Rick, My explanation was for sinusoids not rectangular waves, our radios transmit sinusoids. You are correct about rectangular waves they would have a crest factor of 1 in linear terms or voltage terms, and 0B in non-linear or power terms. Yes MT63 has a crest factor of 13dB. It is very high.
Lets deified a few power terms. Average or mean power is what you get when you multiply RMS voltage and current Peak Instantaneous power or peak power is what you get when you multiply peak instantaneous voltage and current. Peak Envelope power or PEP is what you get when you average the peak power over one RF cycle. Crest Factor is normally given in terms of voltage and is equal to the peak amplitude of a waveform divided by the RMS value. In terms of power this is the 10log(peak power/average power). The relationship between peak power and PEP in a sinusoid is 3 dB. This is very easy to prove. The relationship between peak voltage and RMS voltage is the square root of 2. 20 log of the square root of 2 is 3dB. Lets use a more complicated example. Lets say we generate a sinusoid from two equal amplitude tones. A two tone test. On an oscilloscope we observe that the peak voltage is 1 voltage unit for each tone which makes the peak power 1 power unit for each tone. The peak voltage of the envelope is 2 voltage units , so the peak power is 4 power units for the envelope. Each tone's RMS voltage is 1/square root of 2 or approximately .707 voltage units. The average power is the RMS voltage squared or .5 units. The total average power of the two tones is .5 + .5 or 1 unit. When using N tones to produce an envelope, PEP to average power ratio is 1/N. In this case it is .5, which means that the PEP is 2 units. Here are the relationships Peak power of the envelope = 4 PEP of the envelope = 2 Average power of the envelope = 1. PEP to average ratio = 3dB Peak to average ratio = 6 dB Difference = 3 dB This same example can be worked with any number of tones. Patrick used two programs if I remember correctly to calculate the peak and mean power for the various modes listed in the documentation for Multipsk. The two programs were Cool Edit Pro and Sox. In Cool Edit Pro the peak value given in the statistics is PEP. What Patrick is giving you is the PEP to average ratio. I have proven this in Cool Edit Pro using the 2 tone example above. 73, Mark N5RFX At 09:12 AM 8/24/2006, you wrote: >How does the crest factor relate to the mean power vs the peak power? It >doesn't seem correct to add 3 to that figure to come up with the crest >factor. > >Patrick has the peak and mean power for the various modes listed in the >documentation for Multipsk, but I am not clear how to convert them to >crest factor. > >My understanding is that the peak power and average power of a >rectangular wave is 1. It can't be correct to add 3 to that value to >come up with 4, can it? > >And MT-63 which has a peak to average of 10 times has a crest factor of 13? > >If you want to "broadcast" a message from one to many, then the only >practical alternative is to use a non-ARQ mode, typically with a large >amount of FEC. While this is done on amateur frequencies for sending a >bulletin, calling CQ, and having a roundtable, if your goal is to have >accurate messaging, then I don't see any option other than a good ARQ >system. > >If Clover II would have worked better, I would have considered keeping >my HAL P-38 board. But it was not that good with weak signals. Also, the >P-38 had serious problems with Pactor back then. I remember someone >later criticizing me for not using a 386 computer for the card. But at >that time the 386 was barely even invented and 286 machines were state >of the art. > >73, > >Rick, KV9U > >Mark Miller wrote: > > >At 10:33 PM 8/23/2006, you wrote: > > > > > >>I am not very knowledgeable on CRF (Crest Factors). Can you give us an > >>idea of converting peak power/average power into CRF? > >> > >> > > > > > >Using powers, crest factor = Peak Instantaneous Power / Average Power. A > >more piratical way of measuring crest factor is (PEP/Average Power) + 3dB. > > > >I agree that ARQ has its benefits, but we still have to rely on the modem > >scheme. This was my point earlier, that we reach a limit because we are > >power and bandwidth limited. Because we are using HF frequencies, we pay a > >coding penalty. Also if we look at the broadcast nature of non-ARQ modes, > >it is apparent that they are much more efficient than ARQ modes. This does > >not mean that ARQ does not have its place, it certainly does. The more > >tools in the tool box the better. > > > >BTW I am an AMTOR OT myself. I remember when APLINK was used before > >unattended operation was allowed on HF. I miss keyboarding with > >AMTOR/PACTOR and CLOVER. > > > >73, > > > >Mark N5RFX > > > > > > > > > >Need a Digital mode QSO? Connect to > <Telnet://cluster.dynalias.org>Telnet://cluster.dynalias.org > > > >Other areas of interest: > > > >The MixW Reflector : > <http://groups.yahoo.com/group/themixwgroup/>http://groups.yahoo.com/group/themixwgroup/ > >DigiPol: > <http://groups.yahoo.com/group/Digipol>http://groups.yahoo.com/group/Digipol > (band plan policy discussion) > > > > > >Yahoo! Groups Links > > > > > > > > > > > > > > > > > > > > > > > > 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/ <*> 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/
