K3 pwr out on digimodes
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I do not have the benefit of an external wattmeter
at the moment and frequently use digital modes, esp. JT65A. Assuming I
want to transmit 25 W or less, if I have PWR set at 25 and adjust the
mic gain for ALC just under 1 bar (basically just until one bar
disappears), approximately how much power would be transmitted? The
resolution of the 100W rf scale doesn't really help at low levels.
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On my K3 currently I would expect to get more than 60W rms output if PWR was set to 25. Since I imagine that there would be a lot more complaints about this if everyone had the same problem, my guess is that it actually depends on the individual K3. All I can say is that the PWR control cannot be relied upon for setting the power level in data modes, which means if you don't have a thru-line power meter you have little choice but to try and use the built in meter to set the power. I have given up using my K3 until this problem is fixed, as it's too easy to forget this and overdrive the PA with dire results.
Julian, G4ILO. K2 #392 K3 #222 KX3 #110
* G4ILO's Shack - http://www.g4ilo.com * KComm - http://www.g4ilo.com/kcomm.html * KTune - http://www.g4ilo.com/ktune.html |
Re: K3 pwr out on digimodes
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In reply to this post by Benson-2
Benson,
I've done some measurements some time ago with my K3 #1212 and i had the following values: K3 power set to 20W, f=7.040MHz 25W 50 Ohms dummy load MCE/Weinschel LP-100A Wattmeter mode USB 1 kHz sine audio at rear line-input, level adjusted to have the desired ALC bar configuration ALC bar(s) Mesured [W] (avg) 0 8.16 1 blinking 9.4 1steady+1blk 15.95 2steady+1blk 20.72 3steady+1blk 21.2 These values correspond to the above mentioned set-up (K3 #1212 uP rev 2.78) and displayed on the LP-100A with RF head #1143 73 QRO fr Rudolf, HB9ARI Benson wrote: > I do not have the benefit of an external wattmeter at the moment and > frequently use digital modes, esp. JT65A. Assuming I want to transmit > 25 W or less, if I have PWR set at 25 and adjust the mic gain for ALC > just under 1 bar (basically just until one bar disappears), > approximately how much power would be transmitted? The resolution of > the 100W rf scale doesn't really help at low levels. > ------------------------------------------------------------------------ > > _______________________________________________ > 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 Benson-2
Rudolf, the problem is not one associated with the accuracy of the K3
meter, but one of the ALC being fairly "slack" with the end result that a fluctuating audio input from speech or from a sound card on many data modes results in widely varying power, unfortunately often exceeding the level set by the power control. An oscilloscope or peak reading Wattmeter, such as the LP-100, will catch and display the peaks far better than can be read from the K3 meter. I hope Elecraft continue their efforts to fix this irritating problem, as not only does it make the use of some digital modes tedious, but running a linear on SSB results in power levels which often exceed the legal power limit - even when being very careful to set the drive level (UK power limit 400W, using an Acom 1000 which does not use ALC feedback). 73 Dave, G4AON K3/100 #80 ------------- <SNIP> I've done some measurements some time ago with my K3 #1212 and i had the following values: K3 power set to 20W, f=7.040MHz 25W 50 Ohms dummy load MCE/Weinschel LP-100A Wattmeter mode USB 1 kHz sine audio at rear line-input, level adjusted to have the desired ALC bar configuration <SNIP> Rudolf, HB9ARI _______________________________________________ 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 hb9ari@bluewin.ch
Thanks for this table. It appears we should be aiming for 2-3 bars not 6!
