A quick reply since I'm on my way out ... I'll look more in depth
later.
I am concerned about the audio waveform generated by your WaveNode
device. I see peaks to 128 +/- and dips to 64 +/- with a significant
amount of asymmetry. The asymmetry would make me wonder if there is
not some clipping (bad transistor) in the LPA, KPA3 or in the WaveNode
device itself.
Perhaps the only way to know for sure would be to use a second receiver
and look at the *recovered* audio.
> Mine is using the more steep-sided 8 pole filter and has the new
> synthesizer board and the latest firmware updates.
I'm also using the 2.8 KHz filter, new synthesizer and most recent
production firmware for the KSYN3A. Note there was no change in DSP
code to support the KSYN3A so I would not expect the firmware to be
an issue.
> PEP/average (power) ratio is the (voltage) crest factor squared. It
> is hard to get the effective(average) value of the wave by eyeball.
> But you could take the min/max and divide by 2.
No - Crest factor is 10*log(Peak/Average) in terms of power and
20*log(Peak/Average) in terms of voltage. Since the modulation is
single sine waves (not a complex waveform) the average (RMS) is 0.7
x peak. The lowest voltage I see is 0.8V, the highest is slightly
less than 1.0 (call it 0.98). Using the average of 0.98 and 0.80
(there should be about as many of each tone) we get 20Log(.98/.89)
or 0.84 dB which is a reasonable match to the Peak to Average ratio
reported by the LP-100.
I tried backing down the line level to where no ALC action was
visible but there are still "dips".
Can't do that. With less than 4 bars of ALC the DSP code will try
to "follow level" and may make things worse depending on the time
constant.
73,
... Joe, W4TV
On 2015-05-29 10:04 AM, Ken wrote:
Good job Joe.
My understanding is that the monitor output of the K3 should be a
fair representation of what another receiver would see - minus the
effects of propagation and any external power amplifier. But it is
just really something convenient to use (as evidenced by the
quickness of your response).
From a subjective/eyeball view of the waveform - we can see your K3
is doing a better job than mine. I wonder what the differences
are?
Mine is using the more steep-sided 8 pole filter and has the new
synthesizer board and the latest firmware updates.
PEP/average (power) ratio is the (voltage) crest factor squared. It
is hard to get the effective(average) value of the wave by eyeball.
But you could take the min/max and divide by 2. On your graph, the
max is 1.0 and I see two points where it dips to about 0.75 (at 0.5
ms and 11.5 ms). That gives a crest factor of 1.14 and a PEP/average
power ratio of 1.3. In decibels that is 2.28 dB which is similar to
what a filter passband ripple might be. Anyway, it's better that
what I am seeing.
Some other artifacts are visible on the 2 kHz segments. For example,
at 2 ms there is a cycle that is shorter than the cycles on either
side; at about 11.5 ms there is a cycle that is taller than the ones
on either side. Some of this is probably in the actual signal as
generated. Looking back at my "no-radio" graph I can see a small
fluctuation in the level of a 2 kHz segment where there are 9 cycles
in a row...
In terms of RF sample, my power meter provides a scope function right
off the RF detector. I have included two pictures of this. These are
several overlaid scans snatched from a CQ message. The power readings
of my wattmeter must come from squaring this voltage measurement. It
has pretty high frequency response (0.1 ms features can easily be
seen - this is a bit much if used for the power meter readings
imho).
One of the things I tried yesterday was some "pre-emphasis" using a
software sound equalizer on my audio. The tone levels at the monitor
output are closer in level, to each other, with the equalizer
inserted. But there are still ups and downs in the envelope of
monitored waveform. In terms of power, the graph with the
equalization "on" shows fewer upward peaks in the power level (second
file attached). I have not tried with the linear amplifier on yet,
but it looks like the PEP/Average ratio has been reduced a bit with
the equalizer on (from 1.8 to 1.6) so I guess I will keep it.
The "dips" in power are present in both graphs. Perhaps that is
inherent in the modulation? I don't know how to measure audio power
at the input to the radio.... if the signal from the sound card does
not have these dips, then the radio must be doing it somehow. I tried
backing down the line level to where no ALC action was visible but
there are still "dips".
Later Ken
-----Original Message----- From: Joe Subich, W4TV
[mailto:[email protected]] Sent: Friday, May 29, 2015 8:35 AM To:
Ken_ke2n; [email protected] Subject: Re: [Elecraft] K3 FSK
power transients
I don't know what a *monitor* output proves since it is *not* an RF
sample. However, I have attached a Spectrum Lab Time Domain capture
as requested. Notice the crest factor is well less than 1 dB.
73,
... Joe, W4TV
On 2015-05-29 7:45 AM, Ken_ke2n via Elecraft wrote:
Joe - I am using data mode with "DATA A" selected. (This mode
uses the SSB filter and turns off equalization and compression. But
of course the ALC is "on").
What would be really helpful is if you would download a copy of
Spectrum Lab and run the monitor output of your K3 through it while
transmitting FSK441. Then we would both have a common point of
comparison (eliminating the vagaries of power meter PEP
algorithms).
http://www.qsl.net/dl4yhf/spectra1.html
The time domain scope is under the "components" tab. The default
settings with the initial install will work fine, although you
will have to select your input device (audio card) if it is not the
system default. That is under the Options/Audio settings tab.
Regards
Ken
From: Joe Subich, W4TV-4 [via Elecraft]
[mailto:[email protected]] Sent: Thursday,
May 28, 2015 10:27 PM To: Ken_ke2n Subject: Re: K3 FSK power
transients
Are you using DATA A or trying to force FSK-442 through the K3 in
USB with the TX_EQ enabled? Again, I see *NO* frequency effects
(crest factor < 0.1 dB at 30, 60 and 100 W) with my K3 when using
DATA A and the LINE In.
Also make sure your sound card does not have any "enhancements"
enabled.
73,
... Joe, W4TV
On 2015-05-28 9:53 PM, Ken_ke2n via Elecraft wrote:
2015-05-27_20_48_16-Time_domain_scope_no_radio.gif
<http://elecraft.365791.n2.nabble.com/file/n7603596/2015-05-27_20_48_1
6-Time
_domain_scope_no_radio.gif>
2015-05-27_19_07_20-Time_domain_scope.gif
<http://elecraft.365791.n2.nabble.com/file/n7603596/2015-05-27_19_07_2
0-Time
_domain_scope.gif>
I hope this works.
I have shown, in two attached images, the tones being produced
by WSJT FSK441 and then the monitor output of the K3. You can
see a substantial drop off of the low frequency tones and some
kind of additional modulation
of the overall envelope (most noticeable with the higher
frequency tone,
but
I think it affects all). Not sure if this is ALC action or
something else.
Anyway, the K3 makes a bit of a mess out of some otherwise
nice-looking tones.
Ken
----- 73 Ken
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