[Elecraft] L31 change

[John, KI6WX]

I am the person responsible for the design change of L31 from 10uH to 12uH.
When I designed the temperature compensation circuit, I needed to get a
wider swing out of the PLL reference oscillator to make up for the reduced
voltage swing at the varactor diodes.  The easiest way to do this was to
increase the value of L31 which will pull the 12 MHz crystal about 20% more.
This worked fine with the crystals that ECS was shipping in early 2003.

Over time, the motional inductance of the ECS crystals has dropped.  In the
beginning of 2003 it was about 6.7mH, but toward the end of 2003 it is now
less than 6mH.  This increases the frequency swing of the PLL reference
oscillator, which should normally be in the range of 11 to 15 kHz.  As the
frequency range increases, it decreases the effectiveness of the temperature
compensation circuit.  This can be compensated either by changing the
resistor values in the temperature compensation circuit or reducing the
value of L31.

It is a lot easier to reduce the value of L31, so this is the approach that
has been adopted.  If a K2 shows a PLL reference frequency range greater
than 15 kHz, Elecraft will send a 10uH inductor to get it back within the
normal range.  This is done to better match the temperature compensation
circuit; changing the inductor has no other effect on the K2's performance.

-John
 KI6WX

----- Original Message ----- 
From: "Don Brown" <DolfinDon@msn.com


Hi

The newest manual still has it at 12 uH. I just bought the newest version of
the manual as well as I downloaded it. The errata sheet was included with
the manual with the note to change it to 10 uH. I am building a K2 now and I
had already installed a 12 uH, but it seems to work to spec that way. I was
just wondering if I should replace it with the 10 uH and re-run CAL PLL. I
have not heard any information on why it was changed back and if it improves
anything.

Don

  ----- Original Message ----- 
  From: Arthur Tan<mailto:ab4rl@amsat.org>
  To: Don Brown<mailto:DolfinDon@msn.com>
  Sent: Sunday, March 07, 2004 9:54 AM
  Subject: Re: [Elecraft] L31 change


  Hi Don,

  I never saw an answer to your post but I was curious about it too.  Do
  you know what the value of L31 should be now?

  73, Art AB4RL



  From Don Brown (Fri, Mar 05, 2004 at 10:32:27AM -0600):

  > Hi
  >
  > I noticed that L31 has been changed back to 10 uH from 12 uH in the
manual errata dated Feb 3 04. This is the value that it was before the temp
stability mod changed it to 12 uH. Is there any reason to change it to 10 uH
if the 12 is installed. I still have the old 10 uH I removed when I did the
mod so it would not be a problem to change it back if it makes some
improvement.
  >
  > Don Brown
  > KD5NDB