45' high, 25.8 sloping wire at the top, 29 feet high at the far end. #12
THHN Insulated copper wire, stranded.

Predicted Radiation Resistance: 25.8 ohms, very good ground (rich pastoral,
midwest).

With no radials, I get a flat 50 ohm match at 3595 khz. Obviously this would
indicate ground losses of approximately 25 ohms, if I'm thinking about this
right. Also, predicted efficiency would then be 50 % (25/(25+25), indicating
a 3 dB loss. Forgetting about fresnel region losses, this seems to be better
than I had expected. 2:1 vswr bandwidth is very broad....broader than what I
get with EZnec 4.x with a 25 ohm load in the base.

This means one of two things to me:

Either my ground losses are much higher than the 25 ohms I'm indirectly
calculating, or I have made some sort of conceptual error in thinking about
what the implications are of a 25 or 26 ohm feedpoint. All my references
point toward a 25 ohm radiation resistance for my 42' vertical x 25.8 ft
inverted L (with sloping top wire instead of flat top wire). What is wrong
with my logic here? If the R(rad) is 25 ohms, and I measure a flat VSWR (on
two other meters) at 3600 khz, then isn't the remaining 25 ohms, ground
loss?

I also show about 37 ohms resistance and 0 ohms reactance at 3600 khz with
my MFJ-269, which is really confusing, in that if I have 25 ohms for Rrad,
then I have 13 ohms of ground losses. Further, 37 ohms is around 1.3 to 1.
So I have two other vswr meters showing 1:1 at 3600, and the MFJ showing 37
ohms. This is a pretty large percentage difference.

I would be inclined to believe the 25.8 ohms predicted by both EZnec 4 and
the Low Band DX'rs Handbook. In any case, I'll put out 4 radials tomorrow
morning and repeat all my measurements, looking for narrowing bandwidth and
lowered input Z as my ground losses decrease.

Ultimately, I'm going to put down 16, 66' radials, in steps of four, taking
measurements of input Z (mfj-269) and vswr bandwidth for 2:1, at 0,4,8 and
16 radials. I'll report what happens as I go along.

Anywho, without any radials at all there are quite a few distant signals on
80m this evening, that are consistently louder on the newly installed
inverted L, than on my Carolina Windom at 45'. Most signals as one pans the
band, are louder (at 2 hours after sunset) on the C. Windom than on the
radial-less inverted L, but ones from several states away are equal or
better on the radial-less inverted L. Both seem to make good sense at this
point. I sure will be interested to see the effects of 4 and then 8 and on
up radials, but that is going to take a few days, because I don't want to
make radial changes unless I have access to low angle signals, which only
happens at night or just before sunrise.

Tomorrow is radial day. I will be laying out 4 radials 65' long to begin
with. I have resistance and reactance measurements every 50 khz as a
baseline, before installing radials. 4 in the early morning, 4 more just
before sunset, then 4 more the next morning, and the final 4 the next
evening. #14 THHN stranded insulated copper wire for the radials, btw.

Depending on what I end up seeing for "effect" I'll go to 24 or 32 radials
by winter....but only if the improvement is both measurable and "observable
on the air"...radials are a pain in the rear (or more accurately, the knees)
to put in.

What fun!

....hasan, N0AN

Starting point for the inverted L with sloping top loading wire.

45' high, 25.8' sloping wire at the top, 29 feet high at the far end. #12
THHN Insulated copper wire, stranded. Mounted 7" above the earth, directly
to a 3' ground rod (strictly for mechanical support, as I had a prefab mount
with 3/8x24 on one end and SO-29 on the other)

Predicted Radiation Resistance (Devoldere): 25.8 ohms, very good ground
(rich pastoral, midwest).


I see I had confused feedpoint impedance and radiation resistance (after
reading some more in Devoldere's "Low-Band DX'ing")

According to Figure 9-94, the radiation resistance for my inverted L is
approximately 25 ohms. According to EZnec 4.1, source data says:

Impedance = 25.58 + J 1.872 ohms at 3600 khz.

