Questions on Inverted L antenna
gwe...@hfx.eastlink.ca
to a tree - it's about 24 feet off the ground (a paved parking area). I
am currently using my clothesline for an antenna. I am using a "UnUn"
to match impedance, and I run a ground line from the UnUn and a coax
feed into my flat. Although I think it works reasonably well, I have
nothing to which I can compare it.
So, some question on the Inverted L antenna.
For SW receiving, what is the advantage, or primary difference between
a correctly installed Inverted L antenna vs. an end fed horizontal?
Is there any advantage over my current horizontal antenna for receiving
if I suspend a 65 foot, end fed wire (with UnUn and ground) off the
bottom of the clothesline and run it over to the tree and down to the
base of the tree?
Is it OK to run a ground line from the horizontal end of such an
antenna or is it best to ground the Inverted L at the base of the tree
where it's nearest the ground?
Inverted L antennas seem to be specific about feeding the receiver from
the bottom of the vertical end. Is this required, or just for
convenience? If I feed the antenna to the receiver from the end of the
horizontal element, will this degrade the performance of the Inverted
L?
I am just curious about trying something different, but I would like to
know if there is any advantage before I purchase the material and set
up and test alternatives.
Gary Weber
J999w
the low bands when you don't have the means to put up a BIG vertical. The
veritical polarization will aid in really long haul DX work. A horizontally
polarized antenna at low heights (less than 60 or 70+ ft) will favor higher
angles and be less effective for long haul DX.
The inverted L needs a GOOD ground at the feed point just like any vertical,
otherwise you loose a LOT in efficiency due to ground losses.
Give it a try.
I had a 100 ft wire that sloped from my basement up to the top of a 70 ft tree
... was KILLER on the 90m band, horrible on 41m.
John K9RZZ
Milwaukee
Merwin Dooley
down alot of the background noise. The L will improve your reception, not
matter it's length.
I use a 100 foot wire going from 10 foot high out 80 feet to a tree
about 30 feet up,and then drops 20 feet at about a 120 degree angle. Fed
with a 9:1 balun at the 10 foot end and grounded there also.
Mer
starman
How long is the ground wire from the balun to the ground?
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gwe...@hfx.eastlink.ca
Gary
RHF
.
Why the Inverted "L" Antenna is recommended by many including
myself; is that it's 'basic' Lay-Out and Structure; allow the
user to build what is called a Low Noise Shortwave Listener
(SWL) Antenna.
.
For the Shortwave Listener (SWL) considering building / erecting
an Inverted "L" Antenna within the Space Available for them to
build the Antenna.
- The 1ST Step is finding / determining where you will locate
the Vertical Up-Leg of the Inverted "L" Antenna.
- The 2ND Step is then determining the Mounting/Rigging Point
for the Far-End Horizontal Out-Arm.
.
For the Shortwave Listener's (SWLs) Inverted "L" Antenna
the "Work-Around-Center" is the BASE of the Vertical Up-Leg.
.
1. It is at this BASE that the Ground Rod is installed.
.
2. It is at this BASE that the Matching Transformer (UnUn)
Magnetic Longwire Balun (MLB) is located and installed.
TIP - Mount the Matching Transformer directly to the Top
of the Ground Rod; making a solid strong Ground Connection.
{Now You Are Really Grounded.}
.
3. It is at this BASE that the Coax Cable from the Radios
and Receivers in the Shack is connected to the Matching
Transformer and then Run/Routed along the ground or buried
under the ground to the Shack.
.
4. It is at this BASE that the Wire Antenna Element is
connected to the Matching Transformer and will start its
Vertical Up-Leg; and the Horizontal Out-Arm.
.
THE RESULT - With all of the above PARTS of an Inverted
"L" Antenna installed and properly connected; you have
a 'relatively' Low Noise Antenna.
.
.
ABOUT - The Inverted "L" Antenna :
.
The most 'common' form of the Random Wire Antenna used by
SWLs is the Inverted "L" Antenna.
.
The Inverted "L" Antenna 'Configuration-Shape' lends itself
to the Design Concepts of a "Low Noise Antenna" that has been
popularized by John Doty; consisting of: Antenna Element;
Matching Transformer; Grounding Point; Coax Cable Feed-in-Line;
and Radio/Receiver.
http://groups-beta.google.com/group/rec.radio.shortwave/msg/776c390272c6c91f
.
