[Elecraft] [KX3] Auto-spot, tuning aids, and the arcane history of CW pitch-matching

Howard Hoyt hhoyt at mebtel.net
Tue Jan 22 15:27:03 EST 2019 

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_photog at 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 n6kr at elecraft.com 
>> <mailto:n6kr at elecraft.com> [KX3] <KX3-noreply at yahoogroups.com 
>> <mailto:KX3-noreply at 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
>>
>
> __._,_.___
> ------------------------------------------------------------------------
> Posted by: Mel Snyder <ct_digital_photog at yahoo.com>
> ------------------------------------------------------------------------
> Reply via web post 
> <https://groups.yahoo.com/neo/groups/KX3/conversations/messages/65003;_ylc=X3oDMTJyOGZ0NTd0BF9TAzk3MzU5NzE0BGdycElkAzc0NTIwOTQ3BGdycHNwSWQDMTcwNTA2MzEwOARtc2dJZAM2NTAwMwRzZWMDZnRyBHNsawNycGx5BHN0aW1lAzE1NDgxODMyMDE-?act=reply&messageNum=65003> 
> 	• 	Reply to sender 
> <mailto:ct_digital_photog at yahoo.com?subject=Re%3A%20%5BKX3%5D%20Auto-spot%2C%20tuning%20aids%2C%20and%20the%20arcane%20history%20of%20CW%20pitch-matching> 
> 	• 	Reply to group 
> <mailto:KX3 at yahoogroups.com?subject=Re%3A%20%5BKX3%5D%20Auto-spot%2C%20tuning%20aids%2C%20and%20the%20arcane%20history%20of%20CW%20pitch-matching> 
> 	• 	Start a New Topic 
> <https://groups.yahoo.com/neo/groups/KX3/conversations/newtopic;_ylc=X3oDMTJmZW5odm5zBF9TAzk3MzU5NzE0BGdycElkAzc0NTIwOTQ3BGdycHNwSWQDMTcwNTA2MzEwOARzZWMDZnRyBHNsawNudHBjBHN0aW1lAzE1NDgxODMyMDE-> 
> 	• 	Messages in this topic 
> <https://groups.yahoo.com/neo/groups/KX3/conversations/topics/65002;_ylc=X3oDMTM3ajhnNzRwBF9TAzk3MzU5NzE0BGdycElkAzc0NTIwOTQ3BGdycHNwSWQDMTcwNTA2MzEwOARtc2dJZAM2NTAwMwRzZWMDZnRyBHNsawN2dHBjBHN0aW1lAzE1NDgxODMyMDEEdHBjSWQDNjUwMDI-> 
> (2)
>
> ------------------------------------------------------------------------
> Have you tried the highest rated email app? <https://yho.com/1wwmgg>
> With 4.5 stars in iTunes, the Yahoo Mail app is the highest rated 
> email app on the market. What are you waiting for? Now you can access 
> all your inboxes (Gmail, Outlook, AOL and more) in one place. Never 
> delete an email again with 1000GB of free cloud storage.
> ------------------------------------------------------------------------
> Visit Your Group 
> <https://groups.yahoo.com/neo/groups/KX3/info;_ylc=X3oDMTJmcDMzNTc0BF9TAzk3MzU5NzE0BGdycElkAzc0NTIwOTQ3BGdycHNwSWQDMTcwNTA2MzEwOARzZWMDdnRsBHNsawN2Z2hwBHN0aW1lAzE1NDgxODMyMDE-> 
>
>
> Yahoo! Groups 
> <https://groups.yahoo.com/neo;_ylc=X3oDMTJlaGZwbzdlBF9TAzk3NDc2NTkwBGdycElkAzc0NTIwOTQ3BGdycHNwSWQDMTcwNTA2MzEwOARzZWMDZnRyBHNsawNnZnAEc3RpbWUDMTU0ODE4MzIwMQ--> 
>
> • Privacy 
> <https://info.yahoo.com/privacy/us/yahoo/groups/details.html> • 
> Unsubscribe 
> <mailto:KX3-unsubscribe at yahoogroups.com?subject=Unsubscribe> • Terms 
> of Use <https://info.yahoo.com/legal/us/yahoo/utos/terms/>
>
> SPONSORED LINKS
> .
>
> __,_._,___

More information about the Elecraft mailing list