Re: NEC-LIST: Anyone have impedance data on typical loran-c whip?

Hi Steve,
Yes, the issue is getting the best receiver performance given a very poor
antenna. But, interestingly, when I run what I believe to be a reasonable
NEC simulation of the antenna (an 8 foot piece of wire fed at the base), I
get an impedance of .004338 - J68240. This is, indeed, highly capacitive
(at 23.3 pf, just about what was suggested, but it has a very low resistive
component, not the 10k to 20k or more that has been suggested.

Any additional information on where I made my mistake, or if this is,
indeed, the approximate antenna impedance, and what is usually done with
these very short antennas to get maximum receiver performance would be
greatly appreciated.

Also, my understanding is that the fact that the antenna is very "poor"
because it is so short is not a big deal with loran because the
environmental noise is so high that a "proper" antenna does not really
help, since the S/N ratio would not get any better because of the high
noise component.

Regards,
Ed

At 08:08 PM 1/20/2002 +1300, you wrote:
>Hi Ed,
>
>Loran works at low frequencies, as you know. This means that for optimum
>reception, you need maximum voltage, not maximum power transfer. It is
>usual to terminate the high R ,low C, and high impedance whip antenna with
>an even higher impedance receiver input impedance, to minimise the voltage
>drop due to the antenna impedance. Is there another reason for requesting
>the impedance ? What matters is signal-to-noise ratio.
>
>Ed Troy wrote:
> >
> > I have been calling all over the place, and searching all around, and
> > nobody seems to have any clue as to what the typical impedance is for a
> > loran-c whip. I know they range from about 18 inches to about 8 feet
> > (typically an 8 foot whip, at least for marine purposes), but that is all
> > anyone seems to know. I assume they are spirally wound around a fiberglass
> > core, of some sort, but I am not sure about that, either. One person
> > speculated that they look like 20k to 50K ohms resistive in parallel with
> > about 30 pf, but I have no idea if that is accurate. I know the antennas
> > are highly capacitive, since they work at 100 kHz, but I would love to find
> > out more detail about what the actual impedance of a loran-c whip antenna
> > is. Does anybody on the list have that info?
> > --
> > The NEC-List mailing list <nec-list_at_gweep.ca>
> > http://www.gweep.ca/mailman/listinfo.cgi/nec-list
>
>--
>sringe_at_actrix.gen.nz-------------------------------------------------
>Steve Inge, ZL2BDV, Engineering Analyst, Broadcast Communications Ltd.
>147-161 Tory Street, Wellington, New Zealand. fone: +64 4 914 8036.
>Home: 9 High Street, Island Bay. Fone +64 4 3838 422, Fax: +64 4 3838 691.

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