K3 Harmonic Distortion
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G'day,
Perhaps someone suitably qualified and tooled up might like to try and replicate and comment upon the view presented by Rob Sherwood at the Dayton convention. According to him the K3 audio amp stage has serious shortcomings. Regards, Mike VP8NO ----- Original Message ----- From: "Jim Brown" <[hidden email]> To: "Elecraft List" <[hidden email]> Sent: Monday, September 01, 2008 11:45 PM Subject: Re: [Elecraft] K3 Harmonic Distortion | On Mon, 01 Sep 2008 18:45:36 -0400, Jack Smith wrote: | | >I've found that the LIN OUT port has typical third harmonic levels | >around -45 dB from the fundamental, with the LIN OUT level set at 10, | >the factory default. The headphone port, under the same conditions, | will | >show the third harmonic down about 70 dB or so at levels appropriate | for | >my Sony high sensitivity headphones. Cranking the audio level up will | >cause higher distortion on the headphone port, but only at levels that | >are impossible to listen to as they are so loud as to be unbearable. | | >I've also seen some non-harmonic artifacts, particularly when very | >strong signals are pumped into the K3's antenna port. | | Jack, | | I assembled the first of the following reports in June after getting my | first K3 running, and sent privately to the guys at Elecraft. That's why | the new default LIN OUT gain is 10 rather than 50. It's also why there's | a note in the new manual about LIN OUT level. | | http://audiosystemsgroup.com/K3FilterStudy.pdf | | A month or two later, I prepared a report on filters in my Yaesu | FT1000MPs (mostly Inrads) and my K3. | | http://audiosystemsgroup.com/FilterTestNotes.pdf | | This second report describes the test methodology use for the earlier | work, which uses rather a high quality pro audio FFT system (EASERA | SysTun). | | My measurements compare pretty well with yours, but use a very different | measurement method that is not dependent on the distortion of a signal | generator. My method also makes the IM stick out like a sore thumb! | | As you can see from the first graph in the first pdf, distortion at the | headphone output (the black curve) is 0.02% 2nd harmonic, 0.014% 3rd | harmonic, and IM on the order of 0.1%. This was done at about 1 VRMS, | and was done after the LIN OUT measurements without changing levels. | | The only difference between Joe's measurements and mine is that my | analyzer has a bit more resolution, but we're all getting the same | result. The headphone out is VERY VERY VERY good, but the LiN Out starts | producing distortion at a rather low level. BUT, that low level is quite | sufficient to drive a sound card. | | As to the setting of 3 or 10. The distortion is mainly caused by the | output transformer, and distortion in an output transformer increases | rapidly at low frequencies when it approaches its amplitude limit. The | data output is MOSTLY intended for decoding digital signals, especially | RTTY, and the distortion at 2 kHz is a LOT less than at 400 Hz for the | same levels. But distortion is excited not only from signal, but from | noise, and impulse noise can get pretty high. | | Taking all of this into account, I run my LIN OUT gain at 3, and | recommend that setting. | | 73, | | Jim K9YC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Berni G0IDA
>Anyway, the "noise/distortion" is still there coming out of the
headphone socket. Berni, this is a technical group and as such we need hard data and not subjective descriptions of what you hear coming out of the headphone jack. I don't doubt that you are hearing something. There is very little I can do with your description however. Please download spectrum analysis software such as Spectrum Laboratory which will give you a way to actually show us some hard data. This is freeware but very capable and will allow you to show us something real. The HRD DM780 is a great tool but it isn't designed to analyze harmonic distortion as you can't measure signal amplitude levels. Here is the download link for spectrum labs. http://freenet-homepage.de/dl4yhf/spectra1.html#download Also, you need to run the input to your sound card from your headphone out jack and not line out if you want to discuss artifacts that you are hearing. If you want to discuss artifacts you are seeing on a waterfall for data modes then run the input to your sound card from the line out. So far your discussion is about what you are hearing but your description of waterfall effects is with line out. These are apples and oranges. Mike Scott - AE6WA Tarzana, CA (DM04 / near LA) K3-100 #508/ KX1 #1311 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: K3 Harmonic Distortion
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In reply to this post by Jack Smith-6
It would be nice to see this problem with the the K3IO board addressed
at some point. It may be, as Jim K9YC has hinted, related to core saturation from low frequency components that could attenuated before reaching the board. Or it may be that the transformers that fit in the space are as big as they can be, and a third-party outboard audio amplifier and isolation board is necessary, bypassing the transformers in the K3. But whatever the solution is, I'm looking forward to it, as using PSK with a waterfall display on the K3 requires me to ride the AGC, LIN OUT, and filters in a way that I didn't on the K2. Leigh/WA5ZNU > I've found that the LIN OUT port has typical third harmonic levels > around -45 dB from the fundamental, with the LIN OUT level set at 10, > the factory default. The headphone port, under the same conditions, > will show the third harmonic down about 70 dB or so at levels > appropriate for my Sony high sensitivity headphones. Cranking the > audio level up will cause higher distortion on the headphone port, but > only at levels that are impossible to listen to as they are so loud as > to be unbearable. > > I've also seen some non-harmonic