Hal,
I wonder what all the molocules in their blood, and their genes have to say by
setting directly under all that power? I have heard of several cases of cancer
they think was caused by it, along with blindness. As far as splatter, if you
live in the town it's happening at, forget watching TV for a while.
Best,
Will
*********** REPLY SEPARATOR ***********
On 5/16/06 at 12:57 PM Harold Mandel wrote:
>What a fine presentation!
>
>Thanks for your easy-to-understand explanation
>of distortion-related inefficiency.
>
>I read of these "CB Shoot-Outs" where mobile operators
>run 15KW for 30 seconds or so, from homebrew amplifiers
>that are designed for raw power only and wonder what
>a spectrum analysis of their transmitted waveforms
>would look like, even at the 7th and 9th order.
>
>Hal
>W4HBM
>
>
>
>-----Original Message-----
>From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>Behalf Of Theo Bellamy
>Sent: Tuesday, May 16, 2006 8:43 AM
>To: garyschafer@comcast.net; amps@contesting.com
>Subject: Re: [Amps] How intermod limits your PEP
>
>Gary,
>
>Great piece ... thanks! I always wondered about the actual numbers. Talked
>to some goofball at a hamfest a while back who was telling me about his
>pair
>of 3-500Z with 5KV on them, and how they would "put out more" than an 8877.
>I said that would be great if he can keep all those watts spewing out on
>the
>frequency he wanted. Got a blank stare from him on that one.
>
>73 - Theo K4MO
>
>
>
>-----Original Message-----
>From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
>Behalf Of Gary Schafer
>Sent: Tuesday, May 16, 2006 12:39 AM
>To: amps@contesting.com
>Subject: [Amps] How intermod limits your PEP
>
>
>HOW INTERMOD LIMITS YOUR PEP.
>
>
>
>Some interesting notes on PEP and intermod.
>
>
>
>With 1000 watts PEP output and 3rd order IM products down -30 db from PEP
>(-24 db from from one tone of a two tone test ) the useful PEP output is
>only 873.6 watts. The other 126 watts PEP is wasted power.
>
>
>
>At -20 db 3rd order products from PEP (-14 db from 1 of two tones) the
>useful PEP output power is only 636 watts.
>
>
>
>Here?s how it works:
>
>P = E squared / R.
>
>1000 watts PEP into 50 ohms is around 223 volts at 50 ohms.
>
>-30 db down from 1000 watts is 1 watt. 1 watt is about 7 volts at 50 ohms.
>
>
>
>With a two tone test signal there are two signals that are 6 db down from
>the PEP power. 6 db down is ½ the voltage so each of those signals will
>have
>111.5 volts. (111.5 volts is = ~ 250 watts average power in each signal.)
>
>
>
>To find PEP all voltages of all parts of the signal must first be added
>together. Then squared and divided by 50 ohms. Thus if we add 111.5 + 111.5
>we get 223 volts. That squared and divided by 50 ohms gives us the 1000
>watts PEP.
>
>
>
>But we also have our 3rd order distortion products present and it is not
>just one signal that makes it up but two! We have 1 watt (-30db) signal on
>the high side of the original two tones and we have another 1 watt (-30db)
>product on the low side of the original two tones. Each of those 1 watt
>signals contains 7 volts of signal.
>
>
>
>When we figure PEP we need to add all the voltages together first. So with
>7
>volts in each that makes 14 volts of distortion products.
>
>
>
>223 volts in the two tone signals plus 14 volts in the two 3rd order IM
>signals gives us 237 volts. Square that and divide by 50 ohms gives us 1123
>watts PEP.
>
>
>
>If we limit the amplifier power output to 1000 watts PEP (maybe that?s all
>it is capable of) we first subtract the distortion products to find useful
>PEP output.
>
>Since our amplifier is limited to 1000 watts PEP output we must subtract
>the
>14 volts from the 223 volts that make up the 1000 watt signal. That leaves
>209 volts for both of the two tone signals, as high as we can run them.
>Square 209 and divide by 50 ohms leaves us with 873 watts PEP of useful
>power for our 1000 watt amplifier.
>
>
>
>This leaves us with 418.5 watts of average power (½ of PEP) rather than 500
>watts average power output that the amplifier would be capable of. Even
>though the IM products are only 2 watts average power out the amplifier
>must
>be throttled back to limit the peak envelope power to the amplifier
>capability.
>
>
>
>At -20 db 3rd order below PEP (-14 db below 1 of two tones) we have 10
>watts
>in each 3rd order product. That gives us 1432 watts PEP output with only
>1000 watts of useful power out.
>
>
>
>Or if we limit the amplifier to 1000 watts PEP output the useful power will
>be around 636 watts PEP from our 1000 watt amplifier.
>
>
>
>Now if we add in the 5th order products things get even worse.
>
>
>
>But you can see how even moderate levels of IM products add to the peak
>envelope power of an amplifier which can give a very false impression of
>what is really useful power.
>
>Since we are limited by the FCC to peak envelope power it is to our
>advantage to limit distortion products to the lowest levels in order to not
>hit the PEP limit too soon.
>
>
>
>73
>
>Gary K4FMX
>
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