Hi Mel,
I experienced the same reading Wayne's highly informative post!!
I started off in 1970 with a homebrew 6L6/807 xtal xmtr with maybe 12
xtals and a Hallicrafters S-38 which gave me hundreds of mesmerizing
hours in my parents basement. That rig gave me my first huge shock as
well, so it is indeed memorable. What idiot thought it was a good idea
to put the 500 V B+ connection on an unguarded terminal strip on the
back panel? Wait, that was me...
Still, I thought I was in heaven until my high school club bought a
Drake R-4B/T-4XB which blew me away and I ended up owning a pair in the
early 1980s and still love the Drake twins to this day. However they
have been gathering dust since I got my K3, which is the best rig
overall I have used to date, and love my KX3 in the car and on travel.
Although it works well, I don't use Auto Spot is because it scrambles my
feeble brain as to where I am tuned; I am just not used to a rig
changing frequency without me intentionally doing it. Perhaps this is a
mental artifact of heavy contesting, where I am loathe to leave a good
RUN frequency, indeed I often lock VFO A so I don't accidentally bump
the VFO A knob.
Cheers & 73,
Howie / WA4PSC
On 1/22/2019 1:51 PM, Mel Snyder ct_digital_pho...@yahoo.com [KX3] wrote:
Wow, this is *great,* Wayne! Thanks. I am away from home, but will be
interested to test the auto-spot when I get home.
A wonderful trip down memory lane. While you were swapping crystals
with your HW-16, I was a few years ahead of you as KN3AFW, swapping
them first into my home-brew 6AG7-6L6 rig, and then, a borrowed Eico 720.
I still own a lovely Johnson Ranger II, and an SB-301 Heathkit
receiver with the original 500Hz filter, the combination of which
require your explained tuning the VFO to the note of the received
signal. But both are on my list to sell, along with my HW-9 and
FT-707, inasmuch with my KX3 for good band conditions and my
inherited/restored TS-940S when they’re poor, they are all surplus
space-consumers.
Every time I turn on my KX3, I am in awe of how far ham radio has
progressed in the past 61 years since I was licensed. Like taking a
cell call on my Apple Watch, it’s beyond anything I dreamed of as a
kid back then. So glad I stopped by the Elecraft exhibit at the 2014
Hartford ARRL convention, and was taken by the enthusiasm of KX3 users
that gathered there - and decided to join the cult.
Mel, W3PYF
On Jan 22, 2019, at 12:09 AM, Wayne Burdick n...@elecraft.com
<mailto:n...@elecraft.com> [KX3] <kx3-nore...@yahoogroups.com
<mailto:kx3-nore...@yahoogroups.com>> wrote:
Elecraft's auto-spot and CWT features -- available on the
K3/K3S/KX2/KX3 -- are very useful tools for CW operators, especially
those not experienced in pitch-matching. Here's a bit of history on
where these features came from and how they work.
CW Spotting History
When a station finishes a CQ in CW mode, the operator faces the
challenge of copying someone who's calling back. Callers may be weak
or obscured by QRM; the op can usually deal with both problems by
narrowing the filter passband. However, callers may also be off
frequency. A calling station may be using a wide filter passband
themselves, not attempting to carefully match their VFO frequency to
that of the CQing station. The result may be no QSO, even when
propagation is excellent.
In the Days of Yore, a frequency offset between stations didn't
always matter. Sometimes both stations used crystal-controlled
transmitters, so operators had to patient tune around after calling CQ.
As a 14-year-old novice I embraced this operating style for a year or
so, armed with a dozen or so crusty FT-243 crystals for my Heath
HW-16. I nearly wore out the socket swapping them in and out. After
calling CQ, it was not unusual to find a caller 30 or more kHz away!
(Away from "where" was a poorly answered question, as my
Hallicrafters receiver dial wasn't exactly digital.)
Fortunately I soon acquired an outboard VFO, a life-changing addition
to my station. Jealous friends doubled up on their paper routes to
pay for their own. Girls suddenly paid more attention to me.
These days virtually everyone has a VFO, along with the expectation
that they won't have to tune theirs very far, if at all, to tune you
in. Not only that, they're stable and well calibrated, not like the
beasts we had to skillfully tame. Progress!
Manual Spotting (SPOT switch)
Once I had a VFO I quickly learned to do *manual* pitch matching.
Older rigs did't provide a way to do that explicitly, so you'd
improvise. Basically, you had to coerce a very weak signal out of
your own transmitter, say by turning on only the driver, then tune
the transmit VFO until you could hear your signal on your own
receiver -- superimposed on the calling station, at the same pitch.
This is what we call spotting.