artifacts, particularly when very > strong signals are pumped into the K3's antenna port. > > Jack K8ZOA > > Julian, G4ILO wrote: >> I think it was me who used the term "ghost" signals when referring to >> the >> harmonically related CW traces I could see on the CW Skimmer display. I >> probably would have been completely unaware of it if I had never >> tried this >> program. It was only obvious as I was listening to CW with a narrow >> filter >> and the "ghost" traces were appearing in the part of the waterfall >> that you >> would be expect to be dark because it was outside of the passband. I >> would >> agree with the suggestion that the harmonics are at a low level >> relative to >> the main signal because they are masked by band noise when you open the >> filter up. I don't think there is much risk of calling someone on the >> third >> harmonic by mistake. I don't know what the voltage level of the line >> output >> is but the traces disappear if you turn the level down to 2, which >> unfortunately is too low for most sound card programs. >> >> I don't know if those same harmonics are present on the speaker or >> headphone >> outputs, as distinct from the computer audio feed. I can only say that I >> find the K3 audio exceptionally pleasant to listen to. I much prefer >> it to >> the K2, or the FT-817, which are the only other radios I have. The only >> other radio I have had that sounded as clean and low-distortion as >> the K3 >> was an IC-756PRO that I had many years ago. >> >> If the harmonics are down by the kind of amounts that others have >> measured >> then the distortion figure is still within the specification for what >> after >> all is not meant to be an audiophile quality hi-fi output stage. >> >> ----- >> Julian, G4ILO. K2 #392 K3 #222. >> http://www.g4ilo.com/ G4ILO's Shack http://www.ham-directory.com/ Ham >> Directory http://www.g4ilo.com/kcomm.html KComm for Elecraft K2 >> and K3 > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Working through the K3's schematic this morning, it seems that both the
headphone output port and the LIN OUT port are driven by similar devices, a Texas Instruments DAC with integrated headphone amplifier. (Two DACs, one for LIN OUT and one for headphones and speaker output.) As near as I can see from tracing from one sheet to another, U29, a TLV320ACC23 DAC with integrated headphone amplifier drives the TTC-108 LIN OUT transformers directly. Headphone and speaker audio, in contrast, are derived from a second TLV320 DAC driving a LM4950 amplifier for speaker output and an LM4811 for headphone output. I've ordered a couple of TTC-108 transformers today and will run some experiments with them over the next week or so. I've looked at similar transformers developed for modem and telephone line coupling, but not the TTC-108 specifically, when trying to find a cheaper output transformer to use with the Softrock Lite receivers. There, the emphasis was more on high frequency response, up to 100 KHz, but distortion was also a major issue. The solution of choice in my opinion for the Softrock receivers turns out to be a MILSPEC Triad transformer, SP-70, with excellent frequency response and quite low distortion. In single lot prices, an SD-70 costs about four times as much as a TTC-108. Jack Leigh L. Klotz, Jr WA5ZNU wrote: > It would be nice to see this problem with the the K3IO board addressed > at some point. It may be, as Jim K9YC has hinted, related to core > saturation from low frequency components that could attenuated before > reaching the board. Or it may be that the transformers that fit in > the space are as big as they can be, and a third-party outboard audio > amplifier and isolation board is necessary, bypassing the transformers > in the K3. > But whatever the solution is, I'm looking forward to it, as using PSK > with a waterfall display on the K3 requires me to ride the AGC, LIN > OUT, and filters in a way that I didn't on the K2. > > Leigh/WA5ZNU > >> I've found that the LIN OUT port has typical third harmonic levels >> around -45 dB from the fundamental, with the LIN OUT level set at 10, >> the factory default. The headphone port, under the same conditions, >> will show the third harmonic down about 70 dB or so at levels >> appropriate for my Sony high sensitivity headphones. Cranking the >> audio level up will cause higher distortion on the headphone port, >> but only at levels that are impossible to listen to as they are so >> loud as to be unbearable. >> >> I've also seen some non-harmonic artifacts, particularly when very >> strong signals are pumped into the K3's antenna port. >> >> Jack K8ZOA >> >> Julian, G4ILO wrote: >>> I think it was me who used the term "ghost" signals when referring >>> to the >>> harmonically related CW traces I could see on the CW Skimmer display. I >>> probably would have been completely unaware of it if I had never >>> tried this >>> program. It was only obvious as I was listening to CW with a narrow >>> filter >>> and the "ghost" traces were appearing in the part of the waterfall >>> that you >>> would be expect to be dark because it was outside of the passband. I >>> would >>> agree with the suggestion that the harmonics are at a low level >>> relative to >>> the main signal because they are masked by band noise when you open the >>> filter up. I don't think there is much risk of calling someone on >>> the third >>> harmonic by mistake. I don't know what the voltage level of the line >>> output >>> is but the traces disappear if you turn the level down to 2, which >>> unfortunately is too low for most sound card programs. >>> >>> I don't know if those same harmonics are present on the speaker or >>> headphone >>> outputs, as distinct from the computer audio feed. I can only say >>> that I >>> find the K3 audio exceptionally pleasant to listen to. I much prefer >>> it to >>> the K2, or the FT-817, which are the only other radios I have. The only >>> other radio I have had that sounded as clean and low-distortion as >>> the K3 >>> was an IC-756PRO that I had many years ago. >>> >>> If the harmonics are down by the kind of amounts that others have >>> measured >>> then the distortion figure is still within the specification for >>> what after >>> all is not meant to be an audiophile quality hi-fi output stage. >>> >>> ----- >>> Julian, G4ILO. K2 #392 K3 #222. >>> http://www.g4ilo.com/ G4ILO's Shack http://www.ham-directory.com/ Ham >>> Directory http://www.g4ilo.com/kcomm.html KComm for Elecraft K2 >>> and K3 >> > > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Jack