Inverted "L' Antenna Reading List
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/374
.
"LOW NOISE SWL ANTENNA" - by Mark Connelly [WA1ION]
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/119
"Another Look at Noise-Reducing Antenna Systems"
.
Inverted "L" Antenna as an 'available space' SWL Antenna
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/54
.
"LOW NOISE SWL ANTENNA" - popularized by John Doty.
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/2
.
.
REMEMBER: "The Shortwave Antenna is 55.5% of the . . .
Radio/Receiver and Antenna/Ground Reception Equation"
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/288
A Shortwave Antenna is "Equally" Important for Good Reception [.]
.
.
iane ~ RHF
.
All are WELCOME and "Invited to Join" the
Shortwave Listener (SWL) Antenna eGroup on YAHOO !
<http://groups.yahoo.com/group/Shortwave-SWL-Antenna/>
.
Some Say: On A Clear Day You Can See Forever.
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/502
.
I BELIEVE: On A Clear Night . . .
You Can Hear Forever and Beyond, The BEYOND !
With a Shortwave Listener SWL Antenna of your own making.
"If You Build It {SWL Antenna} You Will Hear Them !"
.
.
gwe...@hfx.eastlink.ca
> For the Shortwave Listener's (SWLs) Inverted "L" Antenna
> the "Work-Around-Center" is the BASE of the Vertical Up-Leg.
> .
> 1. It is at this BASE that the Ground Rod is installed.
> .
> 2. It is at this BASE that the Matching Transformer (UnUn)
> Magnetic Longwire Balun (MLB) is located and installed.
>
> and Receivers in the Shack is connected to the Matching
> Transformer and then Run/Routed along the ground or buried
> under the ground to the Shack.
> .
> 4. It is at this BASE that the Wire Antenna Element is
> connected to the Matching Transformer and will start its
> Vertical Up-Leg; and the Horizontal Out-Arm.
> .
> THE RESULT - With all of the above PARTS of an Inverted
> "L" Antenna installed and properly connected; you have
> a 'relatively' Low Noise Antenna.
So does this mean that an antenna that is configured as an Inverted L
but grounded and fed from the end of the horizontal unit will perform
significantly different, and is not in fact an "Inverted L"?
The inverted L design seems designed to work for feeding a Rx at ground
level. I live on the third floor. Furthermore, it is often suggested
that the wire for most antennas should be away from the dwelling for
best performance. So back to my original questions, which are
essentially...
If I wish to install an inverted L from a third floor location, am I
better off a) with the vertical portion away from the building (at the
other end of the horizontal portion) or b) against the dwelling?
What kind of performance difference do these two options represent?
Gary
RHF
.
What About an . . . End-Fed Inverted "L" Antenna ?
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/1971
.
>From what I understand from what you have write here:
.
You have a 45 Foot Horizontal [Flat] "Random" Wire Antenna
that is about 22 Feet above the ground.
.
You are using a Matching Transformer "UnUn" {MLB} with the
Wire Antenna and also using a Coax Cable Feed-in-Line to your
Radio/Receiver.
.
You have a Ground Wire that is about 22 Feet long connected to
the Matching Transformer ? Coax Cable ? Radio/Receivers ?
.
You 'want' to "Connect" a Piece-of-Wire to the End of
the Horizontal Random Wire Antenna to convert it into
an END-FED Inverted "L" Antenna.
.
YOUR QUESTION ARE :
.
Will your END-FED Inverted "L" Antenna Work ? - Yes.
.
Will END-FED Inverted "L" Antenna Work like a normal
bottom fed Inverted "L" Antenna ?
- For a Shortwave Listener (SWL) Antenna in a word "YES".
.
HOWEVER - Since you have a Ground Wire going up vertically
at the END-FED 'end' of the Inverted "L" Antenna.
- You may find that your Inverted "L" Antenna exhibits
some 'directivity' toward the Far-End Vertical Down-Leg.
.
.
SO THINGS TO CONSIDER :
.
What are you using for your 'primary' Ground Point ?
- Is it an Eight Foot (8') Ground Rod ?
