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Shunt feed tower for Aircraft NDB beacon Help
I have installed a FAA approved NDB beacon here at our private
airport located in Manchester,TN . The Beacon is transmitting on 529 KHZ Carrier power is 50 watts the facility Id is : LYQ I have shunt feed a 120 foot high Rhon 25G tower. The tap wire (3/8 dia aluminum 'power line' cable) is at the 90 foot level runs down the face of the tower with 24 inch spacing to the matching network. I am using the 'Gamma' match network : the SWR is down to 1.2 or so. The top of the tower has 4 ten foot radials The base of the tower has 8 200 foot 3/ 8 inch aluminum cable radials we plan to add more. The tower has a 3/8 'power line' type cable from the top to the base to ensure bonding of each section. When I fly the Company's Jetstar from 1000 to 41,000 feet, I get solid points on the RMI indicator: when I pass right over the beacon tower the RMI needle swings to the tail indicating positive station passage. The problem is the range of the LYQ beacon it seems to work 10 miles or less??? The airplane has dual ADF systems that work perfect. As an aside, 10 miles away, is another ADF beacon on 332 KHZ 25 watts! using the traditional three strand 'flat top' suspended between two telephone poles. The vertical radiator for this beacon is less than 60 feet high : I can track the beacon out to 70 miles or so! Is a shunt feed tower lossy??? poor radiator??? comments??? I am a Ham op WA4SZE : by the way, we will QSL the beacon when we get it commissioned. Thanks!! |
Shunt feed tower for Aircraft NDB beacon Help
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Shunt feed tower for Aircraft NDB beacon Help
On Jul 4, 8:45 pm, wrote:
wrote: I have installed a FAA approved NDBbeaconhere at our private airport located in Manchester,TN . TheBeaconis transmitting on 529 KHZ Carrier power is 50 watts the facility Id is : LYQ I have shunt feed a 120 foot high Rhon 25G tower. The tap wire (3/8 dia aluminum 'power line' cable) is at the 90 foot level runs down the face of the tower with 24 inch spacing to the matching network. I am using the 'Gamma' match network : the SWR is down to 1.2 or so. The top of the tower has 4 ten foot radials The base of the tower has 8 200 foot 3/ 8 inch aluminum cable radials we plan to add more. The tower has a 3/8 'power line' type cable from the top to the base to ensure bonding of each section. When I fly the Company's Jetstar from 1000 to 41,000 feet, I get solid points on the RMI indicator: when I pass right over thebeacontower the RMI needle swings to the tail indicating positive station passage. The problem is the range of the LYQ beaconit seems to work 10 miles or less??? The airplane has dual ADF systems that work perfect. As an aside, 10 miles away, is another ADFbeaconon 332 KHZ 25 watts! using the traditional three strand 'flat top' suspended between two telephone poles. The vertical radiator for thisbeaconis less than 60 feet high : I can track thebeaconout to 70 miles or so! Is a shunt feed tower lossy??? poor radiator??? comments??? I am a Ham op WA4SZE : by the way, we will QSL thebeaconwhen we get it commissioned. Thanks!! More radials certainly won't hurt, especially since at this freq 200 feet is short. What's the ground around it like? -- Jim Pennino Remove .spam.sux to reply. open land flat, somewhat damp covered with grass the radials lay on top of the ground The beacon is on air right now going to leave it on tonight for reception reports do you think a shunt feed tower is not good?? I could jack up the tower and insulate from ground it then series feed do you think that would be better??? lots of work but might be worth the effort! |
Shunt feed tower for Aircraft NDB beacon Help
On Jul 4, 8:59 pm, wrote:
