Putting Up a New Doublet Antenna – First Impressions

I took advantage of the nice weather today and put up a new doublet antenna! ☀️

Antenna Specs:

• Total length: ~30 meters
• Height: ~10 meters up
• Feedline: 18 meters of 450-ohm ladder line
• Balun: LDG 4:1 to transition to coax
• Shack connection: Short length of coax

How to Calculate the Antenna Length

A doublet antenna is essentially a center-fed dipole, designed to be used across multiple bands with a tuner. The general formula for calculating the total length of a half-wave dipole (which also applies to a doublet) is:

[ L = \frac{468}{f} \text{ (in feet)} ]

[ L = \frac{143}{f} \text{ (in meters)} ]

where f is the lowest frequency in MHz that you want to operate on.

Since I wanted good performance down to 40 meters (7.1 MHz), I used:

[ L = \frac{143}{7.1} \approx 20.1 \text{ meters (per leg)} ]

So, the total length is about 40.2 meters, but I opted for 30 meters to fit my available space.

First Tests & Next Steps

After a quick test, everything seems to be working well! Doublets are fantastic for multi-band operation, especially when paired with a good tuner. The 450-ohm ladder line should help minimize losses across the bands.

I’ll do some proper signal reports soon, but for now, I’m happy with the install!

Anyone else running a doublet? Have you found an optimal length that works best for your setup?