- If 'not' then consider Installing an Eight Foot (8')
Ground Rod to be your 'primary' Ground Point for your
Antenna and Radio Equipment.
.
What are you using for your Ground Wire ?
- Is it a Copper # 10 AWG Wire or Larger Wire ?
- If 'not' then consider Installing an Copper # 10 AWG Wire
or Larger Wire.
Telamon
gwe...@hfx.eastlink.ca wrote:
How long is the ground wire from the balun to the ground?
> About 22 feet.
Then the BALUN is not at RF ground but at the end of a counterpoise.
That ground connection will only be good at DC. This is still of some
use depending on how the BALUN is configured it could at least take
static charges to ground.
--
Telamon
Ventura, California
J999w
>but grounded and fed from the end of the horizontal unit will perform
>significantly different, and is not in fact an "Inverted L"?
I'd call it a bent random wire.
If you're up 30 to 40 ft, then you'll have a reasonably low take off for 12
mhz and up.
I'd just get it up as high as possible and long as possible.
:^]
jw
k9rzz
RHF
.
AHaaaaa :o)
We have a difference of 'opinion' and a matter of perspectives ;-)
.
I would agree with you that it could be called a "Bent" Random
Wire Antenna: If the Lay of the Wire Antenna Element was in the
Horizontal Plane [Flat].
- Across-and-Out View
- - Top-Down Perspective
- - - Only Horizontal Polarized
.
However, in this instance the Lay of the Wire Antenna Element
is both in the Horizontal Plane and the Vertical Plane.
- Bottom-Up View
- - Side Perspective
- - - Both Horizontal and Vertical Polarized
.
Then Again - Going back to the 'original' 45 Foot Horizontal Wire
Antenna with a 22 Foot Vertical Ground Wire; that is fed with a
Matching Transformer. It could be 'viewed' as an Off-Center-Fed
Dipole with One Side Terminated.
.
NOW - If the 'original' 45 Foot Horizontal Wire Antenna with a
22 Foot Vertical Ground Wire is Modified with the addition of
a Vertical Down-Leg at the End of the Horizontal Wire; and still
is Fed with a Matching Transformer at the Top Near Corner.
It could be 'view' as directive array of Two Vertical Elements;
on the Far-End a Driven Vertical Element and on the Near-End
a Vertical Reflector Element.
.
for any piece of wire being used as an antenna . . .
- there are no rights or wrongs
- - its all a matter of perspective
- - - what works - works !
.
iane ~ RHF
.
starman
>
> So does this mean that an antenna that is configured as an Inverted L
> but grounded and fed from the end of the horizontal unit will perform
> significantly different, and is not in fact an "Inverted L"?
A properly installed inverted-L will have the balun near the ground at
the end of the vertical downlead wire. This allows for a short ground
wire from the balun to a grounding rod. The receiver is fed with coax
from the balun to the house.
>
> The inverted L design seems designed to work for feeding a Rx at ground
> level. I live on the third floor. Furthermore, it is often suggested
> that the wire for most antennas should be away from the dwelling for
> best performance. So back to my original questions, which are
> essentially...
See my reply above. When you install it that way, you can run the coax
most anywhere to the receiver and still have a good RF ground to lower
the noise from domestic sources.
>
> If I wish to install an inverted L from a third floor location, am I
> better off a) with the vertical portion away from the building (at the
> other end of the horizontal portion) or b) against the dwelling?
A low noise inverted-L will have the vertical downlead at the far end of
the horizontal section with the balun located at the lower end of the
single wire downlead, near the ground. Then you can run coax back to the
house from the balun. The near end of the horizontal section shouldn't
be too close to the house where it might pick up noise.
>
> What kind of performance difference do these two options represent?
The 'low noise inverted-L' (paragraph above) can make a big difference
in lowering the noise that the antenna picks up from local sources.
Jack Painter
"starman" <sta...@tech.net> wrote
> A low noise inverted-L will have the vertical downlead at the far end of
> the horizontal section with the balun located at the lower end of the
> single wire downlead, near the ground. Then you can run coax back to the
> house from the balun. The near end of the horizontal section shouldn't
> be too close to the house where it might pick up noise.