I have seen postings on the main reflector recommending settings as low as 3 to avoid distortion products that are being attributed to transformer distortion. This did not really make sense to me, especially at such low levels where consumer sound cards tend to get non-linear and nasty. I took a look at the specifications for the TTC-108 audio transformer used in the line out of the K3 Nominally it's specified as having an operating level of -45dBm to +7dBm THD is specified at 0.5% @0dBm 300Hz to 3.5 Khz @ 0dBm this would make the transformer related harmonics worst case at -46dB relative to the fundamental I did some measurements with an s9 CW signal zero beat at various pitch settings I used an old copy of SMAART pro that I have from my Sound engineering days. the sound card is a delta44 Lin = 100 Pitch 300 pitch 550 pitch 800 DR3 47.3dB 51.4dB 54dB Lin = 50 Pitch 300 Pitch 550 Pitch 800 DR3 43.1dB 47.6dB 50.6dB Lin = 10 Pitch 300 Pitch 550 Pitch 800 DR3 35dB 39.7dB 43.1dB Lin = 5 Pitch 300 Pitch 550 Pitch 800 DR3 31.9dB 37.7dB 42.7dB Lin = 3 Pitch 300 Pitch 550 Pitch 800 DR3 31dB 40.3db 47.6dB DR3 is the Dynamic range between the fundamental and the 3rd harmonic (the most dominant harmonic by a wide margin) I did a quick look at 5th and 7th orders too, again the best performance here was found with LIN = 100 LIN = 100 is an output level of approximately 700mv for an S9 CW sig on my K3 The Harmonic distortion does not increase with higher line out levels, it actually improves. This does not appear to be a transformer saturation issue With lin = 100 users will see a ghost on the waterfall and may risk over-driving some consumer sound cards. lowering LIN may get rid of the visible ghost by reducing the 3rd Harmonic to below the waterfall threshold (& perhaps the sound card input noise floor ) but also reduces the overall usable dynamic range 73 Brendan EI6IZ -- Don‘t complain. Nobody will understand. Or care. And certainly don‘t try to fix the situation yourself. It‘s dangerous. Leave it to a highly untrained, unqualified, expendable professional. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Jack Smith-6
On Tue, 02 Sep 2008 11:53:23 -0400, Jack Smith wrote:
>The solution of choice in my opinion for the >Softrock receivers turns out to be a MILSPEC Triad transformer, SP-70, >with excellent frequency response and quite low distortion. In single >lot prices, an SD-70 costs about four times as much as a TTC-108. You should look at Jensen (www.jensen-transformers.com) and Lundahl (www.lundahl.se) which are pretty much THE standard in the pro audio world. Jensen is well known for excellent applicactions engineering support, with real engineers (not salesmen) answering the questions. Bill Whitlock, the owner, is a Fellow of the AES. The guys who work for him are also very good. Both companies make "good, better, and best" products, depending on the needs of the installation, but Jensen's best is significantly better than Lundahl's best. The old line mfrs like Triad and UTC are dead meat in the world of pro audio. BTW -- there's another problem with the transformers in the K3 -- they're unshielded, so they pick up whatever magnetic fields surround them. Like the fields from the power transformer(s) for your power amp! This can be either a small problem (hum about -35dB carrier) or hum that regenerates to full transmit power! I have the small problem, my neighbor has the big problem. If you have this problem, you can hear the hum with nothing connected to the line input (if the line input is on). IMO, the transformers need to go away. My Ham Interfacing tutorial shows convincingly why they are completely un-necessary if all the gear in your station is properly bonded together. Leigh Klotz said, >It may be, as Jim K9YC has hinted, related to core saturation The most important difference between the Line Out and the Headphone Out IS the transformer and the 600 ohm resistors, and it IS the cause of the much higher distortion on the Line Out. BTW -- 600 ohms has not been good engineering practice in audio for at least 40 years (since the days of TUBES). Modern audio stages have LOW source impedances and HIGH input impedances. 73, Jim Brown K9YC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Brendan Minish
Brendan:
You might wish to look at the measurements I made, with LIN OUT settings from 2 to 100. There's an animated GIF that steps through the LIN OUT settings so you can see the effect. The data was taken at 600 Hz. http://www.cliftonlaboratories.com/elecraft_k3_receive_audio.htm about half way down the page Like you, I see a relatively constant 45 dB or so offset between the fundamental and 3rd harmonic for LIN OUT values of 10 and over. However, setting the LIN OUT at 2 results in quite a bit better odd order harmonic suppression, on the order of nearly 70 dB. By the time LIN OUT is set to 5, however, the odd order suppression is reduced to a bit more than 60 dB. At LIN OUT = 10, it's 45 dB or so where it stays at all values of LIN OUT tested between 10 and 100. (For some reason, the 2nd harmonic pops up at certain settings, but not others higher or lower, but that's not of immediate concern.) There's a related issue with the AGC. The audio output is proportional to RF signal level, as the AGC has a slope to it. Hence, even though the LIN OUT might be set to, say, 2, the actual audio level and hence the distortion, will vary as the RF signal level changes. The degree of audio level variation with RF input changes depends on how the user has set the K3's AGC slope and intercept parameters. I'll make the measurements on a couple of TTC-108 parts when they arrive as a matter of trying to understand where the harmonic distortion arises. To duplicate the K3's audio chain, I'll drive the TTC-108s from an op-amp so that it will be hit with a low Z source, instead of the standard audio generators available to me, with 50 or 600 ohm output Z. Jack Brendan Minish wrote: > Jack > > I have seen postings on the main reflector recommending settings as low > as 3 to avoid distortion products that are being attributed to > transformer distortion. This did not really make sense to me, especially > at such low levels where consumer sound cards tend to get non-linear and > nasty. > > I took a look at the specifications for the TTC-108 audio transformer > used in the line out of the K3 > > Nominally it's specified as having an operating level of -45dBm to > +7dBm > THD is specified at 0.5% @0dBm 300Hz to 3.5 Khz @ 0dBm > this would make the transformer related harmonics worst case at -46dB > relative to the fundamental > > I did some measurements with an s9 CW signal zero beat at various pitch > settings > I used an old copy of SMAART pro that I have from my Sound engineering > days. the sound card is a delta44 > > Lin = 100 Pitch 300 pitch 550 pitch 800 > DR3 47.3dB 51.4dB 54dB > > Lin = 50 Pitch 300 Pitch 550 Pitch 800 > DR3 43.1dB 47.6dB 50.6dB > > Lin = 10 Pitch 300 Pitch 550 Pitch 800 > DR3 35dB 39.7dB 43.1dB > > Lin = 5 Pitch 300 Pitch 550 Pitch 800 > DR3 31.9dB 37.7dB 42.7dB > > Lin = 3 Pitch 300 Pitch 550 Pitch 800 > DR3 31dB 40.3db 47.6dB > > DR3 is the Dynamic range between the fundamental and the 3rd harmonic > (the most dominant harmonic by a wide margin) > > I did a quick look at 5th and 7th orders too, again the best performance > here was found with LIN = 100 > > LIN = 100 is an output level of approximately 700mv for an S9 CW sig on > my K3 > > The Harmonic distortion does not increase with higher line out levels, > it actually improves. This does not appear to be a transformer > saturation issue > > With lin = 100 users will see a ghost on the waterfall and may risk > over-driving some consumer sound cards. lowering LIN may get rid of the > visible ghost by reducing the 3rd Harmonic to below the waterfall > threshold (& perhaps the sound card input noise floor ) but also reduces > the overall usable dynamic range > > > 73 > Brendan EI6IZ > > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Jack Smith-6
There are three distinct audio channels in the K3, and they all have
slightly different characteristics. LINE OUT This has its own digital-to-analog converter (DAC) and is transformer isolated. PHONES This shares a DAC with the speaker channel, but has its own amplifier and isolating resistors to help reduce the impact of plugging in two sets of headphones. SPEAKER This shares a DAC with the headphones, but has its own stereo amplifier. We are aware of the discussions regarding harmonic distortion and IMD. While it is easy to just say, "The radio meets specs!" (it does :-) we are looking at ways to improve the performance of the entire audio system. 73, Lyle KK7P _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Jack Smith-6
On Tue, 2008-09-02 at 12:28 -0400, Jack Smith wrote:
> > However, setting the LIN OUT at 2 results in quite a bit better odd > order harmonic suppression, on the order of nearly 70 dB. This might be due to simply running out of usable bits to represent accurately the harmonics at the low end of the K3 internal D to A side of things. > By the time > LIN OUT is set to 5, however, the odd order suppression is reduced to a > bit more than 60 dB. At LIN OUT = 10, it's 45 dB or so where it stays at > all values of LIN OUT tested between 10 and 100. The issue I have with this is that even with a quiet 24Bit semi Pro card but the time you go to Lin = 2 you are some 40dB down on Full scale input on the sound card assuming Consumer line level Leaving aside all other noise sources this only leaves you with 40 to 50dB or so usable dynamic range. On the other hand if you run near flat out your wanted signal (along with the unwanted harmonics ..) are way above soundcard input amp & mixer noise, induced magnetic noise due to the unscreened transformer, Noise picked up internally in the PC etc. This is why I suspect that realworld results will in fact be better at the hotter levels. Visible waterfall ghosts can be resolved by setting your waterfall dynamic range and sensitivity appropriately 73 Brendan EI6IZ -- Don‘t complain. Nobody will understand. Or care. And certainly don‘t try to fix the situation yourself. It‘s dangerous. Leave it to a highly untrained, unqualified, expendable professional. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: K3 Harmonic Distortion
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In reply to this post by KK7P
Date: Tue, 02 Sep 2008 09:34:31 -0700
From: Lyle Johnson <[hidden email]> There are three distinct audio channels in the K3, and they all have slightly different characteristics. LINE OUT This has its own digital-to-analog converter (DAC) and is transformer isolated. PHONES This shares a DAC with the speaker channel, but has its own amplifier and isolating resistors to help reduce the impact of plugging in two sets of headphones. SPEAKER This shares a DAC with the headphones, but has its own stereo amplifier. We are aware of the discussions regarding harmonic distortion and IMD. While it is easy to just say, "The radio meets specs!" (it does :-) we are looking at ways to improve the performance of the entire audio system. And you have lots of help, too!!! I'm sure sorting it all out is sometimes difficult, but.... 73, doug _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Jack Smith-6
There are three distinct stereo audio channels in the K3, and they all
