[Elecraft] Data mode filters

[Charles Greene]

At 02:04 AM 1/23/2002 +0000, Samuel Ramac wrote:
>Can anyone comment on the proper way of setting the data mode filters?

Samuel,

It depends upon whether you have the KAF2 audio filter installed and plan 
to use it or not.  I find it useful.  If so, you should align all the 
crystal filters using the KAF2 frequency as center frequency.  Always align 
FL1 to OP1 for best look at the entire audio band and to eliminate the 
"TX/RX frequency offset" you get when switching in any filter other than 
OP1.  Also do you plan to use CAT control using the KIO2?  A couple of the 
programs that each have several digital modes are MixW and Zakanaka, and 
both have an "align" macro that changes the audio frequency to your 
selected audio frequency usually the center frequency of the K2 filters and 
at the same time, change your K2 dial setting a corresponding amount so you 
still transmit the same frequency.  Use Tom Hammond's procedure using
Spectrogram and a noise source for alignment which is on the K2 website.  I 
have my filters set at as follows: FL1=OP1, FL2=1200hz, FL3=600Hz, FL4=150 
Hz with the same center frequency set the same as KAF2.

Having said this, there's some merit to having two filters with slightly 
offset frequencies.  Concerning QRM, if it is right on you and is strong, 
no filter is going to help.  But usually it is a little one side or the 
other of your frequency.  So you might want to set FL3 and FL4 both at 
150hz wide and set  FL3 with a center frequency of 850 hz  and 750 for FL4 
so you can get rid of QRM either low or high around a center frequency of 
800 hz, for example.  It's somewhat like Eric's idea of setting the SSB 
filters to give high pass, low pass and band pass.  In this case,  the band 
pass right on your operating frequency can be the KAF2 but the nice thing 
is you can use KAF2 in conjunction with either FL3 or FL4.

I only tried this briefly and have not explored it thoroughly before taking 
down my K2 for mods.  You might try aligning your CW filters the same way.

If you don't have KAF2 or don't plan to use it, it is a good idea to align 
the filters with a center frequency for all in the range of 1200 to 1400 
Hz. That way, you stay away from operating at the lower audio frequencies 
as they are prone to have audio harmonics in your transmit filter 
bandpass.  It isn't possible to use a common frequency for the center 
frequency  for all filters much above 1400 Hz.

GL,


73, Chas, W1CG