Sunday, January 8, 2017

My TenTec Eagle sounds better than my Elecraft KX3

Your eardrums will thank you

Coming back to the hobby in 2015 I re-entered as a CW / QRP operator and I searched for a good QRP radio.  The Elecraft KX3 certainly qualified and it has been a great radio to use, especially when portable.

Elecraft KX3 -- stellar radio for portable QRP operations

But a few months after getting my KX3 an old TenTec Century/21 found it's way onto my desk and through numerous blog entries you may note that for some reason I kept gravitating to use it rather than my KX3 when I operated from the shack, even though the KX3 beats the old C21 technically in absolutely EVERY regard.  I just enjoyed operating CW with the old radio more than the KX3. I couldn't explain why.

Fast forward to late March of 2016.  I purchased a used TenTec Eagle from my friend AA4XX and began using it as my primary radio when I wasn't portable.   Here again the KX3 trumps the Eagle in nearly every technical aspect and offers dozens more features.  I just kept gravitating to use the TenTec radios rather than the Elecraft.

I used the my KX3 for Field Day in 2016 and after I packed up and brought it home the KX3 stayed in my backpack and only came out for portable outings.  It did not go back on my desk.  The KX3 cried little electronic tears while the Eagle gloated...

Ten-Tec Eagle -- compact / simple HF transceiver

Why no love for the KX3?

Time passed, and over the new year break I got to thinking about what I missed about having my KX3 on the desk; like its RX/IQ output for HDSDR and the ease working DX splits using it's dual watch capability and it's integration to logging applications like the ability to trigger CW macros from my logging software.  The list of "nice-stuff" goes on and on since the KX3 contains multiple kitchen sinks...  So I re-organized my desk to make room for the KX3 again and operated with it exclusively over the past few days...

I was getting ear fatigue and my ears rang in the evenings.  This was not the sort of ringing in the New Year that I wanted. I had been previously operating the same amount with the Eagle over the past month without the earaches.  Something was amiss.

Had I finally discovered why I keep going back to my TenTec radios?

Audio, Audio, Audio

So over time, even when I switched back and forth between radios there was a subtle "ouch" occurring when I used the KX3.  I enjoy CW and digging out weak signals can be fun... or it can be painful.  I guess when I sat down to use a radio and my hand hovered between the "Oh-so-feature-rich" KX3 and the "Nice-personality" Eagle my brain was saying "choose the nice personality" you're happier that way.

But there was a underlying reality to the choice I was making.

Just the facts mam

I used an audio frequency analyzer to capture audio from each radio by sandwiching the microphone in my headphones.  It hears what I would hear.  And the graphs tell a tale.

Below is one graph for each radio.  The RED graph line in each chart is the averaged "peaked" frequency output audio during the same QSO.  Ignore the green line as it was just the instantaneous  audio at the time I froze the display between takes.  The CW sidetone on each radio is set to 620Hz.

I re-ran this capture for each radio a few times during a lengthy ragchew between two stations.  The signal strength was around S5-S7.  It wasn't a strong signal which is typical of what I work, especially as the Solar cycle winds down.

I tried the captures with and without noise reduction on each radio.  The RF was rolled off as evenly as I could determine for each and both were set to a DSP filter bandwidth of approximately 400Hz.  Both radios were using the same antenna and everything was as similar as I make it.  RCVR EQ was set flat for the KX3.

Elecraft KX3 CW audio (ignore green graph line)
Ten-Tec Eagle CW audio (ignore green graph line)

The CW audio output from each of the two radios is distinctive

KX3 audio demonstrates
shoulder noise
Eagle has clean audio
There's clearly a CW signal peak around 620Hz in each radio but the KX3 shows a significant shoulder of audio just 9dB down from the peak below the center frequency 

Whereas the Eagle has a clear peak presenting a narrow tone range at the sidetone pitch with narrow shoulders down to the filter width.

Confirmation of my subjective tests

When I saw this I literally said "Aha!"   

This confirmed what my ears and my subconcious had been telling me.  The KX3 is more fatiguing to listen to than the Eagle because it presents more noise in the audio or at least a wider audio signal given the same DSP filter setting.  I've always remarked about my TenTec radios that their CW seemed to float above the noise.  I believe it's related to the cleaner audio filtering. The TenTec Eagle just has cleaner audio out of the box. It has no audio adjustments beyond AF and NR, no menus for fine tuning.  My old TenTec Century/21 sounds the same when using its 500Hz selectivity setting. 

In my opinion Ten-Tec just got CW right.

Yes, I have tried using the KX3 RCVR EQ settings to reduce that lower frequency noise and the problem IMO is that the EQ is more for SSB audio.  I think the Q for each setting is too broad and when I try to reduce the low frequency noise IMO it just makes the audio sound mushy.  I just can't get as "clean" sounding CW tone out of the Elecraft as I can the Ten-Tec.