Ideally, everyone will have an accurate RF power meter in circuit. If you know the PA current, which you can read accurately and the voltage which can also be read, you can calculate your input power. All you then need to know is the power required for 25W output on your band(s) of choice. This assumes a good match which is safe as no K3 user would operate into a poor match, but many power meters will not give accurate readings at high VSWR either. For example with Bird Thrulines you need to do a calculation to find the true forward power if there is significant reflected power. Meters like the LP100 do read true forward power, but can still lose accuracy if the VSWR is high. < irrelevant nostalgia> When I started out I bought an FT290, an antenna and a VSWR meter. Back then in the UK it was a license requirement to know what your transmitted power was relative to the 100W limit, or failing that your input power and to be able to demonstrate to an inspector that you were within limits. Our limits were 100W carrier power, considered to be 100W of CW/FM and 400W PEP for AM/SSB. Non-coders were only allowed above 144MHz, previously 430MHz, and the VHF/UHF activity was maybe 10 times what it is now. </ irrelevant nostalgia>
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Re: K3 pwr out on digimodes
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In reply to this post by Dave, G4AON
Dave,
I followed the problem you described on the group and this is the reason i do some measurements around the power output because i was a little bit anxious! At the beginning, my only 2 "ham" references were my MiniVNA output (calibrated at my office at -2.04 dBm , 7.040MHz with 50 Ohms load) and a 25W MCE/Weinschel bi-directional attenuator (calibrated as 50.1 Ohms and 29.83 dB attenuation) These 2 "references" have permitted to "verify" the "coupling" factor of my LP-100A RF Sensor as 29.12 db for the 29.1 dB used by Larry!! The LP-100A is now my 3rd "ham" reference instrument. I also do some peak/average power ratio measurements for different digi modes and results were ok between 0 db (FSK) and 15 dB (EasyPAL during digital picture transmission) (the 2 extremes "tested" with software running in my PC). After that, i do also power output measurements with and without ALC (with a lot of caution!) for the K3 and.found something like ~ 1dB more power without ALC (ONLY for TESTING!) With ALC ON, i measured a mean error < +/- 0.1 dB between 1W and 12W and < 0.45 dB between 13W and 20W. (may be due to the activation of the PA?) During all these measurements, i have my "old" TDS 220 scope (1Gs/s 100MHz BW) connected at my -30dB "dummy load" output for monitoring in case of distortion and/or oscillation but all was ok and i'm very satisfied with these results.The measured P-P values divided by 2*SQR(2) gave me a good confirmation for the RMS value. One more (and last precision...), all measurements were done with a sinus audio single tone, except for peak/average ratio measurements done with some available digi modes. 73 QRO fr Rudolf, HB9ARI Dave G4AON wrote: > Rudolf, the problem is not one associated with the accuracy of the K3 > meter, but one of the ALC being fairly "slack" with the end result that > a fluctuating audio input from speech or from a sound card on many data > modes results in widely varying power, unfortunately often exceeding the > level set by the power control. An oscilloscope or peak reading > Wattmeter, such as the LP-100, will catch and display the peaks far > better than can be read from the K3 meter. > > I hope Elecraft continue their efforts to fix this irritating problem, > as not only does it make the use of some digital modes tedious, but > running a linear on SSB results in power levels which often exceed the > legal power limit - even when being very careful to set the drive level > (UK power limit 400W, using an Acom 1000 which does not use ALC feedback). > > 73 Dave, G4AON > K3/100 #80 > ------------- > <SNIP> > > I've done some measurements some time ago with my K3 #1212 and i had the > following values: > > K3 power set to 20W, f=7.040MHz 25W 50 Ohms dummy load MCE/Weinschel > LP-100A Wattmeter > mode USB 1 kHz sine audio at rear line-input, level adjusted to have the > desired ALC bar configuration > <SNIP> > Rudolf, HB9ARI > > _______________________________________________ > 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 hb9ari@bluewin.ch
I would be quite happy if my K3 consistently gave results such as you tabulated. I was going to produce a similar table to illustrate the problem I am experiencing, only with PWR set to 2.0W rather than 20W. I switched on the radio and observed that I was getting more than 5.0W, with 5 blocks showing on the K3 internal meter. This did not start to reduce until MIC was turned down until no ALC bars were showing. I made a false start in creating the table as I found that the MIC control was too coarse to show all the levels of ALC you tabulated, so I started again using the computer sound card level slider to regulate the input level. At this point I found that the power was now being limited to about 3.0W, with just two blocks showing on the K3 power meter. This is the behaviour which is driving me crazy. There is no setting of the MIC and PWR controls that consistently delivers a given power in DATA A mode. You never know how much power the rig is going to put out the first time you click the TX button after you have switched on, changed band or changed frequency. Once it decides to regulate the power, it does seem to remain fairly consistent as long as you stay on that band and that frequency. The problem with controlling the power using the audio input level instead of setting it to 4 "ALC bars" as Lyle originally advised is that the power output becomes frequency dependent. I can vary the output power between 5.0W and 10.0W just by clicking in a different place on the waterfall, varying the frequency of the audio input. The power at 500Hz or 2000Hz is about half what it is at 1200Hz. It is hopeless for anyone who wants to operate using Digipan "click and call" style operating.
