[Elecraft] Re RFC 15 miniature?

[Dave & Jeanne Robertson]

Bob,

I have just finished my K2 a few days ago and there is a lot I can relate to 
your question about RFC15.

First and most important, these chokes are very fragile and can open up 
quite easily just by flexing the leads too much.

Second I also found the size of these chokes from brown to green body is not 
that much. I chose the brown body 100 mh choke to install as it was slightly 
smaller.

To my demise I couldn't get the PLL circuit to work properly and after 
calling Elecraft they brought my attention to both RFC15 and C88.  When I 
checked I found the choke open. I replaced the choke and the receiver worked 
very well but I seem to have a PLL instability around 7180 KHZ. I was then 
advised to remove RFC 15 and replace it with a wire and be sure C88's leads 
were short. The problem was not solved.  I inserted a ferrite bead on a wire 
that took the place or RFC15 and replace C88 (60 pf) with a 100 pf capacitor 
and the problem is gone.

It is my understanding that not all the K2's have this problem but several 
must have because I got many replies concerning this problem.

Note: Before I started assembly of the K2, I checked all the chokes out with 
a digital Ohm meter to verify they were not resistors. They all measured 
very low resistance so the chokes were good before I mounted them.


Check to make sure RFC-15 is still a low resistance after you solder it in. 
and check around 7175 to 7185 KHZ for instabilities in the VCO.

Good luck and have fun
Dave KD1NA

To: elecraft at mailman.qth.net
Message-ID: <45981271.7060608 at comcast.net>
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Hi Folks,
I am building #5930 and I'm at the point of installing
C91, C88 and RFC 15 on the bottom of the rf board at U4.  The manual talks
about a miniature 100 uH choke, much smaller than the other 100 uH chokes 
and
with a tan body. I have 4 green bodied and one tan bodied 100 uH choke, but 
the tan bodied one is pretty close to the
same size as the green ones, if any thing a little bigger. I have no 
miniature chokes at all  I'm sure I can
solder it to the indicated location, but is this something I should be
concerned about? Bernie W1AZ asked this same question on the list back in 
Sept.
but I can't see where anyone answered him.

Thanks in advance,

Bob   K6GGO