On Jul 4, 8:45 pm, wrote: wrote: I have installed a FAA approved NDBbeaconhere at our private airport located in Manchester,TN . TheBeaconis transmitting on 529 KHZ Carrier power is 50 watts the facility Id is : LYQ I have shunt feed a 120 foot high Rhon 25G tower. The tap wire (3/8 dia aluminum 'power line' cable) is at the 90 foot level runs down the face of the tower with 24 inch spacing to the matching network. I am using the 'Gamma' match network : the SWR is down to 1.2 or so. The top of the tower has 4 ten foot radials The base of the tower has 8 200 foot 3/ 8 inch aluminum cable radials we plan to add more. The tower has a 3/8 'power line' type cable from the top to the base to ensure bonding of each section. When I fly the Company's Jetstar from 1000 to 41,000 feet, I get solid points on the RMI indicator: when I pass right over thebeacontower the RMI needle swings to the tail indicating positive station passage. The problem is the range of the LYQ beaconit seems to work 10 miles or less??? The airplane has dual ADF systems that work perfect. As an aside, 10 miles away, is another ADFbeaconon 332 KHZ 25 watts! using the traditional three strand 'flat top' suspended between two telephone poles. The vertical radiator for thisbeaconis less than 60 feet high : I can track thebeaconout to 70 miles or so! Is a shunt feed tower lossy??? poor radiator??? comments??? I am a Ham op WA4SZE : by the way, we will QSL thebeaconwhen we get it commissioned. Thanks!! More radials certainly won't hurt, especially since at this freq 200 feet is short. What's the ground around it like? -- Jim Pennino Remove .spam.sux to reply. open land flat, somewhat damp covered with grass the radials lay on top of the ground Thebeaconis on air right now going to leave it on tonight for reception reports do you think a shunt feed tower is not good?? I could jack up the tower and insulate from ground it then series feed do you think that would be better??? lots of work but might be worth the effort! As an aside, I wonder if this is proof that a shunt feed tower is no good??? I can SEE the tower (runway) over the nose of the airplane at 15 miles out! yet the RMI indicator is wandering! The beacon ID is in the noise! I get a good match but the band width is NARROW! this indicates to me that the Q is high just as it should be? the RF amp meter is showing current thru the vertical run up the tower face if your careless around the 2300 pf vac cap you get a nice RF burn. By the way, I made a mistake, I am using an omega match the values of the caps: C-1 500 pf ( from 50 ohm coax center conductor to 2300 PF Vac Var cap ) C-2 2300 pf vertical wire run thru C-2 2300 pf cap then ground thanks!!!! |
Shunt feed tower for Aircraft NDB beacon Help
On Jul 4, 5:56 pm, wrote:
Is a shunt feed tower lossy??? poor radiator??? comments??? I am a Ham op WA4SZE : by the way, we will QSL the beacon when we get it commissioned. Thanks!! The tower would not be the most efficient thing, being a 1/4 wave at that freq is about 442 ft. The four 10 ft radials, which I assume are a top hat, will be fairly useless at that freq. Too short to really do any good. How long is the top horizontal wire is the "T" they are using at the other airport? I bet it's pretty long across. What I would do if possible, is lengthen the top hat wires to be as long as you can. There does not really have to be four.. Two is enough, as you can see from the other station. I don't know what the current distribution is with that setup, but it would seem that max current is at your matching device. The longer you can make that tower look electrically, the better. I'm not sure what the norm is for the usual NDB antenna systems.. I would basically use the same measures I would running a short mobile whip.. Longer top hat wires would greatly help current distribution if they are long enough. To resonate the tower at that freq with no coil loading, you would need wires about 315 ft... :/ But you could use shorter, and compromise a bit. The ground is pretty important, but I think the current distribution across the tower equally so. I think all your current is huddled up around your matching device, and ground area.. Not really where you want it. MK |
Shunt feed tower for Aircraft NDB beacon Help
As an aside, I wonder if this is proof that a shunt feed tower is no
