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| intermod calculations http://interceptradio.com/bbs/viewtopic.php?f=1&t=2082 |
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| Author: | gregz [ Mon Apr 28, 2008 8:50 am ] |
| Post subject: | intermod calculations |
Intermodulation between a set of frequencies is pretty easy to understand and calculate. what I was wondering is do I need to calculate intermod across a WIDE range of frequencies. for instance: when calculating intermod for 5 UHF transmitters in the 500MHz range, do I need to worry about VHF and 900MHz transmitters in the vacinity as well? The front end has a 50MHz filter on it so I'm thinking anything farther then that I don't need to worry about right? thanx |
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| Author: | chpalmer [ Mon Apr 28, 2008 9:34 am ] |
| Post subject: | Re: intermod calculations |
Ill put up a VHF example... 151.500 * 3 = 454.500 This isnt intermod but an example of harmonics. If the transmitter does not have a true bandpass filter or harmonic filter on its output then the harmonic will be heard by a receiver on the uhf frequency just like its supposed to be there. These harmonics can mix also. Unfortunately duplexers sold today are hybrids and pass out of band frequencies freely. We spec our equipment to have an added bandpass cavity on every transmitter and receiver port just because of this. Unless the filter design includes bandpass cavities already... This article by a friend of mine http://k7pp.com/art003.html is a good read. Its not an answer to your question but might open up an answer your looking for... Hopefully someone else that knows this end better than I can also comment... :mrgreen: |
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