When I measure the antenna with the MFJ-269, I get:

R=37 and X=0

If Devoldere and EZNEC are correct (although EZNEC may or may not be
measuring radiation resistance), then my radial-less inverted L is showing
ground losses of 37-25=12 ohms. If so, then my efficiency, without radials
is:
25/(25+12) or 25/37 or approximately 67%.

Before installing radials this morning, I just want to make sure I'm looking
at the right variables and interpreting them properly. 4 radials, laying on
the ground, will be ready to install when the sun comes up. 4 more later in
the day, etc., up to a total of 16 (the amount of wire I have ready to go).
Each time I put down 4, I'll take another measurement with the 269. For
kicks, I might take a measurement with just one or two first.

....hasan, N0AN

At what point in the system are you making your measurements?

hasan schiers wrote:

45' high, 25.8 sloping wire at the top, 29 feet high at the far end. #12
THHN Insulated copper wire, stranded.

Predicted Radiation Resistance: 25.8 ohms, very good ground (rich pastoral,
midwest).

With no radials, I get a flat 50 ohm match at 3595 khz. Obviously this would
indicate ground losses of approximately 25 ohms, if I'm thinking about this
right. Also, predicted efficiency would then be 50 % (25/(25+25), indicating
a 3 dB loss. Forgetting about fresnel region losses, this seems to be better
than I had expected. 2:1 vswr bandwidth is very broad....broader than what I
get with EZnec 4.x with a 25 ohm load in the base.

This means one of two things to me:

Either my ground losses are much higher than the 25 ohms I'm indirectly
calculating, or I have made some sort of conceptual error in thinking about
what the implications are of a 25 or 26 ohm feedpoint. All my references
point toward a 25 ohm radiation resistance for my 42' vertical x 25.8 ft
inverted L (with sloping top wire instead of flat top wire). What is wrong
with my logic here? If the R(rad) is 25 ohms, and I measure a flat VSWR (on
two other meters) at 3600 khz, then isn't the remaining 25 ohms, ground
loss?

I also show about 37 ohms resistance and 0 ohms reactance at 3600 khz with
my MFJ-269, which is really confusing, in that if I have 25 ohms for Rrad,
then I have 13 ohms of ground losses. Further, 37 ohms is around 1.3 to 1.
So I have two other vswr meters showing 1:1 at 3600, and the MFJ showing 37
ohms. This is a pretty large percentage difference.

I would be inclined to believe the 25.8 ohms predicted by both EZnec 4 and
the Low Band DX'rs Handbook. In any case, I'll put out 4 radials tomorrow
morning and repeat all my measurements, looking for narrowing bandwidth and
lowered input Z as my ground losses decrease.

Ultimately, I'm going to put down 16, 66' radials, in steps of four, taking
measurements of input Z (mfj-269) and vswr bandwidth for 2:1, at 0,4,8 and
16 radials. I'll report what happens as I go along.

Anywho, without any radials at all there are quite a few distant signals on
80m this evening, that are consistently louder on the newly installed
inverted L, than on my Carolina Windom at 45'. Most signals as one pans the
band, are louder (at 2 hours after sunset) on the C. Windom than on the
radial-less inverted L, but ones from several states away are equal or
better on the radial-less inverted L. Both seem to make good sense at this
point. I sure will be interested to see the effects of 4 and then 8 and on
up radials, but that is going to take a few days, because I don't want to
make radial changes unless I have access to low angle signals, which only
happens at night or just before sunrise.

Tomorrow is radial day. I will be laying out 4 radials 65' long to begin
with. I have resistance and reactance measurements every 50 khz as a
baseline, before installing radials. 4 in the early morning, 4 more just
before sunset, then 4 more the next morning, and the final 4 the next
evening. #14 THHN stranded insulated copper wire for the radials, btw.

Depending on what I end up seeing for "effect" I'll go to 24 or 32 radials
by winter....but only if the improvement is both measurable and "observable
on the air"...radials are a pain in the rear (or more accurately, the knees)
to put in.

What fun!

...hasan, N0AN

Question: Where was I taking my measurements.

