Do we lose power, If we select a longer Antenna?

[Shahriar]

Hi

It is said that a very simple calculation for antennas length, is 1/4 * wavelength. my question is:
if we select a longer antenna, do we have lose output power? The anttena I mean is for transmitter.

ThanX in advance
Shahriar

[Guest SM2GXN]

Hi Shahriar!

A 1/4 wave vertical will do just fine for most communication demands.
Not necessarily on your question about extended antenna, it depends a lot on what kind of communication you are talking about.
Any length of conductor whether it's a wire or alumnium pipe it can be matched to any transmitter impedance usually 50-75ohms but the efficiency can suffer.
You can make a 5/8 wavelength vertical and get somewhat more gain compared to the 1/4 wave but impedance matching is needed and the radiation pattern will be changed as well.
If more gain is needed then directional antennas is to be used.
There is antennas called zepp and rhombic just to name some of a big number of different antennas that could be several wavelengths long but these are usually being used at lower frequencys= longer wavelengths.

Bjorn

[Guest Alun]

Electrically short antennas behave as capacitances and electrically long ones behave inductively, to get the best results you can include a capacitor of inductor (often vairiable and will depend on whether it's electrically long or short) to tune it to resonance.

1/2 wavelengh dipole is the best simple type to use even though a 1/4 wave monopole is the most used and will do for most applications.

Normal 1/2 or 1/4 aerials don't have any gain as they're omnidirectional, to get more gain a yagi array or log periodic antenna is used.

[Shahriar]

ThanX all for your replies

Shahriar