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#9
May 31st 07, 04:54 PM
posted to rec.radio.amateur.antenna
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Splitter For Two Scanners And One Antenna ?
In message , Roy Lewallen
writes J. B. Wood wrote: In article , Roy Lewallen wrote: One of the properties of the splitter, as opposed to just a tee connector, is that the two receivers are isolated from each other. So turning one on or off or disconnecting it should have no effect on the other. Roy Lewallen, W7EL Hello, Roy, and all. I would also add that the degree of isolation achieved in an n-way splitter is predicated on how well the port being split n-ways is terminated in the splitter's design characteristic impedance (e.g. 50 or 75 ohms). Sincerely, John Wood (Code 5550) e-mail: Naval Research Laboratory 4555 Overlook Avenue, SW Washington, DC 20375-5337 A good point, and one I hadn't considered. The chances of the antenna impedance being 50 ohms over the band of frequencies likely to be used by a scanner is about the same as its being 75 ohms, which is to say about zero. (This is almost certainly true for most TV antennas over the whole TV frequency range also.) Whether the isolation is good enough will have to be determined by experiment. If it isn't, the only solution would be to put a pad at the splitter input to stabilize the impedance. It probably wouldn't take much attenuation to make an appreciable improvement in the isolation. But this application might not require a great deal of isolation anyway. Roy Lewallen, W7EL Just buy it and try it (a TV splitter will only cost a couple of dollars). It will probably work more than well enough, even if the isolation is well short of the (say) 25 to 30dB you might get under 'ideal' conditions. I wouldn't add any extra attenuation just to ensure that the input port is matched better. You're already going to lose 3dB + just because you are splitting. Ian. -- |
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