Re: Topband: Buffaloed by a bias tee
On 1/22/2014 7:56 PM, Mike Waters wrote: That's the conclusion I came to after reading this article: http://www.ad5x.com/images/Articles/BiasT3amp.pdf But pay attention to what W8JI just said! 73, Mike www.w0btu.com I have been using exactly the same 40 uH inductor cited in the article in bias tees for decades. Works great. Rick N6RK _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Anyone purchased the ARRL book on Short Antennas for160???
A very respected authority on radial systems, Rudy Severns N6LF, has this
to say about 4 elevated radials:
"Since my QST article I've done some modeling to explore the sensitivity of
a simple 4-radial system to asymmetries in the radial fan. The modeling
easily replicates Weber's results and the news is even worse than Dick
thought! The 4-radial system is indeed very sensitive to quite small
irregularities and/or nearby conductors. It's easy to demonstrate pattern
distortions of 2-3 dB and increased ground losses of 1-2 dB and these are
by no means worst cases. More importantly, the modeling shows that as the
number of elevated radials is increased the sensitivity goes down quickly.
Elevated systems with 10-12 radials are not very sensitive to reasonable
asymmetries. It turns out that a number of hams have observed significant
improvements in their elevated systems by going to 10 or more radials. Both
modeling and
experiment seem to agree.
"I doubt that the average 4-radial system is actually performing as
"advertized". No doubt there are exceptions but the advice I presently give
is to use 10 or more radials whenever possible in an elevated system."
(From
http://rudys.typepad.com/files/december-2010-letter-to-qst-technical-correspondence.pdf
)
See http://www.antennasbyn6lf.com/
73, Mike
www.w0btu.com
On Wed, Jan 22, 2014 at 7:18 AM, Richard Fry wrote:
> C. Cunningham wrote:
>
>> If you get up to 4 symmetrical elevated radials there's not much to be
>> gained by adding more. There's been a lot of work done in the broadcast
>> industry using elevated radials to replace deteriorated buried radial
>> fields that shows that pretty clearly. It was published in some IEEE
>> transactions some years ago.
>>
>
> Probably this refers to the paper of Clarence Beverage titled "NEW AM
> BROADCAST ANTENNA DESIGNS HAVING FIELD VALIDATED PERFORMANCE." It is
> available as a PDF download from http://www.commtechrf.com/downloads.asp .
>
> Below is a quote from that paper showing that the __measured__ groundwave
> field at 1 km radiated by a base-insulated, 1/4-wave vertical using four
> elevated radials was within 0.14 decibels of that from a perfect 1/4-wave
> vertical monopole driven against 120 x 1/4-wave buried radials.
>
> The r-f loss resistance of 120 x 1/4-wave buried radials used in a
> monopole antenna system typically is less than 2 ohms in the MW and low-HF
> bands, regardless of the conductivity of the earth in which they are
> buried. The use of four elevated 1/4-wave radials in this system produced
> almost identical performance to using a full set of 120 x 1/4-wave buried
> radials.
>
> "The first permanent use of an elevated radial ground system appears to be
> at WPCI, 1490 kHz in Greenville, South Carolina. This installation,
> designed by William A. Culpepper, involved replacing a standard buried
> system with a four wire elevated system consisting of #10 solid copper
> wire, one quarter wave in length, and supported on treated wooden posts
> which keep the radials 4.9 meters above ground. The antenna radiation
> efficiency, based on field strength readings on the eight cardinal radials,
> was 302 mV/m at 1 kilometer versus the predicted FCC value of 307 mV/m. The
> WPCI installation was unique in that the tower was base insulated but the
> radials came right up to the tower, 4.9 meters above ground and terminated
> in insulators. The tower was fed from the tuning unit, through a piece of
> coax to the 5 meter point on the tower where the center conductor of the
> coax was attached to the tower and the shield to the elevated radials. This
> feed system resulted in a higher feed resistance than would normally be
> expected. Data on this facility was taken from the FCC files."
>
> Guy Olinger wrote:
>
>> Be careful not to extrapolate very specifically qualified broadcast
>> experience into ham radio. Originally FCC spec radials still make the close
>> foreground earth appear VERY conductive, which is NOT an advantage one will
>> have putting up two or four radials over plain old dirt, unless one is
>> talking about midwest USA 30 millisiemen super dirt.
