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Part 15 AM Coverage

R

rfry

Several posts here have asked what coverage can be expected for a legal
Part 15 AM operation. The text below is based on my response to a
similar question posted on a broadcast-oriented list.

RF [email protected]

+ + +

>Next time a non-D AM tower falls over, let's clean up the mess,
>then install a Rangemaster or other high quality Part 15 transmitter
>on the ground at the center of the radial system and see how far
>it gets out, measure the field strength, etc. The official 3 meter
>antenna to be used.
_____________

A 3-meter vertical radiator is 3.6 electrical degrees long at 1 MHz. Using
Figure 32 in George Brown's paper I referred to in an earlier post, the FCC
efficiency of such a vertical with a ground system consisting of 113 radials
of 0.27 wavelengths each is about 40 mV/m at 1 mile for 1 kW of radiated
power.

Using that efficiency with the FCC's propagation curves for 1 MHz, and
assuming that the Part 15 AM tx could supply 80 mW to the radiator,*
here are the parameters for a ground conductivity of 8 mS/m:

2.00 mV/m @ 0.1751 miles (good signal)
0.500 mV/m @ 0.6695 miles (usable signal)
0.100 mV/m @ 2.9125 miles (noisy signal)

The quality of these signals is given for clear, open terrain and a
good receiver (car, etc). Coverage will be less in urban areas with
buildings, overhead wires, etc.

NEC-2 calculates a base impedance of 0.04 -j6500 ohms for this set of
conditions (4mm constant OD radiator, 3 meters long). No practical
transmitter could deliver its rated power into such an impedance,
but we have ignored that for these calculations. (The reactance term
can be cancelled by using a loading coil, but the required coil would
absorb a large amount of the available power due to its I^2R loss).

Considering that Part 15 AM stations using intentional radiators neither
have the ground system described above, nor can cause the RF current
equivalent to 80 mW to flow in the radiating portion of a 3-meter antenna,
it is clear that any Part 15 "coverage" claimed that approaches or exceeds
what is shown in the calculations above must be related to the use of an
illegal antenna system and/or illegally high tx power, or possibly
just a good amount of user exaggeration.

* AM Part 15 limits the tx to 100 mW of input power.
Output power will be less -- 80 mW was assumed.
 
> Several posts here have asked what coverage can be expected
> for a legal
> Part 15 AM operation. The text below is based on my response
> to a
> similar question posted on a broadcast-oriented list.
>
> RF [email protected]
>
> + + +
>
> >Next time a non-D AM tower falls over, let's clean up the
> mess,
> >then install a Rangemaster or other high quality Part 15
> transmitter
> >on the ground at the center of the radial system and see
> how far
> >it gets out, measure the field strength, etc. The official
> 3 meter
> >antenna to be used.
> _____________
>
> A 3-meter vertical radiator is 3.6 electrical degrees long
> at 1 MHz. Using
> Figure 32 in George Brown's paper I referred to in an
> earlier post, the FCC
> efficiency of such a vertical with a ground system
> consisting of 113 radials
> of 0.27 wavelengths each is about 40 mV/m at 1 mile for 1 kW
> of radiated
> power.
>
> Using that efficiency with the FCC's propagation curves for
> 1 MHz, and
> assuming that the Part 15 AM tx could supply 80 mW to the
> radiator,*
> here are the parameters for a ground conductivity of 8 mS/m:
>
>
> 2.00 mV/m @ 0.1751 miles (good signal)
> 0.500 mV/m @ 0.6695 miles (usable signal)
> 0.100 mV/m @ 2.9125 miles (noisy signal)
>
> The quality of these signals is given for clear, open
> terrain and a
> good receiver (car, etc). Coverage will be less in urban
> areas with
> buildings, overhead wires, etc.
>
> NEC-2 calculates a base impedance of 0.04 -j6500 ohms for
> this set of
> conditions (4mm constant OD radiator, 3 meters long). No
> practical
> transmitter could deliver its rated power into such an
> impedance,
> but we have ignored that for these calculations. (The
> reactance term
> can be cancelled by using a loading coil, but the required
> coil would
> absorb a large amount of the available power due to its I^2R
> loss).
>
> Considering that Part 15 AM stations using intentional
> radiators neither
> have the ground system described above, nor can cause the RF
> current
> equivalent to 80 mW to flow in the radiating portion of a
> 3-meter antenna,
> it is clear that any Part 15 "coverage" claimed that
> approaches or exceeds
> what is shown in the calculations above must be related to
> the use of an
> illegal antenna system and/or illegally high tx power, or
> possibly
> just a good amount of user exaggeration.
>
> * AM Part 15 limits the tx to 100 mW of input power.
> Output power will be less -- 80 mW was assumed.
>


I'll respond to this since no one here is claiming 5 miles+ on 100mw's.

