Hi Brian,

I've just bought a new 406MHz EPIRB for the boat, cost me AUD400, so about
$350 of your variety I think. The "real" problem is that the COSPAS/SARSAT
constellation of satellites had the 121.5/243MHz capability turned off at
the beginning of this year, which suggests tht the 20 inch whip is basically
useless unless there's an aircraft monitoring 121.5 within line of sight.
We've all had to re-equip during this year to cope (I've managed to leave it
until the beginning of our summer, when new stocks became available).
Incidentally, just measured the antenna: 175 mm from the top of the case so
rough approximation not too bad in this case.

Cheers ... MikeW

"brian whatcott" wrote in message
...
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