Julian, G4ILO. K2 #392 K3 #222 KX3 #110
* G4ILO's Shack - http://www.g4ilo.com * KComm - http://www.g4ilo.com/kcomm.html * KTune - http://www.g4ilo.com/ktune.html |
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Further to what I wrote, I have just noted that the power output in DATA A still varies though only by about 2dB across the passband even when the audio input is increased to drive 4-5 bars of "ALC".
In SSB mode, with the audio level adjusted to no more than 2 bars of ALC, and CMP reduced to zero, there is no significant change in TX power output across the whole passband. Furthermore, the power is correctly set to the level specified on the PWR control. Significantly, I observed no difference in IMD measured using my KK7UQ IMD meter whether using DATA mode with no ALC, or SSB with just enough ALC to control variations across the filter passband. The IMD was -29dB in both cases. I believe that when the K3 was released a year ago, the DATA A mode was identical in behavior to SSB except that it disabled CMP and allowed a different selection of input source. If Elecraft would revert to that functionality then I think everyone would be happy. I know I would. (It would actually be nice if DATA A disabled RX EQ and TX EQ as well.)
Julian, G4ILO. K2 #392 K3 #222 KX3 #110
* G4ILO's Shack - http://www.g4ilo.com * KComm - http://www.g4ilo.com/kcomm.html * KTune - http://www.g4ilo.com/ktune.html |
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----- Original Message -----
From: "Julian, G4ILO" <[hidden email]> > > I believe that when the K3 was released a year ago, the DATA A mode was > identical in behavior to SSB... It was *very* flat, I haven't used my K3 for the last year other than to add HRD support. I've been using my TS-480SAT as it's more convenient, I hope to get the K3 running again this summer. I agree that the Data modes should have no equalisation whatsoever and should be as flat as possible. Simon Brown, HB9DRV www.ham-radio-deluxe.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 AD6XY
The K3 suggested ALC level for digital modes is *4* bars. The 6 bar
indication is for SSB (actually listed as 5-7 bars). According to the K3 FAQ page - when the indication is at 5 bars, the DSP ALC is just being "tickled". For data modes, ALC action is not desirable, thus the 4 bar recommendation. Up to (but not including) the 5th bar on the ALC meter, the meter is indicating something similar to VU units rather than ALC action - the 5th bar is the onset of ALC. 73, Don W3FPR AD6XY wrote: > Thanks for this table. It appears we should be aiming for 2-3 bars not 6! > > > _______________________________________________ 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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I did my test for output over a range of frequencies with 4-5 bars of "ALC" and as I stated, the power varied by about 2dB. If ALC is being applied at the DSP that is just plain wrong in my opinion, as it cannot compensate for the variations in gain at different frequencies due to the shape of the filter. When ALC is applied at the output, as in SSB mode, the effect is a flat response. As long as only a little ALC is used there is no adverse effect on transmitted IMD when using PSK31. I think the dangers of using ALC when running PSK31 have been wildly overstated in some quarters. I have always operated PSK31 using just enough audio drive to give a bar or two of ALC and now having the KK7UQ meter I have been able to measure the effect of this when using an FT-817, K2 and K3. On the FT-817 some worsening of the IMD is noticeable but the signal is still clean, typically -27 or -28dB. On the K2 one bar of ALC makes no difference at all. Incidentally the K2 has the cleanest PSK31 signal of all, typically -33 or -34dB at 5W output. The K3 at 5W on 80m measured -28 or -29dB whether using DATA A mode (with no 'real' ALC being applied) or SSB mode with one or two bars of real ALC.