First you assume that 1kw of power at 1mhz is what the the curve is based on, but is 1kw at the antenna? If you think that the efficiency of 100 mw's is directly transmitted to a loading coil that has very low losses due to large wire diameter at the base of the antenna... that all 100 mw's if not close to all of it is not transmitted?

Second the 4mm diameter constant od is probably for a whip antenna that is configuresd for 27-29mhz cb band, while our copper antenna is 12.5-25 mm diameter and much lower resistance than a steel rod of varying thickness, not to mention it's tuned just to the specific frequency of resonace.

The ground radials do not transmit any power but reduces and losses in the system so that 'all' the transmitting power is sent to the antenna and not burned up as heat in the loading coil, which I don't see as happening since the power levels of 100mw's are too small.

So if what you say is true, then the Rangemaster claims are all false and that the ranges of 3-5 miles, or even notes of radios picking up the signal at 10 miles are all false?

I can assure you... get an SSTRAN AMT3000 or Rangemaster, install a radial ground system of 12 gauge or better, use 64 radials to start and work your way up to 120, make the radials 75'-100', make the loading coil as suggested here on this site or others, tune the antenna at a 40-50 foot height and then come back and write us your report before you lay claims of others using illegal setups or 'bad engineering'.

Like I said in my earlier posts, do the field experimentation and base your results first, before you take curves here or there and transpose numbers to suit your results, ... 'that is bad engineering practice'!

Radiopilot
 
Write all you want about the FCC calculations but, some of these TXs do not work a regular 50ohm system "marconi" like most people are used to.

I have said this before, I will prove to anyone on a rangemaster or a jack special "well installed" with the radials, doing 5 miles in "each" direction.








> Several posts here have asked what coverage can be expected
> for a legal
> Part 15 AM operation. The text below is based on my response
> to a
> similar question posted on a broadcast-oriented list.
>
> RF [email protected]
>
> + + +
>
> >Next time a non-D AM tower falls over, let's clean up the
> mess,
> >then install a Rangemaster or other high quality Part 15
> transmitter
> >on the ground at the center of the radial system and see
> how far
> >it gets out, measure the field strength, etc. The official
> 3 meter
> >antenna to be used.
> _____________
>
> A 3-meter vertical radiator is 3.6 electrical degrees long
> at 1 MHz. Using
> Figure 32 in George Brown's paper I referred to in an
> earlier post, the FCC
> efficiency of such a vertical with a ground system
> consisting of 113 radials
> of 0.27 wavelengths each is about 40 mV/m at 1 mile for 1 kW
> of radiated
> power.
>
> Using that efficiency with the FCC's propagation curves for
> 1 MHz, and
> assuming that the Part 15 AM tx could supply 80 mW to the
> radiator,*
> here are the parameters for a ground conductivity of 8 mS/m:
>
>
> 2.00 mV/m @ 0.1751 miles (good signal)
> 0.500 mV/m @ 0.6695 miles (usable signal)
> 0.100 mV/m @ 2.9125 miles (noisy signal)
>
> The quality of these signals is given for clear, open
> terrain and a
> good receiver (car, etc). Coverage will be less in urban
> areas with
> buildings, overhead wires, etc.
>
> NEC-2 calculates a base impedance of 0.04 -j6500 ohms for
> this set of
> conditions (4mm constant OD radiator, 3 meters long). No
> practical
> transmitter could deliver its rated power into such an
> impedance,
> but we have ignored that for these calculations. (The
> reactance term
> can be cancelled by using a loading coil, but the required
> coil would
> absorb a large amount of the available power due to its I^2R
> loss).
>
> Considering that Part 15 AM stations using intentional
> radiators neither
> have the ground system described above, nor can cause the RF
> current
> equivalent to 80 mW to flow in the radiating portion of a
> 3-meter antenna,
> it is clear that any Part 15 "coverage" claimed that
> approaches or exceeds
> what is shown in the calculations above must be related to
> the use of an
> illegal antenna system and/or illegally high tx power, or
> possibly
> just a good amount of user exaggeration.
>
> * AM Part 15 limits the tx to 100 mW of input power.
> Output power will be less -- 80 mW was assumed.
>
 
Please see my comments embedded below:

> First you assume that 1kw of power at 1mhz is what the
> curve is based on, but is 1kw at the antenna?

