[Elecraft] K2 Pre Filter

[Brian Broggie]

We are getting a lot of requests for the parts to make G3RXQ's K2 Pre 
Filter.  To facilitate this, we have made a build list with all the 
parts that we can supply for a nominal charge.  The list is based on the 
description and schematic found on G3RXQ's website.  Included are the 
crystals, caps, toroids, magnet wire, a pc board and an 8 pin 
connector.  The total cost for the parts is $29.00, plus shipping (and 
CA tax to orders inside California).  Please order by part "K2PREFILTER".

While we encourage hams like you to explore and try new circuits and 
ideas with our products, please be aware that any modifications to our 
products come at a tradeoff to the original design. Here are some 
guidelines from the owners of Elecraft and designers of the K2, Wayne 
Burdick and Eric Swartz...

1. Overall receiver gain and noise figure may degrade because the added 
crystal filter will have some loss of around 5 dB.

2. K2s with older crystals in their RF board and KSB2 filters may not 
have the exact same center frequency as the ones we're using (and 
shipping) now. The effect would be that the new filter would overlap the 
old, reducing the effective bandwidth on receive. The only way to ensure 
that this doesn't happen on older K2s would be to replace all 14 
crystals (RF board and KSB2).  A new set of 14 matched crystals can be 
ordered from Elecraft as part "K2KSB2XTLS".

3. The crystal filter does not have the pad in front of it. The Pad 
normally is either part of the KNB2 or the PCB if no KNB2 is installed. 
(The pad gives the 2N5109 amp stage before it a good return loss match.) 
It will degrade K2 IMD Dynamic range by over 10 dB (IMDDR3 and IP3) 
without this pad. Reinstalling the PCB pad will not help as it would end 
up between the two SSB xtal filters.

4. Finally, you should be aware that the KDSP2 does the same thing for 
ultimate rejection, since the regular filter more than filters enough to 
keep off freq signals from pumping the K2s AGC, allowing the DSP to 
clean up any residual blow-by.

Thanks, Wayne and Eric!

So, evaluate the data on G3RXQ's website and what we are presenting in 
this email and order accordingly.

73,
Brian Broggie - W6FVI
Elecraft Parts