RE: [AMRadio] AM Power Level
Joe, When you're aligning your SX-117, check the coupling caps. I had a Hammarlund HQ-110 from the 60's that needed some coupling caps to bring the sensitivity back. Have fun! Ken Zuercher, KC8QO --- Joe Bento <[EMAIL PROTECTED]> wrote: > Thanks all for your help. There are far more > variables than I thought in calculating > the actual PEP output of an AM transmitter. It will > be some time yet till I'm ready to > get on the air in AM mode. Besides the class-E > project, I need to give my > Hallicrafters SX-117 receiver an alignment. It's > become somewhat deaf over the > years. Otherwise, I do not currently have another > HF receiver suitable for AM. My > older Kenwood transceiver is good for CW and SSB > only. > > Thanks for the help! > > > 73 > Joe Bento > N6DGY > Pleasant Grove, Utah > > > > ___ > AMRadio mailing list > AMRadio@mailman.qth.net > http://mailman.qth.net/mailman/listinfo/amradio __ Do you Yahoo!? The New Yahoo! Search - Faster. Easier. Bingo. http://search.yahoo.com
RE: [AMRadio] AM Power Level
Thanks all for your help. There are far more variables than I thought in calculating the actual PEP output of an AM transmitter. It will be some time yet till I'm ready to get on the air in AM mode. Besides the class-E project, I need to give my Hallicrafters SX-117 receiver an alignment. It's become somewhat deaf over the years. Otherwise, I do not currently have another HF receiver suitable for AM. My older Kenwood transceiver is good for CW and SSB only. Thanks for the help! 73 Joe Bento N6DGY Pleasant Grove, Utah
Re: [AMRadio] AM Power Level
Hi Joe, Generally for 100% positive modulation, 1500W PEP translates into a 375Watt carrier. (These are output levels.) But in the real work=ld, this ain't necessarily so... Check WA5BXO's website, there is some interesting reading on AM power regarding carrier and modulation vs. PEP. http://www.qsl.net/wa5bxo/ In particular on John's WA5BXO site, check AM Tech Page, Natural Asymmetrical Modulation, and Amplitude Modulation and PEP. Bacon, WA3WDR - Original Message - From: <[EMAIL PROTECTED]> To: Sent: Sunday, May 18, 2003 1:14 PM Subject: [AMRadio] AM Power Level > I'm a new subscriber to the list, and I have not discovered the way to do a search > through the old archives. Forgive me if this has already been covered. > > I'm currently in the process of collecting the parts to build a Class-E Am transmitter > and Class-H modulator for 75 meters. (I was quite surprised at the relative > simplicity of the circuit!) While I have been a boatanchor collector for years, and > also an on-and-off-again Electric radio subscriber (though I have every issue) I have > never yet been on the air in AM mode. Listening on 75 off and on over the years > has me itching to finally change that. > > I'm interested to know if I understand the newer FCC power guidelines correctly and > how peak power on AM is measured. The FCC now stipulates 1500 watts peak > output. Am I correct in understanding that in AM, the peak output at 100% > modulation is four times the carrier level? Does this mean that if one is to be strictly > within the FCC rules, you can have a carrier of only 375 watts in the AM mode? > > My proposed transmitter will be capable of a unmodulated 600 watt carrier. > Fortunately, it appears to be a simple matter to reduce power in a Class-E amp just > by lowering the supply / modulation voltage to the MOSFET drains. > > Any help in furthering my understanding is appreciated. > > Thanks! > > 73, > Joe > N6DGY > > > ___ > AMRadio mailing list > AMRadio@mailman.qth.net > http://mailman.qth.net/mailman/listinfo/amradio
RE: [AMRadio] AM Power Level
Welcome Joe: What Mike says is 100% true. You might want to look at this web site it may clear things up as to why it is so cloudy. HI http://www.qsl.net/wa5bxo/asyam/aam3.html & http://www.qsl.net/wa5bxo/amplitude-modulation-and%20pep.htm & http://www.qsl.net/wa5bxo/all-about-modulation.htm -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Sunday, May 18, 2003 12:15 PM To: amradio@mailman.qth.net Subject: [AMRadio] AM Power Level I'm interested to know if I understand the newer FCC power guidelines correctly and how peak power on AM is measured. The FCC now stipulates 1500 watts peak output. Am I correct in understanding that in AM, the peak output at 100% modulation is four times the carrier level? Does this mean that if one is to be strictly within the FCC rules, you can have a carrier of only 375 watts in the AM mode? My proposed transmitter will be capable of a unmodulated 600 watt carrier. Fortunately, it appears to be a simple matter to reduce power in a Class-E amp just by lowering the supply / modulation voltage to the MOSFET drains. Any help in furthering my understanding is appreciated. Thanks! 73, Joe N6DGY ___ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio
RE: [AMRadio] AM Power Level
Hi Joe, you have asked a somewhat controversial question about an often misunderstood concept in radio. Unfortunately the answer is NOT simple. Yes, the FCC limits us to 1500 watts PEP. And yes if you modulate an RF carrier with a sinusoidal waveform to 100% - meaning the peak composite envelope is twice the amplitude as the unmodulated carrier - then the PEP (and that is in RMS watts by definition) of the composite envelope is four times that of the unmodulated carrier. Because: Power = E^2/R when the envelope voltage doubles, the power increases by four. Therefore, with the above conditions a 375-watt carrier modulated to 100% with a single sine wave will produce a peak envelope power of 1500 watts RMS. Having said that, we do not modulate with a single sine wave (there is no information in it). Normal audio waveforms are very complex and asymmetrical in nature. That means that the positive peaks are not equal to the negative peaks on average. If we modulate with an asymmetrical waveform so that the larger excursions of the modulating waveform are INCREASING the composite AM waveform, then it is possible to get a composite waveform that is greater than twice the unmodulated carrier. Assuming an unmodulated carrier power of 375 watts, the PEP would be greater than 1500 watts. You would have to lower the power of unmodulated carrier power to stay within 1500 watts. On the flip side if the larger excursions are DECREASING the composite AM waveform - as would be the case if you inverted the waveform somewhere in the audio chain - then when 100% modulation occurs (just pinching off the composite AM waveform) , the peak composite envelope would not double but be something less than double. And a 375-watt carrier would NOT produce 1500 watts PEP. In this case, one could increase the carrier power and still stay within 1500 watts PEP. This is not, however, the optimum situation, because the amount of power in the sidebands would be much less compared to the first case. And audio power is the key as the carrier is "along for the ride." Increasing the positive excursions of the composite AM waveform to greater than 100% while maintaining no greater than 100% on negative excursions will yield stronger audio simply because the average power in the sidebands is greater. Broadcast stations do this as a matter of standard operating procedure. They run the positive excursions to 125% or greater to get that increased audio presence. Does deliberately forcing asymmetry cause distortion? Yes, but not so much as to be unpleasing to the ear. In fact this little bit of distortion helps make the audio sound louder. I hope this helps. See I told you the answer was not simple. I'm sure others will contribute to this discussion. It seems that it goes around on an annual basis -hihi. Get that AM rig on 75 soon! We would love to have you join us on 3880. 73 Mike WA5CMI -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of [EMAIL PROTECTED] Sent: Sunday, May 18, 2003 12:15 PM To: amradio@mailman.qth.net Subject: [AMRadio] AM Power Level I'm a new subscriber to the list, and I have not discovered the way to do a search through the old archives. Forgive me if this has already been covered. I'm currently in the process of collecting the parts to build a Class-E Am transmitter and Class-H modulator for 75 meters. (I was quite surprised at the relative simplicity of the circuit!) While I have been a boatanchor collector for years, and also an on-and-off-again Electric radio subscriber (though I have every issue) I have never yet been on the air in AM mode. Listening on 75 off and on over the years has me itching to finally change that. I'm interested to know if I understand the newer FCC power guidelines correctly and how peak power on AM is measured. The FCC now stipulates 1500 watts peak output. Am I correct in understanding that in AM, the peak output at 100% modulation is four times the carrier level? Does this mean that if one is to be strictly within the FCC rules, you can have a carrier of only 375 watts in the AM mode? My proposed transmitter will be capable of a unmodulated 600 watt carrier. Fortunately, it appears to be a simple matter to reduce power in a Class-E amp just by lowering the supply / modulation voltage to the MOSFET drains. Any help in furthering my understanding is appreciated. Thanks! 73, Joe N6DGY ___ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio
