I've been reading the discussion about ELT antennas with a great deal of
interest.
I have a lot of time flying a DF equipped aircraft finding them and have
seen more than my share of crash sites. I really think it is preferable to use
a whip anetnna mounted right on the connector on the ELT. The reason that I
say this is that if it is a crash that is serious enough to require that you
be found, there is a very high probablilty that the cable will be compromised,
separating the antenna from the ELT and markedly decreasing the signal being
sent. The quarter wave whip mounted on the ELT is certainly not the best
antenna,
but it sure beats none, which is what you have if the cable is broken, pulled
out, or damaged in the crash.
Only my opinion.
Jim-A-283, Punta Gorda, FL
>
> Concerning an ELT antenna: I just used a length of prepared
> coax, RG-58, BNC connector on one end end at least (e.g.,
> allelectronics.com, cheap). Separate the shield and center
> conductor for a length of exacty 21.5 inches, making a
> dipole.
>
> Now I may be cheap when it comes to antennas, especially for
> worthless ELT unless you fly over really remote and harsh
> terrain, but not when it comes to my MFJ-259B antenna
> analyzer. Not particularly cheap, so I get some use out of
> it. This kludge on an antenna checked out perfectly at
> 121.5.
>
> Without a "balun," the feedline shield will radiate a bit.
> MFJ-259B doesn't detect that. The mitigator is the fact
> that a dipole, within five feet of the ground, will radiate
> sharply upward, about 45-deg at least. A monopole whip
> antenna on a flat ground plane won't quite do that for you.
> That's likely to be the situation of the "crashed" fuselgage
> w/r/t to earth.
>
> In installing the coax antenna to the fuselage side, like
> with RTV silicone, have the two poles about a 30-deg angle
> from vertical -- further fills in the natural void to
> upstairs satellites or search planes, if the dipole legs
> were in a straight line.
>
> Reg,
> Fred F.
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