CHA MPAS 2.0 Counterpoise, Ground, and Common-Mode Engineering

An unbalanced portable antenna needs a return-current path. If the intended counterpoise is missing or poorly placed, the feed line and nearby conductors can become more involved.

Build the documented shape

• Use the 25 ft counterpoise in the configurations that specify it.
• Attach it at the documented feed-point connection.
• Route it as shown for the selected geometry rather than alongside the radiator or coax.
• Use optional radial systems only where the current guide documents them.

Why an operator chooses it

Ground conductivity changes losses and coupling, but direct contact with natural ground is not a controlled “earth ground” of fixed quality.

Read the site before opening the bag

Record whether the site is wet, dry, sandy, rocky, snow-covered, or close to large metal. That context explains why a repeated build may measure differently.

Common ways this goes wrong

• Calling the counterpoise optional because the tuner still finds a match.
• Adding a separate 12 in choke when the selected coax already has an integrated feed-point choke.
• Inferring radial compatibility from a banana plug or eyelet.
• Using the vehicle body as a return path without a documented build.

Before you transmit

• Confirm the exact radiator, matching unit, return path, feed line, and support arrangement.
• Keep conductors and supports clear of power lines and uncontrolled public access.
• Reproduce the guide dimensions before experimenting.
• Inspect every connection and begin testing at low power.
• Record geometry, band, tuner state, and the result before changing one variable.