"Al Lorona" wrote in
:
....
Thank you for the references. Not good. I didn't realize that the
feedpoint contains a 50 ohm resistor ( 40m EZNEC model on KG4JJH's
web site cited above).

He does not mention a "50 ohm resistor" in his review document, not show it
in his feedpoint picture.

Are you quite sure of what you say?

He does include load of 50+j500 in shunt with the feedpoint, presumably
modelling the shunt coil... has that got you confused?

The next question is whether such a load is a good characterisation of the
actual coil. The value of R seems rather high.

Owen

Owen Duffy wrote:

He does include load of 50+j500 in shunt with the feedpoint, presumably
modelling the shunt coil... has that got you confused?

The next question is whether such a load is a good characterisation of the
actual coil. The value of R seems rather high.


Wouldn't that correspond to a Q of 10, which is pretty bad for a air
core coil. I'd say something like 30 or 100 would be more realistic
(unless it's wound with really fine wire)
(I don't have eznec, so I can't open the .ez file)

On Aug 9, 6:53*pm, Jim Lux wrote:
Owen Duffy wrote:
He does include load of 50+j500 in shunt with the feedpoint, presumably
modelling the shunt coil... has that got you confused?

The next question is whether such a load is a good characterisation of the
actual coil. The value of R seems rather high.

Wouldn't that correspond to a Q of 10, which is pretty bad for a air
core coil. I'd say something like 30 or 100 would be more realistic
(unless it's wound with really fine wire)
(I don't have eznec, so I can't open the .ez file)

I opened the document in 4NEC2. Whilst my version of EZNEC cannot read
or write .NEC decks, 4NEC2 can read .EZ format.

If you look at the pic of the coil, a Qi of 10 seems very low.
Nevertheless, it doesn't consume much power.

Owen

"Owen Duffy" wrote in message
...

Are you quite sure of what you say?


Beats me... I've never seen one of these antennas and am going only by the
EZNEC model on that web site, as I said in my last post. Says that there's
50 + j500 at the feedpoint. That's a 50 ohm resistor in series with an
inductor, isn't it? Or, as you say, a coil with a real low Q. Either way,
it's an extremely lossy device that adversely affects the results. Try
adjusting the R to a more reasonable value for an average coil and
re-simulating in EZNEC and take a look at the result. KG4JJH has measured
data in that review that definitely coincides with a 50 +j500 device at the
feedpoint.

Al W6LX

On Aug 10, 10:35*am, "Al Lorona" wrote:
"Owen Duffy" wrote in message

...



Are you quite sure of what you say?

Beats me... I've never seen one of these antennas and am going only by the
EZNEC model on that web site, as I said in my last post. Says that there's
50 + j500 at the feedpoint. That's a 50 ohm resistor in series with an
inductor, isn't it? Or, as you say, a coil with a real low Q. Either way,
it's an extremely lossy device that adversely affects the results. Try
adjusting the R to a more reasonable value for an average coil and
re-simulating in EZNEC and take a look at the result. KG4JJH has measured
data in that review that definitely coincides with a 50 +j500 device at the
feedpoint.


I though about this while on the road this morning. Sometimes
enlightenment comes when there is not a keyboard to confuse things.

I assumed that he intended to model the shunt coil, and correctly
modelled it, but in fact his load is in series with the feedpoint...
so it hasn't captured the shunt coil.

Removing the load, and running the model gives a feedpoint Z of 16-
j500. A shunt coil with Qi around 100, and L around 29uH will
transform that to 50+jX. That coild has an equivalent shunt R of 120k,
so negligible power is lost in it.

I haven't looked closely at the model in all respects, but it seems to
do some crazy things that certainly give unrealistically low
efficiency.

Owen

Thanks, Owen. That makes sense. I agree it looks like a modeling error.

Regards,

Al

"Owen Duffy" wrote in message
...
On Aug 10, 10:35 am, "Al Lorona" wrote:
"Owen Duffy" wrote in message

...



Are you quite sure of what you say?

Beats me... I've never seen one of these antennas and am going only by the
EZNEC model on that web site, as I said in my last post. Says that there's
50 + j500 at the feedpoint. That's a 50 ohm resistor in series with an
inductor, isn't it? Or, as you say, a coil with a real low Q. Either way,
it's an extremely lossy device that adversely affects the results. Try
adjusting the R to a more reasonable value for an average coil and
re-simulating in EZNEC and take a look at the result. KG4JJH has measured
data in that review that definitely coincides with a 50 +j500 device at
the
feedpoint.


I though about this while on the road this morning. Sometimes
enlightenment comes when there is not a keyboard to confuse things.

I assumed that he intended to model the shunt coil, and correctly
modelled it, but in fact his load is in series with the feedpoint...
so it hasn't captured the shunt coil.

Removing the load, and running the model gives a feedpoint Z of 16-
j500. A shunt coil with Qi around 100, and L around 29uH will
transform that to 50+jX. That coild has an equivalent shunt R of 120k,
so negligible power is lost in it.

I haven't looked closely at the model in all respects, but it seems to
do some crazy things that certainly give unrealistically low
efficiency.

Owen