K3 FSK D Mode: possible Bug?
Posted by N6JW on Sep 26, 2010; 10:55am
URL: http://elecraft.85.s1.nabble.com/K3-FSK-D-Mode-possible-Bug-tp5571721.html
As indicated in my previous email, the K3 works well in FSK D mode.
However, I think I may have discovered a (rare) bug in the firmware,
that has been 'bugging' me for a long time! If I am right, I believe this
issue could have been there from the beginning. I have K3 #936 and I
noticed the problem early on (but had no idea what was happening).
I would very much appreciate it if others could check it out and perhaps
confirm what I am experiencing; thus ruling out the likelihood that it is
unique to my rig/situation.
Reading my previous email (unfortunately, also rather long!) would
help in setting the context for my use of the FSK D mode in what follows.
Briefly stated, here is the problem: While in FSK D data mode,
if one is sending a "chained" stored message, upon returning to
receive, the audio frequency is "offset" by (I believe) the selected
Mark pitch frequency (e.g. 915hz or 1275 hz). The 'offset' remains,
but some commands can reset things to normal.
Here are some important notes and observations:
1. The TX frequency does not change and is always correct! I did not
realize this until recently. I originally thought that something was
wrong on my side and that I was off frequency, because the station
would come back to me on a 'different' frequency. This led to many
busted QSO's and undoubted frustration on the part of those I was
trying to contact. Having the P3 helped me figure out what was
happening.
2. As far as I can tell, the problem only occurs after using 'chained'
memories (e.g. M1-M4) for sending. For example, tapping M1
(programed with my callsign + IM) twice will cause the problem. But
NOT if it is only tapped once. Likewise, tapping M1 then M2 (e.g.
stored exchange + IM) while M1 is still running (thus chaining them
together) WILL cause the problem. If the K3 returns to receive
between sending each memory, the problem will not occur. Of
course, in practice the problem appeared intermittent, and I had no
good idea of what was happening until receipt of the P3 and extensive
work with FSK D this weekend.
3. The IM (..--) prosign is NOT causing the problem. Chained
messages without it, will still cause the 'offset'.
4. This is NOT RFI related in any way. The problem can be reliably
reproduced with TX in test mode and no RF output at all.
5. The problem can be reliably reset (restored to normal) by tapping
the A/B button twice. This switches the K3 to VFO B and then back to
VFO A. While running FSK D mode, I have VFO A & B set to the same
filter, width, etc. The only difference between VFO A & B would be
frequency. Upon testing, the following buttons will reset the problem:
A/B, REV, PITCH, DATA MD. The list might not be complete.
6. One can see the audio 'offset' quite clearly on the P3 (6 khz scan).
With the passband set to 300 hz (DSP; 500 hz roofing filter), I get
good text copy with the right-hand (Mark?) tone set right on the
P3's center frequency mark. When the problem occurs the tones
are offset in the passband (the audio goes higher, at least on 20m).
7. Other possible menu settings (e.g. CONFIG menu: FSK POL = 1) or
ALT Mode Button (for sideband reverse) that might have an effect
have been checked and are OK. The RIT or XIT is NOT on. Split
mode is not in effect (the Sub-RX is off), and the yellow Delta LED
is not lit.
8. When the problem is in effect, the built-in decoder will not work (i.e.
copy correctly), and the RX frequency is noticeably different, until the
frequency has been re-adjusted either with the VFO knob (thus moving
both the RX and TX) or with just the RIT. Checking the RIT offset, leads
me to believe that the offset is about the same as the PITCH setting for
the Mark frequency.
9. As far as I can tell, the problem is not related to any recent firmware
version, or the addition of the P3. I distinctly remember the problem as
an intermittent from my early days with the K3. I started using the
memories with stored info from the start of experimenting with FSK D.
It is very likely that I 'chained' memories together early on in doing so.
At the time I just put it down to not knowing enough about RTTY.
Finally, here are the particulars of my setup:
K3/100 #936; with Sub-RX; ATU; DVR; I/O & Audio boards; original
unmodified DSP board.
P3 #597
Currently running K3 firmware, 4.05 DSP 2.60; P3 vr.0.32
If this can be reproduced, corroborated, and confirmed,
is there a prize for the one who finds the most 'ancient'
bug still in the system? :)
73
John
N6JW