good??? I can SEE the tower (runway) over the nose of the airplane at 15 miles out! yet the RMI indicator is wandering! The beacon ID is in the noise! I get a good match but the band width is NARROW! this indicates to me that the Q is high just as it should be? the RF amp meter is showing current thru the vertical run up the tower face if your careless around the 2300 pf vac cap you get a nice RF burn. By the way, I made a mistake, I am using an omega match the values of the caps: C-1 500 pf ( from 50 ohm coax center conductor to 2300 PF Vac Var cap ) C-2 2300 pf vertical wire run thru C-2 2300 pf cap then ground thanks!!!! I have just run a preliminary NEC model. I am showing a gain of -9 dBi at an elevation angle of 10 deg. at 530 kHz. Directly overhead the gain is about -26 dBi. A typical matching network should have a loss of about 4 dB, for a TRP of around 1 W or so. The input impedance will be about 0.2+j176. You should have about 10 A RMS in the base of the gamma match vertical wire and, 1.7 kV RMS , assuming a 4 dB loss in the matching network. My model needs some refinement, but should give a ball park idea of what to expect. I did not understand exactly how you are using two capacitors to match the antenna. Regards, Frank (VE6CB) |
Shunt feed tower for Aircraft NDB beacon Help
WA4SZEwrote
I have installed a FAA approved NDB beacon here at our private airport located in Manchester,TN .... Is a shunt feed tower lossy??? poor radiator??? comments??? _____________ Other things equal, a shunt fed MW vertical monopole can produce essentially the same radiation pattern shape and gain as when series fed. The link below leads to an analysis of what might be expected for either case for the system you described. Assumptions made in the analysis: 1) The four top-hat radials added 10 feet to the electrical height of the tower 2) The ground radials described have a net r-f resistance of 25 ohms at the operating frequency. The analysis shows that for 50 watts of available power, this system could generate an inverse-distance groundwave field strength of better than 700 µV/m at a radius of about 15 miles. Of course, earth losses along the groundwave path will reduce that value, but even with 6 dB of additional loss the field should still be better than 350 µV/m, and higher than that for higher elevations above the earth at that distance (as would be true for airborne receive systems). The performance you are describing indicates that the antenna is not radiating much of the available power, which may point to problems with the feed system. http://i62.photobucket.com/albums/h8...alRadiator.gif RF |
URL Correction
On Jul 5, 7:57 am, "Richard Fry" wrote:
Apologies, the link in my first post was an analysis for 25 watts instead of 50 watts. Here is the correct one: http://i62.photobucket.com/albums/h8...rticalRadiator... RF You need a flat top to pull the current node higher from the ground... Our NDB at KHYX is less than 100 feet tall, has a series fed vertical wire with a long, multiwire flat top and is easily copied from 80 miles away at night and 40 miles in the day... denny |
Shunt feed tower for Aircraft NDB beacon Help
"Frank" wrote
At 1000 m, between a height of zero meters, and 1000 m the field strength is in the range of 5 mV/m peak. (i.e. including ground wave). Not sure why the calculation does not agree with Richard Fry's analysis, but may be due to the fact that NEC computes ground losses for the surface wave. _____________ Below is a development of my earlier analysis, now based on the worst-case ground conductivivity for a site in Tennessee, per the FCC's "M3" map of same for the contintental US. The field strength values below are referenced to the MW propagation charts of the FCC for the power, radiator efficiency and presumed groundwave path conductivity in this situation. These values are traceable to measured data. This approach shows an inverse distance field strength at 1 mile to be 11.2 mV/m. At 1 km the inverse distance field would be about 1.61 X that much, or about 18 mV/m (which agrees with the analysis I posted earlier in this thread). Groundwave path loss at 1 km for 529 kHz is very small regardless of earth conductivity, so the measured field at that distance should be almost the same as the calculated inverse distance field (18.5 mV/m). Using "real" earth conductivity shows (below) less field at about 15 miles than in my first analysis. But there I just picked an arbitrary value of 6 dB for ground loss at that distance. As a side note, the FCC permits shunt-fed monopoles for use by some non-directional AM broadcast stations, and they must (and do) produce the same minimum allowable field strength for 1 kW at 1 km as if they were series-fed. + + + + FCC Approach Frequency = 529 kHz Power = 0.05 kW Inverse Distance Field at 1 mile = 11.2 mV/m Groundwave Path Conductivity = 2.0 mS/m Radius to a Given Field Strength: Field Strength Radius 0.500 mV/m 10.3 miles 0.250 mV/m 15.5 miles RF |