I started out at the actual feedpoint...then put in about 55' of LMR-400,
and started a new set of measurements in the shack. Here is the latest data:

Radials 2:1 Fo 2:1 BW Z VSWR @ Fo
0 3340 3522 3920 580 36,0 1.3
2 3354 3524 3774 420 45,0 1.0
4 3419 3533 3741 322 60,1 1.2
8 3445 3550 3742 297 65,4 1.3

The formatting is bad, but in order, left to right:

Number of Radials
Lower 2:1 vswr point
Resonant Freq point
Upper 2:1 point
Bandwidth in kilohertz
Impedance as shown on the MFJ 269 at resonance.

I'm a bit confused by the rising feedpoint impedance with increasing number
of radials. That seems backwards to me.

73,

....hasan, N0AN

VSWR shown by MFJ 269 at resonance
"Ham op" wrote in message
...
At what point in the system are you making your measurements?

hasan schiers wrote:

45' high, 25.8 sloping wire at the top, 29 feet high at the far end. #12
THHN Insulated copper wire, stranded.

Predicted Radiation Resistance: 25.8 ohms, very good ground (rich
pastoral, midwest).

With no radials, I get a flat 50 ohm match at 3595 khz. Obviously this
would indicate ground losses of approximately 25 ohms, if I'm thinking
about this right. Also, predicted efficiency would then be 50 %
(25/(25+25), indicating a 3 dB loss. Forgetting about fresnel region
losses, this seems to be better than I had expected. 2:1 vswr bandwidth
is very broad....broader than what I get with EZnec 4.x with a 25 ohm
load in the base.

This means one of two things to me:

Either my ground losses are much higher than the 25 ohms I'm indirectly
calculating, or I have made some sort of conceptual error in thinking
about what the implications are of a 25 or 26 ohm feedpoint. All my
references point toward a 25 ohm radiation resistance for my 42' vertical
x 25.8 ft inverted L (with sloping top wire instead of flat top wire).
What is wrong with my logic here? If the R(rad) is 25 ohms, and I measure
a flat VSWR (on two other meters) at 3600 khz, then isn't the remaining
25 ohms, ground loss?

I also show about 37 ohms resistance and 0 ohms reactance at 3600 khz
with my MFJ-269, which is really confusing, in that if I have 25 ohms for
Rrad, then I have 13 ohms of ground losses. Further, 37 ohms is around
1.3 to 1. So I have two other vswr meters showing 1:1 at 3600, and the
MFJ showing 37 ohms. This is a pretty large percentage difference.

I would be inclined to believe the 25.8 ohms predicted by both EZnec 4
and the Low Band DX'rs Handbook. In any case, I'll put out 4 radials
tomorrow morning and repeat all my measurements, looking for narrowing
bandwidth and lowered input Z as my ground losses decrease.

Ultimately, I'm going to put down 16, 66' radials, in steps of four,
taking measurements of input Z (mfj-269) and vswr bandwidth for 2:1, at
0,4,8 and 16 radials. I'll report what happens as I go along.

Anywho, without any radials at all there are quite a few distant signals
on 80m this evening, that are consistently louder on the newly installed
inverted L, than on my Carolina Windom at 45'. Most signals as one pans
the band, are louder (at 2 hours after sunset) on the C. Windom than on
the radial-less inverted L, but ones from several states away are equal
or better on the radial-less inverted L. Both seem to make good sense at
this point. I sure will be interested to see the effects of 4 and then 8
and on up radials, but that is going to take a few days, because I don't
want to make radial changes unless I have access to low angle signals,
which only happens at night or just before sunrise.

Tomorrow is radial day. I will be laying out 4 radials 65' long to begin
with. I have resistance and reactance measurements every 50 khz as a
baseline, before installing radials. 4 in the early morning, 4 more just
before sunset, then 4 more the next morning, and the final 4 the next
evening. #14 THHN stranded insulated copper wire for the radials, btw.

Depending on what I end up seeing for "effect" I'll go to 24 or 32
radials by winter....but only if the improvement is both measurable and
"observable on the air"...radials are a pain in the rear (or more
accurately, the knees) to put in.

