I would like to see the solution to the math problem. However, I think
that it is important for us to remember that Gary's point is valid.
Many of those that look at their wattmeters and say they're running 1500
Watts output should consider how much of that power is someplace other
than their intended operating frequency.
Recently I listened to a guy on 75 meters brag about running 1300 Watts
output from his AL-80B. He was proud of how he had is buddy, who was
listening to his 40 over signal, switch sidebands and tell him his IMD
was 30 dB down. These are the ones we hear popping and splattering up
and down the band and no amount of arguing will convince them otherwise.
Good solid data with the math to back it up would be a good thing to
have laying around. Maybe some of them would discover it and think about
what they're doing.
73, Tony W4ZT
Dr. David Kirkby wrote:
> 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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>> Amps@contesting.com <mailto:Amps%40contesting.com>
>> http://lists.contesting.com/mailman/listinfo/amps
>
>
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