Yes, the FCC Curves show for various carrier frequencies the groundwave field
strength produced at various distances from a vertical radiator with 1kW of
input power, over terrain of various ground conductivities. Field strengths
for other power levels can be determined accurately from these same curves, by
simple mathematical means. The curves are based on measured data.

> If you think
> that the efficiency of 100 mw's is directly transmitted to a
> loading coil that has very low losses due to large wire
> diameter at the base of the antenna... that all 100 mw's if
> not close to all of it is not transmitted?

Even a loading coil with only a few ohms of DC resistance can have 20X or more resistance than the radiation resistance of a 3-meter MW radiator. As the coil is in series with the 3-m section, that means that the coil will absorb much of the power available from the transmitter. If the coil DC resistance is 20X higher than the radiation resistance of the antenna, only 1/20 of the available tx power will be radiated as a radio wave. The rest just heats up the coil.

> Second the 4mm diameter constant od is probably for a whip
> antenna that is configuresd for 27-29mhz cb band, while our
> copper antenna is 12.5-25 mm diameter ...

Using a larger OD radiator reduces its capacitive reactance and can improve system bandwidth, but doesn't much change its RADIATION resistance.

> ...and much lower
> resistance than a steel rod of varying thickness, not to
> mention it's tuned just to the specific frequency of
> resonance.

The important parameter here is RADIATION resistance, not the DC resistance of the conductor used as the antenna. Radiation resistance is governed by the electrical length of the radiator at the operating frequency, not the ohmic resistance value of the material used to make the antenna.

The DC resistance of the radiator also will reduce the power available to be radiated, but by a much smaller amount than the reductions caused by coil and ground system losses.

> The ground radials do not transmit any power but reduces and
> losses in the system so that 'all' the transmitting power is
> sent to the antenna and not burned up as heat in the loading
> coil, which I don't see as happening since the power levels
> of 100mw's are too small.

The radiating efficiency of an antenna system is the ratio of the radiation resistance of the antenna to the total resistance of the antenna system. The total resistance of the antenna system is comprised mainly of ground losses, coil losses, and radiation resistance.

Here are some representative values:

Radiation resistance: 0.1 ohm
Coil resistance: 2 ohms
Ground resistance: 50 ohms (a simple ground rod). Note this is not
the resistance of the wire leading to earth ground, but the resistance
of the buried ground conductor(s) to the earth, itself.

The radiation efficiency of this system is 0.1/52.1 = 0.0019, or about 0.2%.

So it is clear that very, very little power that is generated by the tx actually is converted to useful radiation by a legal Part 15 antenna.

This is intentional -- the FCC wants to limit the coverage of these unlicensed systems. Still they can produce enough field strength at short distances to serve the function that the FCC intended for them when they were allowed.

> So if what you say is true, then the Rangemaster claims are
> all false and that the ranges of 3-5 miles, or even notes of
> radios picking up the signal at 10 miles are all false?

The claims may be true, but they also may not be based on the legal use of Part 15 AM equipment. For example, installing a tx and its 3-meter antenna on a 6-meter pole, and connecting the tx chassis to earth ground via a vertical wire will produce a significant increase in distant field strength. The reason? Because the "ground wire" actually is part of the antenna, and in fact, will radiate more than the antenna will in this scenario. But then, that antenna installation is not permitted by Part 15.

> Like I said in my earlier posts, do the field
> experimentation and base your results first, before you take
> curves here or there and transpose numbers to suit your
> results, ... 'that is bad engineering practice'!

The comments I have made ARE based on real field data, which has been proven accurate in thousands of measurements made over the last 60+ years in the broadcast industry.
 
sir, I respect the fact that you are writting on a 50ohm based "marconi" radiator BUT these part15 TXs ie: rangemaster1000 does not apply the 50 ohm theory!

It apply the tesla theory of generating an extreme high of voltage on the antenna "well so call antenna" which is a 32 pf capacitor.

YES! these 5 mile (3 miles city grade) claims are true and legal using real part15.








> Please see my comments embedded below:
>
> > First you assume that 1kw of power at 1mhz is what the
> > curve is based on, but is 1kw at the antenna?
>
> Yes, the FCC Curves show for various carrier frequencies the
> groundwave field
> strength produced at various distances from a vertical
> radiator with 1kW of
> input power, over terrain of various ground conductivities.
> Field strengths
> for other power levels can be determined accurately from
> these same curves, by
> simple mathematical means. The curves are based on measured
> data.
>
> > If you think
> > that the efficiency of 100 mw's is directly transmitted to
> a
> > loading coil that has very low losses due to large wire
> > diameter at the base of the antenna... that all 100 mw's
> if
> > not close to all of it is not transmitted?
>
> Even a loading coil with only a few ohms of DC resistance
> can have 20X or more resistance than the radiation
> resistance of a 3-meter MW radiator. As the coil is in
> series with the 3-m section, that means that the coil will
> absorb much of the power available from the transmitter. If
> the coil DC resistance is 20X higher than the radiation
> resistance of the antenna, only 1/20 of the available tx
> power will be radiated as a radio wave. The rest just heats
> up the coil.
>
> > Second the 4mm diameter constant od is probably for a whip
>
> > antenna that is configuresd for 27-29mhz cb band, while
> our
> > copper antenna is 12.5-25 mm diameter ...
>
> Using a larger OD radiator reduces its capacitive reactance
> and can improve system bandwidth, but doesn't much change
> its RADIATION resistance.
>
> > ...and much lower
> > resistance than a steel rod of varying thickness, not to
> > mention it's tuned just to the specific frequency of
> > resonance.
>
> The important parameter here is RADIATION resistance, not
> the DC resistance of the conductor used as the antenna.
> Radiation resistance is governed by the electrical length of
> the radiator at the operating frequency, not the ohmic
> resistance value of the material used to make the antenna.
>
> The DC resistance of the radiator also will reduce the power
> available to be radiated, but by a much smaller amount than
> the reductions caused by coil and ground system losses.
>
> > The ground radials do not transmit any power but reduces
> and
> > losses in the system so that 'all' the transmitting power
> is
> > sent to the antenna and not burned up as heat in the
> loading
> > coil, which I don't see as happening since the power
> levels
> > of 100mw's are too small.
>
> The radiating efficiency of an antenna system is the ratio
> of the radiation resistance of the antenna to the total
> resistance of the antenna system. The total resistance of
> the antenna system is comprised mainly of ground losses,
> coil losses, and radiation resistance.
>
> Here are some representative values:
>
> Radiation resistance: 0.1 ohm
> Coil resistance: 2 ohms
> Ground resistance: 50 ohms (a simple ground rod). Note
> this is not
> the resistance of the wire leading to earth ground, but
> the resistance
> of the buried ground conductor(s) to the earth, itself.
>
> The radiation efficiency of this system is 0.1/52.1 =
> 0.0019, or about 0.2%.
>
> So it is clear that very, very little power that is
> generated by the tx actually is converted to useful
> radiation by a legal Part 15 antenna.
>
> This is intentional -- the FCC wants to limit the coverage
> of these unlicensed systems. Still they can produce enough
> field strength at short distances to serve the function that
> the FCC intended for them when they were allowed.
>
> > So if what you say is true, then the Rangemaster claims
> are
> > all false and that the ranges of 3-5 miles, or even notes
> of
> > radios picking up the signal at 10 miles are all false?
>
> The claims may be true, but they also may not be based on
> the legal use of Part 15 AM equipment. For example,
> installing a tx and its 3-meter antenna on a 6-meter pole,
> and connecting the tx chassis to earth ground via a vertical
> wire will produce a significant increase in distant field
> strength. The reason? Because the "ground wire" actually
> is part of the antenna, and in fact, will radiate more than
> the antenna will in this scenario. But then, that antenna
> installation is not permitted by Part 15.
>
> > Like I said in my earlier posts, do the field
> > experimentation and base your results first, before you
> take
> > curves here or there and transpose numbers to suit your
> > results, ... 'that is bad engineering practice'!
>
> The comments I have made ARE based on real field data, which
> has been proven accurate in thousands of measurements made
> over the last 60+ years in the broadcast industry.
>
 
Rich, your info is greatly appreciated here and I definately don't want this to get out of hands for the common person just wanting to buy a simple $50-$100 dollar 'kit' and put up simply in the hopes of transmitting a 50 mile contour!

I believe some of the models you have based on field measurements may apply to large 25-100kw stations, but those measurements have no real basis other than a casual glance for ref on simple systems as we propose here!

I design aerospace products for the commercial/military aircraft on a large scale (Boeing, NASA, Lockheed Martin, etc.), but I cannot take those measurements/data and expect I'm going to build a single seater EAA airplane for pleasure only, some data may apply but asa a whole the whole analysis has to be applied differently.....

Having said that read my comments btween the lines....