What fun!

...hasan, N0AN

If your antenna is over a PERFECT ground, an EM mirror, then the
mutually coupled impedance between the antenna and it's image antenna
gets to be a bit difficult to calculate or estimate. The Apex and it's
image are 80 feet apart. That is 107 degree spacing, and the ends are 77
degrees apart. The mutual impedance along the length of the antenna
changes due to the difference in phase shift.

Change from perfect reflecting ground to 'real' ground with varying
conductivity and permittivity as a function of length, width and depth
and the problem becomes much more complicated.

Your measurements, in your location, with your installation indicate, to
me, that your 8 radial solution is starting to converge to best
solution. I say this for two reasons. Your 2:1 VSWR bandwidth is narrow
and your Z is approaching 73 ohms.

I would use the eight radial solution and trim the antenna length to
your desired center frequency. Remember, a 2:1 VSWR indicates that 90%
of your energy is going into the antenna.

For the best analysis of your installation, the soil characteristics
would have to be known and controlled for several wavelengths square and
approximately 1/4 wavelength deep. Your radials [counterpoise] are
simplifying and stabilizing your solution.

Roy Llewellen is much better qualified than I to proceed deeper into the
EM Physics regarding all the possible interactions. If the science of
what's happening is your interest then contact Roy off-line [Roy, sorry
to volunteer you without your consent]. If a brief understanding of
possible contributing EM effects is your desire, then I hope this
contributes to your understanding.

Ham Op

hasan schiers wrote:

Question: Where was I taking my measurements.

I started out at the actual feedpoint...then put in about 55' of LMR-400,
and started a new set of measurements in the shack. Here is the latest data:

Radials 2:1 Fo 2:1 BW Z VSWR @ Fo
0 3340 3522 3920 580 36,0 1.3
2 3354 3524 3774 420 45,0 1.0
4 3419 3533 3741 322 60,1 1.2
8 3445 3550 3742 297 65,4 1.3

The formatting is bad, but in order, left to right:

Number of Radials
Lower 2:1 vswr point
Resonant Freq point
Upper 2:1 point
Bandwidth in kilohertz
Impedance as shown on the MFJ 269 at resonance.

I'm a bit confused by the rising feedpoint impedance with increasing number
of radials. That seems backwards to me.

73,

...hasan, N0AN

VSWR shown by MFJ 269 at resonance
"Ham op" wrote in message
...

At what point in the system are you making your measurements?

hasan schiers wrote:


45' high, 25.8 sloping wire at the top, 29 feet high at the far end. #12
THHN Insulated copper wire, stranded.

Predicted Radiation Resistance: 25.8 ohms, very good ground (rich
pastoral, midwest).

With no radials, I get a flat 50 ohm match at 3595 khz. Obviously this
would indicate ground losses of approximately 25 ohms, if I'm thinking
about this right. Also, predicted efficiency would then be 50 %
(25/(25+25), indicating a 3 dB loss. Forgetting about fresnel region
losses, this seems to be better than I had expected. 2:1 vswr bandwidth
is very broad....broader than what I get with EZnec 4.x with a 25 ohm
load in the base.

This means one of two things to me:

Either my ground losses are much higher than the 25 ohms I'm indirectly
calculating, or I have made some sort of conceptual error in thinking
about what the implications are of a 25 or 26 ohm feedpoint. All my
references point toward a 25 ohm radiation resistance for my 42' vertical
x 25.8 ft inverted L (with sloping top wire instead of flat top wire).
What is wrong with my logic here? If the R(rad) is 25 ohms, and I measure
a flat VSWR (on two other meters) at 3600 khz, then isn't the remaining
25 ohms, ground loss?

I also show about 37 ohms resistance and 0 ohms reactance at 3600 khz
with my MFJ-269, which is really confusing, in that if I have 25 ohms for
Rrad, then I have 13 ohms of ground losses. Further, 37 ohms is around
1.3 to 1. So I have two other vswr meters showing 1:1 at 3600, and the
MFJ showing 37 ohms. This is a pretty large percentage difference.

