Building antennas.....

[nmfire10]

Dumb question. I was making a little chart for myself showing the full, 1/2, and 1/4 wave length antenna lengths and realized I wasn't sure about something in regards to matching coils.

Which one do you and which ones do you not need a coil for? I know 1/4 wave you don't, what about 1/2 and full wave? Also, would 1/2 wave be concidered a gain antenna over a simple 1/4 wave or would it have the same radiation pattern?

[Susan157]

1/4 wave does not need a coil but most mobile gain antennas will use a coil.

Here in Canada when we get antennas (Like Maxrad etc)
A chart comes with about 10 antenna charts on the info
sheets.
This has been like that for 20 years.

Go to the Ham sites and you can download antenna
programs that will let you make your own antenna "cheap"

[wa2zdy]

1/4 wave is close enough to 50 ohms at the feedpoint at resonance that it needs no matching transformer (that's what the coil actually is.) A high band (or 2m ham) 1/4 wave is also a 3/4 wave at UHF (440 ham), and will exibit gain as well as provide a decent match on both bands.

1/2 wave as a VERY high impedance at the feedpoint, as does the 5/8, so they get transformers. Both will exibit gain, though the 5/8 is a little better gain though.

3/4 wave also does not need a transformer (read above).

[nmfire10]

Interesting. I like the VHF/UHF thing.

Here's one. The low Band antennas we use are 1/4 length whips but still have coils. What is up with that?

[Nand]

[007]

A high band (or 2m ham) 1/4 wave is also a 3/4 wave at UHF (440 ham), and will exibit gain as well as provide a decent match on both bands.

Like how good of a match, in terms of SWR? This may solve my antenna issue for a stealth car that I'm doing.