>
> The 'low noise inverted-L' (paragraph above) can make a big difference
> in lowering the noise that the antenna picks up from local sources.
>
There is not one ounce of truth to an "Inverted-L" being ANY quieter than a
45 degree random wire, and especially a horizontal-dipole, which is
generally quieter than any antenna with a vertical component. Most
interference is vertically polarized, and the verticals, random-wires,
slopers, or inverted-L antenna designs all pick up more vertically polarized
"noise" than a horizontally polarized antenna. Adding a vertical or even a
45 degree sloped component to an antenna DOES make it less directional than
a horizontal, and that is all it does. Any noise-limiting realized from
these designs comes strictly from the grounded-Balun and not the design,
configuration or dimensions of the antenna. Shield-grounding (for static and
lightning protection) at the feedpoint will achieve 99% of the
noise-limiting benefit that a grounded Balun does. The missing 1% is an
equal loss of signal and noise through the Balun. All RF noise (but not all
energy has RF components) is coupled right across the Balun windings, their
function of electrically decoupling is true of some DC energy, but not RF
energy, which is rather efficiently coupled across the Balun by design.
The same application of a grounded-Balun works equally well on both the
random (straight) wire antennas and inverted-L antenna btw. Both the random
wire and inverted-L benefit from (require in most cases) a counterpoise
ground or radials to provide effective transmitting. Neither a counterpoise
nor radials affect reception from the either the random wire or inverted-L,
however.
Jack Painter
Virginia Beach, Virginia
RHF
When All Is Said and Done {Written}.
.
For the casual Shortwave Radio Listener; the Inverted "L" Antenna
is easy to visualize and conceive of building.
.
READ - The 'simple' Answer (in most cases) is the
Low Noise Inverted "L" Antenna
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/1785
.
When properly laid-out, arranged and constructed;
the Inverted "L" Antenna provides a relatively 'low noise'
"Omni-Directional" Shortwave Listener's (SWL) Antenna.
.
READ - The Inverted "L" Antenna - It's 'basic' Lay-Out
and Structure {Why It Works}
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/1969
.
For the 'non-technical' Shortwave Listener the Inverted
"L" Antenna meets the "KISAP" Test and that is good.
KISAP = Keep-It-Simple And Practical [.]
TIP - For those who do not wish to go through the process
of building their own Inverted "L" Antenna; they can buy a
pre-build Random {LongWire} Wire Antenna and configure it
as an Inverted "L" Antenna - Two come to mind:
READ - Par EF-SWL End-Fed Shortwave Antenna configured
as an Inverted "L" Antenna
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/1562
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/1711
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/1717
READ - High-Z Shortwave Longwire Antenna with Matching Transformer
(MLB) and SO-239 Connector
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/1659
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/1709
.
I applaud your level of technical expertise and the mastery
of the subject of Antennas. But for many casual Shortwave
Listeners; it is a burden of knowledge that they do not wish to
acquire; just to simply Listen and Enjoy their Radios a little
better.
READ - Inverted "L' Antenna Reading List
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/374
.
When All Is Said and Done {Written}
. . . What Works - WORKS !
Telamon
"Jack Painter" <223...@cox.net> wrote:
I agree with all that you wrote except for that last sentence.
Every location is a different situation and so generalizations can be
made about antenna type, radials or ground performance but there are no
absolutes here. What is better in one place will not necessarily be
better in another. Likely yes, but not necessarily.
Some locations may be far better off with a counterpoise of some type
rather than depending on RF ground return through the radio and mains
supply, which is all that is left if that one ground rod the BALUN is
connected to is not up to the job.
As one example if you have good ground conductivity then that one rod
might be all you need but if ground conductivity is poor then a radial
or radials will make an improvement. You can always lay wires on the
ground and see if they help. If they do then you can go through the
trouble to make them perminent.
Any type of single element antenna (unbalanced) requires a good RF
ground to be effective. The RF ground is the other half of the antenna.