I would be inclined to believe the 25.8 ohms predicted by both EZnec 4
and the Low Band DX'rs Handbook. In any case, I'll put out 4 radials
tomorrow morning and repeat all my measurements, looking for narrowing
bandwidth and lowered input Z as my ground losses decrease.

Ultimately, I'm going to put down 16, 66' radials, in steps of four,
taking measurements of input Z (mfj-269) and vswr bandwidth for 2:1, at
0,4,8 and 16 radials. I'll report what happens as I go along.

Anywho, without any radials at all there are quite a few distant signals
on 80m this evening, that are consistently louder on the newly installed
inverted L, than on my Carolina Windom at 45'. Most signals as one pans
the band, are louder (at 2 hours after sunset) on the C. Windom than on
the radial-less inverted L, but ones from several states away are equal
or better on the radial-less inverted L. Both seem to make good sense at
this point. I sure will be interested to see the effects of 4 and then 8
and on up radials, but that is going to take a few days, because I don't
want to make radial changes unless I have access to low angle signals,
which only happens at night or just before sunrise.

Tomorrow is radial day. I will be laying out 4 radials 65' long to begin
with. I have resistance and reactance measurements every 50 khz as a
baseline, before installing radials. 4 in the early morning, 4 more just
before sunset, then 4 more the next morning, and the final 4 the next
evening. #14 THHN stranded insulated copper wire for the radials, btw.

Depending on what I end up seeing for "effect" I'll go to 24 or 32
radials by winter....but only if the improvement is both measurable and
"observable on the air"...radials are a pain in the rear (or more
accurately, the knees) to put in.

What fun!

...hasan, N0AN

Interesting observations.

The 2:1 swr points are only being mentioned to show that the bandwidth is
narrowing with increasing number of radials. That makes sense.

What doesn't make sense is the increasing feedpoint Z at resonance in
response to increasing radial numbers. There could be some minor trimming,
but 3 or 4 ohms reactance is probably close enough...the antenna is near
resonance and the resistive component is not likely to change much by
trimming the last 3 or 4 ohms of reactance out. The problem is, I can't
explain the the 65 ohm feedpoint impedance.

Most installations, start with a Z too high (because it includes ground
losses), and as radials are added, the feedpoint Z drops (as the loss
resistance disappears). This is the classical 1/4w ground mounted vertical
case. You know when to stop adding radials when the measured feedpoint
impedance at resonance is equal to the Z of the antenna over a "perfect"
ground.

Another way to accomplish the same thing is to keep adding radials until the
2:1 vswr bandwidth no longer narrows. I think I'm approaching that right
now.

The anomaly I'm trying to deal with is why the feedpoint Z has increased as
I went from 0 to 2, to 4, to 8 radials, when it should have decreased. I
wouldn't care a whit, if the terminal (end point) feedpoint Z was 65 ohms
resistive with no reactive component.

This is a technical element that I want to understand...no further changes
are likely to make any real difference in performance. What is it Johnny
Cochran said, "If the data don't fit, I just won't quit."? vbg

73,

....hasan, N0AN
"Ham op" wrote in message
news
If your antenna is over a PERFECT ground, an EM mirror, then the mutually
coupled impedance between the antenna and it's image antenna gets to be a
bit difficult to calculate or estimate. The Apex and it's image are 80
feet apart. That is 107 degree spacing, and the ends are 77 degrees apart.
The mutual impedance along the length of the antenna changes due to the
difference in phase shift.

Change from perfect reflecting ground to 'real' ground with varying
conductivity and permittivity as a function of length, width and depth and
the problem becomes much more complicated.

Your measurements, in your location, with your installation indicate, to
me, that your 8 radial solution is starting to converge to best solution.
I say this for two reasons. Your 2:1 VSWR bandwidth is narrow and your Z
is approaching 73 ohms.

I would use the eight radial solution and trim the antenna length to your
desired center frequency. Remember, a 2:1 VSWR indicates that 90% of your
energy is going into the antenna.

