Current through coils
 

Jerry Martes wrote:
"I figured you realized that the HP Vector Voltmeter wasn`t capable of
providing the data needed for this discussion."

More likely necessary. It is dead simple.

You have a whip with a loading coil somewhere in the circuit under it.
The r-f energy is reflected by the open circuit at the tip of the
antenna. It must return toward the sender. There is no place else to go.

Anything feeding the antenna is in the path. Volts and amps at any and
all points along the way are acted upon by the incident and the
peflected waves. Straight wire or coil, the effect is the same as there
is a periodic variation in volts and amps due to the combination of the
effects of volts and amps from both directions.

Should the current at both terminals of a loading coil happen to be the
same, it would likely be a rare coincidence.

Best regards, Richard Harrison, KB5WZI

Current through coils
 

Jerry Martes wrote:
No Cecil, I didnt. Maybe I wrote my address wrong.

I think the Reply All feature on my newsreader must not be
working. I didn't get any notice that it didn't go through.
I'll send you a regular email.

I figured you realized that the HP Vector Voltmeter wasnt capable of
providing the data needed for this discussion.

Here's the procedure for measuring the electrical length of
a base loading coil. That's the same as the delay through
the coil.

1. Mount your base loading coil on your vehicle and remove
the stinger. Note that the current is zero at the top of
the coil with the stinger removed.

2. Use an antenna analyzer, like an MFJ-259B to locate the
self-resonant frequency. It will be the first frequency
going up in frequency for which the reactance is zero and
the resistance is very low. My 75m bugcatcher coil has
a self-resonant frequency of 6.6 Mhz which is an
electrical 90 degrees at 6.6 MHz.

3. Calculate the length of the RF cycle at the self-resonant
frequency. 1/6600000 = 152 nS for 360 degrees at 6.6 MHz.
The coil is an electrical 90 degrees long on its self-resonant
frequency so the delay through the coil is 152/4 = 38 nS.

38 nS is also the approximate delay through the coil when
used as a base loading coil on 4 MHz. One RF cycle on 4 MHz
takes 250 nS so 90 degrees (1/4WL) of that cycle is 62.5 nS.
The coil is providing 38/62.5 = 61% of the antenna on 4 MHz.

Forget the bogus coil delays posted by the "experts". They
are measuring standing wave current which is known not to
change phase on either end of the coil and it doesn't do a
bit of good to measure something that doesn't ever change.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

Richard Harrison wrote:
Should the current at both terminals of a loading coil happen to be the
same, it would likely be a rare coincidence.

All one has to do to see radical changes in the currents
at the ends of the coil is move the coil up and down
a 3/4WL radiator. One can find a place where current
at the top of the coil is five times the current at
the bottom of the coil. That's just the way standing
wave current works. Too bad there are so many myths
and old wives' tales being spread about it by alleged
"experts" who have forgotten EE201.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

On Mon, 13 Mar 2006 03:41:34 GMT, Cecil Moore wrote:
I'll send you a regular email.
....
Use an antenna analyzer, like an MFJ-259B to locate the
self-resonant frequency.

Vector VOLTmeter?
VECtor Voltmeter?!!!

I don' need no stinkin' VECtor VOLTmeter!

Hi Jerry,

Can you take another dumpster dive and see if you can find a Raster
Ammeter?

73's
Richard Clark, KB7QHC

Current through coils
 

"Richard Clark" wrote in message
...
On Mon, 13 Mar 2006 03:41:34 GMT, Cecil Moore wrote:
I'll send you a regular email.
...
Use an antenna analyzer, like an MFJ-259B to locate the
self-resonant frequency.

Vector VOLTmeter?
VECtor Voltmeter?!!!

I don' need no stinkin' VECtor VOLTmeter!

Hi Jerry,

Can you take another dumpster dive and see if you can find a Raster
Ammeter?

73's
Richard Clark, KB7QHC

Hi Richard

There are sooo many things I dont know anything about. Raster Ammeter is
one of the many things I havent even heard about.
I sure would like to learn how to use a Vector Voltmeter.
Right now, I cant measure impedance (with any confidance of accuracy) when
their VSWR is below about 1.5 to 1 on a 50 ohm line at 137 MHz.

Jerry

Current through coils
 

On Mon, 13 Mar 2006 06:39:03 GMT, "Jerry Martes"
wrote:

Raster Ammeter is one of the many things I havent even heard about.

"It's a joke, son."
Foghorn Leghorn

Current through coils
 

"Richard Clark" wrote in message
...
On Mon, 13 Mar 2006 06:39:03 GMT, "Jerry Martes"
wrote:

Raster Ammeter is one of the many things I havent even heard about.

"It's a joke, son."
Foghorn Leghorn

Hi Richard

The "raster" had all the earmarks of an imaginary device. I sensed it
was a put on. The problem I have is my inexperience requires that I dont
assume *anything*.
I feel like Rip Van Winkle. The engineering community has developed a
whole lot of nice things since I left it in 1969. And, its like I've
been sleeping for 37 years.

Jerry

Current through coils
 

On Mon, 13 Mar 2006 06:39:03 GMT, "Jerry Martes"
wrote:
[snip]

There are sooo many things I dont know anything about. Raster Ammeter is
one of the many things I havent even heard about.

Reminds me of my youth. I worked in an automotive parts store back
when you actually had to know something about cars and how to read a
paper catalog. We'd test the new guys by asking them to find a
radiator cap for a Corvair, a set of spark plugs for a Cummins, an oil
pan gasket for a Powerglide transmission....


I sure would like to learn how to use a Vector Voltmeter.
Right now, I cant measure impedance (with any confidance of accuracy) when
their VSWR is below about 1.5 to 1 on a 50 ohm line at 137 MHz.

Have you looked at this?

http://www.k6mhe.com/n7ws/AN77-3.pdf

Current through coils
 

Richard Clark wrote:

Cecil Moore wrote:
Use an antenna analyzer, like an MFJ-259B to locate the
self-resonant frequency.

Vector VOLTmeter?
VECtor Voltmeter?!!!

I don' need no stinkin' VECtor VOLTmeter!

Actually, unlike Tom (who rushes in where angels fear to
tread) I cannot figure out how to use the VVM to make
a valid measurement of what we are trying to measure. If
I cannot figure that out, then the VVM won't do me any
good as Tom's setup didn't do him any good and just
confused him all over again by tricking him into making
his measurement in an SWR = 16000:1 environment. I'm
truly surprised his standing-wave current delay
measurement wasn't zero.

Guess everyone sees the danger in trying to guess what
the results of someone else's measurement will be. Tom
should have measured something around 15.6 degrees. The
fact he didn't sends up a very large red flag.

Another problem is that the delay through the coil
changes drastically between bench isolation and being
installed directly above a GMC pickup's ground plane
because of the enormous increase in coil capacitance
to that ground plane. So the delay through the coil
needs to be measured in the physical environment in
which it is operated. It is virtually impossible to
eliminate reflections from a 75m mobile bugcatcher
system so the VVM can't measure what we are trying
to measure.

The question is: For a well-designed coil, is the self-
resonance method valid for determining the delay through
a coil at HF frequencies below the self-resonant frequency?
Since that's been an accepted way of doing it for more
than a century, I don't see how anyone could object.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

Jerry Martes wrote:
I feel like Rip Van Winkle. The engineering community has developed a
whole lot of nice things since I left it in 1969. And, its like I've
been sleeping for 37 years.

Ever heard of a "Triactuated Multicomplicator"?
--
73, Cecil http://www.qsl.net/w5dxp