Julian, G4ILO. K2 #392 K3 #222 KX3 #110
* G4ILO's Shack - http://www.g4ilo.com * KComm - http://www.g4ilo.com/kcomm.html * KTune - http://www.g4ilo.com/ktune.html |
Re: K3 pwr out on digimodes
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Julian, > I did my test for output over a range of frequencies with 4-5 > bars of "ALC" and as I stated, the power varied by about 2dB. > If ALC is being applied at the DSP that is just plain wrong > in my opinion, as it cannot compensate for the variations in > gain at different frequencies due to the shape of the filter. This is incorrect ... the purpose of ALC is not to control the shape of the passband across the SSB filter it is to prevent a SSB signal in total from overdriving the power amplifiers. The purpose of equalization is to flatten the filter response. ALC and EQ are not the same ... you need to use the proper tool for the job. No ALC system can compensate for the filter ripple. ALC is nothing more than a system of compression (or clipping). In general, ALC does not act until the drive reaches the threshold. In a "traditional" transceiver ALC is derived from grid (or base/gate) current in the final amplifier and there is no ALC action until the grid/base/gate current begins to rise. To obtain a constant power output, the user must adjust the drive level as the drive to the final amplifier changes based on modulating frequency. If the user does not adjust for changes in gain across the transmit passband, operating just before the onset of ALC with one frequency will result in significant ALC on another modulating frequency ... conversely, operating with (audio) drive at the threshold of ALC where the filter losses are least will result in significant lowering of power where the filter ripple is the greatest. The effect is NO DIFFERENT than the variation of output power with modulating frequency in the K3. If the DSP based ALC in the K3 keeps the level of the 15 KHz RF constant, the output power will vary with frequency based on the response of the IF filter. The purpose of ALC is not power level control. It's purpose is to keep the drive level below the point at which any stage in the RF chain begins to saturate (compress or clip). The responsibility of output power control with any radio is the power level control (PWR in the K3). However, the K3 PWR control is not a closed loop control. The power control simply sets the 15 KHz drive based on the system gain (with filter loss) at the single frequency used when performing the power calibration. If you want to tune by clicking around in the waterfall instead of using the tuning knob you need to do one of two things ... use EQ to compensate for the filter response or design your software to compensate by adjusting the audio level with frequency. In short, you are asking both the ALC and PWR controls to do something that they are not designed to do. The ONLY WAY to maintain a constant output level on any transceiver is to use a closed loop power control. Closed loop power controls are not appropriate to SSB systems because time constants sufficient to maintain constant power across the IF passband for digital operation would result in frequency dependent clipping and/or compression in voice operation. The only ways to maintain constant levels across the passband are by using an IF filter with very low ripple or by generating RF "on frequency" 73, ... Joe, W4TV > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of Julian, G4ILO > Sent: Friday, January 16, 2009 8:53 AM > To: [hidden email] > Subject: Re: [Elecraft] K3 pwr out on digimodes > > > > > > Don Wilhelm-4 wrote: > > > > The K3 suggested ALC level for digital modes is *4* bars. The 6 bar > > indication is for SSB (actually listed as 5-7 bars). > > According to the K3 FAQ page - when the indication is at 5 > bars, the DSP > > ALC is just being "tickled". For data modes, ALC action is not > > desirable, thus the 4 bar recommendation. > > > > Up to (but not including) the 5th bar on the ALC meter, the meter is > > indicating something similar to VU units rather than ALC > action - the > > 5th bar is the onset of ALC. > > > > > > I did my test for output over a range of frequencies with 4-5 > bars of "ALC" and as I stated, the power varied by about 2dB. > If ALC is being applied at the DSP that is just plain wrong > in my opinion, as it cannot compensate for the variations in > gain at different frequencies due to the shape of the filter. > > When ALC is applied at the output, as in SSB mode, the effect > is a flat response. As long as only a little ALC is used > there is no adverse effect on transmitted IMD when using PSK31. > > I think the dangers of using ALC when running PSK31 have been > wildly overstated in some quarters. I have always operated > PSK31 using just enough audio drive to give a bar or two of > ALC and now having the KK7UQ meter I have been able to > measure the effect of this when using an FT-817, K2 and K3. > On the FT-817 some worsening of the IMD is noticeable but the > signal is still clean, typically -27 or -28dB. On the K2 one > bar of ALC makes no difference at all. Incidentally the K2 > has the cleanest PSK31 signal of all, typically -33 or -34dB > at 5W output. The K3 at 5W on 80m measured -28 or -29dB > whether using DATA A mode (with no 'real' ALC being applied) > or SSB mode with one or two bars of real ALC. > > ----- > 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 > -- > View this message in context: > http://n2.nabble.com/K3-pwr-out-on-digimodes-tp2163956p2168256.html > Sent from the Elecraft mailing list archive at Nabble.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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I agree with you. As applied to a voice SSB signal or even a wideband data mode that is completely correct. But in practise with a narrowband signal like PSK31 the effect will be to keep the output RF at the same power, whatever audio frequency the signal is being generated at, because only a narrow band of frequencies is being used at any one time. If the filter response varies across the passband, which it does, the ALC will vary the amount of gain used to try to keep the RF level to the amount it is set at, whether the signal is being generated near the edge of the passband or at the center. This is important to the PSK31 operator who does not want to tune every signal to the center of the passband sweet spot before hitting TX in order to get maximum power out.