URL Correction
"Richard Fry" wrote in message ... Apologies, the link in my first post was an analysis for 25 watts instead of 50 watts. Here is the correct one: http://i62.photobucket.com/albums/h8...Radiator-1.gif RF The antenna fed with a gamma match appears to be just a very narrow loop, with very high copper losses. Eliminating the gamma match, and base feeding the tower I noticed in my previous analysis that I had read the wrong E-field column. With 50 W input the peak E-field at 1000 m is 62.9 mV/m (44.5 mV/m RMS). At 24 km the E-field is 2.2 mV/m (1.5 mV/m RMS), at ground level, and 2.0 mV/m (1.4 mV/m RMS) at 10,000 m elevation. These results appear to be very close to Richard Fry's analysis, though not sure why there is a 6 dB difference. Frank CM 523 kHz NDB Antenna CE GW 1 1 0 0 0 0 2 -0.25 0.03125 GW 2 99 0 2 -0.25 0 200 -0.25 0.03125 GR 1 8 GW 12 60 0 0 0 0 0 120 0.03125 ce GW 13 5 0 0 90 0 2 90 0.03125 ce GW 14 45 0 2 90 0 2 2 0.03125 ce GW 15 5 0 2 2 0 0 2 0.03125 GS 0 0 0.304800 GE -1 -1 0 GN 2 0 0 0 4.0000 0.0100 EX 0 12 1 0 5173.59784 0.00000 FR 0 1 0 0 0.53 0.01 LD 5 0 0 0 5.8001E7 RP 1 1001 1 0000 0 90 1 1 1000 NE 0 1 1 11 0 1000 0.0 1.0 1.0 10 NE 0 1 1 11 0 24000 0.0 1.0 1.0 1000 EN |
URL Correction
"Denny" wrote
You need a flat top to pull the current node higher from the ground... Our NDB at KHYX is less than 100 feet tall, has a series fed vertical wire with a long, multiwire flat top and is easily copied from 80 miles away at night and 40 miles in the day... ______________ Your NDB might have been in a location with much better ground conductivity than this one. I was attempting to analyze the hardware described in the OP, and used rather pessimistic assumptions in doing so. But even then, the FCC MW propagation curves for this power, radiator efficiency, frequency and assumed earth conductivity (2 mS/m) show a groundwave field of about 35 µV/m at 40 miles. I don't know if that would be called "easy copy" in the daytime using the receivers intended for this application. Does anyone know? I assumed an r-f ground loss of 25 ohms. That loss for an AM broadcast station is around 2 ohms. Reducing the loss in the r-f ground would help here, at the penalty of reducing the r-f bandwidth. RF |
Shunt feed tower for Aircraft NDB beacon Help
"Frank" wrote
At 1000 m, between a height of zero meters, and 1000 m the field strength is in the range of 5 mV/m peak. (i.e. including ground wave). Not sure why the calculation does not agree with Richard Fry's analysis, but may be due to the fact that NEC computes ground losses for the surface wave. ____________ At the bottom of this post is a link to another analysis, this time using NEC-2 with the input assumptions of my first "spreadsheet" approach. It shows a field of 84.12 mV/m at 1 km for 1 kW of radiated power. Adjusting that 1 km field that for the power reduction to 50 watts brings it to 18.8 mV/m -- which is in close agreement with my spreadsheet value of 18.5 mV/m. NEC-2 cannot deal with buried radials, but the 1 km NEC-2 field as calculated here for a perfect ground can be plugged into the applicable FCC propagation curves to show the groundwave field for a given distance, frequency and conductivity, as I did in earlier post. Repeating those: Field Strength Radius 0.500 mV/m 10.3 miles 0.250 mV/m 15.5 miles In another post, Frank, you wrote "With 50 W input the peak E-field at 1000 m is 62.9 mV/m (44.5 mV/m RMS). At 24 km the E-field is 2.2 mV/m (1.5 mV/m RMS), at ground level, and 2.0 mV/m (1.4 mV/m RMS) at 10,000 m elevation. These results appear to be very close to Richard Fry's analysis, though not sure why there is a 6 dB difference." I think you were looking at my first post, where I guesstimated 6 dB ground loss for a 24 km path, and showed 0.773 mV/m there. The (much) more accurate FCC approach shows only 0.25 mV/m for a 24 km path with 2 mS/m conductivity, and the difference between that and your 1.5 mV/m is 15.6 dB -- rather significant. I don't know for sure what explains all this, but it is interesting to consider. http://i62.photobucket.com/albums/h8...adiatorNEC.gif RF |
