LORAN ant question

I knew that was going to come up (grin)!

Well, I have several old LORANs laying around, and am not interested in
forking over for a new GPS right now. And yes, LORAN is still doing fine in
the Gulf. LORAN will do fine for my close inshore purposes. I used it for
years.
 >> Stay informed about: LORAN ant question 

"RB" <rbig.RemoveThis@bellsouth.nospam.net> wrote in
news:vxyge.13542$eJ4.2944@bignews4.bellsouth.net:

> Does the length of a LORAN metal whip matter much?

Yes, it matters a lot. Loran operates at 100 Khz, Very Low Frequency. The
antennas are heavily coil loaded to tune them at this low a frequency and
very narrow banded. The whip length is part of this tuning and if you
change it to a different length the antenna is way out of tune and not near
as sensitive. It may still function out of tune, but signals will be down.
 >> Stay informed about: LORAN ant question 

}}} The
antennas are heavily coil loaded {{{

Not sure about this in my situation here. Both my units (one is Morrow, the
other Sitex) have base coupler units. These couplers have a circuit board
inside them, and seem to have dc powering that circuit board through the
coax to the coupler. Haven't seen any coil.
 >> Stay informed about: LORAN ant question 

Morrow is one of the companies that use "active" antennas to
overcome the fatal signal losses resulting from enormously
high impedance (~ 1 Megohm, albeit mostly reactive) of
extremely short antennas fed into 50-ohm receiver inputs.

Your circuit board probably contains an FET follower to
convert the high impedance of the antenna to a low impedance
of 50 ohms. To do this with a coil would probably render the
system so lossy as to not work at all.

You should be able to vary the antenna length modest amounts
(I'm thinking +/- 20%)with no noticeable difference. Just
how far you can go will be a question you can answer easily
by trying different lengths of substitute antenna.

On the other hand, if it was working fine with no antenna at
all, (was the coax connected to the circuit board?) do you
really need to go to this trouble?

Good luck, and let us know how you make out!

Chuck

RB wrote:
> Does the length of a LORAN metal whip matter much? I recall a time when I
> found I didn't even have an antenna on my LORAN (years ago); just a coil of
> coax under the console, and it worked fine. So, can I stick just about any
> whip on the coupler and get good results? Or, is there some reasonant
> length that is needed?
>
> I'm putting a LORAN in my 18' cc, and want to use a short metal whip on the
> coupler, if that'll work OK.
>
>
 >> Stay informed about: LORAN ant question 

Larry W4CSC wrote:
> "RB" <rbig.RemoveThis@bellsouth.nospam.net> wrote in
> news:vxyge.13542$eJ4.2944@bignews4.bellsouth.net:
>
>> Does the length of a LORAN metal whip matter much?
>
> Yes, it matters a lot. Loran operates at 100 Khz, Very Low
> Frequency. The antennas are heavily coil loaded to tune them at this
> low a frequency and very narrow banded. The whip length is part of
> this tuning and if you change it to a different length the antenna is
> way out of tune and not near as sensitive. It may still function out
> of tune, but signals will be down.

That's about the same frequency as my sextant works on.
 >> Stay informed about: LORAN ant question 

Talked to Sitex and they said anything 4' or over would do. There are now
several 4' fiberglass antennas marketed for LORAN, so just ordered one of
those. I just didn't want a long whip on top of the bimini, if I could get
by with a shorter antenna.
 >> Stay informed about: LORAN ant question 

Hi,

Your post interested me because I need a coupler for a SITEX unit. I am
not an electronics expert but have successfully fabricated circuits from
schematics in the past. The long and short of is that I would like to
attempt to build my own coupler. Do you or anyone else here have access
to SITEX service manuals that may show the circuit used. I would think
that such low frequency stuff would not be too touchy to fabricate if
one had the schematic and parts list. I have a SITEX LORAN 797.

TIA

Bob

chuck wrote:
>
> Morrow is one of the companies that use "active" antennas to
> overcome the fatal signal losses resulting from enormously
> high impedance (~ 1 Megohm, albeit mostly reactive) of
> extremely short antennas fed into 50-ohm receiver inputs.
>
> Your circuit board probably contains an FET follower to
> convert the high impedance of the antenna to a low impedance
> of 50 ohms. To do this with a coil would probably render the
> system so lossy as to not work at all.
>
> You should be able to vary the antenna length modest amounts
> (I'm thinking +/- 20%)with no noticeable difference. Just
> how far you can go will be a question you can answer easily
> by trying different lengths of substitute antenna.
>
> On the other hand, if it was working fine with no antenna at
> all, (was the coax connected to the circuit board?) do you
> really need to go to this trouble?
>
> Good luck, and let us know how you make out!
>
> Chuck
>
> RB wrote:
> > Does the length of a LORAN metal whip matter much? I recall a time when I
> > found I didn't even have an antenna on my LORAN (years ago); just a coil of
> > coax under the console, and it worked fine. So, can I stick just about any
> > whip on the coupler and get good results? Or, is there some reasonant
> > length that is needed?
> >
> > I'm putting a LORAN in my 18' cc, and want to use a short metal whip on the
> > coupler, if that'll work OK.
> >
> >
 >> Stay informed about: LORAN ant question 

"Dennis Pogson" <dennis_pogson.TakeThisOut@ntlworld.com> wrote in
news:X8Kge.4215$f5.879@newsfe6-win.ntli.net:

> That's about the same frequency as my sextant works on.
>

You should see the TRANSMITTER and it's huge antenna at this frequency.
I've visited many LORAN "C" installations across the South and calibrated
their test equipment in a mobile cal lab. Try reading a scope in between
megawatt power pulses when you're lab is located BETWEEN the huge capacitor
hat 800' above you and the massive ground system buried right under you.
Everything in miles has LORAN pulses on it....

If you ever get the chance to go by any LORAN station, do so. Knock on the
door and tell the Coasties thanks for providing you with nav at sea.
They'll be glad to show you their beast.

The antenna, by the way is 800' high with a 36 spoke capacitor hat about
500' diameter made of bridge cables at the top to tune it at such a low
frequency. The transmitters are all solid state. The output power
actually comes from multiple drawers of Silicon Controlled Rectifiers,
thousands of amps, pulsing from cesium-beam frequency standards as the
pulse timing of LORAN is very critical to its positional accuracy.

It's all obsolete, now that GPS works so good. Politics keeps it on the
air....

LORAN "A", the one from WW2, was on 1.9-2.0 Mhz above the standard
broadcast band. Its antennas were much smaller because of the higher
frequency. It was useless at night or in a storm because of the "skip",
same physics that lets you listen to an AM radio station 800 miles away all
night. Charleston had one on the very northern tip of Folly Beach run by a
few sailors who lived across the street from the transmitter. Fine duty
back in the analog days...(c;
 >> Stay informed about: LORAN ant question