50 ohm to 75 ohm

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grey4trains

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Jun 6, 2008
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Greeting

I'm building a homebrew dipole for listening to the R.R. band (161-162M). I have a R-Shack PRO-2018 base scanner, I'm using a short piece (12') of RG8 coax (50 ohm) and a ferrite bead 1:1 balun. The antenna is indoor, going to be mounted up in the vaulted area of my ceiling. Problem is..Doesn't a vertical dipole have an inductance of 75-ohms? Would it make much difference to the scanner that requires a 50-ohm input? While I'm on the subject, can I mount the dipole horizontal instead of vertical (to give it a few more feet of height)? Thanks guys for any response.

M. Grey
 

zz0468

QRT
Joined
Feb 6, 2007
Messages
6,036
Greeting

I'm building a homebrew dipole for listening to the R.R. band (161-162M). I have a R-Shack PRO-2018 base scanner, I'm using a short piece (12') of RG8 coax (50 ohm) and a ferrite bead 1:1 balun. The antenna is indoor, going to be mounted up in the vaulted area of my ceiling. Problem is..Doesn't a vertical dipole have an inductance of 75-ohms? Would it make much difference to the scanner that requires a 50-ohm input? While I'm on the subject, can I mount the dipole horizontal instead of vertical (to give it a few more feet of height)? Thanks guys for any response.

M. Grey
It'll work fine. The word you're looking for isn't inductance, it's impedance. A dipole (vertical or horizontal) has an impedance of around 73 ohms. The mismatch between that and 50 ohms is not worth worrying about in receive antennas, so if that's what you have, it'll be fine.

Mounting it horizontally instead of vertically will be a problem. The railroads use vertical polarization, and there's a 20-30 db loss between cross polarized antennas. The few extra feet gained would give you a lot of extra loss.
 
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