Shunt feed tower for Aircraft NDB beacon Help
Correcting myself in this clip::
I think you were looking at my first post, where I guesstimated 6 dB ground loss for a 24 km path, and showed 0.773 mV/m there. The number from my post for those conditions was around 0.35 mV/m. The 0.773 mV/m value was the inverse distance field at 24 km. Sorry. RF |
Shunt feed tower for Aircraft NDB beacon Help
This is a 125-foot tower, fed at 90 feet, by a cable 2 feet from a face
of the tower. This makes a loop about 184 feet in perimeter. This perimeter is less than 0.1 wavelength. Thus, we have almost equal currents flowing in opposite directions at any two points in the loop and they are diametrically opposite each other. If there were no separation between the cable and the tower, there would be no radiation resistance, As it is there is very little radiation resistance. Radiation resistance can be increased by lengthening the loop or widening the loop. As long as the loop`s perimeter is less than 1/2-wavelength, it will have an inductive reactance which may be tuned out by the vacuum variable capacitor. Were the tower a 1/4-wavelength, it would be self-resonant and require no tuning. It is much shorter than that. To boost radiation, I would suggest extending the feed-cable to the top of the tower to get current up there and to raise the feed-loop radiation resistance. 1/4-wave folded unipoles radiate almost the same as open-circuit unipoles. Shorter antennas will suffer by comparison. I`ve installed aircraft beacons at my company`s airstrips around the world but they were series-fed and used the 3-strand top loading referred to in this thread. They all worked fine on original fire-up. Best regards, Richard Harrison, KB5WZI |
Shunt feed tower for Aircraft NDB beacon Help
"Richard Fry" wrote in message ... "Frank" wrote At 1000 m, between a height of zero meters, and 1000 m the field strength is in the range of 5 mV/m peak. (i.e. including ground wave). Not sure why the calculation does not agree with Richard Fry's analysis, but may be due to the fact that NEC computes ground losses for the surface wave. ____________ At the bottom of this post is a link to another analysis, this time using NEC-2 with the input assumptions of my first "spreadsheet" approach. It shows a field of 84.12 mV/m at 1 km for 1 kW of radiated power. Adjusting that 1 km field that for the power reduction to 50 watts brings it to 18.8 mV/m -- which is in close agreement with my spreadsheet value of 18.5 mV/m. NEC-2 cannot deal with buried radials, but the 1 km NEC-2 field as calculated here for a perfect ground can be plugged into the applicable FCC propagation curves to show the groundwave field for a given distance, frequency and conductivity, as I did in earlier post. Repeating those: Field Strength Radius 0.500 mV/m 10.3 miles 0.250 mV/m 15.5 miles In another post, Frank, you wrote "With 50 W input the peak E-field at 1000 m is 62.9 mV/m (44.5 mV/m RMS). At 24 km the E-field is 2.2 mV/m (1.5 mV/m RMS), at ground level, and 2.0 mV/m (1.4 mV/m RMS) at 10,000 m elevation. These results appear to be very close to Richard Fry's analysis, though not sure why there is a 6 dB difference." I think you were looking at my first post, where I guesstimated 6 dB ground loss for a 24 km path, and showed 0.773 mV/m there. The (much) more accurate FCC approach shows only 0.25 mV/m for a 24 km path with 2 mS/m conductivity, and the difference between that and your 1.5 mV/m is 15.6 dB -- rather significant. I don't know for sure what explains all this, but it is interesting to consider. http://i62.photobucket.com/albums/h8...adiatorNEC.gif RF Calculating space wave plus surface wave at 24 km, at ground level, NEC shows 0.79 mV/m peak (0.55 mV/m RMS). I used a ground conductivity of 2 mS/m and relative permittivity 4. The vertical tower was modelled with 3/8" dia. aluminum, neglecting the actual lattice structure. I have not added the capacity hat. I used eight 200 ft radials 3" below ground, also 3/8" aluminum (6063-T832 alloy). The input impedance is 6 - j 1008, and I am driving it with 4.1 kV peak (50 W). Don't understand why I am getting different results than the FCC method at 0.25 mV/m. This analysis does assume a lossless matching network, where practical systems would show 3 or 4 dB of additional loss. Frank |