--
Telamon
Ventura, California
Jack Painter
"Telamon" <telamon_s...@pacbell.net.is.invalid> wrote
I agree with that. While only some "incomplete" (unbalanced wire) antennas
can radiate without a good RF ground, all antennas can receive with no RF
ground at all. But some receivers can benefit from better ground than the
AC-grounded case of the radio provides. Noise limiting is one reason we do
try to improve both the DC and RF ground capabilities of the coax-shield to
improve this possibility, agreed.
starman
I think you've missed the point. A so called 'low noise' inverted-L is
intended to reduce noise on the feed line to the receiver which comes
from domestic sources like appliances in the home. This is not the same
as the noise being received by the antenna wire itself. When the feed
line is part of the vertical section of the antenna, like the typical
inverted-L or random wire, it can pick up noise from the domestic
environment. The solution is to use a coax feed line which connects to a
balun near the ground. The vertical section of the antenna comes down to
the balun. This allows for a short RF ground from the coax shield to
earth which decouples the noise on the shield.
Jack Painter
"starman" <sta...@tech.net> wrote
Well I didn't mean to miss the point, and I'm afraid you're far off base in
suggesting that an inverted-L radiates part of the feedline or that feedline
(coax-shield) noise has anything to do with an antenna configuration. The
use of coax minimizes feedline noise, and shield-grounding the coax further
reduces noise from either being brought into the shack or carried to the
antenna from the shack. In an inverted-L, either a Balun or a choke is
always used to prevent inadvertent feedline radiation. The vertical portion
of the end-fed inverted-L is where the feedline ends and the antenna begins.
The real noise-limiting design of any beverage-style or inverted-L wire
antenna is to ground one half of the Balun output. This is whether the coax
shield is grounded earlier or not. That does affect signals picked up on the
antenna wire itself, although experts are not agreed as to whether there is
a measurable improvement in signal to noise ratio as a result of this. As
Telemon mentioned, having a counterpoise or good RF ground could make a
difference there. In my particular case, there is a marked improvement in
signal strength and possibly some reduction in noise when the connection
from ground rod to Balun is made. I also transmit through this antenna with
pretty good results. The original concept of grounding one-half of a
current-type wire-fed Balun for noise limiting came from an 1980's issue of
Fine Tuning's PROCEEDINGS. I was borrowing the issue from a friend and
cannot remember the original author of this but I don't believe it was the
venerable John Doty to which it is lately accredited.
starman
If the coax shield of an inverted-L does not have a good RF ground,
which requires a short ground wire to earth, the domestic noise on the
shield can couple to the center conductor of the coax where it connects
to the antenna. The noise will then become part of the antenna signal to
the radio. That's the point I think you missed.
Jack Painter
OK I didn't restate the obvious, agreed.
The best place to terminate the antenna and mount the Balun is *at* the
ground rod, which means the connection is about 4 inches long. Ty-wrap the
Balun to the protruding ground rod. After applying coax-seal to the
wire-wrapped and then soldered connections, cut the bottom and slit one side
of a plastic beverage bottle to just fit over the Balun and tape the bottle
shut afterwards. Spray paint the bottle with bow-flex cammo and it becomes
part of the background, and weather-proofed for years of service. Some
designs advise terminating the vertical drop of the inverted-L about 6 feet
above ground. That's more important for a center fed or off-center fed
(dipole type) antenna than the end-fed wires. Users should have no problems
terminating the inverted-L at ground level, and sink a good ground rod (with
buried radials if you desire) at that same point.
starman
I mounted my balun in a plastic electrical junction box with a cover
gasket, the kind used with plastic conduit. The ground wire to the rod
is about 2-feet long.
Jack Painter
Something I intend to experiment with, is running two radials from the
Balun/ground/feedpoint; one under the entire length of the antenna and the
other 180 degrees away from the feedpoint. Since this antenna was
deliberately located as far from the house as possible (on the property
line), I could not run radials in a 360 degree fashion. But I think if
radials will help at all, two of them (at 0 and 180 degrees) would show
results. Ever try this? The antenna is for 2182 thru 16000 khz marine.
Jack
RHF
If IIRC the one Radial that helps the most, is the one
that lays directly under the Horizontal Out-Arm of the
Inverted "L" Antenna.
This is why I suggest that 'if' possible to Flip Starting
Point (Back-to-Front) with the Vertical Up-Leg of the
Inverted "L" Antenna and have the Coax Cable Feed-in-Line
lay directly under the Horizontal Arm of the Inverted "L"
Antenna.