have slightly different characteristics. LINE OUT This has its own digital-to-analog converter (DAC) and is transformer isolated. PHONES This shares a DAC with the speaker channel, but has its own amplifier and isolating resistors to help reduce the impact of plugging in two sets of headphones. SPEAKER This shares a DAC with the headphones, but has its own stereo amplifier. We are aware of the discussions regarding harmonic distortion in these audio paths. While it is easy to just say, "The radio meets specs!" (and it does :-) we are looking at ways to improve the performance of the entire audio system. 73, Lyle KK7P _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Jack Smith-6
I find virtually the same results here using 50uV RF from an
Elecraft signal source, and measuring using Wave Spectra. An offset of 43 to 45dB, and below LIN OUT = 5 the harmonics drop rapidly. 73 Stewart G3RXQ On Tue, 02 Sep 2008 12:28:02 -0400, Jack Smith wrote: > Brendan: > > You might wish to look at the measurements I made, with LIN OUT settings > from 2 to 100. There's an animated GIF that steps through the LIN OUT > settings so you can see the effect. The data was taken at 600 Hz. > http://www.cliftonlaboratories.com/elecraft_k3_receive_audio.htm about > half way down the page > > Like you, I see a relatively constant 45 dB or so offset between the > fundamental and 3rd harmonic for LIN OUT values of 10 and over. > > However, setting the LIN OUT at 2 results in quite a bit better odd > order harmonic suppression, on the order of nearly 70 dB. By the time > LIN OUT is set to 5, however, the odd order suppression is reduced to a > bit more than 60 dB. At LIN OUT = 10, it's 45 dB or so where it stays at > all values of LIN OUT tested between 10 and 100. > > (For some reason, the 2nd harmonic pops up at certain settings, but not > others higher or lower, but that's not of immediate concern.) > > There's a related issue with the AGC. The audio output is proportional > to RF signal level, as the AGC has a slope to it. Hence, even though the > LIN OUT might be set to, say, 2, the actual audio level and hence the > distortion, will vary as the RF signal level changes. The degree of > audio level variation with RF input changes depends on how the user has > set the K3's AGC slope and intercept parameters. > > I'll make the measurements on a couple of TTC-108 parts when they > arrive as a matter of trying to understand where the harmonic distortion > arises. To duplicate the K3's audio chain, I'll drive the TTC-108s from > an op-amp so that it will be hit with a low Z source, instead of the > standard audio generators available to me, with 50 or 600 ohm output Z. > > Jack > > > Brendan Minish wrote: >> Jack >> >> I have seen postings on the main reflector recommending settings as low >> as 3 to avoid distortion products that are being attributed to >> transformer distortion. This did not really make sense to me, especially >> at such low levels where consumer sound cards tend to get non-linear and >> nasty. >> >> I took a look at the specifications for the TTC-108 audio transformer >> used in the line out of the K3 >> >> Nominally it's specified as having an operating level of -45dBm to >> +7dBm >> THD is specified at 0.5% @0dBm 300Hz to 3.5 Khz @ 0dBm >> this would make the transformer related harmonics worst case at -46dB >> relative to the fundamental >> >> I did some measurements with an s9 CW signal zero beat at various pitch >> settings >> I used an old copy of SMAART pro that I have from my Sound engineering >> days. the sound card is a delta44 >> >> Lin = 100 Pitch 300 pitch 550 pitch 800 >> DR3 47.3dB 51.4dB 54dB >> >> Lin = 50 Pitch 300 Pitch 550 Pitch 800 >> DR3 43.1dB 47.6dB 50.6dB >> >> Lin = 10 Pitch 300 Pitch 550 Pitch 800 >> DR3 35dB 39.7dB 43.1dB >> >> Lin = 5 Pitch 300 Pitch 550 Pitch 800 >> DR3 31.9dB 37.7dB 42.7dB >> >> Lin = 3 Pitch 300 Pitch 550 Pitch 800 >> DR3 31dB 40.3db 47.6dB >> >> DR3 is the Dynamic range between the fundamental and the 3rd >> (the most dominant harmonic by a wide margin) >> >> I did a quick look at 5th and 7th orders too, again the best performance >> here was found with LIN = 100 >> >> LIN = 100 is an output level of approximately 700mv for an S9 CW sig on >> my K3 >> >> The Harmonic distortion does not increase with higher line out levels, >> it actually improves. This does not appear to be a transformer >> saturation issue >> >> With lin = 100 users will see a ghost on the waterfall and may risk >> over-driving some consumer sound cards. lowering LIN may get rid of the >> visible ghost by reducing the 3rd Harmonic to below the waterfall >> threshold (& perhaps the sound card input noise floor ) but also reduces >> the overall usable dynamic range >> >> >> 73 >> Brendan EI6IZ >> >> > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Brendan Minish
On Tue, 02 Sep 2008 17:06:29 +0100, Brendan Minish wrote:
>I used an old copy of SMAART pro that I have from my Sound engineering >days. I have that software, and have long used it to analyze ham filters. >the sound card is a delta44 I don't know this card, but it's own noise floor (or input stage) may be the limiting factor. Look at the first data set in http://audiosystemsgroup.com/K3FilterStudy.pdf The black curve (the Headphone output) and the red curve (Lin Out) are set to produce the SAME output level, but the harmonic distortion is 55 dB stronger at the Line Output! The difference between the LF traces is IM, and is also significantly greater at the Headphone output. Notice also the dynamic range of this measurement, which is 90 dB. The excitation is band noise, so there's another 10 dB or so between the top of the screen and digital clip. My measurement system is EASERA SysTune (considerably more advanced than Smaart Pro), and the input device is the EASRA Gateway, which has a 24-bit A/D and Firewire interface. I'm fairly confident that the noise floor in my measurements is the radio, not the measurement system! That first data screen shows 3rd harmonic at -55 dB for a gain setting of 1 (and that is the noise floor of the radio). At a gain setting of 2, it's -54 dB. At a gain setting of 3, it's -49 dB. At a gain setting of 5, it's -40 dB. For a setting of 10, it's -28 dB, and at 20, it's - 29 dB. Note also the very significant difference in excitation. My test signal is not a CW signal, but broadband noise from an antenna, band- limited by the IF filters. Your test signal is a sine wave. My test signal is somewhat representative of trying to copy a signal in QRN, or pick one signal out of many in a contest. Your signal is representative of a test bench or a signal with little or no noise on it. As I'm sure you know, those of us working in pro audio find pink noise far more useful than sine waves help us hear real world problems in systems. 