Elecraft SSBCAPKT User Manual
Page 2
Elecraft
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831-662-8345
The wider bandwidth filters require that the BFO be tuned to a higher frequency for receiving USB on
the lower bands. For the 2.4 kHz bandwidth, the BFO must be able to reach approximately 4916.5 kHz and for
the 2.6 kHz bandwidth it must reach approximately 4916.8 kHz. Be sure and check your maximum BFO
frequency before attempting to use a wider filter bandwidth. To measure BFO frequency, attach your K2
frequency probe to TP2 and use CAL FCTR to read the BFO frequency. While in this mode, press BAND UP to
set the BFO to its max frequency and BAND DOWN to set it to its minimum frequency. It may be possible to
increase the maximum BFO frequency in a K2 by removing turns off of L33 or changing capacitor sizes without
raising the minimum frequency too high. Contact
if you have questions regarding changing
the maximum BFO frequency.
The following table shows the new capacitors for each reference designator (CA, CP etc.) on the KSB2 board.
Remove the old capacitors and install the new ones as indicated for your chosen bandwidth in the table. If
necessary (as noted above) also remove and replace the crystals.
After installation you will need to re-optimize your USB and LSB transmit BFO settings (BF1t) in CAL FIL.
See ‘Transmit BFO Optimization’ on page 22 of the latest KSB2 manual. (Available on our manual download
web page at
http://www.elecraft.com
)
Nominal
BW
(kHz)
Predicted
6 dB BW
(kHz)
Predicted
Loss
(dB)
Predicted
Ripple
(dB)
CA,CP
(pF)
CB,CN
(pF)
CC,CM
(pF)
CD,CL
(pF)
CE,CK
(pF)
CF,CJ
(pF)
CG,CH
(pF)
Original
2.1 8.3 3.2
100
10 33
Short
47
56
47
2.4 2.4 7.5 1.5 39
Open
27
Short
39
100
39
2.6 2.65 7.3
1.9 39 Open 27 Short 33 150 33
App. Note: Using Spectrogram to make filter measurements
Spectrogram (
http://www.visualizationsoftware.com/gram.html
) may be used to measure the response of the
K2 filters with your PC sound card. To make a measurement of a K2’s filter, use the following procedure:
1. Connect a noise generator to the antenna input of the K2 (Elecraft N-gen etc.). Using antenna noise for
this purpose will be much less accurate.
2. Connect the audio output of the K2 to the sound card input on a PC. If you use the headphone output of
the K2 for this purpose, be sure to place a 10 ohm resistor to ground to avoid rolling off the high
frequencies due to C105/C106.
3. If your K2 has a KAF2 or KDSP2 installed in it, be sure to put it in bypass mode. If left in line, the
higher audio frequencies will be attenuated and will decrease your amplitude measurement accuracy.
4. Set Spectrogram at Scan Input to 22k Sample Rate, 16 bit Resolution, Line Plot, 90 dB Scale, 1024
FFT, and Average Count to 32. Then press OK. Move the slider at the right to the top of its range.
The displayed spectrum should not exceed –30 dB or you risk overloading the sound card input.
5. Set the K2 to 7100 kHz. Turn AGC Off. Set the AF Gain to about its mid-point. Select the filter for
which you wish to measure its frequency response. Adjust the RF Gain so that the maximum level
displayed is –30 dB or less.
6. If you wish to see the KSB2 SSB filter response without it being modified by the K2’s 2nd Xtal Filter,
place 0.1uF caps across X5 and X6 on the RF Board.
7. When you have completed the measurements, return the KAF2 or KDSP2 , if present, to its normal
mode.
8. Spectrogram provides an easy way to look at the filter responses of all of the K2’s filters. You are
limited to a dynamic range of less than 60 dB. The noise fluctuations will be several dB, but you can
reduce this by increasing Average Count to 128. Additional reductions can be accomplished by
averaging several sets of readings.