READ - Flipping the Inverted "L" Antenna 'Back-to-Front'
= Better Performance
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/2013
http://groups-beta.google.com/group/rec.radio.shortwave/msg/6079890656d94af1
Maybe some one could use some software amd 'model' a
Shortwave Listener's (SWLs) Inverted "L" Antenna with
a single Ground Radial directly under the Horizontal
Out-Arm.
# 1 The 'small' SWL (V1:H2) Inverted "L" Antenna using a
15 Foot Vertical Up-Leg and 30 Foot Horizontal Out-Arm
Plus 30 Foot Ground Radial directly under the Horizontal
Out-Arm section of the Antenna.
.
# 2 The 'medium' SWL (V1:H2.5) Inverted "L" Antenna using a
20 Foot Vertical Up-Leg and 50 Foot Horizontal Out-Arm
Plus 50 Foot Ground Radial directly under the Horizontal
Out-Arm section of the Antenna.
# 3 The 'large' SWL (V1:H3) Inverted "L" Antenna using a
25 Foot Vertical Up-Leg and 75 Foot Horizontal Out-Arm
Plus 75 Foot Ground Radial directly under the Horizontal
Out-Arm section of the Antenna.
Test Results should be provided for these Shortwave Bands :
@ 60M Band ~ 5 MHz
@ 49M Band ~ 6 MHz
@ 31M Band ~ 9.7 MHz
@ 25M Band ~ 11.8 MHz
@ 22M Band ~ 13.7 MHz
@ 19M Band ~ 15.5 MHz
starman
I've never tried ground radials but it's worth a try. Would you still
run a short ground wire too?
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Jack Painter
Per above, my 4:1 Balun/coax-feedpoint is already attached/connected
directly to a ground rod, not just near one. The radials will both be part
of common ground already, their tie-point at the same ground rod that the
feedpoint and Balun are attached to. Radials are normally shallow-buried,
both for protection and to minimize pickup of yet more noise. It's a lot of
work to bury long radials, so I will first just lay them out along the
surface, then experiment with various coastal stations to determine if there
is any gain from the radials.
Due to the lightning protection design at my station, any new ground radials
also have to be bonded to the station ground and AC service entry ground,
the entire system is common-bonded. Because it's winter time and small
likelihood of lightning (we had a nearby strike during a snowstorm 2 weeks
ago!) I will wait to add the bonding conductors until after the antenna is
tested for any possible xmit/receive improvements. Those bonding connectors
will have to run 90 degrees from the end of each of the two new radials,
and they may also alter the radiation pattern of the antenna. I'll let you
know how that works out.
Jack
Telamon
wrote:
If a ground wire is not short it will not behave as if it is connected
to ground period.
The problem is that a wire has inductance. The value of inductance is
based on the diameter of the wire or cross sectional area for other
shapes over its length. The smaller the cross sectional area is or the
longer the wire the is the higher the inductance of that wire.
The inductance of the wire will become a greater problem at higher
frequencies and less of a problem the lower in frequency you want to
operate on because the reactance of the wire always increases with
frequency.
Since you want the wire to behave as a ground connection you have to
calculate its self inductance and then its inductive reactance at the
highest frequency you want it to behave as a ground connection.
If you don't want to calculate it then make it as short as practical.
If the connection turns out to be more than a few inches in length then
use three inch minimum width copper tape instead of wire.
--
Telamon
Ventura, California
starman
Given all the talk about grounding systems on this group in the past, I
think most of us here know that a good RF ground wire must be short to
avoid introducing too much inductance into the grounding system. I asked
the question because I wanted to know more about the relationship
between a good (short) RF ground wire and a ground radial system. Does
one work better than the other or should both be used together? Where's
John Doty when we need him? :-)
jimg
it's always important to keep the ground wire length well below 1/4
wavelength of the max freq your interested in. Assuming it's short
enough to prevent distributed effects, the self inductance of a
straight 16ga wire is about 0.33uH/foot...so 50' at 10MHz is about
1Kohm...thats a fair amount of impedance and is why you pick up all
that noise.....