Julian, G4ILO. K2 #392 K3 #222 KX3 #110
* G4ILO's Shack - http://www.g4ilo.com * KComm - http://www.g4ilo.com/kcomm.html * KTune - http://www.g4ilo.com/ktune.html |
Re: K3 pwr out on digimodes
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> If the filter response varies across the passband, which it > does, the ALC will vary the amount of gain used to try to > keep the RF level to the amount it is set at, whether the > signal is being generated near the edge of the passband or at > the center. This is your fundamental misunderstanding of ALC. Traditional ALC does NOT (and can not) increase gain - it can only DECREASE gain to bring the grid/base/gate current down to the level at which the final amplifier is not being overdriven. DSP based ALC is similar, it can only adjust the modulator (DSP) output to the level determined to be appropriate at the single point in the IF filter at which the power calibration (5W/50W) was made. ALC (and power control) can not compensate for differences in gain across the passband - in other words, non-flat response. If you wanted to compensate for that non-flat response, it would be necessary to calibrate the power (5W/50W) at regular intervals across the passband and build a gain vs. frequency table. The DSP would then need to measure the frequency of any narrow band modulation and adjust the assumed gain of the power control circuit based on the gain of the IF chain at that frequency. > This is important to the PSK31 operator who does > not want to tune every signal to the center of the passband > sweet spot before hitting TX in order to get maximum power out. The PSK31 operator must adjust his drive (mic gain or power control) with ANY transmitter if he changes his "subcarrier" frequency. Even with conventional ALC if the drive is set to the ALC threshold when operating at the point of maximum gain, the output will be reduced when operating at other places in the passband (particularly when operating at the edges of the passand). Try this experiment with your FT-817 ... set the power level to the maximum, turn off any compression, set your soundcard to 1700 Hz and the level for 15 Watts out of the FT-817 with NO ALC. Now, without making any other changes measure the power output with a 200 Hz tone and a 3200 Hz tone. Is it identical AT ALL THREE points? 73, ... Joe, W4TV > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of Julian, G4ILO > Sent: Friday, January 16, 2009 12:52 PM > To: [hidden email] > Subject: Re: [Elecraft] K3 pwr out on digimodes > > > > > > Joe Subich, W4TV-4 wrote: > > > > > > the purpose of ALC is not to control the > > shape of the passband across the SSB filter it is to prevent a > > SSB signal in total from overdriving the power amplifiers. > > > > > > I agree with you. As applied to a voice SSB signal or even a > wideband data mode that is completely correct. > > But in practise with a narrowband signal like PSK31 the > effect will be to keep the output RF at the same power, > whatever audio frequency the signal is being generated at, > because only a narrow band of frequencies is being used at > any one time. > > If the filter response varies across the passband, which it > does, the ALC will vary the amount of gain used to try to > keep the RF level to the amount it is set at, whether the > signal is being generated near the edge of the passband or at > the center. This is important to the PSK31 operator who does > not want to tune every signal to the center of the passband > sweet spot before hitting TX in order to get maximum power out. > > ----- > 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 > -- > View this message in context: > http://n2.nabble.com/K3-pwr-out-on-digimodes-tp2163956p2169671.html > Sent from the Elecraft mailing list archive at Nabble.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 |
Re: K3 pwr out on digimodes
Administrator
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In reply to this post by Joe Subich, W4TV-4
Joe W4TV wrote:
> Closed loop power controls are not appropriate to SSB systems because time > constants sufficient to maintain constant power across the > IF passband for digital operation would result in frequency > dependent clipping and/or compression in voice operation. Most digimode programs include a tune button which outputs a tone at the selected output; psk's idle is a simple two-tone. One option (and I expressed this a year or so ago to the Elecraft folks) would be to offer an IMD calibration at the IF level for a known two-tone response, to determine whether at least that stage is being overdriven. The DSP should have a fairly good idea at that point. If the two-tone signal used is a PSK idle tone at the selected AF on the waterfall display, a rig control command to read the IMD calculated would be just peachy. Digimode programs could then have a dedicated button to send an idle tone, read the IMD, and adjust the power. Regular communications could then commence. A further advantage of this approach is that the actual power out could be measured during this calibration period from either the built-in wattmeter or the rig control command, and reported in real time, and