I did a simulation also this evening (after off line discussion with N1AL) and
can confirm what Alan has said.
A 1 dB amplitude modulation only increases the keyclick noise floor by 0.5 dB 2
kHz away from the signal. It took a 6 dB difference in amplitude to raise the
keyclicks 2 kHz away by
After properly performing the TX Gain calibrations, I don't
see any significant difference between tones (K3 s/n 477):
Mark Space Difference
at 100W100.50 100.40 -0.004 dB
80W 80.70 79.50 -0.06 dB
60W 60.90 60.00
The effect of the skew (difference in amplitude of the mark and space
tones) is to cause an undesired amplitude modulation in addition to the
desired frequency modulation of the FSK. If the skew is due to a
constant slope in the frequency response, then the shape of the
modulation is the same for
I decided that rather than depend on a hand-waving argument I would go
ahead and do a Mathcad simulation to calculate the effect of 1 dB of
tone skew (unequal mark and space tone amplitudes) on the transmitted
FSK spectrum. Basically, I found that it made no significant
difference.
A PDF of the
I know this has been discussed before and the fix is on the list
but after 24 hours of watching the watt meter bounce on the two
fsk tones, is the solution getting closer?
Mark n2qt
(using 5 pole filters which I understand accentuates this)
I may be all wet here, but I seem to think this is understandable.
FSK uses two tones, one is the MARK and one is SPACE. There are only
two states, you will have one or the other tones on the air all the
time. One tone is the base, and if the signal is un-modulated, it
would be
I also noticed this, and it was quite pronounced. In my case, the higher
output tone resulted in higher output than the pwr control setting. It
seemed the lower output tone produced the output the K3 was set for, but
the higher output tone was about 10% higher. I was operating FSK. When I
Mark and space switch between two frequencies 170 Hz apart. There should be
no change in amplitude between mark and space.
With my K3 the difference between mark and space is about 1 dB. Too much.
Elecraft is aware of the problem, and the sooner it gets fixed the better.
Side note. There were
Hi Hank,
The difference in amplitude is due to the small amount of ripple in
the crystal filter. The effect on transmission bandwidth is
negligible, and it's also extremely unlikely to affect copy.
Nonetheless, we're planning to provide a way to tune out the difference.
73,
Wayne
N6KR
On
5 pole 2.7 kHz SSB filters will also have a little more natural ripple
than the 8 pole 2.8s.
73,
Eric
On 1/10/2011 3:35 PM, Wayne Burdick wrote:
Hi Hank,
The difference in amplitude is due to the small amount of ripple in
the crystal filter. The effect on transmission bandwidth is
On Jan 10, 2011, at 3:35 PM, Wayne Burdick wrote:
The effect on transmission bandwidth is negligible, and it's also extremely
unlikely to affect copy.
It depends.
Consider an RTTY demodulator that includes automatic threshold correction
(ATC). It will treat such a signal as one with 1 dB
On Jan 10, 2011, at 3:35 PM, Wayne Burdick wrote:
The effect on transmission bandwidth is negligible, and it's also extremely
unlikely to affect copy.
Hank W6SX had written to ask me for a rough guess of transmission bandwidth
when there is a 1 dB difference in level between mark and
12 matches
Mail list logo