>>
>
> A monopole system using ~ four evenly spaced, horizontal, elevated radials
> or an "FCP" does not need (or use) a highly-conductive region ("FCC spec
> radials") around the base of the vertical radiator, because in such antenna
> systems the r-f currents flowing on its vertical and horizontal wires to
> produce radiation do not travel through the earth.
>
> Note that the system described in the quote from Clarence Beverage's paper
> (above) was installed/tested near Greenville, South Carolina -- a region
> having earth conductivity of not more than 4 mS/m per the FCC M3
> conductivity map, and probably less than that. Yet it produced almost 100%
> radiation efficiency as measured by a broadcast consulting engineer using a
> calibrated field intensity meter.
>
> Such characteristics would apply to the use of elevated radial systems by
> ha
Re: Topband: Buffaloed by a bias tee
> > On 1/22/2014 12:32 PM, Pete Smith N4ZR wrote: > 45 uH is a little marginal, but doesn't explain your problem. 100 uH would > be better. > That's the conclusion I came to after reading this article: http://www.ad5x.com/images/Articles/BiasT3amp.pdf But pay attention to what W8JI just said! 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Buffaloed by a bias tee
This is really not rocket science--it's a simple matter of knowing what you are doing. Please contact me off line. After doing this for 40+ years I have had more than a modicum of sucess Hardy N7RT - Original Message - From: "Pete Smith N4ZR" To: "topband reflector" Sent: Wednesday, January 22, 2014 3:20 PM Subject: Topband: Buffaloed by a bias tee Thanks to everyone for their suggestions - consensus seems to be that the homebrew chokes are not enough reactance at 1.8 MHz, so I'll get some store bought ones at 220 uH or more. I tried battery power for the whole system, but no difference. I'm going to try battery power for the remote box and omitting the bias tee entirely, at least as a test. -- 73, Pete N4ZR Check out the Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com. For spots, please go to your favorite ARC V6 or VE7CC DX cluster node. _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Buffaloed by a bias tee
On 1/22/2014 12:32 PM, Pete Smith N4ZR wrote: . However, as soon as I connect a 12V regulated supply to the bias tee - one of the little radio shack variable wallwarts - the measured R drops to 5 ohms and the X goes up to 19. Possibly the current through the choke is saturating it. If you connect the power supply but disconnect the load drawing current, does the impedance go back to normal? That would clinch it. For the choke, be sure that you are NOT using a toroidal choke. It needs to be a solenoidal type wound on a ferrite rod. Also, do NOT use "shielded" inductors. Ferrite beads will also saturate. Most chokes you come across are the wrong kind. I just bought some chokes today. They only had two bins of suitable ones, out of several thousand bins of inductors. 45 uH is a little marginal, but doesn't explain your problem. 100 uH would be better. Rick N6RK _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Buffaloed by a bias tee
Thanks to everyone for their suggestions - consensus seems to be that the homebrew chokes are not enough reactance at 1.8 MHz, so I'll get some store bought ones at 220 uH or more. I tried battery power for the whole system, but no difference. I'm going to try battery power for the remote box and omitting the bias tee entirely, at least as a test. That doesn't make sense for your complaint. Your choke is a little light, but you said it changes when you plug the supply in. That probably indicates you are dumping ripple or noise into the 259. I'm really surprised the diodes did not pop. 45 uH is about 500 ohms, which is OK for a choke in a 50-75 ohm line. While it would increase SWR a bit, especially with poor bypassing (.01uF) and probably no additional decoupling, it is not a disaster. Read my other post. You are running a risk with the system you have. Never do what you are doing with a bias T, especially when it has a .1uF isolation cap. A .01uF is 8 ohms on 160. That is a pathetic bypass cap, but a reasonable series cap. You might want to step it up to a .05 uF or larger when you get parts. The bypass cap has to be a small fraction of the supply impedance and the choke impedance. I'd use a .33uF there, and some other decoupling. You could probably step the choke up a little, but don't use the 259 that way!!! _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Buffaloed by a bias tee
The quickest way to blow up any test equipment, from a MFJ259 up to an HP network analyzer, is to use a bias T without input safeguards on the test gear. :-) I'm still wrestling with the bias tee for my 1-of-8 remote beverage switch. If I use a cliplead to connect a 270-ohm dummy load, bypassing the relay, and connect an MFJ-259B to the receiver port on the controller, the impedance looks completely reasonable - with a 3:1 binocular transformer, 89 ohms R and X=5, measured by the MFJ. However, as soon as I connect a 12V regulated supply to the bias tee - one of the little radio shack variable wallwarts - the measured R drops to 5 ohms and the X goes up to 19. Is the supply regulated? Is it filtered? Does it have ripple? Do you have a shunt DC bypass on the MFJ meter side? My history major's diagnosis is inadequate isolation between the DC supply and the RFline, but why? The series RF