For the best analysis of your installation, the soil characteristics would
have to be known and controlled for several wavelengths square and
approximately 1/4 wavelength deep. Your radials [counterpoise] are
simplifying and stabilizing your solution.

Roy Llewellen is much better qualified than I to proceed deeper into the
EM Physics regarding all the possible interactions. If the science of
what's happening is your interest then contact Roy off-line [Roy, sorry to
volunteer you without your consent]. If a brief understanding of possible
contributing EM effects is your desire, then I hope this contributes to
your understanding.

Ham Op

hasan schiers wrote:

Question: Where was I taking my measurements.

I started out at the actual feedpoint...then put in about 55' of LMR-400,
and started a new set of measurements in the shack. Here is the latest
data:

Radials 2:1 Fo 2:1 BW Z VSWR @ Fo
0 3340 3522 3920 580 36,0 1.3
2 3354 3524 3774 420 45,0 1.0
4 3419 3533 3741 322 60,1 1.2
8 3445 3550 3742 297 65,4 1.3

The formatting is bad, but in order, left to right:

Number of Radials
Lower 2:1 vswr point
Resonant Freq point
Upper 2:1 point
Bandwidth in kilohertz
Impedance as shown on the MFJ 269 at resonance.

I'm a bit confused by the rising feedpoint impedance with increasing
number of radials. That seems backwards to me.

73,

...hasan, N0AN

VSWR shown by MFJ 269 at resonance
"Ham op" wrote in message
...

At what point in the system are you making your measurements?

hasan schiers wrote:


45' high, 25.8 sloping wire at the top, 29 feet high at the far end. #12
THHN Insulated copper wire, stranded.

Predicted Radiation Resistance: 25.8 ohms, very good ground (rich
pastoral, midwest).

With no radials, I get a flat 50 ohm match at 3595 khz. Obviously this
would indicate ground losses of approximately 25 ohms, if I'm thinking
about this right. Also, predicted efficiency would then be 50 %
(25/(25+25), indicating a 3 dB loss. Forgetting about fresnel region
losses, this seems to be better than I had expected. 2:1 vswr bandwidth
is very broad....broader than what I get with EZnec 4.x with a 25 ohm
load in the base.

This means one of two things to me:

Either my ground losses are much higher than the 25 ohms I'm indirectly
calculating, or I have made some sort of conceptual error in thinking
about what the implications are of a 25 or 26 ohm feedpoint. All my
references point toward a 25 ohm radiation resistance for my 42'
vertical x 25.8 ft inverted L (with sloping top wire instead of flat top
wire). What is wrong with my logic here? If the R(rad) is 25 ohms, and I
measure a flat VSWR (on two other meters) at 3600 khz, then isn't the
remaining 25 ohms, ground loss?

I also show about 37 ohms resistance and 0 ohms reactance at 3600 khz
with my MFJ-269, which is really confusing, in that if I have 25 ohms
for Rrad, then I have 13 ohms of ground losses. Further, 37 ohms is
around 1.3 to 1. So I have two other vswr meters showing 1:1 at 3600,
and the MFJ showing 37 ohms. This is a pretty large percentage
difference.

I would be inclined to believe the 25.8 ohms predicted by both EZnec 4
and the Low Band DX'rs Handbook. In any case, I'll put out 4 radials
tomorrow morning and repeat all my measurements, looking for narrowing
bandwidth and lowered input Z as my ground losses decrease.

Ultimately, I'm going to put down 16, 66' radials, in steps of four,
taking measurements of input Z (mfj-269) and vswr bandwidth for 2:1, at
0,4,8 and 16 radials. I'll report what happens as I go along.

Anywho, without any radials at all there are quite a few distant signals
on 80m this evening, that are consistently louder on the newly
installed inverted L, than on my Carolina Windom at 45'. Most signals as
one pans the band, are louder (at 2 hours after sunset) on the C. Windom
than on the radial-less inverted L, but ones from several states away
are equal or better on the radial-less inverted L. Both seem to make
good sense at this point. I sure will be interested to see the effects
of 4 and then 8 and on up radials, but that is going to take a few days,
because I don't want to make radial changes unless I have access to low
angle signals, which only happens at night or just before sunrise.

