# How does a Dual Band Handheld Antenna work?

Looking to get a (highly recommended) NAGOYA NA-771 37cm "Dual band (2M/70cm) handheld antenna" for my Baofeng UV-5R.

If my math is correct - this is about a half-wavelength antenna for 70cm, but doesn't seem to correlate to anything for 2m.

What does this mean? Is it really good for 70cm but no so much for 2m, or am I misunderstanding the principals/construction of this antenna. (Also, it's just a handheld antenna, so it's not a "dipole" nor does it have an evident "ground" - so I might not just understand what it "is").

A half-wave dipole, or a quarter-wave monopole, are resonant on their fundamental frequencies and all odd harmonics thereof. 2m and 70cm have that harmonic relationship, 70cm being approximately the first odd harmonic of 2m:

$$144 \mathrm{MHz} \cdot 3 = 432 \mathrm{MHz}$$

So, an antenna that looks like a half wavelength on 2m will look like 1.5 wavelengths on 70cm. Although the radiation pattern is different, the antenna impedance is the same, and so will provide a good match to the radio in either case.

Keep in mind that handheld antennas are usually monopole antennas, like a vertical. They are approximately equivalent to a dipole of twice the length. There is no obvious ground plane as there is with a vertical because mobile antennas usually sacrifice performance for size. See How do Handheld antennas work without ground?

For further reading, I suggest antenna-theory.com, which expands on some math and shows diagrams of radiation patterns under various conditions.

• Both awesome links. Very useful info. Thank you!