choke in the DC line is 7 turns on a ferrite core, measures 45 uH at 2 MHZ, and the bypass capacitor is a 0.01 uF disk, on thesupply side of the choke. Theseries cap between the Antenna and the RX jacks on the controller is a .1 uF disk (it was what I had). I do not yet have a safety choke between the RX side and ground, but will add one before I deploy it, if I can ever figure out what's going on. The MFJ, like many sensitive RF measurement devices, has diodes on the antenna port. The charging current for the .1uF goes through those diodes, as will any hum or noise, or any transients as you switch. While that stuff does not bother receivers, which have filters and other protection and pretty rugged parts, it can really tear up RF measurement stuff. If it doesn't damage it, it at least throws the readings off if the supply has any noise or hum. You should use the .01 as a coupling cap and the .1 as a bypass if that is all you have. :-) The RF choke may also be changing inductance from DC current, but first you need to make life easier on the 259 by changing the caps around and by bypassing the RX port with a choke. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Buffaloed by a bias tee
Thanks to everyone for their suggestions - consensus seems to be that the homebrew chokes are not enough reactance at 1.8 MHz, so I'll get some store bought ones at 220 uH or more. I tried battery power for the whole system, but no difference. I'm going to try battery power for the remote box and omitting the bias tee entirely, at least as a test. -- 73, Pete N4ZR Check out the Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com. For spots, please go to your favorite ARC V6 or VE7CC DX cluster node. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Anyone purchased the ARRL book on Short Antennas for160???
No doubt! Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Merv Schweigert Sent: Wednesday, January 22, 2014 2:08 PM To: topband@contesting.com Subject: Re: Topband: Anyone purchased the ARRL book on Short Antennas for160??? I live on a former AM BC site, and cannot see any way that you could put up 4 elevated radials and disconnect the ground system that was in place. The ground system here is typical installation and it is bonded with 4 inch copper strap to everything and anything in sight. The tuning networks in the antenna huts were built on aluminum panels that are grounded with 4 inch strap to the radial field, all gear in the transmitter building is grounded with 4 inch to the radial field ground. So its virtually impossible to isolate the gear etc from the ground system, installing 4 elevated radials really showed nothing at all unless they dug up the entire radial field and pulled them out. My door and window frames, steel roof and every water pipe are connected to the radial system. When running 50KW you dont enjoy RF burns. My field here has 120 - 300 ft plus and 120 - 60 foot radials, Im sure 4 elevated radials will do very well. 73 Merv K9FD/KH6 > Dave W0FLS wrote: >> With the radials being 4.9 meters above ground, do the radials >> literally come up to the tower and then travel down the leg to >> connect to the ground side of the insulator or do they travel in >> close to the tower and angle downward? > >> From the text of that paper, it appears that the four horizontal >> radials are > attached to the monopole by insulated supports at 4.9-m elevation > points above the earth, and terminate there. The coax center > conductor is bonded to the tower at that same elevation, and the coax > outer conductor attaches to the common point of the four horizontal > radials at that elevation. > > There is no need as far as system radiation efficiency for any of the > conductors of this antenna system to have a physical connection to the > earth. Probably this system does have conductive paths provided by a > static drain choke to a "lightning ground" buried in the earth (maybe > a few ground rods), and an arc gap across the base insulator -- but > the paper did not include those details. They would have almost no > affect on the radiation efficiency of this system, in any case. > >> Does a FS measurement taken at 1 kilometer fully reflect the true >> angle of radiation and overall performance of the antenna for >> purposes of distant signals? > > The relative field (E/Emax) of the vertical plane field pattern > radiated by __all__ monopoles of ~ 1/4-wave in height and less is very > close to the cosine of the elevation angle. The cosine of zero > degrees is 1 (unity), which means that maximum field is radiated > toward the horizon. The cosine of 30 degrees is 0.87, which means > that the field at that elevation angle is 87% of the field in the > horizontal plane. Etc. > > Referencing back to Clarence Beverage's data, this means that the > field at 1 km radiated by that system toward a 30-deg elevation angle > is 0.87 x 302 mV/m = 263 mV/m (approx). > > The relative values of those fields at an infinite distance over a > real-earth ground plane no longer have the relationships they had at 1 > km, but that does not alter the fact that those relationships existed > at that 1 km distance, in the first place. > > R. Fry > _ > Topband Reflector Archives - http://www.contesting.com/_topband > _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Buffaloed by a bias tee
