Hello Rick, >the peak and mean power for the various modes listed in the
In Multipsk, you have the ratio between the average power and the peak power. The peak power is obtained if you have no band base windowing and if you are always transmitting one carrier at a given time (RTTY, MFSK16...). If you have one carrier (PSK31, for example) but a windowing or many carriers at a the same time (CMT/HELL for Video ID or MT63), you ratio is less than 1 (close to 1 for PSK31 and close to 0 for CMT/HELL for Video ID or MT63). It means that at the maximum, remaining linear, you cannot transmit much power: for aexample, 10 watts in MT63 for a 100 watts standard transceiver. This supposes that the AF is a sine. The crest factor of a sine is about -3 dB compared to a square wave (AF signal completly saturated). But there is no reason to transmit an AF square wave. There would not be a decoding gain (because the power considered by the decoder would be the one of the fondamental which would be -3 dB compared to the total power) and the signal would be found on all the AF spectrum (fondamental and harmonics). So the ratio to be considered is the one considered by Multipsk (taking into account that the figures are not very precise, but sufficient for comparizons). 73 Patrick ----- Original Message ----- From: KV9U To: digitalradio@yahoogroups.com Sent: Thursday, August 24, 2006 4:12 PM Subject: Re: [digitalradio] The digital throughput challenge on HF 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 > >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 > > > > > > > > > > > [Non-text portions of this message have been removed] 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/