> Please see my comments embedded below:
>
> > First you assume that 1kw of power at 1mhz is what the
> > curve is based on, but is 1kw at the antenna?
>
> Yes, the FCC Curves show for various carrier frequencies the
> groundwave field
> strength produced at various distances from a vertical
> radiator with 1kW of
> input power, over terrain of various ground conductivities.
> Field strengths
> for other power levels can be determined accurately from
> these same curves, by
> simple mathematical means. The curves are based on measured
> data.


This data may apply for 1kw and higher and the fields measured may apply for engineers building large structures and high power but I'm sure it would not apply to these small systems.


>
> > If you think
> > that the efficiency of 100 mw's is directly transmitted to
> a
> > loading coil that has very low losses due to large wire
> > diameter at the base of the antenna... that all 100 mw's
> if
> > not close to all of it is not transmitted?
>
> Even a loading coil with only a few ohms of DC resistance
> can have 20X or more resistance than the radiation
> resistance of a 3-meter MW radiator. As the coil is in
> series with the 3-m section, that means that the coil will
> absorb much of the power available from the transmitter. If
> the coil DC resistance is 20X higher than the radiation
> resistance of the antenna, only 1/20 of the available tx
> power will be radiated as a radio wave. The rest just heats
> up the coil.
>


Again the type loading coil is based on 12-16 gauge wire and I believe that is around 1.2 - 4.1 ohms per 1000 ft. and of course the loading coil is only 150 turns max so I believe the length is around 100 ft or less of wire so then the ohms is 1/10 of the above figures ( 0.1 - 0.4 ohms)... hardly negligable in terms of DC resistance and 'heating up' in the coil?


> > Second the 4mm diameter constant od is probably for a whip
>
> > antenna that is configuresd for 27-29mhz cb band, while
> our
> > copper antenna is 12.5-25 mm diameter ...
>
> Using a larger OD radiator reduces its capacitive reactance
> and can improve system bandwidth, but doesn't much change
> its RADIATION resistance.


I admit this is true but if the capacitance/loading coil is much closer to a correct match.. true magic happens.... Resonace!


>
> > ...and much lower
> > resistance than a steel rod of varying thickness, not to
> > mention it's tuned just to the specific frequency of
> > resonance.
>
> The important parameter here is RADIATION resistance, not
> the DC resistance of the conductor used as the antenna.
> Radiation resistance is governed by the electrical length of
> the radiator at the operating frequency, not the ohmic
> resistance value of the material used to make the antenna.


But you mentioned DC RESISTANCE of the conductor not me!


>
> The DC resistance of the radiator also will reduce the power
> available to be radiated, but by a much smaller amount than
> the reductions caused by coil and ground system losses.
>
> > The ground radials do not transmit any power but reduces
> and
> > losses in the system so that 'all' the transmitting power
> is
> > sent to the antenna and not burned up as heat in the
> loading
> > coil, which I don't see as happening since the power
> levels
> > of 100mw's are too small.
>
> The radiating efficiency of an antenna system is the ratio
> of the radiation resistance of the antenna to the total
> resistance of the antenna system. The total resistance of
> the antenna system is comprised mainly of ground losses,
> coil losses, and radiation resistance.
>
> Here are some representative values:
>
> Radiation resistance: 0.1 ohm
> Coil resistance: 2 ohms
> Ground resistance: 50 ohms (a simple ground rod). Note
> this is not
> the resistance of the wire leading to earth ground, but
> the resistance
> of the buried ground conductor(s) to the earth, itself.
>
> The radiation efficiency of this system is 0.1/52.1 =
> 0.0019, or about 0.2%.


But ground resistance is not 50 ohms if a good radial system is in place, the resistance is much lower on the order of 1-10 ohms or better ... plus the coil resistance is not 2 ohms but may be a smaller variable as I mentioned earlier...


>
> So it is clear that very, very little power that is
> generated by the tx actually is converted to useful
> radiation by a legal Part 15 antenna.
>
> This is intentional -- the FCC wants to limit the coverage
> of these unlicensed systems. Still they can produce enough
> field strength at short distances to serve the function that
> the FCC intended for them when they were allowed.
>
> > So if what you say is true, then the Rangemaster claims
> are
> > all false and that the ranges of 3-5 miles, or even notes
> of
> > radios picking up the signal at 10 miles are all false?
>
> The claims may be true, but they also may not be based on
> the legal use of Part 15 AM equipment. For example,
> installing a tx and its 3-meter antenna on a 6-meter pole,
> and connecting the tx chassis to earth ground via a vertical
> wire will produce a significant increase in distant field
> strength. The reason? Because the "ground wire" actually
> is part of the antenna, and in fact, will radiate more than
> the antenna will in this scenario. But then, that antenna
> installation is not permitted by Part 15.