thus the knob could (or again, rig control) could be used to achieve the output power desired by the user. Elecraft's response was that perhaps the IMD calculation could be done on the computer side; I'm not clear whether the new monitor out function makes that possible or not, but if it does, that would be an approach that could be made to work today, modulo the limitation that the IMD calculated from the sound card will be a little worse due to the additional ADC of the sound card, whereas a digital report from the K3 IF would be accurate. (And not to mention that an overdriven line input would result in a drastically wrong IMD, but that's likely to have been already taken care of by the digimode RX setup.) In summary, I believe it's possible to provide closed loop control for both power and drive/IMD readings for modes such as PSK, but not during a QSO where the signal characteristics vary; instead provide enough CAT commands and signal quality measurements from the K3 RF OUT and IF OUT stages so that and digmode authors are willing to provide a "TX CAL" tune button. (Doing in the k3 utility wouldn't be helpful because the precise audio settings used by the digimode program for TX are important.) I'm willing to step up and try this for fldigi. Leigh/WA5ZNU _______________________________________________ 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 Joe Subich, W4TV-4
No, I do not misunderstand what ALC does. Perhaps I am just not very good at explaining what I am trying to say. I realize that ALC can only reduce the gain. That is why it is necessary to set the audio drive level so that you get a little bit of ALC across the whole passband range that you want to use. Then, the ALC will be able to reduce the gain by the necessary amount so that the RF output is constant across that passband range. No. This misses the whole point of the convenience of "click and call" operating with programs like Digipan and HRD. I never suggested that the drive must be set to the ALC threshold when operating at the point of maximum gain. It must be set so that you get some ALC across the whole of the passband you wish to use (probably corresponding to no more than the -3dB bandwidth points, beyond that and the steepness of the filter slopes would cause unacceptable distortion of even a narrowband signal such as PSK31.) Then you will achieve constant power across that range, because the ALC will be able to apply varying amounts of gain reduction to achieve that constant power level. The K2 can do this. Why can't the K3? The FT-817 is not capable of 15W. But that is beside the point. What would this experiment prove? I know as well as you do that it would not be identical. That's why I am saying that some form of level control needs to be in operation across the whole of the passband you wish to use. A small amount of ALC with a slow time constant will not harm the IMD in PSK31 mode. The K2 demonstrates this. In SSB mode the K3 ALC provides the level control I am describing. If I turn CMP off and switch the audio source to LINE IN it works exactly as I expect it to work in data modes (apart from not disabling EQ, which is a different issue.) In DATA A mode it does not do this, so you must constantly tweak the drive level whenever you change frequency if you wish to transmit a specific power level. If this is how the K3 is supposed to operate then I shall put it up for sale right away, because it is not something that people who use data modes a lot want to do. (Well, perhaps there are some, because if I have learned nothing else from my participation in ham forums like this, it is that some people actually like doing things the hard way.)
Julian, G4ILO. K2 #392 K3 #222 KX3 #110
* G4ILO's Shack - http://www.g4ilo.com * KComm - http://www.g4ilo.com/kcomm.html * KTune - http://www.g4ilo.com/ktune.html |
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In reply to this post by Leigh L. Klotz Jr WA5ZNU
I'm not sure that what you are suggesting is entirely possible. Surely IMD depends on a lot of other variables that happen after the IF, such as output power level, supply voltage level and SWR? I don't see how the K3 could actively monitor IMD without building functionality akin to the KK7UQ meter into it. In any case, there are other modes besides PSK31 to which the IMD issue does not apply, but the problem of varying power levels across the passband still do. I think this whole issue has come about because the K3 is trying to be too clever and prevent people from transmitting a PSK31 signal with poor IMD. If someone is dumb enough to put too much audio into the input and use way too much ALC then that is their lookout. We are supposed to be trained operators who understand what we are doing. If we make mistakes, we learn. The K3 doesn't try to stop people winding the mic gain up too much when using SSB. Why should it act any differently just because the DATA mode is selected? DATA mode is just SSB. Its only purpose is to facilitate selection of a different input source, disabling compression, and disabling passband equalization. Nobody expects it to behave in any other respect differently from how it handles SSB.