Of course spotting is a lot more convenient these days, as many rigs
include a SPOT switch. This function is easy for a modern transceiver
designer to add, because the radio's firmware is quite capable of
turning on only the CW sidetone without transmitting.
That is the purpose of the SPOT switch on all Elecraft transceivers.
Tap SPOT, and you'll hear your sidetone pitch. Most people can do a
good job of adjusting the VFO such that the CQing station's pitch
matches that of the SPOT tone. This ensures that when you call them,
you'll be close to their own frequency.
Tuning Aids: Filtering (APF), PLL (NE567), and Spectral (CWT)
Since not everyone has an inherent musical ear, various
hardware-enhanced means of tuning in CW signals have been developed.
The simplest method is to just narrow your receiver passband so much
that, if you can hear a station calling CQ at all, you're guaranteed
to be "right on top of him." This assumes that your transceiver
enforces alignment between its transmit and receive pitch...true of
all Elecraft gear.
Narrow filtering has gone through decades of evolution. Some filters
were based on op-amps (active filters), while others were based on LC
filtering, conscripting humongous toroidal cores scavenged from telco
equipment. I acquired my stash of these from a haphazard mound of old
switching racks, decaying in an abandoned aircraft hanger on the
Bermuda U.S. Navy base. (That irresistible junk pile was also a
mother load of TO5 transistors, multi-pound electrolytic capacitors,
and tetanus, but that's another story.) Typically the toroids were 88
millihenries -- a huge value for a high-Q inductor, permitting
resonance in the low audio range.
Later, such filters migrated to digital signal processing, in the
form of switched-capacitor ICs or DSPs. You can still buy these
switched-capacitor chips, like the MF10, from various sources. It's
instructive to roll your own tunable filter, just for fun.
Whether passive or active, the goal of filtering is typically to
achieve a narrow passband, say 250 Hz or less. With DSP, nearly
perfect filters with "brick wall" passbands can be created. But these
have the disadvantage of ringing like a bell when pinged by a CW
signal or noise, making copy difficult.
One solution incorporated into the K-line and KX-line is the Audio
Peaking Filter (APF), which provides a 30-Hz bandwidth at -3 dB, but
broad skirts, preventing ringing from occurring. As our customers
will attest, APF works like magic on weak signals obscured by noise.
Another forerunner to DSP techniques was the audio phase-locked-loop,
using inexpensive ICs like the legendary LM567. When locked on a
signal that matched its center frequency, the circuit would turn on
an LED, alerting the operator that the VFO was now properly tuned.
With the DSPs in our K-line and KX-line radios, we can provide a much
more powerful tool: CWT, or "CW Tuning Aid." When enabled, CWT turns
the upper portion of the rig's S-meter into something of a mini
spectrum analyzer. The pitch of the strongest signal in the passband
is analyzed by the DSP, then represented as a single segment of the
bar graph. For CWT-enhanced manual spotting, the operator simply
tunes the VFO slowly until the center CWT segment is flashing along
with the keyed signal.
Manual tuning with CWT can also be used in FSK-D and PSK-D modes as
described in the owner's manual..
Closing the Loop: Auto-Spotting (SPOT + CWT)
The Elecraft K3/K3S/KX2/KX3 take CW tuning another step forward by
providing a way to *automatically* retune the VFO frequency to match
that of a received signal. How does this work?
When CWT is turned on, firmware treats the SPOT switch as AUTO-SPOT.
The DSP analyzes the incoming signal, and with a bit of processing,
determines its exact audio pitch. From there all that's needed is a
bit of math to offset the VFO to match this pitch to the CW sidetone.
There's another subtlety, though. Since a CW signal is generally
being keyed on and off, the CWT algorithm has to ensure that it
doesn't "take off," chasing a signal that's not there. To avoid this,
we keep track of the energy in the passband, and slew the VFO
incrementally over an average of about 0.5 second, moving only when
the target signal is present.
How to Use Auto-Spot
I encourage you to give the auto-spot feature a try. It's best to
start with a fairly narrow passband, say 400-600 Hz; narrower if
there's a lot of QRM. Find a signal, turn on CWT, then tap SPOT to
tune it in. A second tap of SPOT may get even closer, especially if
there's a lot of band noise.
Auto-spot can also be used in Elecraft's PSK-D mode, i.e. for
PSK31/PSK63. As with CW mode, just turn on CWT, tune in a prospective
signal, and tap SPOT. Since PSK auto-decoding requires very accurate
tuning, it's best to set the filter bandwidth to 50 Hz, then let
auto-spot dial things in down to the last 2 or 3 Hz. If you have text
decode turned on, you should start seeing text characters scroll by
after auto-tuning has completed. Tapping a second time or fine-tuning
the VFO a bit in 1 Hz steps may improve copy.
73,
Wayne
N6KR
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