Bob & Eric, Bob, I tried the use of the CPDR with poor results. At the second lowest setting of the CPDR (2 db) the audio quality was degraded significantly introducing a lot of distortion. At the lowest setting, (1 db) the distortion was less, but still very prevalent. At these setting, there was no difference in RF power output between using CPDR and not.
I did the same test using just the COMP and the results were similar, but I had to use higher values (4 & 2 dB respectively). Even at 1 dB there was still noticeable distortion. Using the TX EQ did help some, but I had to add a lot of gain to make a slight difference and adding that much gain resulted again in a distorted audio signal. So I tried some more testing... Using a PSK steady tone (carrier only), I set the output gain until I was showing 50 watts Peak and Avg. power output (1/2 of the rated value of the PA). I used this value to "calibrate" my non-peaking reading watt meter. I also verified this with a CW carrier and they were very close. With the MIC setting peaking at 0 dB, the RF output is just 20 watts. The Peak power meter showed a max peak of 46 watts. I have a true peak reading watt meter on order that should be here next week so I can more accurately measure RF output and I will run my test using it. I also did an "on air" test where I used Preview 7 and Preview 12 using the same configuration, only adjusting the MIC gain to give equal 0 dB on peak readings and was told that the Preview 7 was much stronger and didn't have any distortion on the audio signal (subjective opinion, of course). With Preview 12, the signal was much weaker and the observer couldn't tell any discernable difference in the audio quality other than to say both sounded very good, but because the preview 12 version was less strong, he couldn't give a honest opinion to if it was less over driven or not. I understand how SSB works and I don't expect to "see" 80-100 watts output continuously, but the behavior I expect is to see some peaks above 50 watts and a higher value for average power. I also understand your explanation concerning the AGC limiting the RF output and not wanting to over drive the PA, but when I can get 100 watts (and more) out on CW and PSK distortion free, 20 watts on SSB voice seems to me a little bit aggressive. Maybe the AGC is working "too" well. My testing methodology is the best I can do right now with the tools I have and if there is some flaw in my logic, I'd like to know so I can make the appropriate changes. I am very pleased with the changes made to the RX in this preview stream, but a four fold decrease in TX output from preview 7 to 12 is obviously not what I was expecting. I just don't have the antenna system to start working QRP :-) Do you have any suggestions for parameter I can work within the software that might elevate the low TX power issue that wouldn't adversely affect the RX quality? I'm not criticizing or complaining, just concerned that one of the features of the radio I expect to behave at a certain level is not. I am open to any suggestions other than to just live with the low power output or use only preview 7. -Tim --- Tim Ellison ( [EMAIL PROTECTED] ) Integrated Technical Services ( http://www.itsco.com ) -----Original Message----- From: Robert McGwier [mailto:[EMAIL PROTECTED] Sent: Friday, January 20, 2006 11:58 PM To: Tim Ellison Cc: [EMAIL PROTECTED] Subject: Re: Steady drop in output power with successive Previews. All things where the peak used to exceed the target level by a lot, will be rolled back now that the agc is actually working correctly for the first time. The reason for the fast/slow track agc is so the average power will not be lowered significantly but the peaks will be rolled back. Bob Tim Ellison wrote: >Bob, > >Thanks for the explanation. I am actually using both the FWD PWR meter >and an external meter. I don't claim absolute accuracy and it is hard >to get accuracy without a true peak reading watt meter. I have a fairly >good idea what the power reading is close to, but I am mostly using it >to judge changes in magnitude assuming that it is close in linearity. > >Would the AGC changes also be responsible for reducing the effect of the >limiter as well? > >I'll trying playing with the CPDR tomorrow after work. > >-Tim >--- >Tim Ellison ( [EMAIL PROTECTED] ) >Integrated Technical Services ( http://www.itsco.com ) > > >-----Original Message----- >From: Robert McGwier [mailto:[EMAIL PROTECTED] >Sent: Friday, January 20, 2006 11:12 PM >To: Tim Ellison >Cc: [EMAIL PROTECTED] >Subject: Re: Steady drop in output power with successive Previews. > >We are in fact throttling way back on the peaks with the fast channel in > >the agc algorithm. However, let me say that we have been letting the >amplfier be seriously overdriven, in fact, into nonlinearity. The >patterns we are seeing on the oscilloscope are nearly perfect Christmas >tree patterns. Trying engaging the CPDR and also adjusting the TX EQ >for your voice to attempt to raise the average power level. The CPDR >should work with much less distortion now. I am sure you are seeing >the fast channel agc in action. It appeared in Release 8 and has >steadily been improving in its action. > >Are your readings done with the TX meter or an external power meter? > >Bob > > > > > >Tim Ellison wrote: > > > >>Eric et. al., >> >>Starting with Preview 8 and above, I have noticed a stepped gradual >> >> >loss > > >>of TX output power. Preview 12 is by far the worst culprit. >> >>As a reminder so we are on the same page, I did some testing a few >> >> >weeks > > >>back between Preview 7 and Preview 8 & 10 and found that having the >>leveler on when using preview 7, the output was between 80-110 watts >>(SSB) and in Preview 8 using exactly the same settings and a constant >>audio input source, the output was down about significantly (~50%). >>This behavior still exists in Preview12 - there is no change in output >>no mater if the leveler is on or off >> >>I downloaded Preview 12 tonight and imported my Preview 7 database to >>test the output since there was a change in the MIC algorithm. I set >>the MIC value to 0 dB and tried the test again. My RF output is now >>down to about 20 watts (peaks on an external watt meter). I re-ran >> >> >the > > >>PA adjustments to make sure that there wasn't any gain variance between >>version 7 and 12. It made no difference. >> >>I use Preview 12 for RX but resort to Preview 7 for TX/RX >> >>Got any clues tests or any tests you want me to try? >> >>BTW, the AGC just keeps getting better! Obrigado! >> >>73 de W4TME >> >>-Tim >>--- >>Tim Ellison <mailto:[EMAIL PROTECTED]> >>Integrated Technical Services <http://www.itsco.com/> >>Apex, NC USA >>919.674.0044 Ext. 25 / 919.674.0045 (FAX) >>919.215.6375 - cell >> >> >> >> >>>>>PGP public key available at all public KeyServers <<< >>>>> >>>>> >>>>> >>>>> >> >> >> >> >> >> >> > > > > -- AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats, NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman Laziness is the number one inspiration for ingenuity. Guilty as charged!