I'm still wrestling with the bias tee for my 1-of-8 remote beverage switch. If I use a cliplead to connect a 270-ohm dummy load, bypassing the relay, and connect an MFJ-259B to the receiver port on the controller, the impedance looks completely reasonable - with a 3:1 binocular transformer, 89 ohms R and X=5, measured by the MFJ. However, as soon as I connect a 12V regulated supply to the bias tee - one of the little radio shack variable wallwarts - the measured R drops to 5 ohms and the X goes up to 19. My history major's diagnosis is inadequate isolation between the DC supply and the RFline, but why? The series RF choke in the DC line is 7 turns on a ferrite core, measures 45 uH at 2 MHZ, and the bypass capacitor is a 0.01 uF disk, on thesupply side of the choke. Theseries cap between the Antenna and the RX jacks on the controller is a .1 uF disk (it was what I had). I do not yet have a safety choke between the RX side and ground, but will add one before I deploy it, if I can ever figure out what's going on. I'd really appreciate some ideas of what to try. Thanks in advance! -- 73, Pete N4ZR Check out the Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com. For spots, please go to your favorite ARC V6 or VE7CC DX cluster node. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Anyone purchased the ARRL book on Short Antennas for160???
Guy Olinger wrote (responding to a quote from me that he included): "Such characteristics would apply to the use of elevated radial systems by ham radio operators as well as they do for AM broadcast stations." Such a statement requires qualification if the basis of the BC experience includes the previous dense radial field in poor earth **which was not dug up**, and in all likelihood deliberately left in place by the engineer for the now well-known enhancement of sparse elevated radials over poor earths. Just to note that several installations of new AM broadcast antenna systems using elevated radials have been installed at sites where rocky earth prevented the use of ANY buried radials, and none ever were installed. Even though earth conductivity at / near those sites was very poor, the radiation efficiencies of those antenna systems were very close to those of perfect monopoles over a perfect ground plane. R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Anyone purchased the ARRL book on Short Antennas for160???
I live on a former AM BC site, and cannot see any way that you could put up 4 elevated radials and disconnect the ground system that was in place. The ground system here is typical installation and it is bonded with 4 inch copper strap to everything and anything in sight. The tuning networks in the antenna huts were built on aluminum panels that are grounded with 4 inch strap to the radial field, all gear in the transmitter building is grounded with 4 inch to the radial field ground. So its virtually impossible to isolate the gear etc from the ground system, installing 4 elevated radials really showed nothing at all unless they dug up the entire radial field and pulled them out. My door and window frames, steel roof and every water pipe are connected to the radial system. When running 50KW you dont enjoy RF burns. My field here has 120 - 300 ft plus and 120 - 60 foot radials, Im sure 4 elevated radials will do very well. 73 Merv K9FD/KH6 Dave W0FLS wrote: With the radials being 4.9 meters above ground, do the radials literally come up to the tower and then travel down the leg to connect to the ground side of the insulator or do they travel in close to the tower and angle downward? From the text of that paper, it appears that the four horizontal radials are attached to the monopole by insulated supports at 4.9-m elevation points above the earth, and terminate there. The coax center conductor is bonded to the tower at that same elevation, and the coax outer conductor attaches to the common point of the four horizontal radials at that elevation. There is no need as far as system radiation efficiency for any of the conductors of this antenna system to have a physical connection to the earth. Probably this system does have conductive paths provided by a static drain choke to a "lightning ground" buried in the earth (maybe a few ground rods), and an arc gap across the base insulator -- but the paper did not include those details. They would have almost no affect on the radiation efficiency of this system, in any case. Does a FS measurement taken at 1 kilometer fully reflect the true angle of radiation and overall performance of the antenna for purposes of distant signals? The relative field (E/Emax) of the vertical plane field pattern radiated by __all__ monopoles of ~ 1/4-wave in height and less is very close to the cosine of the elevation angle. The cosine of zero degrees is 1 (unity), which means that maximum field is radiated toward the horizon. The cosine of 30 degrees is 0.87, which means that the field at that elevation angle is 87% of the field in the horizontal plane. Etc. Referencing back to Clarence Beverage's data, this means that the field at 1 km radiated by that system toward a 30-deg elevation angle is 0.87 x 302 mV/m = 263 mV/m (approx). The relative values of those fields at an infinite distance over a real-earth ground plane no longer have the relationships they had at 1 km, but that does not alter the fact that those relationships existed at that 1 km distance, in the first place. R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Anyone purchased the ARRL book on Short Antennas for160???
