First, it ignores all the empirical evidence to the contrary. This alone would make the statement suspect.
Second, it ignores the different methods and implementations of ALC in different transmitters. One of the first effects of ALC is the imposition of an amplitude modulation on the RF envelope. This looks like a sawtooth whose shape is determined by the ALC characteristics of attack and delay time and whose amplitude is determined by the amount of ALC. The end result are pairs of sidebands that look like IMD. The stronger you drive ALC the stronger the sidebands will be. This is taken from "HF Radio Systems & Circuits" by Sabin and Schoenike. Another effect is that ALC occurs after the fact. This means a sudden "pulse" like a data tone may very well overdrive any gain controlled stages before rectified and amplified ALC voltage is applied. Depending on the decay time, this can occur on each off/on transition. Lastly, ALC's main purpose is to prevent overdriving amplifiers, not as some say to "increase average power output". You can achieve an increase in average power, but only by depending upon ALC to act as an RF clipper. Any time clipping is done, you introduce distortions that can severly impact the quality of the output. This also requires that ALC be adjusted properly so that RF amplifiers are kept in their linear region. This alone is probably not the case in many ham transmitters that haven't been aligned since their date of manufacture. By using very low levels of ALC or none at all, you eliminate all of the factors above insuring a good signal. Of course, even that assumes everything in your transmitter is operating linearly and as designed. Jim WA0LYK --- In digitalradio@yahoogroups.com, "Andrew O'Brien" <[EMAIL PROTECTED]> wrote: > > I found this quote today, anyone care to comment ? > > " Although it is a common belief to the contrary, it is in fact quite > alright to let the > transmitter ALC line operate on PSK31. The ALC line will control the drive > level without > clipping in the same way that it does on voice operation" > > Andy K3UK > Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/digitalradio/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/