity of -135.7dBm
> (approximately).
>
> I installed the KAT2, tuned in to a dummy load on ANT1 that measured
> 51ohms on an ohmmeter, and set the KAT2 to calS mode. I ran the test
> again without changing any controls from the first test. The speaker
> volume was only 55mV, about 1/10th what it was without the KAT2.
> Calculated senstivity was around -128dBm.
>
> Sensitivity seems a bit lower with the KAT2. Perhaps I should have
> upped the volume setting but I thought I should try and do a more
> direct comparison to the bare K2.
>
> Center conductor of ANT1 to KAT2 output is only 1 ohm so there is
> nothing obviously wrong at DC levels. I don't like the 10 fold drop in
> speaker volume with the KAT2 installed with all other things being
> equal. Is this considered "normal" or is this an indication of a
> problem in my KAT2? Any thoughts what to look for if this 10 fold drop
> in output is not normal?
>

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Jim Brown-10

Re: Problem with KAT2?

On 7/10/2013 7:42 PM, Don Wilhelm wrote:
> There is one possibility that your 51 ohm load (measured at DC) is not
> a good 51 ohm pure resistance at the frequency you were measuring.
> Borrow an antenna analyzer and test your load at the frequency of
> operation.

There's also the simple issue of tolerance on both the resistor and the
calibration of the analyzer. A 1 ohm error in a 50 ohm resistor is
only 2%, and many dummy loads have a much wider tolerance. I recently
went searching for calibration loads for my VNA. One rated for a watt or
so with a 4% tolerance goes for hundreds of dollars.

73, Jim K9YC
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Kevin Cozens-2

Re: Problem with KAT2?

In reply to this post by Don Wilhelm-4

On 13-07-10 10:42 PM, Don Wilhelm wrote:
> There is one possibility that your 51 ohm load (measured at DC) is not a
> good 51 ohm pure resistance at the frequency you were measuring. Borrow an
> antenna analyzer and test your load at the frequency of operation.

I seem to have thrown people off by including the mention of tuning the KAT2
with a dummy load attached as it is not relevant to the problem. I stated
that I set the K2 to calS mode which is supposed to put the KAT2 in to
bypass mode according to the manual. The only effect the KAT2 should have on
the incoming signal should be minimal based on stray L/C. The 10 fold drop
in signal just doesn't seem right to me.

--
Cheers!

Kevin.

http://www.ve3syb.ca/ |"Nerds make the shiny things that distract
Owner of Elecraft K2 #2172 | the mouth-breathers, and that's why we're
| powerful!"
#include <disclaimer/favourite> | --Chris Hardwick
______________________________________________________________
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Help: http://mailman.qth.net/mmfaq.htm
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Don Wilhelm-4

Re: Problem with KAT2?

Kevin,

Your logic is flawless as long as everything in the KAT2 is working
properly. Yours apparently has some ills.
For instance, if one of the relays is not working, that could leave an
inductor or capacitor in the circuit at all times, or if you have a bad
connection somewhere in the KAT2, that would account for your problem.
I have seen repairs where a BNC jack had its ground pin vaporized
(perhaps by lightning) - tough to diagnose, but it would not work until
such things were located.
.
My suggestions are for the beginning steps of checking everything in
your external setup first. If the dummy load is not 50 ohms pure
resistive at the operating frequency, your measurements will be
misleading. If the coax has a problem, you end up with incorrect
conclusions. Overlook nothing, things of that nature have been problems
with similar behaviors before.
"Know your tools and know that they are operating properly before using
them" - quote from one of my college lab professors, and it has not
failed me yet, but has 'saved my skin' several times.

73,
Don W3FPR

On 7/12/2013 5:41 PM, Kevin Cozens wrote:

> On 13-07-10 10:42 PM, Don Wilhelm wrote:
>> There is one possibility that your 51 ohm load (measured at DC) is not a
>> good 51 ohm pure resistance at the frequency you were measuring.
>> Borrow an
>> antenna analyzer and test your load at the frequency of operation.
>
> I seem to have thrown people off by including the mention of tuning
> the KAT2 with a dummy load attached as it is not relevant to the
> problem. I stated that I set the K2 to calS mode which is supposed to
> put the KAT2 in to bypass mode according to the manual. The only
> effect the KAT2 should have on the incoming signal should be minimal
> based on stray L/C. The 10 fold drop in signal just doesn't seem right
> to me.
>