On Wed, 1 Dec 2004 9:11 am, Eric Ward wrote:
I was interested in WA5ZNU's recent post about tri-state and side tone
levels on the KX1.
Eric,
My proposal requires hardware and firmware changes to the KX1 and was
somewhat telegraphic as it was aimed at Elecraft.
N6KR has I am sure already figured out a better way to accomplish my
ask...I think all of the interest in CW zero beat on the list may help
raise the priority, though. (One problem is that my proposal has some
current draw as it requires biasing...maybe there is a way around it, or
maybe there is another way to achieve the desired result of easier CW
tuning on the KX1.)
Here is my long description of the issue, with background in response to
your question.
When you have a QSO, you generally you want to be on the same frequency
as the OM. (Ok, ignore split and repeaters.) With SSB you tune about
until the OM or YL sounds good. Our brains do this fairly easily. With
CW though, you need to do a little work.
With separate transmitters and receivers, hams used to "spot" the signal
with a low-power TX and listen at the same time, and match the pitch.
Even so, after calling CQ you often had to tune up and down a few KC to
find an answer. A transceiver, though, shares enough parts internally
that there are shortcuts. Usually transceivers use the same pitch for
the CW sidetone as the transmit offset, mimicing the sound that the OM
will hear if both of you are both transmitting on the eame frequency.
(You effecively listen at an offset, and this offset is the CW tone you
hear, plus or minus the carrier frequency. That is what CW and CWR are
about. If you were receiving and transmitting on the exact same
frequency then you would hear a 0Hz tone, i.e. nothing, so the BFO
offset takes care of that.) Since the RX and TX are coupled by a fixed
offset in a transceiver, the question devolves to how to set the RX
frequency quickly and accurately.
Assuming a fixed offset (say, 600Hz default on the Elecraft KX1 and K2
rigs) then your task when tuning is to set your RX frequency such that
the OM's CW tone sounds like 600Hz. Then you will be assured of
transmitting on the same frequency as the OM.
The trick is for you how to do this.
Here are three ways:
1. Tune for loudest signal
This, coupled with a bit of pitch recognition, is what most hams do. It
is pretty easy and works unless your KX1 variable crystal filter is set
too tightly, say below 500 Hz, in which case the maximum volume point
shifts a bit and you need to use RIT to get it back to the filter
center. So it is slightly less convenient to do this on the KX1 than on
the K2, which lets you preset the BFO setting for each filter width to
accomodate for this shift.
2 Tune until you hear 600Hz audio.
2a This is easy if you have perfect pitch.
2b If not, you can use a music tuner (see my previous message).
2c Use one of the PLL-based devices that N0SS has been providing and
various folks have designed, to light up an LED.
3. Turn on the sidetone and tune until they are both the same pitch.
This works FB on the K2 and many other rigs, and you just tune until you
hear the OM "disappear" behind the sidetone or until you hear the
minimum wah-wah-wah beating sound.
Most folks use #1 or #3, but you can't use #3 on the KX1 because the KX1
mutes the sidetone during operation, and I believe it is because there
weren't enough volume levels available on the KX1 sidetone to allow it
to be adjusted to a comfortable level for TX sidetone and a louder level
for matching that 599+ OM. So, you cannot press the sidetone test menu
and tune the RX and listen for the two tones (sidetone and the OM you
are listening to) to match. This is the issue that my previous message
about the PIC chip was designed to address.
Also, the sidetone is lightly-filtered square wave, thus having strong
3rd and 5th harmonics. Some hams are tone-deaf enough to try to beat
the OM's signal at 6*3=1800Hz, or to accidently beat QRM nearby against
it. The extra levels could be used to generate more of a sine wave, by
stepping the output voltage during the sidetone generation, but the
amount of code space and effort this would take is probably not worth
it, and I suspect analog filtering with an additional capacitor would do
the same job more cheaply.
If you got this far, you have a lot of patience!
73,
Leigh WA5ZNU
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