Homebrew un-mod kit

[Gary Hvizdak]

Jean-François wrote:

... I was inspired by un-mod kit that was posted on the reflector a few
weeks ago....

I did mine. So when I want to remove a module to isolate a problem, or
simply to make more space to work in the K2 when trying some
experimentation, simply replace the module removed with ready homemade
jumpers !!!


Hi Jean-François,

    As a follow up to your post this morning, did you used the correct value
for the resistor on the output leg of your UN-KNB2 header?  This resistor
should be 560 ohms.  If you built yours using the information in our
preliminary User's Guide, or the recently posted / updated schematics now on
our homepage, then you would have used the correct value.

    However, if you followed the instructions in Mark Dulecy's original
article (hosted by W5BIG), then you may have used a 470 ohm resistor in
error.  Whereas your receiver will still function, the wrong resistor value
results in a 5 db attenuator with a somewhat lower output impedance than the
intended 150 ohms.  It is possible that the resulting impedance mismatch
could cause some intermodulation distortion in your receiver.

    See the following links for more on this subject ...

 
http://www.ac6rm.net/mailarchive/html/elecraft-list/2005-04/msg00148.html

        http://home.cfl.rr.com/garyhvizdak/KI4GGX/unpcbs.htm#Guide

        http://groups.yahoo.com/group/unpcbs/

    With regard to the second link, check out our updated UN-KNB2 schematic
by scrolling down to the fifth diagram.  It shows the KNB2 supplied
replacement 2.7 k ohm RF-R88 which is in parallel with the output leg
resistor on your header.  This explains why the output resistor should be
560 rather than 470 ohms.

    Very soon we will replace the five individual diagrams on our homepage
with a single hybrid schematic / block diagram showing a "big picture" view
of the K2, and the relationship between each of the un-modules.  This
diagram will be included in our updated User's Guide which will be released
in just a few days.

    Please note that our homepage is continually being updated, so it is
likely that second link (above) will not be supported indefinitely.  One
link that will be, is the third link to our Yahoo group unpcbs website.

73,
Gary, KI4GGX
K2 #4067

P.S. To all of you who have already placed an order for our kit, we are on
track to begin shipping by Monday August 22nd and possibly even sooner.  If
you are one of the few who pre-ordered but haven't yet followed up with your
payment, please do so by August 15th to ensure that you can still get a kit
from our first production run.

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[JEAN-FRANCOIS MENARD-3]

Ooops.

I think I make a mistake ont his one. I read in the instruction that  
if we need to remove the KNB2 later, we should put back the jumper  
between pin 1 and 6 of J12. That's it.

I will revise all links you send me to properly build the KNB2 jumpers.

Remember that my jumpers are not as long as the connector inside the  
K2, the reason for the red dot on each jumper.

II will modifiy this one right now...

Thanks for your remark !!

73

Le 05-08-10 à 13:56, Gary Hvizdak a écrit :

>
>     However, if you followed the instructions in Mark Dulecy's  
> original
> article (hosted by W5BIG), then you may have used a 470 ohm  
> resistor in
> error.  Whereas your receiver will still function, the wrong  
> resistor value
> results in a 5 db attenuator with a somewhat lower output impedance  
> than the
> intended 150 ohms.  It is possible that the resulting impedance  
> mismatch
> could cause some intermodulation distortion in your receiver.
>
>     See the following links for more on this subject ...
>

======

Jean-François Ménard / VA2VYZ

======


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