Posted by
Guy, K2AV on
Feb 15, 2009; 8:57pm
URL: http://elecraft.85.s1.nabble.com/K3-Beta-firmware-rev-2-80-Improvements-to-AFSK-A-DATA-A-SSB-AM-FM-DVR-tp2305650p2331419.html
My MP has those bumps also, and it's full of INRAD's.
With only a minor amount of Spectrogram investigation in my K3, I see a 2db
variation across the passband in the 2.7 filter. It is easily seen on RX,
particularly if one lies about how wide it is to put the DSP out at 4.0
whilst being confined only by the 2.7 roofing filter. Further the 2.7
filters on my 2 RX K3's have nearly identical response, and the order of the
bumps reverses perfectly when I go from DATA to DATA REV. Whether that
would be more predictable with a 2.8 8 pole filter would depend. I don't
own one so cannot comment. (The shape of the two 2.7's are closer than the
shapes on the two 1.8's.)
Therefore, without TX EQ set only for DATA mode, power will vary up and down
depending on the filter when using a fixed segment audio width of the band
and letting the PSK program pick the transmit audio tone.
I note that me ears cannot detect changes in the mid-passband. What I hear
when shifting RX passband is the drop or addition of lows and highs as the
passband *skirts* move. This is to enforce that for SSB, the passband
ripple cannot be heard.
The data mode transmit exposes what the ear cannot hear only because
operators apparently look for variability less than half a db. Given the
characteristics of some amplifier tubes and the sudden onset of grid
saturation and high current, etc, the desire to control power is
understandable.
Given the circumstances, would seem to be an interesting idea to have a data
mode only TX eq that flattens out the filter *and properly flips* for data
rev mode. It would remain to be seen, though whether introduction of the
equalization does anything negative to transmitted IMD.
Approaching it from the other direction, Wayne & Co seem reluctant to
embrace any automatic leveling of data mode transmitted power. It would seem
on the surface that data is far more predictable than SSB, that a quick
attack, slow release and clamped-across-RX-state auto gain adjustment would
work well. There may be a lot more to it than that, but this too seems a
good idea.
73, Guy.
----- Original Message -----
From: "Kok Chen" <
[hidden email]>
To: "elecraft list" <
[hidden email]>
Sent: Sunday, February 15, 2009 12:31 PM
Subject: Re: [Elecraft] K3 Beta firmware rev. 2.82
> On Feb 15, 2009, at 2/15 8:58 AM, Guy Olinger, K2AV wrote:
>
>> Taking the DATA A readings below at face value, the more than 2 db
>> bump
>> around 1000 Hz is rather startling. I'm not sure what could cause
>> that, but
>> at least to me that seems to be screaming for an explanation.
>> There's an
>> old fireman's adage "never go past fire" to keep from being trapped
>> by fire
>> closing around behind.
>
> While I agree that a 2 dB bump is really, really bad for us guys who
> use frequency-agile digital transmission, this phenomenon is not
> restricted to just the K3.
>
> The FT-1000MP has a similar 3 dB peak when you select PKT (i.e.,
> AFSK); and, like the K3, the rig is flat when using voice SSB
> modes. In the case of the FT-1000MP, it appears to be a
> deliberately designed peaking -- the peak is "centered" near the AFSK
> tone pair that you have selected to use.
>
> To see the FT-1000MP's variability, you can look at the following URL
>
>
http://homepage.mac.com/chen/w7ay/cocoaModem/UsersManual/> UsersManual.html#equalizer
>
> Scroll below the two control panels and you will see the graphical
> display of the variability. (In this program, you enter the measured
> power in that second column on the left, and the program splines the
> "curve" to produce the power correction that is applied to the
> transmitted signal when you "click on the waterfall.")
>
> 73
> Chen, W7AY
>
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