Julian, G4ILO. K2 #392 K3 #222 KX3 #110
* G4ILO's Shack - http://www.g4ilo.com * KComm - http://www.g4ilo.com/kcomm.html * KTune - http://www.g4ilo.com/ktune.html |
Re: K3 pwr out on digimodes
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In reply to this post by Julian, G4ILO
> No, I do not misunderstand what ALC does. Perhaps I am just > not very good at explaining what I am trying to say. I > realize that ALC can only reduce the gain. That is why it is > necessary to set the audio drive level so that you get a > little bit of ALC across the whole passband range that you > want to use. Then, the ALC will be able to reduce the gain by > the necessary amount so that the RF output is constant across > that passband range. Absolutely not! When conventional rigs are generating ALC their final amplifiers are ALREADY in compression and they are generating IMD in the PSK31 signal. PSK31 can not have ANY compression or clipping without causing increased IMD. Increasing the drive to the point that a comventional rig generates some level of ALC at all points virtually assures the generation of unacceptable IMD at most frequencies in the IF passband. > The FT-817 is not capable of 15W. But that is beside the > point. OK, do it at 5 watts ... > What would this experiment prove? I know as well as you do > that it would not be identical. That's why I am saying that > some form of level control needs to be in operation across > the whole of the passband you wish to use. That's my point exactly. The K3 does not provide level control across the passband it provides a constant output from the DSP modulator (15 KHz IF). > A small amount of ALC with a slow time constant will not harm > the IMD in PSK31 mode. Wrong! ANY COMPRESSION OR CLIPPING will effect the INTENTIONAL amplitude shaping in the PSK31 signal designed to prevent IMD and control the banwidth of the transmitted signal. So called IMD is the result of a non-linear amplitued response in the audio/IF/RF chain. PSK31 drive can be thought of as a signal that has been "predistorted" in such a way to cancel the modulation sidebands. If that (amplitude) predistortion is lost due to compression or clipping at any point in the transmitter chain, the result is the appearance of the normal modulation sidebands (known as IMD). > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of Julian, G4ILO > Sent: Friday, January 16, 2009 4:40 PM > To: [hidden email] > Subject: Re: [Elecraft] K3 pwr out on digimodes > > > > > Joe Subich, W4TV-4 wrote: > > > > > > This is your fundamental misunderstanding of ALC. Traditional > > ALC does NOT (and can not) increase gain - it can only DECREASE > > gain to bring the grid/base/gate current down to the level at > > which the final amplifier is not being overdriven. DSP based > > ALC is similar, it can only adjust the modulator (DSP) output > > to the level determined to be appropriate at the single point > > in the IF filter at which the power calibration (5W/50W) was > > made. > > > > ALC (and power control) can not compensate for differences in > > gain across the passband - in other words, non-flat response. > > If you wanted to compensate for that non-flat response, it > > would be necessary to calibrate the power (5W/50W) at regular > > intervals across the passband and build a gain vs. frequency > > table. The DSP would then need to measure the frequency of > > any narrow band modulation and adjust the assumed gain of the > > power control circuit based on the gain of the IF chain at > > that frequency. > > > > > > No, I do not misunderstand what ALC does. Perhaps I am just > not very good at explaining what I am trying to say. I > realize that ALC can only reduce the gain. That is why it is > necessary to set the audio drive level so that you get a > little bit of ALC across the whole passband range that you > want to use. Then, the ALC will be able to reduce the gain by > the necessary amount so that the RF output is constant across > that passband range. > > > > > The PSK31 operator must adjust his drive (mic gain or power > > control) with ANY transmitter if he changes his "subcarrier" > > frequency. Even with conventional ALC if the drive is set > > to the ALC threshold when operating at the point of maximum > > gain, the output will be reduced when operating at other places > > in the passband (particularly when operating at the edges of > > the passand). > > > > No. This misses the whole point of the convenience of "click and call" > operating with programs like Digipan and HRD. I never > suggested that the > drive must be set to the ALC threshold when operating at the point of > maximum gain. It must be set so that you get some ALC across > the whole of > the passband you wish to use (probably corresponding to no > more than the > -3dB bandwidth points, beyond that and the steepness of the > filter slopes > would cause unacceptable distortion of even a narrowband > signal such as > PSK31.) Then you will achieve constant power across that > range, because the > ALC will be able to apply varying amounts of gain reduction > to achieve that > constant power level. The K2 can do this. Why can't the K3? > > > > > Try this experiment with your FT-817 ... set the power level > > to the maximum, turn off any compression, set your soundcard > > to 1700 Hz and the level for 15 Watts out of the FT-817 with > > NO ALC. Now, without making any other changes measure the > > power output with a 200 Hz tone and a 3200 Hz tone. Is it > > identical AT ALL THREE points? > > > > The