Shunt feed tower for Aircraft NDB beacon Help
WA4SZE wrote:
"I have shunt fed a 120 foot high Rohn 25G tower." The Rohn has a 1-ft face, so the h/d is about 120. That`s OK. What`s wacko is a 23-degree tower over (8) 200-ft radials at 529 KHz. Ground connection resistance is high and eating up all the signal. Shunt - feeding is OK. Bill Orr and Stu Cowan give feed capacitors for scalimg in "All About Vertical Antennas". Brown, Lewis and Epstein would be disappointed with your radials. Shoot for the broadcast practice of (120) evenly distributed around from the tower base. A short tower radiates almost as well as a 1/4-wave. but it has a very low radiation resistance so can`t tolerate any loss resistance. Kraus gives advice for Electrically Small Antennas in the 3rd edition of "Antennas". Page 710 says: "To increase the radiation efficiency requires an increase in the radiation resistance Rr or a decrease in the loss resistance Rl or both. The SWR of a dummy load usually looks fine, but radiation is just incidental. Best regards, Richard Harrison, KB5WZI |
Shunt feed tower for Aircraft NDB beacon Help
"Richard Harrison" wrote
Brown, Lewis and Epstein would be disappointed with your radials. Shoot for the broadcast practice of (120) evenly distributed around from the tower base. _________ BL&E's 1937 measurements show (Fig 30) that a vertical monopole of 25 to 90 electrical degrees used with 113 buried radials each of 0.412 wavelength produced a measured groundwave field within a few percent of the theoretical maximum for such radiators over a perfect ground (notwithstanding that the conductivity at their test site was around 4 mS/m). In Fig 32 of that paper it can be seen that if the 113 radials are only 0.274-wavelengths long, then at the 25-degree electrical height of this Rohn tower, the measured field was about 79% of theoretical field over a perfect ground. .. So it's not just the number of radials that is important, but also their length. The referenced figures are linked below, under the "fair use" provisions of copyright law. http://s62.photobucket.com/albums/h8...BLERadials.gif RF |
BL& Link Correction
Here is the correct link to BL&E Figs 30 and 32.
http://i62.photobucket.com/albums/h8...ndERadials.gif |
Shunt feed tower for Aircraft NDB beacon Help
On Sat, 7 Jul 2007 15:53:36 -0500, "Richard Fry" wrote:
The referenced figures are linked below, under the "fair use" provisions of copyright law. http://s62.photobucket.com/albums/h8...BLERadials.gif RF Richard, I just now tried to access your link above, but it says the file is no longer available. Do you have any other source of this data? I worked with BL&E, so I'm kinda partial to having all the data from their 1936 experiment that I can find. I have their 1937 IRE paper. Walt, W2DU |
BL& Link Correction
On Sat, 7 Jul 2007 16:02:11 -0500, "Richard Fry" wrote:
Here is the correct link to BL&E Figs 30 and 32. http://i62.photobucket.com/albums/h8...ndERadials.gif Got it, Richard, but I see the two figs are simply from their 1937 IRE paper. Thanks anyway. Walt |
Shunt feed tower for Aircraft NDB beacon Help
"Walter Maxwell"
Richard, I just now tried to access your link above, but it says the file is no longer available. Do you have any other source of this data? I worked with BL&E, so I'm kinda partial to having all the data from their 1936 experiment that I can find. I have their 1937 IRE paper. _________ Walt - I showed the working link in another post I made in followup, which should work for you. The link (again) is http://i62.photobucket.com/albums/h8...ndERadials.gif But if you have their 1937 paper, you already have the figures I referred to. RF |
Shunt feed tower for Aircraft NDB beacon Help
Richard Fry wrote:
"So it`s not just the number of radials that is important, but also their length." True. I don`t have B.L. and E`s work to refer to but do recall an observation that to get the best ground connection for the least copper it might be wise to cut the radials in half so that their number might be doubled. The FCC standard is 120 radials, each 1/4-wavelength long, which may seem extreme but it produces a near perfect ground connection. Fortunately, the length of radials does not need to be increased in direct proportion to wavelength below the broadcast band as skin effect varies with the square root of the frequency so as we go lower in frequency we need to increase length of the radials by the square root of the wavelength to keep the resistance of our contact constant. Best Regards, Richard Harrison, KB5WZI |
