LORAN antenna difference?

[JFLEISC]

Can someone tell me the differences between a loran antenna and a comm or VOR
nav antenna? I guess what I'm looking for is why they would not be
interchangable, i. e. is the loran signal totally incompatible with others? is
it an absolute necessity for a preamp in the loran antenna (I would assume that
would eliminate the possibility of using that antenna to transmit, for
instance)? can a loran signal be received off of a dipole nav antenna? I'm
basically trying to be a little more knowledgable on the subject.

Jim

[Jerry J. Wass]

LOran is very low frequency, follows the earth curvature--originally used for ships
& submarines..--Best results with a roll-out trailing antennae, but will work with
a cabin to rudder antenna--longer the better. jerry

JFLEISC wrote:

> Can someone tell me the differences between a loran antenna and a comm or VOR
> nav antenna? I guess what I'm looking for is why they would not be
> interchangable, i. e. is the loran signal totally incompatible with others? is
> it an absolute necessity for a preamp in the loran antenna (I would assume that
> would eliminate the possibility of using that antenna to transmit, for
> instance)? can a loran signal be received off of a dipole nav antenna? I'm
> basically trying to be a little more knowledgable on the subject.
>
> Jim

[John_F]

Both antennas look the same on the outside but on the inside they are
totally different.
The loran works at 0.1 MHz, the com works at 130 Mhz.
The com antenna is resonant at near 1/4 wavelength and has an
impedance near 50 ohms.
Since the loran antenna is electrally short at 0.1% of a wavelength
the matching impedance is very high ( about 50,000 ohms ) hence this
is why the preamp is in the antenna with zero coax length to the
preamp. The preamp built into the antenna matches the 50K ohm antenna
impedance to the 50 ohm coax. You can get away from using a pre amp
but you must use a MUCH longer antenna feeding the coax or you will
not have any signal left by the time it gets to the receiver because
of the antenna to coax impedance mismatch.
The preamp power is fed down the signal coax from the loran receiver.
Due to this if you connect a grounded com antenna to the loran
receiver you will fry the power feed coupler in the loran receiver.
You can hook up a length of wire that is not grounded to see what
signal strength you get. You may be surprised at how long a wire it
takes to get the same signal strength as the amplified antenna.

If you transmit into a electrically short loran antenna you can kiss
it good bye because you just fried the preamp.
John

On 22 Dec 2004 23:00:48 GMT, (JFLEISC) wrote:

>Can someone tell me the differences between a loran antenna and a comm or VOR
>nav antenna? I guess what I'm looking for is why they would not be
>interchangable, i. e. is the loran signal totally incompatible with others? is
>it an absolute necessity for a preamp in the loran antenna (I would assume that
>would eliminate the possibility of using that antenna to transmit, for
>instance)? can a loran signal be received off of a dipole nav antenna? I'm
>basically trying to be a little more knowledgable on the subject.
>
>Jim

[JFLEISC]

Thanks folks, this does answer a lot of questions.

Jim

[w]

Yeah, like why is there smoke coming out the back or your loran unit..:)

JFLEISC wrote:
> Thanks folks, this does answer a lot of questions.
>
> Jim

[RST Engineering]

I am not aware of any LORAN designs that did not use a preamp. Some of them
have the preamp buried in the base of the antenna, and some of them use a
short (24" or so) wire whip with the preamp box bolted onto the airframe
very near the bottom of the antenna. II Morrow old designs, for instance,
provide a 6" length of coax to go from the base of the antenna to the preamp
connector. As the author says, much more coax than this and the antenna
signal approaches zero.

Jim



"John_F" > wrote in message
...
>
.. You can get away from using a pre amp
> but you must use a MUCH longer antenna feeding the coax or you will
> not have any signal left by the time it gets to the receiver because
> of the antenna to coax impedance mismatch

[B2431]

>From: w
>Date: 12/23/2004 20:15 Central Standard Time
>Message-id: >
>
>Yeah, like why is there smoke coming out the back or your loran unit..:)
>
>JFLEISC wrote:
>> Thanks folks, this does answer a lot of questions.
>>
>> Jim

When in doubt tune for maximum flame and minimum smoke.

Dan, U.S. Air Force, retired