dennis12amplify@aol.com wrote:
> Dave,
>
> Sounds like the only correct solution would be the point of convergence
> of two simultaneous equations...
>
> Regards,
>
> Dennis O.
> Motorola
Yes, you are right.
There are two simultaneous equations which would need to be solved to do
it properly.
This is reminding me a bit of one of the 'RMS power' arguments on Amps.
I eventually solved that one (to my satisfaction anyway).
http://www.g8wrb.org/useful-stuff/rmspower.shtml
But I'll leave this PEP/IM program for Gary to solve!
dave G8WRB.
> -----Original Message-----
> From: Dr. David Kirkby <david.kirkby@onetel.net>
> To: amps@contesting.com <amps@contesting.com>
> Sent: Wed, 17 May 2006 07:06:45 +0100
> Subject: Re: [Amps] How intermod limits your PEP
>
> Gary Schafer wrote:
>
>> Hi David,
>>
>> Yes I am in error, thank you, but only on the examples where the PEP is
>> greater than 1000 watts (1123 watt example) I believe.
>
> But as you say, as soon as you add any IMD, to a signal, whilst keeping
> the signal level constant at 1000 W PEP, the PEP power will exceed 1000
> W due to the distortion.
>
> Are you talking about an AM signal, with a carrier and two sidebands, or
> an SSB one, with no carrier? I assume it is AM.
>
>> The signal should be 223 (not 233 as you noted).
>
> No, see below.
>
>> My attempt is to show how distortion products, however small they may seem,
>> add to the PEP.
>
> Agreed.
>
>> Keeping PEP to 1000 watts would require reducing the signal level as you
>> noted and keeping the IM level the same.
>
> No!! It distorts (pun intended) the figures.
>
> If you run up your amp to something over 1000 W, then decide to turn it
> down to 1000 W (by for example lowing the input drive), whilst keeping
> the IM products the same amount down (-30 dB to take one of your
> examples), then *both* the signal *and* IMD signal must be reduced - not
> just the signal. So the power of the IM products must fall below 1 W
> each or 7 V RMS.
>
> Symbols (P1, P2, f1, f2 ... etc) would make it a lot easier to see. One
> could then do it for any signal levels or IMD you want.
>
>> My first example of PEP being greater than 1000 watts would indeed give a
>> ratio where the distortion products would be better than 30 db below PEP but
>> not by much. It would be 30.5 db rather than 30 db if I am now doing that
>> right.
>
> I am a bit confused exactly what you are doing, so are not going to work
> it out. But I think your method is flawed.
>
>> It would probably be easier to just relate distortion products to the level
>> of one of the signals of the two tone signal rather than to PEP and show how
>> PEP changes.
>
> Well this is one of the things you can do any number of ways - it just
> depends on what you want.
>
> As long as you state it, then it does not matter. But as it is, I don't
> think the explanation is clear. Others clearly disagree, as several have
> commented on it being clear. Perhaps it is just me.
>
>> Thanks for the comments.
>
> You are welcome.
>
>> 73
>> Gary K4FMX
>>
>>
>>
>
>
> --
> Dr. David Kirkby BSc MSc PhD CEng MIEE
> Chartered Engineer
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--
Dr. David Kirkby BSc MSc PhD CEng MIEE
Chartered Engineer
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