Tomorrow is radial day. I will be laying out 4 radials 65' long to begin
with. I have resistance and reactance measurements every 50 khz as a
baseline, before installing radials. 4 in the early morning, 4 more just
before sunset, then 4 more the next morning, and the final 4 the next
evening. #14 THHN stranded insulated copper wire for the radials, btw.

Depending on what I end up seeing for "effect" I'll go to 24 or 32
radials by winter....but only if the improvement is both measurable and
"observable on the air"...radials are a pain in the rear (or more
accurately, the knees) to put in.

What fun!

...hasan, N0AN

I'm a bit confused by the rising feedpoint impedance with increasing
number
of radials. That seems backwards to me.

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

SWR increases the further the impedance, either HIGHER or LOWER,
departs from 50 ohms.

The only way to measure antenna input impedance is by means of an
impedance bridge. Try one of the small antenna analysers.
----
Reg.

That is exactly what I'm using Reg, and why I"m puzzled. I'm getting rising
feedpoint impedance with increasing numbers of radials. The 2:1 bandwidth is
getting narrower, as it should, but what accounts for the increasing
feedpoint impedance? MFJ-269 antenna analyzer is what generated the table I
posted earlier.

Very strange?

....hasan, N0AN
"Reg Edwards" wrote in message
...
I'm a bit confused by the rising feedpoint impedance with increasing
number
of radials. That seems backwards to me.

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

SWR increases the further the impedance, either HIGHER or LOWER,
departs from 50 ohms.

The only way to measure antenna input impedance is by means of an
impedance bridge. Try one of the small antenna analysers.
----
Reg.

Hasan,

I think you are measuring the input impedance of an Inverted-L against
a system of ground radials.

You are trying to estimate the input resistance of the ground radials
by subtracting the CALCULATED radiation resistance of the Inverted-L
from the measured antenna input resistance.

Excellent, there is no better way of doing it!

First of all, the overall length of the antenna must be 1/4-wavelength
resonant at the testing frequency such that its input impedance is
PURELY RESISTIVE. The measured input resistance, of course, will be
greater than the calculated radiation resistance referred to its base.
The difference between them is the required input resistance of the
ground radials.

The hard part of the exercise is calculating the radiation resistance
referred to the base of the Inverted-L. The radiation resistance is a
very complicated function of the dimensions, overall length and
height, of the antenna.

However, for the purposes of estimating ground loss resistance, (it
changes with rainfall and temperature of the season), the following
approximation for radiation resistance is good enough.

RadRes = 18 * ( 1 - Cos( Theta ) ) ohms,

where Theta is an angle = 180 * H / ( H + L ) / Lambda degrees,

H = height of vertical portion of Inverted-L,
L = length of horizontal portion of Inverted-L
and Lambda is the free-space wavelength.

This formula applies ONLY when L+H is 1/4-wave resonant. Which is the
condition under which you are working if you are doing the job
correctly.

You will not find the formula in the books of bible-writer Terman.
Nor in any of the works of the other regular gurus. If you ask from
where it came from, it came from one of my old notebooks and I worked
it out for myself, years back.

Bear in mind it is only an approximation. It would take 6 months to
work out how precisely accurate it is and I don't have the time. But
it's as least as accurate as you can make impedance measurements. I
do hope I have copied it out correctly.

By the way, as the number of your radials increases and the ground
loss resistance gets very low, don't be surprised if you calculate
negative values of ground loss resistance.
----
Reg, G4FGQ

On Sat, 3 Sep 2005 09:27:52 -0500, "hasan schiers"
wrote:

Question: Where was I taking my measurements.

I started out at the actual feedpoint...then put in about 55' of LMR-400,
and started a new set of measurements in the shack. Here is the latest data:


Radials 2:1 Fo 2:1 BW Z VSWR @ Fo

Hassan,

Where are the radials (above ground, buried, how far)?

I think you told us that they radial wire is insulated, is that
correct?

Why did you choose 66' long radials?

Owen
--