FT-817 is not capable of 15W. But that is beside the > point. What would > this experiment prove? I know as well as you do that it would not be > identical. That's why I am saying that some form of level > control needs to > be in operation across the whole of the passband you wish to > use. A small > amount of ALC with a slow time constant will not harm the IMD > in PSK31 mode. > The K2 demonstrates this. > > In SSB mode the K3 ALC provides the level control I am > describing. If I turn > CMP off and switch the audio source to LINE IN it works > exactly as I expect > it to work in data modes (apart from not disabling EQ, which > is a different > issue.) In DATA A mode it does not do this, so you must > constantly tweak the > drive level whenever you change frequency if you wish to > transmit a specific > power level. > > If this is how the K3 is supposed to operate then I shall put > it up for sale > right away, because it is not something that people who use > data modes a lot > want to do. (Well, perhaps there are some, because if I have > learned nothing > else from my participation in ham forums like this, it is > that some people > actually like doing things the hard way.) > > ----- > 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 |
Re: K3 pwr out on digimodes
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In reply to this post by Leigh L. Klotz Jr WA5ZNU
> One option (and I expressed this a year or so ago to the > Elecraft folks) would be to offer an IMD calibration at the > IF level for a known two-tone response, to determine whether > at least that stage is being overdriven. Unfortunately, the PA will be overdrive far before the IF. Doing any kind of IF IMD calibration will provide almost no benefit since the IF appears to be clean at almost any level (measured on the XVTR IF output). > Digimode programs could then have a dedicated button to > send an idle tone, read the IMD, and adjust the power. Digimode programs can already be programmed to send an idle signal and read the Power Meter (BG get) if the display is set to the proper mode. That would allow the software to adjust for a specific power level. However, that requires K3 specific software. Its also very possible to adjust the drive for a specific ALC level - again using BG if the meter is set to read ALC instead of Power. However, the important parameter in the K3 is probably power output rather than ALC level. 73, ... Joe, W4TV > -----Original Message----- > From: Leigh L. Klotz, Jr. WA5ZNU [mailto:[hidden email]] > Sent: Friday, January 16, 2009 2:18 PM > To: [hidden email] > Cc: 'Julian, G4ILO'; [hidden email] > Subject: Re: [Elecraft] K3 pwr out on digimodes > > > Joe W4TV wrote: > > Closed loop power controls are not appropriate to SSB > systems because > > time constants sufficient to maintain constant power across the IF > > passband for digital operation would result in frequency dependent > > clipping and/or compression in voice operation. > > Most digimode programs include a tune button which outputs a > tone at the selected output; psk's idle is a simple two-tone. > One option (and I expressed this a year or so ago to the > Elecraft folks) would be to offer an IMD calibration at the > IF level for a known two-tone response, to determine whether > at least that stage is being overdriven. The DSP should have > a fairly good idea at that point. If the two-tone signal > used is a PSK idle tone at the selected AF on the waterfall > display, a rig control command to read the IMD calculated > would be just peachy. Digimode programs could then have a > dedicated button to send an idle tone, read the IMD, and > adjust the power. Regular communications could then commence. > > A further advantage of this approach is that the actual power > out could be measured during this calibration period from > either the built-in wattmeter or the rig control command, and > reported in real time, and thus the knob could (or again, rig > control) could be used to achieve the output power desired by > the user. > > Elecraft's response was that perhaps the IMD calculation > could be done on the computer side; I'm not clear whether the > new monitor out function makes that possible or not, but if > it does, that would be an approach that could be made to work > today, modulo the limitation that the IMD calculated from the > sound card will be a little worse due to the additional ADC > of the sound card, whereas a digital report from the K3 IF > would be accurate. (And not to mention that an overdriven > line input would result in a drastically wrong IMD, but > that's likely to have been already taken care of by the > digimode RX setup.) > > In summary, I believe it's possible to provide closed loop > control for both power and drive/IMD readings for modes such > as PSK, but not during a QSO where the signal characteristics > vary; instead provide enough CAT commands and signal quality > measurements from the K3 RF OUT and IF OUT stages so that and > digmode authors are willing to provide a "TX CAL" tune > button. (Doing in the k3 utility wouldn't be helpful because > the precise audio settings used by the digimode program for > TX are important.) > > I'm willing to step up and try this for fldigi. > > Leigh/WA5ZNU > > > _______________________________________________ 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 pwr out on digimodes
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In reply to this post by Joe Subich, W4TV-4
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