[Elecraft] K2: Filter and BFO Settings for RTTY

[Don Wilhelm]

  Jon,

The default BFO frequencies for the RTTY filter set will not be optimum 
for your K2, you will have to optimize them the same as you must do for 
SSB and CW if you are to achieve decent filters.  A note of interest - 
due to the varactors that were supplied with K2s over the past year, the 
wide (greater than 1.00) filter widths are much greater than that 
indicated by the K2 display.  The "cure" is to use Spectrogram (or other 
audio spectrum analyzer) to measure the actual width of the filters for 
SSB and possibly for RTTY.

I suggest you use Spectrogram to set the filters.  RTTY is not much 
different than either the SSB or the CW filters.  See part 3 of the K2 
Dial Calibration article on my website www.w3fpr.com for information 
about using Spectrogram for filter alignment.

Set FL1 to the OP1 filter since the OP1 filter will be always be used 
for transmit.  Set the BFOs for FL1  the same as you have for SSB - yes, 
RTTY should be the same as LSB and RTTYr should be the same as USB.  The 
low frequency -3dB corner of the filter passband should ce located at 
300 Hz.   That will provide you with a full width filter for use with 
most PSK31 applications.

I usually set FL2 at a 1.00 kHz bandwidth, FL3 at 0.70, and FL4 at 
0.40.  You may vary those if you prefer different widths.
Whatever your chosen widths, set the BFOs for those filters to center on 
1000 Hz.  Use Spectrogram to see the filter passband and where it is 
positioned.

Those settings will give you narrow filters for PSK31 when there are 
strong signals nearby and good narrow filters for RTTY (set the RTTY 
application to use 915 Hz as the mark frequency).  When using the narrow 
filters, tune the desired signal to the vicinity of 1000 Hz on the 
waterfall display using the K2 VFO.

If you have the KDSP2 installed, you must change the DSP RTTY filter AF2 
through AF4 center frequencies to center on 1000 Hz to agree with the IF 
filter frequencies.  Leave the AF1 setting at LO PASS.

On the RTTY power question, that recommendation you referenced is for 
the base K2 without the KPA100.  With the KPA100, you can operate 
continuously at 35 watts, or for 1 to 2 minute periods at 70 watts with 
no harm.

73,
Don W3FPR


On 10/1/2010 11:20 PM, Jon Perelstein wrote:
> I'm having a problem with the BFO settings for RTTY.  The outputs on the
> different filters are centered at significantly different places in the
> waterfall.  For R-Reverse, they're as follows:
>
> Filter      Width            Center on Waterfall
> -------      --------             ---------------------------
> FL1        2.5 KHz            1.1 KHz
> FL2        1.3 KHz            2.0 KHz
> FL3        0.6 KHz            1.6 KHz
> FL4        0.3 KHz            1.1 KHz
>
>
> Thus, a station centered at 1.0 KHz on my waterfall when using FL1 is not
> visible in the waterfall when using FL2 or FL3, but is again visible when using
> FL4.
>
> My understanding from the main K2 manual is that R-Normal is LSB, and R-Reverse
> is USB.  Based on that, I used the KSB2 LSB BFO settings for R-Normal and the
> KSB2 USB BFO settings for R-Reverse.  The settings for R-Reverse were:
>
> Filter  Width   BFO
> -------  --------    ---------
> FL1    Op1     4916.3
> FL2    1.40     4916.1
> FL3    0.70     4915.5
> FL4    0.20     4914.7
>
> These R-Reverse BFO settings are the same as I have set with USB.
>
> By comparison, for USB, using the same BFO settings, I get all four filters
> centered at about 1.1 KHz.  A station at 1.0 KHz on my waterfall is visible on
> FL1, FL2, FL3, and FL4.
>
> I took the measurements with a straight stereo cable from the headphone out to
> the line in on my computer.  I also re-did them with a SignaLink USB and got the
> same results.  Similarly, I tried both fldigi and DM-780 as my software and got
> the same results.
>
> What am I doing wrong?  I didn't find anything in either the K2 Operating Guide
> or the KSB2 Operating Guide for any BFO calibrations related  to the RTTY mode.
>
> By the way, I re-did the KPA-100 bias adjustment on my rig and it was pretty
> close to correct to begin with.  I did notice that the K2 Operating Guide
> recommends against transmitting at more than 10w for more than 1-2 minutes at a
> time for continuous duty cycle RTTY/data modes.
>
> As always, thanks for your help,
>
> Jon
> KB1QBZ
>