If Reduced Carrier AM is such a such a Good ThingTM, why use regular AM at all?
Mni tnx and hope everybody is recovering from their Thanksgiving meal.
I find your question very interesting. I have wondered what the envelope of AM looks like on the Flex. Is it 100 percent modulation? If so, the instantaneous peak power can be as high as four times the carrier power. Due to this restriction the final amplifier can run no more than 25 Watts of average power to attain full 100 percent modulation. It will be interesting to see how this thread unfolds.
There is no theoretical advantage to using AM. It is more of a legacy mode and many hams make a "career" of restoring vintage radios and reliving the days of yesteryear. It is fun to join in as many of the AM users are very knowledgeable technicians and engineers and enjoy making their radios sound like they are of broadcast quality. I have heard several users using the Flex 5000 with linear amplifiers and they sound magnificent.
What has not been said about reduced carrier is that the carrier for 100% modulation is full carrier, and this is what you typically see on POP music broadcast. Listen to some talk radio and you will see the carrier drop during quiet portions and will also hear the background noise rise due to your AGC action.
The carrier for (averaged) lower modulation percentages is reduced but still sufficient to produce clean detection. Note: This is also the definition of compression if the AGC is very fast but for normal or slow AGC then the audio levels will be a factor of the peak modulation power for signals that go into high % modulation; slightly exaggerated compression for signals that peak out at lower than 100% modulations.
Re-reading this I see the mud rising to cover the whole explanation.
The audibility of distortion is a complex subject, too. If the peak to average ratio of the modulating signal is high, clipping distortion won't seem quite as annoying. And if the modulating audio has boosted treble, clipping distortion will seem less objectionable for most listeners.
One of the great things about double-sideband transmission is that it is actually dual-frequency diversity SSB. This gives the guy on the receiving end the ability to rapidly switch between USB and LSB reception for best signal-to-noise ratio in a rapidly-changing QRM situation, without the guy who is transmitting having to change anything. There is even a way -- using a Costas or W3DUQ detector -- to reject the interference from one sideband or the other while still getting the desired signal from both sidebands. This kind of detector is now available on some SDR software platforms.
The adjustable carrier on the 6000 will allow something like this. but use it sparingly.
Ken - NM9P
I decided to introduce this discussion into the AMFONE forums. The guys who hang out there are primarily AM operators who use both SDR radios, Class E and legacy “boat anchors”. Some very interesting facts have been exchanged, especially the one I quoted below.
Last night I tried an experiment. I currently use my 6500 to drive an ACOM 1000. With the AM Carrier set to max, I adjust the unmodulated AM output of my 6500 to produce 200W out of the ACOM 1000. This produces ~ 800W out on peaks. Next, while applying an unmodulated signal, I reduced the AM carrier setting to decrease the ACOM’s output to 100W. We compared both scenarios. I received several signal reports, none of which noted anything negative, but no improvements with stations where I was weak. While my signal was not any better, I definitely noted a decrease in the ACOM’s air exhaust temperature. If for nothing else, AM Reduced Carrier can probably be used to reduce power consumption and amplifier wear and tear. If AM operation is of interest to you, please check out the discussion below.
“(AM Reduced Carrier) will not increase talk power or any other kind of power. The Flex has a maximum PEP capability. You can utilize this PEP capability by running the carrier at about 1/4 the max PEP and modulating 100% or you can run less carrier and modulate more the 100% on positive peaks. In any case, you will achieve the same exact output on the receiver at the far end. There is no free lunch.”