73, Jim Brown K9YC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by KK7P
Hi Lyle,
only to be sure - if I have in CONFIG: LINE OUT - PHONES which D/A is used - this one for SP/PHONES ? Then LINE OUT level is controlled by AF knob so I suppose that PH/SP channel is used but not sure. Thanks Lexa, OK1DST Lyle Johnson napsal(a): > There are three distinct stereo audio channels in the K3, and they all > have slightly different characteristics. > > LINE OUT > > This has its own digital-to-analog converter (DAC) and is transformer > isolated. > > PHONES > > This shares a DAC with the speaker channel, but has its own amplifier > and isolating resistors to help reduce the impact of plugging in two > sets of headphones. > > SPEAKER > > This shares a DAC with the headphones, but has its own stereo amplifier. > > We are aware of the discussions regarding harmonic distortion in these > audio paths. While it is easy to just say, "The radio meets specs!" (and > it does :-) we are looking at ways to improve the performance of the > entire audio system. > > 73, > > Lyle KK7P > > > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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> only to be sure - if I have in CONFIG: LINE OUT - PHONES which D/A is
> used - this one for SP/PHONES ? LINE OUT is always driven by the LINE OUT DAC. 73, Lyle KK7P _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: K3 Harmonic Distortion
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In reply to this post by Stewart Baker
The issue isn't the LINE OUT level, it is the voltage level. If you leave the AGC on and AGC SLP > 11 the voltage with an S9 (-73 dBm) signal will not exceed 1V peak (.77 V RMS) and you will not see distortion products through the transformer. If you set turn of the AGC an/or set AGC SLP < 10, the transformers (or audio amplifier) can be easily overdriven and the distortion products will rise significantly - even to the point that harmonics through the 10th or higher are down less than 10 dB. With the line out the entire issue is keeping LINE OUT below 1V Peak. There are other sues with the headphone and speaker output and I'll address them elsewhere. 73, ... Joe, W4TV > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of Stewart Baker > Sent: Tuesday, September 02, 2008 12:59 PM > To: Jack Smith; Brendan Minish > Cc: Elecraft > Subject: Re: [Elecraft] K3 Harmonic Distortion > > > I find virtually the same results here using 50uV RF from an > Elecraft signal source, and measuring using Wave Spectra. > An offset of 43 to 45dB, and below LIN OUT = 5 the harmonics drop > rapidly. > > 73 > Stewart G3RXQ > On Tue, 02 Sep 2008 12:28:02 -0400, Jack Smith wrote: > > Brendan: > > > > You might wish to look at the measurements I made, with LIN OUT > settings > > from 2 to 100. There's an animated GIF that steps through the > LIN OUT > > settings so you can see the effect. The data was taken at 600 > Hz. > > http://www.cliftonlaboratories.com/elecraft_k3_receive_audio.htm > about > > half way down the page > > > > Like you, I see a relatively constant 45 dB or so offset between > the > > fundamental and 3rd harmonic for LIN OUT values of 10 and over. > > > > However, setting the LIN OUT at 2 results in quite a bit better > odd > > order harmonic suppression, on the order of nearly 70 dB. By the > time > > LIN OUT is set to 5, however, the odd order suppression is > reduced to a > > bit more than 60 dB. At LIN OUT = 10, it's 45 dB or so where it > stays at > > all values of LIN OUT tested between 10 and 100. > > > > (For some reason, the 2nd harmonic pops up at certain settings, > but not > > others higher or lower, but that's not of immediate concern.) > > > > There's a related issue with the AGC. The audio output is > proportional > > to RF signal level, as the AGC has a slope to it. Hence, even > though the > > LIN OUT might be set to, say, 2, the actual audio level and > hence the > > distortion, will vary as the RF signal level changes. The degree > of > > audio level variation with RF input changes depends on how the > user has > > set the K3's AGC slope and intercept parameters. > > > > I'll make the measurements on a couple of TTC-108 parts when > they > > arrive as a matter of trying to understand where the harmonic > distortion > > arises. To duplicate the K3's audio chain, I'll drive the > TTC-108s from > > an op-amp so that it will be hit with a low Z source, instead of > the > > standard audio generators available to me, with 50 or 600 ohm > output Z. > > > > Jack > > > > > > Brendan Minish wrote: > >> Jack > >> > >> I have seen postings on the main reflector recommending > settings as low > >> as 3 to avoid distortion products that are being attributed to > >> transformer distortion. This did not really make sense to me, > especially > >> at such low levels where consumer sound cards tend to get > non-linear and > >> nasty. > >> > >> I took a look at the specifications for the TTC-108 audio > transformer > >> used in the line out of the K3 > >> > >> Nominally it's specified as having an operating level of -45dBm > to > >> +7dBm > >> THD is specified at 0.5% @0dBm 300Hz to 3.5 Khz @ 0dBm > >> this would make the transformer related harmonics worst case at > -46dB > >> relative to the fundamental > >> > >> I did some measurements with an s9 CW signal zero beat at > various pitch > >> settings > >> I used an old copy of SMAART pro that I have from my Sound > engineering > >> days. the sound card is a delta44 > >> > >> Lin = 100 Pitch 300 pitch 550 pitch 800 > >> DR3 47.3dB 51.4dB 54dB > >> > >> Lin = 50 Pitch 300 Pitch 550 Pitch 800 > >> DR3 43.1dB 47.6dB 50.6dB > >> > >> Lin = 10 Pitch 300 Pitch 550 Pitch 800 > >> DR3 35dB 39.7dB 43.1dB > >> > >> Lin = 5 Pitch 300 Pitch 550 Pitch 800 > >> DR3 31.9dB 37.7dB 42.7dB > >> > >> Lin = 3 Pitch 300 Pitch 550 Pitch 800 > >> DR3 31dB 40.3db 47.6dB > >> > >> DR3 is the Dynamic range between the fundamental and the 3rd > harmonic > >> (the most dominant harmonic by a wide margin) > >> > >> I did a quick look at 5th and 7th orders too, again the best > performance > >> here was found with LIN = 100 > >> > >> LIN = 100 is an output level of approximately 700mv for an S9 > CW sig on > >> my K3 > >> > >> The Harmonic distortion does not increase with higher line out > levels, > >> it actually improves. This does not appear to be a transformer > >> saturation issue > >> > >> With lin = 100 users will see a ghost on the waterfall and may > risk > >> over-driving some consumer sound cards. lowering LIN may get > rid of the > >> visible ghost by reducing the 3rd Harmonic to below the > waterfall > >> threshold (& perhaps the sound card input noise floor ) but > also reduces > >> the overall usable dynamic range > >> > >> > >> 73 > >> Brendan EI6IZ > >> > >> > > _______________________________________________ > > Elecraft mailing list > > Post to: [hidden email] > > You must be a subscriber to post to the list. > > Subscriber Info (Addr. Change, sub, unsub etc.): > > http://mailman.qth.net/mailman/listinfo/elecraft > > > > Help: http://mailman.qth.net/subscribers.htm > > Elecraft web page: http://www.elecraft.com > > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Berni G0IDA
In my previous posting I referenced to a couple of plots I made of the
Line output using a wideband RF noise source I put the 2 plots on my blog here http://ei6iz.com/?p=22 73 Brendan EI6IZ -- Don‘t complain. Nobody will understand. Or care. And certainly don‘t try to fix the situation yourself. It‘s dangerous. Leave it to a highly untrained, unqualified, expendable professional. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: K3 Harmonic Distortion
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In reply to this post by Mike Harris-9
VP8NO writes: > Perhaps someone suitably qualified and tooled up might like to try and > [repeat] and comment upon the view presented by Rob Sherwood at the > Dayton convention. According to him the K3 audio amp stage has > serious shortcomings. I had to listen to the audio of Sherwood's talk before looking in the right area. First, Rob doesn't say the K3 audio has serious shortcomings, he complains about distortion on the speaker. Sherwood also admits that using a high impedance speaker (e.g., amplified computer speakers) or high impedance headphones resolves the issue! My measurements did not show that distortion but I was measuring at the headphone output with a high impedance load - the lowest impedance headphones I use are 32 Ohms. As Jack Smith points out, the headphones and the speakers have separate audio amplifiers but share a common DAC. Since Sherwood's comments were based on the speaker output and a LOW impedance load, I dragged out an old Optimus XTX25 speaker - an unpowered 8 Ohm speaker I've used with other radios for many years. With the 8 Ohm speaker is was easy to generate harmonic distortion - particularly if the K3 were set to SPKRS = 2 with only one speaker connected - simply by turning up the volume until the amplifier was forced into clipping/saturation! With the 8 Ohm speaker, 1 to 2V peak represents a comfortable to loud listening level for me. At those levels, the harmonics are all down more than 65 dB and any other distortion is very acceptable. The following table shows harmonic levels relative to a 500 Hz reference tone at the given voltage across the speaker. 0 dB is 1V Peak (.707V RMS). +10 dB represents 2.25V RMS (signal + distortion). +13 dB is 3.2V RMS (the speaker amplifier is in the compression region at the threshold of clipping) and +15 dB is 4V RMS (the speaker amplifier is in hard clipping). Reference 2nd 3rd 4th 5th 6th 7th 8th 9th ============================================================ +15 dB -37 -15 -45 -26 -60 -43 -51 -37 +13 dB -49 -31 -51 -35 -57 -39 -63 -49 +10 dB -70 -68 -95 -67 -85 -69 -85 -73 0 dB -66 -74 -70 -77 -73 -76 -77 -80 -10 dB -54 -66 -63 -90 -73 -82 -80 -87 -20 dB -50 -78 -68 -74 -73 -74 -74 -78 In order to drive the audio amplifier hard enough to create the distortion, it was necessary to disable the AGC or set AGC SLP to low values (reduce the AGC reduction for strong signals). Again, as in the case of the Line Out, if the audio gain, AGC and RF gain are operated to keep the speaker amplifier out of the clipping range - or away from the compression region just before clipping - the distortion products are entirely acceptable. For those with noisy shacks, impaired hearing or using the internal speaker it may be difficult to find a comfortable listening level without entering the compression region. For those who wish to operate without AGC and with maximum RF gain, I would suggest setting the AF gain to a moderate level and using powered (computer) speakers or a 100 watt per channel stereo amplifier capable of outputs greater than the 1 watt per channel at .1% THD+N specified for the LM4950 with an 8 Ohm load! Note, simply going from 8 to 16 Ohm speakers will improve THD by 8 dB. 73, ... Joe, W4TV _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Clearly I must be missing something.
