On Mar 14, 2006, at 5:47 PM, Michael Jensen wrote:
The result is found in a word in the following location:
http://aprs.the-jensen-dk.net/OZ1BZJK2filter.doc
OK, here are some comments.
The first thing I notice is that the FL1 positions for LSB and USB
don't look right to me. The shape of the USB filter ought to be
exactly backwards of LSB, but yours looks the same, heavy on the low
frequencies and tapering off toward the highs. I wonder if your noise
generator has a bias toward low frequencies, or if there's some
frequency-limiting component in your measurement. Do you have the
KDSP2 installed? Did you disable it when you were taking your
measurements?
The second thing is that the FL1 positions for LSB and USB don't have
(about) the same base frequency. The "knee" of the USB curve is
around 800 Hz, but the same point in the LSB curve is about 600 Hz.
If you listen to LSB and then press CW REV to go to USB, you'd
probably notice a large change in the background noise. This is
because your sidebands don't have sufficient frequency symmetry. (It
is possible to get the LSB and USB background noise to sound ALMOST
exactly the same when properly adjusted. There's a slight shift in
"color" because of asymmetry in the bandpass fiilter)
The third thing is that both LSB and USB seem to be adjusted a bit
high -- the bandpass is a bit far from the carrier. You're going to
lose a lot of low-frequency energy in your voice -- which may be OK
if you are a very high-pitched voice. The bandpass should start to
rise around 300 Hz, with the "knee" about 500 Hz. Your FL2 settings
seems closer to being correct, and are a lot more symmetrical (see
the first two points)
The last thing I'll talk about is the other filter settings for LSB
and USB. I have 1.8 and 1.6 kHz widths programmed in to FL2 and 3 on
my K2, but frankly, I never use them. I don't like the way the
variable-bandwidth filter sounds at these wide settings, because of
it's wild asymmetry. (In fact, I have FL1 programmed for 1.0 kHz in
CW, which makes tuning the band a pretty quiet experience, even in a
contest. 1.0 kHz is about as wide as the variable-bandwidth filter
gets while staying symmetrical) Instead, I use the filtering
capability of the KDSP2 to clean up the sides of the crystal filter.
I also do RTTY and PSK31, but I've programmed the RTTY mode filters
for this mode. I don't recommend using a low frequency for either
PSK31 or RTTY, as you have programmed FL4 to pass 850 Hz. The reason
is that if your AFSK source has any harmonic energy, they'll pass
through the sideband filter and cause adjacent-frequency QRM.
Classic RTTY uses tones of 2125 and 2295 Hz. The "low tones" are 1275
and 1445 Hz. The second harmonic of 1275 is 2550 Hz, which may be
outside the K2 bandpass, depending on your filter.
The K2 makes it tough to use the classic RTTY high tones because of
limited BFO range. You may not be able to get the BFO to shift far
enough for both sidebands. (And as the BFO range increases, the BFO
step accuracy decreases) Even if you get LSB set up correctly, the K2
actually uses the USB settings on 21 MHz and above, due to the
inversion at the first mixer.
I ended up using 1500 Hz as the center frequency for RTTY (I use
tones of 1415 and 1585 Hz). This also made it easy to program the
KDSP2 for RTTY as well. I still had to modify the K2 BFO to get
sufficient range.
Hope this helps
Bill Coleman, AA4LR, PP-ASEL Mail: [EMAIL PROTECTED]
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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