OK, "sound" is a subjective thing.  No two people will hear the same thing the same way and frequencies that bother me may not bother you, but it seems pretty clear from the graphs that the CW audio from the KX3 doesn't match the Eagle.


Admittedly, my test involved a very small sample size of one radio from each manufacturer.  It's just that I'd put the KX3 back on the desk after a many month absence and my ringing ears got me to investigate the cause a bit more scientifically.  

I will continue to use the KX3 for portable ops because it is a great self-contained radio and when I work portable I usually operate for much shorter periods so the audio doesn't become an issue.

Man, I hope Ten-Tec can come back from the grave. They sure made some fine radios for CW operators.

That's all for now...

So lower your power and raise your expectations

Richard AA4OO


  1. Hi Richard,
    Have you tried the KX3 DSP AFX? See page 20 of the KX3 manual: "If you have stereo headphones or stereo external
    speakers, you can take advantage of the KX3’s DSP
    audio effects (AFX). These create an illusion of
    greater acoustic “space,” resulting in a lessfatiguing
    receiver sound and in some cases better
    copy of weak signals.
    MENU:AFX MD is used to select the desired AFX
    setting. Available selections include OFF, DELAY
    (simulated stereo), and PITCH (which “maps”
    signals from left to right according to pitch)."

    I use this feature exclusively with my KX3 and always wear good headphones (radiosport RS20S)
    Bob - W2TAC

    1. Hello Bob. Yes I leave AFX turned on in "pitch" mode. I've tried the other modes but prefer "pitch" to "delay". See the other comments and it seems to be a consensus that most folks prefer the "CW audio" from their other rigs. I even had a fellow email a very detailed analysis of the KX3 audio (and K3 audio) and he found similar issues with the audio chain.

  2. Thank you for your excellent look at KX3 cw audio vs Ten Tec cw audio. I, too, purchased a KX3/PX3 combo ... but prefer operating with my old Ten Tex 516 Argonaut V... which I still have. Also, too many bells-and-whistles on the Elecraft for this old 76 year old operator. After reading your comments -- I guess I need to sell my KX3/PX3 and put the TT Argonaut V back on the table. Thanks -- Randy - K4LJA

  3. I have noticed the same thing with my KX3 and other radios. The KX3 has one of the best receivers of any radio I have as far as sensitivity and selectivity in use goes. But the audio on CW is poor. The SSB is OK but not great. I also own Yaesu, Icom and Kenwood radios all of which are better at CW audio purity. I have used TenTec radios and they have better CW Audio. The TenTec Orion II radio is still commanding high used prices among contesters. I have used a K3 at the same time and it is vastly better. Probably part of why DXpeditions and Contesters love the K3. I have used the KX3 for QRP contesting and it is not great for CW. My ears also hurt after hours of use on CW. The new Flex radios have good CW audio but are not really portable nor lightweight for DXPeditions. The Eagle is a very nicely designed and well performing radio that suffers from the lack of marketing that TenTec had become known for. I too hope the new owners do something with TenTec.

  4. The word is Ten-Tec is making Eagles right now. I mainly use CW as well and I'll validate your statement when comparing the Eagle to a TS-590s. The 590 is much nicer to operate in every way, but the Eagle deals with the noise so very much better. I also have an Argonaut 515 and a Jupiter. The Eagle has a noticeably quieter receiver than the Jupiter, but the Jupiter is still very quiet. I never use noise reduction on the Jupiter or Eagle, but NR1 is on all the time on the 590. I don't remember the audio specs for the Jupiter, but the Eagle is around 1% while the 590 has about 10% audio distortion. I bought my Eagle from Ten-Tec and made sure it had all the CW filters installed. The 590 came standard with all filtering for comparison sake. Tim KE4KE

  5. I too have noticed a "cleaner", less fatiguing audio out of my Tentec rigs ... I have owned two KX3's and an Eagle and an Argo VI... I currently have a KX3 and an Argo VI... When it comes to feature/$, you can't beat the KX3... But when you work predominantly CW, the audio out of the Tentec rigs makes a huge difference in clarity and less ear fatigue. I did testing with my computer, software, and a sound card... I examined the audio in the time domain and in the frequency domain... Your article clearly shows what the differences are in the time domain... If you look at the frequency domain you see the harmonic "noise" difference between the two. It is significant. Rob Sherwood of Sherwood Engineering has done extensive testing on the K3 and in a Dayton Hamfest talk several years ago pointed out the harmonic content in the K3 and ear fatigue....It takes a little digging but you can find the presentation on his website... I saw similar results in the KX3... If you examine the literature on the K3S... you will see the mention of an improved audio chain. Elecraft appears to listening... John N4KV