What happens if I use 75 Ohm RG-59 cable instead of the recommended 50 Ohm cables for my antenna connections? Are lengths more than 3 feet OK? Open

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The RG-59 will work for even longer runs than 3 feet. Assume operation at 600 MHz and 70% velocity factor for the RG-59. You do get some mismatch, but you will get it at any point beyond a 1/8 wavelength which is only 1.7 inches (!). At a 1/4 wavelength, 3.4", you get the worst mismatch but that will still give you 88% of your power. At a 1/2 wavelength, the 75 Ohm cable will look like a perfect 50 Ohm match (!), since whatever impedance is at one end is transformed to the exact same impedance at the other end. At 3/4 wavelength it looks like the 1/4 wavelength case, 88%, and at 1 wavelength it looks like the 1/2 wavelength case or a perfect match again. This just repeats for each additional 1/4 or half wavelength of cable. Added to this small mismatch, you will have the cable loss which is actually lower for RG-59 than for RG-58, since RG-59 is physically larger. You can use RG-59 for up to 15 feet or so where I wouldn't recommend RG-58 beyond 10 feet. 


You will see some mismatch to input or output filters but it isn't severe. Basically under the worst mismatch 1/4 wavelength, the 50 Ohm source or load is transformed into 100 Ohms. Antennas and filters will shift some but it isn't horrible. (RF is weird stuff.)

L
Posted 3 years agoby LectroAdmin
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