Not legal? Alot of these Rangemasters were visited by various field agents only for them to leave them untouched as they were found to be legal! Some of these transmitters were at 100 foot heights, which indicates they had very long ground lines. The FCC site for PART 15 does not state what the ground line/attach point needs to be. It is assumed that the ground would be simply attached to a pipe or grounding lug in the home or field, this is not in the realm of the FCC to enforce what is attached to any ground terminals/pipes/radials.


>
> > Like I said in my earlier posts, do the field
> > experimentation and base your results first, before you
> take
> > curves here or there and transpose numbers to suit your
> > results, ... 'that is bad engineering practice'!
>
> The comments I have made ARE based on real field data, which
> has been proven accurate in thousands of measurements made
> over the last 60+ years in the broadcast industry.
>


I don't dispute the years of aquired knowledge and field data, but the data was not gathered on small 100mw-1 watt transmitters and it's based on large 1-100kw stations, field measurements and field contours...

Part15 is a whole different animal... leave the computer behind, computer models, field data, close the books and try for a minute to believe that perhaps all of us can't be wrong!

I suggest you apply that knowledge by getting your hands on a simpple 100mw tranmitter, build a coil and enjoy what many of us us enjoyed in this hobby.

Radiopilot
 
Please see embedded comments below:

> This data may apply for 1kw and higher and the fields
> measured may apply for engineers building large structures
> and high power but I'm sure it would not apply to these
> small systems.

The same physics applies to all radiators, regardless of their applied power.

> Again the type loading coil is based on 12-16 gauge wire and
> I believe that is around 1.2 - 4.1 ohms per 1000 ft. and of
> course the loading coil is only 150 turns max so I believe
> the length is around 100 ft or less of wire so then the ohms
> is 1/10 of the above figures ( 0.1 - 0.4 ohms)... hardly
> negligable in terms of DC resistance and 'heating up' in the
> coil?

Between the two lines that follow is a Part 15 AM system summary based on your input in this post. The column structure is lost, so you'll have to study it a while to get the numbers. I think you'll see that your assumptions are quite a bit "off."

______

H. Height overall, metres 3.00 J. Coil diameter, mm .......... 75.0
L. Lower antenna dia, mm. 25.4 P. Coil height as percent of Ht 1.0
U. Upper antenna dia, mm. 25.4 G. Ground loss resistance, ohms 10.0
C. Coil length, mm ...... 300 F. Frequency, Megahertz ....... 1.70

Overall antenna height 0.017 wavelengths
Height of coil midpoint 0.18 meters above antenna base
Coil inductance 255.21 microhenries
Number of turns on coil 124
Coil wire diameter 1.60 millimetres = 14 AWG
Self-resonant frequency of coil 4.53 MHz, with self-capacitance.
Coil Q 347 incl effect of self-capacitance.

Radiation resistance 0.12 ohms transformed to feedpoint.
Coil wire loss 9.13 ohms .. .. ..
Antenna conductor loss 0.01 ohms .. .. ..
Feedpoint resistance 19.26 ohms
Feedpoint reactance 0.0 ohms

Radiating efficiency 0.62 percent.
Loss relative to 1/4-wave vertical 21.0 dB when both above same ground.
____________

> I admit this is true but if the capacitance/loading coil is
> much closer to a correct match.. true magic happens....
> Resonance!

Resonance occurs when the reactive component of the base impedance is zero ohms, which can be done by using the right inductance value in a series "loading" coil. But that doesn't change the radiation resistance value of the radiator itself, which remains very low compared to the resistances of the coil and ground connection. "Resonance" does not automatically mean that the Part 15 AM antenna system is efficient -- it certainly is not.

> But you mentioned DC RESISTANCE of the conductor not me!

Here is what you wrote originally, that I responded to:

"Second the 4mm diameter constant od is probably for a whip antenna that is configuresd for 27-29mhz cb band, while our copper antenna is 12.5-25 mm diameter and much lower resistance than a steel rod of varying thickness, not to mention it's tuned just to the specific frequency of resonace."

So you were the one who first mentioned the lower resistance of your copper antenna conductor, compared to steel. I just commented on your statement.

> But ground resistance is not 50 ohms if a good radial system
> is in place, the resistance is much lower on the order of
> 1-10 ohms or better ... plus the coil resistance is not 2
> ohms but may be a smaller variable as I mentioned earlier...

It takes about 120 radials each nearly 1/2-wavelength long to achieve a resistance to true earth ground of about 1 ohm. Ground resistance in a typical Part 15 antenna system is much higher than that. But I used 10 ohms in my Part 15 summary above.

