> I need to made a quick dipole for 21MHz
> I have only:
> RG213 from radio-to-antenna
> It is important not to use balun or any twin leads etc etc etc
> Just simple wire conected to RG213
> Any ideas?
> What length of wire need to be?


If wire is the aerial and not a length of coax.

W = 1 wavelength = 300/Frequency
W= 300/21 = 14.28m
        W in metres
        Frequency in MHz

    REMEMBER THIS USEFUL FORMULA)
    (Based on fact that light travels at ~ 3 x 10^8 m/s)

A dipole is a half wave antenna so total length = W/2 = 7.14m

A small velocity factor may apply but not much if any for open wire. This
rduces length slightly.

Then there's end affect but you are already far enough off optimum that
theabove is probably OK.

A slightly better match can be obtained by using a loop (see most TV
aerials).
Run 7.1m wire from centre and braid of coax in opposite directions as two
arms of arerial and then run a 14.2 m wire all the way from toip to tip.
Wire joins at tips only.
This will being down impedance from about 300 ohm to 75 ohm.

A balun is quite easy and can make a significant difference. I won't
describe here as you say you don't want one (and I should be working) but
should be any number of examples on web. Just a length of coax connected
appropriately.


        RM

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