[Elecraft] Second Crystal Filter Update

[Ron D'Eau Claire]

On more than one occasion, Wayne has stated that he recommends that the
2nd Xfil Flattening Mod be done on *EVERY*  K2.

I believe it was incorporated as an integral part of the basic kit
starting with S/N 3000.

I can tell you from personal experience that it makes a BIG difference
in the audio quality of "phone" signals, even if you don't have the SSB
option and just want to listen in with the CW filters in a wide setting.


This is not something that affects only some K2's; ALL K2's up to S/N
3000 suffer from a rather steep tilt in the bandpass caused by the 2nd
Xfil. The 2nd Xfil crystals are NOT part of the 'replacement' set of
matched crystals that many ops have installed. Installing new crystals
has NO effect on this. 

The 2nd Xfil filter is fairly wide. It is wider than the SSB OPT1
filter. Its function is to roll-off high frequency noise at the output
of the i-f amplifier. In its original form, it does not have a "flat"
bandpass. Signals are attenuated far more on one side than the other.
The mod fixes that. 

You can hear it quite plainly listening to noise on the band with a wide
filter setting (>1 kHz). As you switch between CW normal and CW reverse,
you will hear the background "pitch" shift from high to low. On a phone
signal this can be very irritating as the audio will have high-frequency
emphasis on one sideband and low-frequency emphasis on the other
sideband. Since most Hams normally use one sideband or the other for SSB
on each band based on a long-standing custom, you will notice the
difference by switching from a band where lower sideband phone is the
custom (e.g. 40 meters) and one where upper SSB is the custom (e.g. 15
meters).

On Spectrogram, you will see a definite slope to the bandpass in wide
bandwidths. That is what the mod fixes. Be SURE to take the audio from
the aux speaker jack on the back, NOT the audio jack on the front. The
capacitors in the phones circuit will produce their own "slope" to the
bandpass when feeding your sound card if you use the phones jack.  

Ron AC7AC
K2 # 1289

First, I generally follow the "don't fix it if it ain't broke" rule!  I
am looking for some guidance as to if I should do this mod - because my
subjective (read, "operating") reaction is that I've not had the
problems described. However, I'm 99% cw (but I do want the SSB feature
to work right for the other 1%!)

Using Spectrograph, what should I look for to make a proper decision?

Thanks!

73, Bill K6IFF


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