so what's the ground radial system do? in short, it provides the
counter-poise to the wire strung in the sky. the antenna-ground system
create the differential signal which is applied to your receiver's rf
amp...the better the ground poise, the more 'sensitive' your
antenna...is this some kind of linear relationship? like double the
ground system and double the antenna sensitivity...nope , not that
simple and there's not enuf room here to make all the variables
clear...but the better the grounding system, the better your antenna
will "work"...some ppl have a good enough conduction under the soil
that a simple 10' ground rod intersects this "layer" and the dx cpmes
rolling in...other ppl have rods sunk in the earth and buried in wild
patterns all over the yard to get the same effect.....
so the simple answer(s) is: your ground wire length influences noise
(what we call common-field) pick-up so shorter is better; the ground
radial system improves the signal strength at the receiver
input...and i hate simple answers to a very complicated system...
jimg
Oregon
USA
Jack Painter
"jimg" <jame...@verizon.net> wrote
> it's always important to keep the ground wire length well below 1/4
> wavelength of the max freq your interested in. Assuming it's short
> enough to prevent distributed effects, the self inductance of a
> straight 16ga wire is about 0.33uH/foot...so 50' at 10MHz is about
> 1Kohm...thats a fair amount of impedance and is why you pick up all
> that noise.....
>
> so what's the ground radial system do? in short, it provides the
> counter-poise to the wire strung in the sky. the antenna-ground system
> create the differential signal which is applied to your receiver's rf
> amp...the better the ground poise, the more 'sensitive' your
> antenna...is this some kind of linear relationship? like double the
> ground system and double the antenna sensitivity...nope , not that
> simple and there's not enuf room here to make all the variables
> clear...but the better the grounding system, the better your antenna
> will "work"...some ppl have a good enough conduction under the soil
> that a simple 10' ground rod intersects this "layer" and the dx cpmes
> rolling in...other ppl have rods sunk in the earth and buried in wild
> patterns all over the yard to get the same effect.....
>
> so the simple answer(s) is: your ground wire length influences noise
> (what we call common-field) pick-up so shorter is better; the ground
> radial system improves the signal strength at the receiver
> input...and i hate simple answers to a very complicated system...
>
Well put. It's good to keep it simple! Some re-emphasis:
RF GROUND is at the transmitter-side, where avoidance of 1/4 wave length
prevents monster impedance that is not felt as ground at all. A short path
to multiple ground rods connected in parallel completely avoids this 1/4
wave effect no matter what frequency you xmit on. XMTR RF GROUND has no
effect on receiving at all, *if * the static grounding and radials (below)
are used.
STATIC/LIGHTNING GROUND is grounding the coax-shield at several points,
beginning right outside the shack, at the base of a wire antenna or tower,
mid-point, and top of tower.
RADIALS are for reflecting transmitted energy from the antenna that would
otherwise be lost (absorbed) by the earth. They have a much smaller but
measurable benefit to the receiving aspect of any antenna. They can be above
ground (right under an elevated vertical, where very short lengths work),
along the surface of the ground on a ground-based vertical, or buried in a
large pattern around a vertical, center-fed inverted-L, or in some cases,
random wires or inverted-L's. A 1/2 wave horizontal dipole is a "complete"
antenna and has no benefit from radials, but it must be elevated
sufficiently to avoid ground losses. The coax-shield of feedline to a dipole
should still be grounded per above para.
--
WARNING: That ground screw on the back of your receiver set could get you in
more trouble than it's worth. First, the receiver-case is already grounded
via your home's electrical system. Noise and static on the coax-shield
should be shorted to ground outside from coax-shield grounding. If you
connect your receiver to a separate outside ground, you have major lightning
issues if you leave that receiver-ground connected during storms. This is
true even if *everything* else is disconnected. If any tree or structure
within up to several hundred feet of your property is struck by lightning,
your ground system will be a sink for some of that energy, and draw it right
into the radio via ground connections. Of course the antennas would add to
this problem, but most people remember to disconnect them before a storm.
Putting disconnected antenna feedlines in a mason-jar is an embarrassing
practice that I got away with for about ten years, and I'm sure many
hobbyists play the same odds. Better than nothing (which is the glass-jar
trick) would be to short the antennas to an RF-ground, if you have one.
