Hi,
I'd like to build my own RECEIVER ONLY center fed 1/2 wave dipole for 39-45MHz antenna. While I'm reading through quite a few resources, I thought I'd ask for pointed questions and get direct answers. I'm currently reading through Audio Systems Group, Inc. Publications and trying to figure things out, but your help is appreciated!
c=299.8e6 m/s
f=42e6 Hz
wavelength = c / f = 7.138 m
For 1/2 wave dipole, total length: 3.570m (1.785m per leg)
For 1/4 wave dipole: total length: 1.785m (0.892m per leg)
however to eliminate reactance of the antenna, it should be shortened slightly based on the velocity of electromagnetic wave in the material: Dipole antenna - Wikipedia
For a #10 AWG copper wire, velocity of propagation is about 0.95c, thus lengths are:
1/2 wave: total length: 3.390m (1.695m per leg)
1/4 wave: total length: 1.695m (0.848m per leg)
The larger the wire, the higher the SWR bandwidth. Cut the wire longer, so you could trim it in.
Since Antenna is balanced and coax is unbalanced, I need to use a Current BALUN to match the impedance of the antenna to the coax and also to prevent the coax from acting like part of the antenna.
Questions for receive only antenna:
I'd like to build my own RECEIVER ONLY center fed 1/2 wave dipole for 39-45MHz antenna. While I'm reading through quite a few resources, I thought I'd ask for pointed questions and get direct answers. I'm currently reading through Audio Systems Group, Inc. Publications and trying to figure things out, but your help is appreciated!
c=299.8e6 m/s
f=42e6 Hz
wavelength = c / f = 7.138 m
For 1/2 wave dipole, total length: 3.570m (1.785m per leg)
For 1/4 wave dipole: total length: 1.785m (0.892m per leg)
however to eliminate reactance of the antenna, it should be shortened slightly based on the velocity of electromagnetic wave in the material: Dipole antenna - Wikipedia
For a #10 AWG copper wire, velocity of propagation is about 0.95c, thus lengths are:
1/2 wave: total length: 3.390m (1.695m per leg)
1/4 wave: total length: 1.695m (0.848m per leg)
The larger the wire, the higher the SWR bandwidth. Cut the wire longer, so you could trim it in.
Since Antenna is balanced and coax is unbalanced, I need to use a Current BALUN to match the impedance of the antenna to the coax and also to prevent the coax from acting like part of the antenna.
Questions for receive only antenna:
- What Current BALUN configuration do I use for impedance matching and blocking coax from acting as part of the antenna?
- What core material # do I use, how many turns and using what cable/wire for the BALUN?
- What coax impedance cable do I use, 50ohm or 75ohm considering the scanner has 50ohm termination?