Dave W0FLS wrote: With the radials being 4.9 meters above ground, do the radials literally come up to the tower and then travel down the leg to connect to the ground side of the insulator or do they travel in close to the tower and angle downward? From the text of that paper, it appears that the four horizontal radials are attached to the monopole by insulated supports at 4.9-m elevation points above the earth, and terminate there. The coax center conductor is bonded to the tower at that same elevation, and the coax outer conductor attaches to the common point of the four horizontal radials at that elevation. There is no need as far as system radiation efficiency for any of the conductors of this antenna system to have a physical connection to the earth. Probably this system does have conductive paths provided by a static drain choke to a "lightning ground" buried in the earth (maybe a few ground rods), and an arc gap across the base insulator -- but the paper did not include those details. They would have almost no affect on the radiation efficiency of this system, in any case. Does a FS measurement taken at 1 kilometer fully reflect the true angle of radiation and overall performance of the antenna for purposes of distant signals? The relative field (E/Emax) of the vertical plane field pattern radiated by __all__ monopoles of ~ 1/4-wave in height and less is very close to the cosine of the elevation angle. The cosine of zero degrees is 1 (unity), which means that maximum field is radiated toward the horizon. The cosine of 30 degrees is 0.87, which means that the field at that elevation angle is 87% of the field in the horizontal plane. Etc. Referencing back to Clarence Beverage's data, this means that the field at 1 km radiated by that system toward a 30-deg elevation angle is 0.87 x 302 mV/m = 263 mV/m (approx). The relative values of those fields at an infinite distance over a real-earth ground plane no longer have the relationships they had at 1 km, but that does not alter the fact that those relationships existed at that 1 km distance, in the first place. R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Anyone purchased the ARRL book on Short Antennas for160???
On Wed, Jan 22, 2014 at 8:18 AM, Richard Fry wrote: > "The first permanent use of an elevated radial ground system appears to be > at WPCI, 1490 kHz in Greenville, South Carolina. This installation, > designed by William A. Culpepper, involved replacing a standard buried > system with a four wire elevated system consisting of #10 solid copper > wire, one quarter wave in length, and supported on treated wooden posts > which keep the radials 4.9 meters above ground. Careful here. The buried radials were NOT dug up. "Replacing" means moving the counterpoise connection of the feed system from the buried system to the elevated system. The presence of 0.4 wavelength buried radials turns the ground underneath from the typically inferior Carolina medium into a superior composite medium. Use of four elevated radials **over that composite medium** is far superior to four elevated over 2-3-4 mS/m. You said: "Such characteristics would apply to the use of elevated radial systems by ham radio operators as well as they do for AM broadcast stations." Such a statement requires qualification if the basis of the BC experience includes the previous dense radial field in poor earth **which was not dug up**, and in all likelihood deliberately left in place by the engineer for the now well-known enhancement of sparse elevated radials over poor earths. Why spend a lot of money to dig up the radials? Retire them in place, and harvest the rewards of a far more conductive composite medium underneath the raised radials. I stand by my earlier statements. 73, Guy. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Anyone purchased the ARRL book on Short Antennas for 160???