In my view, all the reported distortion numbers are beyond expectations. After all you are buying a $2K radio, not a many kilobuck audio system. The "problems" people are having with "harmonics" when they listen to CW with a 2.7KHz filter/DSP setting seem to be easily solved by just reducing the DSP bandwidth. The last resort solution is to get a few years older and you won't hear them. Workarounds for other problems seem to given in the postings. I personally hear and see nothing objectional given the above perspective. 73 de Brian/K3KO
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RE: K3 Harmonic Distortion
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> The "problems" people are having with "harmonics" when they > listen to CW with a 2.7KHz filter/DSP setting seem to be > easily solved by just reducing the DSP bandwidth. Reducing the DSP bandwidth will not resolve the harmonics generated in the speaker amplifier and/or Line Out circuits. The solution is simply not pushing the output gain and keeping the output under 1V peak and use high impedance devices. With the speaker amplifier 800 mW into a 16 Ohm speaker shows less than .01% THD+N - if more audio is necessary 1V peak will easily drive a good quality 100 watt per channel stereo system. With Line Out, 1V peak is plenty for good s/n soundcard operation. 73, ... Joe, W4TV > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of alsopb > Sent: Wednesday, September 03, 2008 9:39 AM > To: [hidden email] > Subject: RE: [Elecraft] K3 Harmonic Distortion > > > > Clearly I must be missing something. > > In my view, all the reported distortion numbers are beyond > expectations. After all you are buying a $2K radio, not a > many kilobuck audio system. > > The "problems" people are having with "harmonics" when they > listen to CW with a 2.7KHz filter/DSP setting seem to be > easily solved by just reducing the DSP bandwidth. The last > resort solution is to get a few years older and you won't hear > them. > > Workarounds for other problems seem to given in the postings. > > I personally hear and see nothing objectional given the above > perspective. > > > 73 de Brian/K3KO > > > > Joe Subich, W4TV-3 wrote: > > > > > > VP8NO writes: > > > >> Perhaps someone suitably qualified and tooled up might like to try > >> and [repeat] and comment upon the view presented by Rob > Sherwood at > >> the Dayton convention. According to him the K3 audio amp > stage has > >> serious shortcomings. > > > > I had to listen to the audio of Sherwood's talk before looking > > in the right area. First, Rob doesn't say the K3 audio has > > serious shortcomings, he complains about distortion on the > > speaker. Sherwood also admits that using a high impedance > > speaker (e.g., amplified computer speakers) or high impedance > > headphones resolves the issue! > > > > My measurements did not show that distortion but I was measuring > > at the headphone output with a high impedance load - the lowest > > impedance headphones I use are 32 Ohms. As Jack Smith points > > out, the headphones and the speakers have separate audio > > amplifiers but share a common DAC. > > > > Since Sherwood's comments were based on the speaker output and > > a LOW impedance load, I dragged out an old Optimus XTX25 speaker > > - an unpowered 8 Ohm speaker I've used with other radios for many > > years. With the 8 Ohm speaker is was easy to generate harmonic > > distortion - particularly if the K3 were set to SPKRS = 2 with > > only one speaker connected - simply by turning up the volume > > until the amplifier was forced into clipping/saturation! > > > > With the 8 Ohm speaker, 1 to 2V peak represents a comfortable > > to loud listening level for me. At those levels, the harmonics > > are all down more than 65 dB and any other distortion is very > > acceptable. > > > > The following table shows harmonic levels relative to a 500 Hz > > reference tone at the given voltage across the speaker. 0 dB > > is 1V Peak (.707V RMS). +10 dB represents 2.25V RMS (signal + > > distortion). +13 dB is 3.2V RMS (the speaker amplifier is in > > the compression region at the threshold of clipping) and +15 > > dB is 4V RMS (the speaker amplifier is in hard clipping). > > > > Reference 2nd 3rd 4th 5th 6th 7th 8th 9th > > ============================================================ > > +15 dB -37 -15 -45 -26 -60 -43 -51 -37 > > +13 dB -49 -31 -51 -35 -57 -39 -63 -49 > > +10 dB -70 -68 -95 -67 -85 -69 -85 -73 > > 0 dB -66 -74 -70 -77 -73 -76 -77 -80 > > -10 dB -54 -66 -63 -90 -73 -82 -80 -87 > > -20 dB -50 -78 -68 -74 -73 -74 -74 -78 > > > > In order to drive the audio amplifier hard enough to create > > the distortion, it was necessary to disable the AGC or set > > AGC SLP to low values (reduce the AGC reduction for strong > > signals). > > > > Again, as in the case of the Line Out, if the audio gain, > > AGC and RF gain are operated to keep the speaker amplifier > > out of the clipping range - or away from the compression > > region just before clipping - the distortion products are > > entirely acceptable. For those with noisy shacks, impaired > > hearing or using the internal speaker it may be difficult > > to find a comfortable listening level without entering the > > compression region. > > > > For those who wish to operate without AGC and with maximum > > RF gain, I would suggest setting the AF gain to a moderate > > level and using powered (computer) speakers or a 100 watt > > per channel stereo amplifier capable of outputs greater > > than the 1 watt per channel at .1% THD+N specified for the > > LM4950 with an 8 Ohm load! Note, simply going from 8 to > > 16 Ohm speakers will improve THD by 8 dB. > > > > 73, > > > > ... Joe, W4TV > > > > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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