> Not legal? Alot of these Rangemasters were visited by
> various field agents only for them to leave them untouched
> as they were found to be legal! Some of these transmitters
> were at 100 foot heights, which indicates they had very long
> ground lines.

So it is said. There can be many factors involved in whether or not an FCC inspector first recognizes, and then chooses to pursue a Part 15 violation, but I won't get into those.

> I don't dispute the years of aquired knowledge and field
> data, but the data was not gathered on small 100mw-1 watt
> transmitters and it's based on large 1-100kw stations, field
> measurements and field contours.

As I wrote above, power level is immaterial. The same physics applies to Part 15 AM antenna systems as to commercial AM broadcast antenna systems.
 
> sir, I respect the fact that you are writting on a 50ohm
> based "marconi" radiator BUT these part15 TXs ie:
> rangemaster1000 does not apply the 50 ohm theory!
_________

My comments apply to the approximately 3-meter high vertical radiators used by vitually every Part 15 AM station, and as shown and described on the Rangemaster AM1000 website.

The radiation pattern and intrinsic gain of a vertical radiator is a function of its electrical length, and so is its radiation resistance. Radiators are not required to have a 50 ohm, non-reactive driving impedance in order to "work." Their input impedance can be transformed (with loss of system radiation efficiency) into whatever value is usable by the transmitter to provide its full, rated power into the antenna system.

Those losses are low for commercial AM broadcast stations, because of the higher radiation resistance and lower reactance of their electrically long radiators, compared to Part 15 AM radiators. But the same physics still applies.
 
> My comments apply to the approximately 3-meter high vertical
> radiators used by vitually every Part 15 AM station, and as
> shown and described on the Rangemaster AM1000 website.
>
> The radiation pattern and intrinsic gain of a vertical
> radiator is a function of its electrical length, and so is
> its radiation resistance. Radiators are not required to
> have a 50 ohm, non-reactive driving impedance in order to
> "work." Their input impedance can be transformed (with loss
> of system radiation efficiency) into whatever value is
> usable by the transmitter to provide its full, rated power
> into the antenna system.
>
> Those losses are low for commercial AM broadcast stations,
> because of the higher radiation resistance and lower
> reactance of their electrically long radiators, compared to
> Part 15 AM radiators. But the same physics still applies.

A most interesting and useful thread. Just getting down to the nitty-gritty of the situation: installed according to Rangemaster's setup and tuning instructions, although not necessarily on the ground, range somewhat in excess of your stated figures is entirely possible. It's a matter of what the FCC inspectors who have visited these things defined as "antenna", "ground" or "something else", apparently, under 15.219.

I believe those Part 15 stations which pass FCC inspections are legal, don't you?

(And not to derail this topic entirely, I believe it would be quite appropriate to petition the FCC to invent a new 1W EMRP AM service as is available in the UK. The RSL service apparently operates mostly on a single frequency of 531 kHz. The service permits commercial advertising, as it's clearly understood that 1W stations aren't a threat to group owners or even independent stations. A similar, unused frequency in the US is 1710 Khz. How 'bout it, folks?)
 
What's max p15am range (to fadeout)?

What's the maximum groundwave part 15 AM range, till you're 0dB above the atmospheric noise floor? Assume stereo transmission with a 10kHz (6dB down) frequency response transmission (I understand bandwidth affects where the noise floor is), and an average ground conductivity between 8 and 30. If you have a decent radio and a really good antenna, assuming there aren't other stations interfering with it, what is (based on typical range claimed with good Rangemaster setups) the maximum distance you could theoretically go until the signal is just barely being pulled up out of the noise (but still somewhat intelligible - stronger than just a 10kHz carrier whistle)?
 
Re: What's max p15am range (to fadeout)?

> What's the maximum groundwave part 15 AM range, till you're
> 0dB above the atmospheric noise floor? Assume stereo
> transmission with a 10kHz (6dB down) frequency response
> transmission (I understand bandwidth affects where the noise
> floor is), and an average ground conductivity between 8 and
> 30. If you have a decent radio and a really good antenna,
> assuming there aren't other stations interfering with it,
> what is (based on typical range claimed with good
> Rangemaster setups) the maximum distance you could
> theoretically go until the signal is just barely being
> pulled up out of the noise (but still somewhat intelligible
> - stronger than just a 10kHz carrier whistle)?
>


WSJL did 10 miles<P ID="signature">______________
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Universal Life Ministries (ULC)

http://www.freecycle.org
Join the FreeCycle Revolution</P>
 
Re: What's max p15am range (to fadeout)?