On Wed, Jan 22, 2014 at 1:00 AM, Richard (Rick) Karlquist < rich...@karlquist.com> wrote: > About 30 years ago, I had a 55 foot tower with a feedpoint at the > top. It fed a horizontal wire 55 feet high and 130 feet long against > the tower. The base of the tower was grounded, but no radials. > It loaded up fine, but was nothing great in terms of getting out. > That jibes with models showing the basic pattern you describe. The feed Z is wildly dependent on the nature of the tower ground plus capacitance to miscellaneous conductors on the tower for its specifics. That the tower was grounded, with or without radials, would completely alter the pattern from that of a center fed L with bottom of a vertical wire insulated. The current distribution changes in two ways: 1) the current on the vertical conductor has its maximum at the ground instead of at the feedpoint. 2) this makes the impedance of the vertical conductor go high at the feed, The load presented to the feedline is severely unbalanced, probably beyond the abilities of any "balun" device. Diminished balun function or lack of balun then turns the feedline into a primary radiator. Even if the tower was insulated, if there was a feedline or rotator cable on the tower, it would alter the pattern. If the bend of an end-insulated insulated wire L is supported by a tower, that will also unfavorably alter the pattern. 73, Guy. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Anyone purchased the ARRL book on Short Antennas for160???
Thanks, Richard!
Yes, that's exactly the paper I was trying to remember for Dale Long
HH2/N3BNA last evening. In my "senior moment" I couldn't remember it late in
the evening. Perhaps it was you that sent me that link recently! Thanks so
much, Richard!! Have a good day !!
73,
Charlie, K4OTV
-Original Message-
From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Richard
Fry
Sent: Wednesday, January 22, 2014 8:19 AM
To: topband@contesting.com
Subject: Topband: Anyone purchased the ARRL book on Short Antennas for160???
C. Cunningham wrote:
>If you get up to 4 symmetrical elevated radials there's not much to be
>gained by adding more. There's been a lot of work done in the broadcast
>industry using elevated radials to replace deteriorated buried radial
>fields that shows that pretty clearly. It was published in some IEEE
>transactions some years ago.
Probably this refers to the paper of Clarence Beverage titled "NEW AM
BROADCAST ANTENNA DESIGNS HAVING FIELD VALIDATED PERFORMANCE." It is
available as a PDF download from http://www.commtechrf.com/downloads.asp .
Below is a quote from that paper showing that the __measured__ groundwave
field at 1 km radiated by a base-insulated, 1/4-wave vertical using four
elevated radials was within 0.14 decibels of that from a perfect 1/4-wave
vertical monopole driven against 120 x 1/4-wave buried radials.
The r-f loss resistance of 120 x 1/4-wave buried radials used in a monopole
antenna system typically is less than 2 ohms in the MW and low-HF bands,
regardless of the conductivity of the earth in which they are buried. The
use of four elevated 1/4-wave radials in this system produced almost
identical performance to using a full set of 120 x 1/4-wave buried radials.
"The first permanent use of an elevated radial ground system appears to be
at WPCI, 1490 kHz in Greenville, South Carolina. This installation, designed
by William A. Culpepper, involved replacing a standard buried system with a
four wire elevated system consisting of #10 solid copper wire, one quarter
wave in length, and supported on treated wooden posts which keep the radials
4.9 meters above ground. The antenna radiation efficiency, based on field
strength readings on the eight cardinal radials, was 302 mV/m at 1 kilometer
versus the predicted FCC value of 307 mV/m. The WPCI installation was unique
in that the tower was base insulated but the radials came right up to the
tower, 4.9 meters above ground and terminated in insulators. The tower was
fed from the tuning unit, through a piece of coax to the 5 meter point on
the tower where the center conductor of the coax was attached to the tower
and the shield to the elevated radials. This feed system resulted in a
higher feed resistance than would normally be expected. Data on this
facility was taken from the FCC files."
Guy Olinger wrote:
>Be careful not to extrapolate very specifically qualified broadcast
>experience into ham radio. Originally FCC spec radials still make the close
>foreground earth appear VERY conductive, which is NOT an advantage one will
>have putting up two or four radials over plain old dirt, unless one is
>talking about midwest USA 30 millisiemen super dirt.