If you decide that a separate receiver-ground is important, you should
consider what you will do with that "hot-wire" before lightning occurs
anywhere in a wide-area around your property.
starman
>
> jimg wrote:
> it's always important to keep the ground wire length well below 1/4
> wavelength of the max freq your interested in. Assuming it's short
> enough to prevent distributed effects, the self inductance of a
> straight 16ga wire is about 0.33uH/foot...so 50' at 10MHz is about
> 1Kohm...thats a fair amount of impedance and is why you pick up all
> that noise.....
>
> so what's the ground radial system do? in short, it provides the
> counter-poise to the wire strung in the sky. the antenna-ground system
> create the differential signal which is applied to your receiver's rf
> amp...the better the ground poise, the more 'sensitive' your
> antenna...is this some kind of linear relationship? like double the
> ground system and double the antenna sensitivity...nope , not that
> simple and there's not enuf room here to make all the variables
> clear...but the better the grounding system, the better your antenna
> will "work"...some ppl have a good enough conduction under the soil
> that a simple 10' ground rod intersects this "layer" and the dx cpmes
> rolling in...other ppl have rods sunk in the earth and buried in wild
> patterns all over the yard to get the same effect.....
>
> so the simple answer(s) is: your ground wire length influences noise
> (what we call common-field) pick-up so shorter is better; the ground
> radial system improves the signal strength at the receiver
> input...and i hate simple answers to a very complicated system...
That's a good start. The radials make the signal stronger and a good RF
ground makes it quieter. Both add to the intelligibility of the signal.
RHF
.
Mason-Jar ? Great Balls of Lightning ! ;-}
.
I have used old metal Film Canisters each mounted
to the stations Ground Buss; one per PL-259 Plug.
.
Also a small tall Tin Can mounted to the stations Ground
Buss with two to Four PL-259 Plugs jammed it to it.
.
Now I use an Alpha-Delta Antenna Switch with a
"Disconnected-and-Grounded" Center Position
when things are not in use.
http://www.universal-radio.com/catalog/switch/2415.html
http://www.universal-radio.com/catalog/switch/1864.html
http://www.universal-radio.com/catalog/switch/2811.html
.
Jack Painter
"RHF" <rhf-new...@pacbell.net> wrote
I thought you would get a kick out of the mason-jar trick! Live and learn.
What are your Alpha-Delta Antenna Switches "grounded" to when in the center
position? Where are they mounted?
Some of you will remember I operate a USCG Auxiliary communications station,
and when on duty, do not secure for wx. That required a complete lightning
protection system which cost about $4500 in electrical design, labor and
materials (surge suppression), plus another several hundred in materials
(external ground system and bonding) which I installed. That does not
include the standby power (generator) btw. I researched the grounding,
bonding and surge suppression issues for over two years before embarking on
that plan. Also studied the damages that occurred to stations (amateur,
broadcast and government) who had lightning protection systems, and those
that did not. I still follow every published story of lightning damage to US
communication stations, and have a current library of (US) NEC and NFPA
codes.
My system's baptism by fire came the same afternoon the contractors were
cleaning up to leave in July 2004. Over 1,000 strikes in a 10 mile area,
about 300 in my immediate area, and perhaps a dozen almost on top of me.
Trees in my yard and on both sides of my HF antennas were struck, and the
power spiked relentlessly, eventually calling for the generator due to
electrical noise and high voltages. Dozens of electrical storms later, the
system continues to perform as expected.
When I give advice to SWL hobbyists about lightning safety, it's because I
went through years of worry and learning curves of what works, what doesn't,
and the safest ways to operate (or isolate) from various stages of hobby
listening, to nearly full-time service for the USCG.
Although the antenna systems have changed somewhat from the schematics on
the website, the basic system is described at
http://members.cox.net/pc-usa/station/ground0.htm
This is the time btw, to commence any plans some of you may have had to
install or upgrade lightning protection systems, not in the Spring or Summer
when thunderstorms can occur without warning! O.K. Steve in Detroit you will
have to wait until the ground thaws, lol.
RHF
.
I have an Aluminum Sheet that covers a 1'x2' board that
is mount on the wall. This is the Shack's Ground and the
Alpha-Delta Antenna Switch is mounted on this metal sheet.
.
~ RHF
.
.