Kraus (2nd edition, p. 375) gives a different answer.

Interpolating from the diagram on p. 375 (assuming length/diameter = 472)
it
is about 90-j250.

Why the difference?

==============================

The program takes into account antenna diameter. Does Kraus? And is he on
the same band? Is he at the same height above ground? What sort of ground
or radial system does he have? Have you interpolated correctly? Have you
understood what Kraus is saying? Is the loading coil in the same location?
Is the feedpoint at the same place. Are you comparing like with like?
Spend more time thinking about it.

Is Kraus infallible? Could be he's wrong again.

Who's Kraus anyway? ;o)
----
Reg

"Reg Edwards" wrote in message
...
The program takes into account antenna diameter. Does Kraus?

Yes. My post said length/diameter = 472 (One thing I don't like about the
way Kraus wrote his book is that he gives the formula for only one part of
the feed impedance (R or X) and a diagram for the complex impedance. He
then refers you to someones paper somewhere for the 'complete' formula.. I
have it around here but it would take 2 days to find it.)


And is he on the same band?

In the diagram I was interpolating from the dimensions are in wavelengths.

Is he at the same height above ground? What sort of ground or radial
system does he have?

It is an infinite perfect ground plane---ground mounted. (We are talking
about a 5/8 wave vertical remember).

Have you interpolated correctly?

Probably not.


Have you understood what Kraus is saying?

Yes.

Is the loading coil in the same location?

No 'loading coil' in the Kraus example. He is discussing the feed point
impedance. A loading coil would be either across or in series with the feed
point.

Is the feedpoint at the same place.

Since the original post concerned a 5/8 wave vertical, I assumed it is at
the bottom, which is what Kraus is discussing.

Are you comparing like with like?

Hence my question. Are we? I recall that a 5/8 wave vertical was 'close' to
50 ohms at the feed point and could be 'adjusted' with an inductance across
the feed point (with the feedline at a tap perhaps?). That is the whole
point is using such a 'magic number' as 5/8 wavelength. If you look at the
impedance curves, though, you find that they are quite steep at this point,
so a small error in length causes a large error in impedance, and some
tuning will be needed. The 5/8 wave is not a 'build it and go' antenna!

Spend more time thinking about it.

I have, which is why I looked it up.


Is Kraus infallible? Could be he's wrong again.


=8o Oh no!!! Kraus wrong!?

Who's Kraus anyway? ;o)

Oh, I don't know. Just some guy that signed my Master's Thesis 16 years
ago.


----
Reg



--
Jim
N8EE

to email directly, send to my call sign at arrl dot net

On 12-May-2004, "JLB" wrote:

Hence my question. Are we? I recall that a 5/8 wave vertical was 'close' to
50 ohms at the feed point and could be 'adjusted' with an inductance across
the feed point (with the feedline at a tap perhaps?). That is the whole
point is using such a 'magic number' as 5/8 wavelength.

The resistive part of the Z of a 5/8 wave will closer to 50 ohms than it will be for a 1/2 wave, but
in most cases will be higher than 50. You may be thinking of a vertical close to 3/8 wave which
will be 50 -jx. The -jx (capacitance) can be resonated with a +jx in series for a 50 ohm feedpoint.

Ken Fowler

You may be thinking of a vertical close to 3/8 wave which
will be 50 -jx. The -jx (capacitance) can be resonated with a +jx in series
for a 50 ohm feedpoint.

Ken, we may be talking about two different things, but a 3/8 wave vertical
has inductive reactance, and the R component is no where near 50 ohms. A 2/8,
or 1/4 wave vertical has no reactance, shorter has -jx, and longer, as in 3/8
wave has +jx.
A .26 lambda vertical has about 50+j43 impedance, and the +j43 can be
cancelled with series 154pf at 24 MHZ. This is a common method of matching a
1/4 wave vertical to 50 ohms. Make it a little longer to look inductive,
50+jx, and cancel with a series cap.
According to all the theory I know on this stuff a 3/8 wave vertical will not
be as you describe.

73 Gary N4AST

(JGBOYLES) wrote in message
A .26 lambda vertical has about 50+j43 impedance, and the +j43 can be
cancelled with series 154pf at 24 MHZ. This is a common method of matching a
1/4 wave vertical to 50 ohms. Make it a little longer to look inductive,
50+jx, and cancel with a series cap.
According to all the theory I know on this stuff a 3/8 wave vertical will not
be as you describe.

It shouldn't be too far off. The usual method of tuning a 3/8 vertical
is also by using a series cap to tune out the reactance. Quite common
on 160m, etc where people run the "extended" inv L's that are 185-190
or so ft long. I've used them here, and with a series cap, the SWR was
quite low. The 3/8 impedance is higher than a 1/4 wave, but not enough
to really hurt things, or to make a l/c matching device needed. MK

On 13-May-2004, (JGBOYLES) wrote:

You may be thinking of a vertical close to 3/8 wave which
will be 50 -jx. The -jx (capacitance) can be resonated with a +jx in series
for a 50 ohm feedpoint.

Ken, we may be talking about two different things, but a 3/8 wave vertical
has inductive reactance, and the R component is no where near 50 ohms. A 2/8,
or 1/4 wave vertical has no reactance, shorter has -jx, and longer, as in 3/8
wave has +jx.
A .26 lambda vertical has about 50+j43 impedance, and the +j43 can be
cancelled with series 154pf at 24 MHZ. This is a common method of matching a
1/4 wave vertical to 50 ohms. Make it a little longer to look inductive,
50+jx, and cancel with a series cap.
According to all the theory I know on this stuff a 3/8 wave vertical will not
be as you describe.

Sorry. I mispoke on that. The 3/8 wave will indeed be inductive. However its resistance will be
closer to 50 ohms than it would be for a 1/4 wave. A 1/4 wave would have a resistance of 37 ohms.
I'm not sure about your 50 + j43 for a 0.26 wave. Is that from EZNEC? With what kind of ground?

I didn't take the time to model the 3/8 wave. Sorry.

Ken

I'm not sure about your 50 + j43 for a 0.26 wave. Is that from EZNEC? With
what kind of ground?

Yes it was EZNEC, ground type real/Mininec.
73 Gary N4AST