Can a 2m J-Pole be used at 440?

440 from a 2m Antenna?

Many makers of J-poles for 2 meters claim they can also be used at 70 cm.

It may not be intuitive at first, but the answer, at least from an antenna pattern standpoint, seems to offer some hope.

On a related note the standard 19 inch quarter wave mobile whip exhibits good Return Loss near the UHF FM segment when I measured one on my Ford Taurus roof.

It is more difficult to calculate the feed-point impedance of a J-Pole perfectly since it is a tapped system. However, the calculations I ran for 430 MHz suggest it is somewhat close to a good match.

2m J-Pole Antenna Currents for two bands

Here is a simulation of a J-Pole from Cebik’s collection with 146 and 430 MHz…

2 meter j-pole at 146 and 430 MHz.
2 meter j-pole at 146 and 430 MHz.

The currents on the long vertical section act a bit like a long wire pointing straight up as shown in this comparison plot. The following figures show this J-pole 300 feet above ground level to accentuate the lobe adding ground effect.

2m J-Pole Plot at 146 and 430 MHz
2m J-Pole Plot at 146 and 430 MHz

The pattern for 430 MHz, shown in green, is busy and certainly suggests this is not the ideal antenna for the job. We can clearly see much of the 430 MHz energy heads skyward. However, if you look closely at the low elevation detail…

Close up of 2m J-Pole at 146 and 430 MHz.
Close up of 2m J-Pole at 146 and 430 MHz.

…you will see a reasonable lobe of power at a low angle.

430 MHz on a 2m Antenna might work, but is not ideal

So can you use a 2 meter J-Pole at 430 MHz and expect reasonable results? NEC simulation suggests a cautious yes. Measure the SWR to make sure it is taking power and don’t expect great performance.

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