Shunt feed tower for Aircraft NDB beacon Help
|
Shunt feed tower for Aircraft NDB beacon Help
"Richard Harrison" wrote
Fortunately, the length of radials does not need to be increased in direct proportion to wavelength below the broadcast band as skin effect varies with the square root of the frequency so as we go lower in frequency we need to increase length of the radials by the square root of the wavelength to keep the resistance of our contact constant. ____________ Here is a quote about this from RADIO ANTENNA ENGINEERING by Edmund Laport: "The distance from the antenna at which returning ground currents are of such a low value as to be negligible is of the order of 0.5 wavelength." At least across the AM broadcast band 530-1700 kHz, Laport, Terman, Kraus, and Balanis show _no_ dependence of the lengths of buried radials with frequency -- except, of course, that radials used with lower frequency systems need to be physically longer to reach the desired radius from the monopole, in free-space wavelengths. The FCC uses a computer program (linked below) to calculate the groundwave inverse distance field at 1 km and 1 mile from a MW monopole, based on the radiator height and the number/length of buried radials. On-line users of this program can enter their own system parameters to see their effects on the radiated field. The program does restrict entries to the minimum values acceptable to the FCC for commercial AM broadcast stations. == NOTE: The FCC program applet has no entry block for frequency. Here is the link. The applet starts at the bottom of that web page. http://www.fcc.gov/mb/audio/bickel/figure8.html RF |
Clarification
== NOTE: The FCC program applet has no entry block for frequency.
_________ Yes it does (sorry), but ... == NOTE: The FCC program results are essentially the same regardless of frequency for all systems of a given radiator height and radial length (in wavelengths), when using the same number of radials. RF |
Shunt feed tower for Aircraft NDB beacon Help
wrote in message oups.com... I have installed a FAA approved NDB beacon here at our private airport located in Manchester,TN . The Beacon is transmitting on 529 KHZ Carrier power is 50 watts the facility Id is : LYQ I have shunt feed a 120 foot high Rhon 25G tower. The tap wire (3/8 dia aluminum 'power line' cable) is at the 90 foot level runs down the face of the tower with 24 inch spacing to the matching network. I am using the 'Gamma' match network : the SWR is down to 1.2 or so. The top of the tower has 4 ten foot radials The base of the tower has 8 200 foot 3/ 8 inch aluminum cable radials we plan to add more. The tower has a 3/8 'power line' type cable from the top to the base to ensure bonding of each section. When I fly the Company's Jetstar from 1000 to 41,000 feet, I get solid points on the RMI indicator: when I pass right over the beacon tower the RMI needle swings to the tail indicating positive station passage. The problem is the range of the LYQ beacon it seems to work 10 miles or less??? The airplane has dual ADF systems that work perfect. As an aside, 10 miles away, is another ADF beacon on 332 KHZ 25 watts! using the traditional three strand 'flat top' suspended between two telephone poles. The vertical radiator for this beacon is less than 60 feet high : I can track the beacon out to 70 miles or so! Is a shunt feed tower lossy??? poor radiator??? comments??? I am a Ham op WA4SZE : by the way, we will QSL the beacon when we get it commissioned. Thanks!! The one that works is probably an FAA facility and has a better ground system. The one I helped install had 96 buried radials. I was surprised that they werent that long. Same length as the flat top , Guessing 30 ft. I do know the antenna was 10 meters tall tophat and radials were probably close to being the same. Jimmie |
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