> WSJL did 10 miles

Elementary question, but do these figures represent diameters? Radii? Square area?
 
> A most interesting and useful thread. Just getting down to
> the nitty-gritty of the situation: installed according to
> Rangemaster's setup and tuning instructions, although not
> necessarily on the ground, range somewhat in excess of your
> stated figures is entirely possible.

This added range results from the fact that Part 15 AM antenna systems are much more efficient when the "3-meter" portion of it is elevated above the Earth, and uses a long "ground" conductor to physical earth than when mounted just above the earth, with a very short ground conductor. An illustrated paper showing the reasons for this is available as item #3 on the following web page:

http://rfry.org/Software & Misc Papers.htm

> It's a matter of what the FCC inspectors who have visited these
> things defined as "antenna", "ground" or "something else",
> apparently, under 15.219. I believe those Part 15 stations which
> pass FCC inspections are legal, don't you?

Probably we all recognize that the intent of the FCC Rules for Part 15 was to limit the coverage possible from these unlicensed systems. What is perhaps less recognized by Part 15 AM users and FCC inspectors alike is that elevated 3-m antennas/transmitters using long conductors to physical earth become more efficient as their elevation above the earth increases. This effectively negates the intent of Part 15 to limit the coverage of these systems.

Part 15 users and equipment suppliers like Rangemaster have taken the approach that a ground lead is different than a ground wire or metal tower/pole, and that they don't radiate, anyway, so it doesn't matter how high the 3-m section & transmitter is, or how long is the conducting path to physical earth. Apparently in some cases, FCC inspectors have accepted this point of view. But that doesn't make these beliefs true in real, engineering terms -- they are not. And the fact that an FCC inspector has not found such systems in violation does not mean that they are strictly legal.

My comments are not meant to embarrass anybody or to "blow whistles," but to provide accurate data and information about this application that should be useful to others.
 
I'll jump in here with my $.02.

The fundamental source of controversy here is interpretation of the FCC part 15 rules. Rich's modelling, based on a very short ground lead, shows poor range. His modeling with long ground leads shows much better range. These are technical facts.

Rich seems to lean toward interpreting the FCC "ground lead" rule literally, where others interpret it more loosly.

So, the bottom line is that an elevated antenna radiates a lot better due to radiation from the ground wire/pipe/mast. Is this legal? That's subject to interpretation of the vague "ground lead, if used" part of the FCC rule.

Regardless of how various people may interpret the FCC "ground lead" rule, the reality is that the FCC does not enforce this rule. Why? I don't know (maybe because it is unenforceably vague), and I'm glad they don't. I have been watching this and other forums for a few years and I have yet to see a post that says the FCC has faulted anyone for a long ground run (other than a recent somewhat puzzling post by simcha about a rangemaster that had a ground wire running horizontally for a ways instead of purely vertically).

Rich's technical analysis is on the mark. Enforcement of the "ground lead" rule is an entirely different matter. They are separate issues entirely.

And, to those who may be worrying about the exposure of a dark and dirty secret on public forums, I don't think the FCC is about to change the "ground lead" rule any time soon. The AM band is not popular. There is little likelihood that listeners will complain about a Part 15 station on a clear frequency.

<P ID="signature">______________
Phil B
</P>
 
> (And not to derail this topic entirely, I believe it would
> be quite appropriate to petition the FCC to invent a new 1W
> EMRP AM service as is available in the UK. The RSL service
> apparently operates mostly on a single frequency of 531 kHz.
> The service permits commercial advertising, as it's clearly
> understood that 1W stations aren't a threat to group owners
> or even independent stations. A similar, unused frequency
> in the US is 1710 Khz. How 'bout it, folks?)
>
According to my research 1710 in the US is currently used by the Defense Department. However they have been given notice to vacate the frequency because it will soon be auctioned off. I believe it will be auctioned off to wireless service providers and not radio stations.
 
> And, to those who may be worrying about the exposure of a
> dark and dirty secret on public forums, I don't think the
> FCC is about to change the "ground lead" rule any time soon.
> The AM band is not popular. There is little likelihood that
> listeners will complain about a Part 15 station on a clear
> frequency.
>
Right now, there is no mechanism for the average citizen to complain to the FCC regarding interference to AM listening, such as power line noise or DSL. Go to their website and try to find any info on how to go about registering a complaint. The only thing you can do is contact the station you are having trouble receiving and let them contact the FCC. Anything else will fall on deaf ears.
 
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