Yes indeed, Mike. Or close enough. If you buy the copper tape antenna
and stoppers from the avionics guru who lurks on r.a.homebuilt he will
want to sell you something to trim a little shorter to account for the
local speed of light (c) on a 1/4 .

My nose was a little out of joint initially with yet another slightly
snippy and mis-spelled note from an anonymous poster on this
crap-infested group. [Brings to mind the idea of adolescent poseurs
with dirty ears and dirtier mouths...]
....But he was in fact doing me a service in prompting me to look out the
requirements for 406MHz ELTs in the US.

These turn out to include the requirement for a 406MHz ELT on NEW light
aircraft and ANY light aircraft going international (if I got it right).
This could happen, I suppose. I have made the Oshkosh pilgrimage, and I
am fixing to visit Corpus Christi in the other direction....
I am not thrilled by the prices however. Surely there must be cheaper
examples out there than the $800 specimens? A new Ameriking dual Fx
costs $150 after all....

The initial point was that a glance at a light aircraft will show
whether it is equipped for 121.5 (or 121.5 and 243Mz) or 406Mhz.
The great majority of aircraft that I see, have a 20+ inch whip or rod.

Brian W


MikeW wrote:

g'day Brian,

Call frequency "f". Speed of light c = 3*10^8 metres/second. Wavelength =
c/f in metres. Quarter-wave antenna length then is c/4*f.

So, 406 MHz, call it 400 to simplify a bit. Wavelength = 3*10^8/400*10^6 =
3*10^8/4*10^8 = 0.75 metres. Quarter wave a bit under 20 cm, which would be
a bit under 8 inches old scale.

Cheers ... MikeW.

/snip/

Hi, User posting as Dave,

do you know how to relate emission frequency
to the length of a corresponding quarter wave whip?

Brian W