A monopole system using ~ four evenly spaced, horizontal, elevated radials
or an "FCP" does not need (or use) a highly-conductive region ("FCC spec
radials") around the base of the vertical radiator, because in such antenna
systems the r-f currents flowing on its vertical and horizontal wires to
produce radiation do not travel through the earth.
Note that the system described in the quote from Clarence Beverage's paper
(above) was installed/tested near Greenville, South Carolina -- a region
having earth conductivity of not more than 4 mS/m per the FCC M3
conductivity map, and probably less than that. Yet it produced almost 100%
radiation efficiency as measured by a broadcast consulting engineer using a
calibrated field intensity meter.
Such characteristics would apply to the use of elevated radial systems by
ham radio operators as well as they do for AM broadcast stations.
R. Fry
Broadcast Systems Engr (retired)
_
Topband Reflector Archives - http://www.contesting.com/_topband
_
Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Anyone purchased the ARRL book on Short Antennas for160???
C. Cunningham wrote:
If you get up to 4 symmetrical elevated radials there's not much to be
gained by adding more. There's been a lot of work done in the broadcast
industry using elevated radials to replace deteriorated buried radial
fields that shows that pretty clearly. It was published in some IEEE
transactions some years ago.
Probably this refers to the paper of Clarence Beverage titled "NEW AM
BROADCAST ANTENNA DESIGNS HAVING FIELD VALIDATED PERFORMANCE." It is
available as a PDF download from http://www.commtechrf.com/downloads.asp .
Below is a quote from that paper showing that the __measured__ groundwave
field at 1 km radiated by a base-insulated, 1/4-wave vertical using four
elevated radials was within 0.14 decibels of that from a perfect 1/4-wave
vertical monopole driven against 120 x 1/4-wave buried radials.
The r-f loss resistance of 120 x 1/4-wave buried radials used in a monopole
antenna system typically is less than 2 ohms in the MW and low-HF bands,
regardless of the conductivity of the earth in which they are buried. The
use of four elevated 1/4-wave radials in this system produced almost
identical performance to using a full set of 120 x 1/4-wave buried radials.
"The first permanent use of an elevated radial ground system appears to be
at WPCI, 1490 kHz in Greenville, South Carolina. This installation, designed
by William A. Culpepper, involved replacing a standard buried system with a
four wire elevated system consisting of #10 solid copper wire, one quarter
wave in length, and supported on treated wooden posts which keep the radials
4.9 meters above ground. The antenna radiation efficiency, based on field
strength readings on the eight cardinal radials, was 302 mV/m at 1 kilometer
versus the predicted FCC value of 307 mV/m. The WPCI installation was unique
in that the tower was base insulated but the radials came right up to the
tower, 4.9 meters above ground and terminated in insulators. The tower was
fed from the tuning unit, through a piece of coax to the 5 meter point on
the tower where the center conductor of the coax was attached to the tower
and the shield to the elevated radials. This feed system resulted in a
higher feed resistance than would normally be expected. Data on this
facility was taken from the FCC files."
Guy Olinger wrote:
Be careful not to extrapolate very specifically qualified broadcast
experience into ham radio. Originally FCC spec radials still make the close
foreground earth appear VERY conductive, which is NOT an advantage one will
have putting up two or four radials over plain old dirt, unless one is
talking about midwest USA 30 millisiemen super dirt.
A monopole system using ~ four evenly spaced, horizontal, elevated radials
or an "FCP" does not need (or use) a highly-conductive region ("FCC spec
radials") around the base of the vertical radiator, because in such antenna
systems the r-f currents flowing on its vertical and horizontal wires to
produce radiation do not travel through the earth.
Note that the system described in the quote from Clarence Beverage's paper
(above) was installed/tested near Greenville, South Carolina -- a region
having earth conductivity of not more than 4 mS/m per the FCC M3
conductivity map, and probably less than that. Yet it produced almost 100%
radiation efficiency as measured by a broadcast consulting engineer using a
calibrated field intensity meter.
Such characteristics would apply to the use of elevated radial systems by
ham radio operators as well as they do for AM broadcast stations.
R. Fry
Broadcast Systems Engr (retired)
_
Topband Reflector Archives - http://www.contesting.com/_topband
