Maybe I'm missing something, and wonder - is there a ground connection in your simulation for an elevated antenna mounted to an ATU fed by coax, i.e., is it the coax that's radiating, or the ground?
I also am confused by your posting, rich, which clearly says there's a 20-foot conductor from the raised transmitter down to earth ground.
What is confusing is that this is a reversal of your long standing and oft repeated advisory that such lengthy grounds are not compliant.
Could it be possible that the two units (ATU/iAM) are a balanced circuit through the coax? I mean, IF they are loaded correctly on both ends, no R.F. should emit from the coax, correct?
The Talking House unit has a tuning mechanism built-in to tune the circuit between the xmtr and the ATU. If the ground from the ATU and the shield of the coax is isolated via R.F. chokes or whatever at the ATU, then the shield wouldn't be active with the ATU. Hence, not part of the antenna. (But, the isolation could pass D.C.)
I believe I understood that part of the certification mentioned that the ATU was a seperate R.F. amp. Could it be possible that the coax just feeds R.F. and D.C. to the ATU and has good R.F. isolation so not to backfeed down the coax, making the ATU a totally separate unit? (R.F. wise) Or, maybe they are phased 180 degrees from each other..
That ATU costs big bucks for a reason..
These responses relate to earlier clips in this thread, technical analyses of various documents available on the Internet from Part 15 equipment manufacturers, the FCC and other sources, and the proven principles of physics.
Please consult with the engineering group of the manufacturer of any particular Part 15 AM transmitter to determine how they might apply to their equipment.
I would assume ... that it is the long ground wire in the simulations for an elevated mount that are causing the stronger field intensity.
Conductors adding radiating length to the 3-m whip increase radiation from the transmit system. This is true whether the conductor is a separate wire considered to be a "lightning" ground, a path to the earth via a short wire from the transmitter to a metal supporting structure/tower, audio and d-c conductors leading away from an elevated transmitter, the shield of a coax cable between the transmitter and a remote ATU+whip, or some combination of these.
...an elevated ATU can perform adequately without a ground wire (particularly if you use the supplied power supply, which uses the AC neutral as a ground).
However the added conductor length to reach the a-c power line ground can exceed the radiating length of a Part 15 AM setup allowed by §15.219(b). The a-c power ground typically is provided by a ground rod just outside the wall where the a-c service enters the building. The "neutral" terminal of an a-c outlet does not provide an r-f ground until that conducting path reaches the ground rod -- which path may have dozens of feet of conductor length (which can radiate).
is there a ground connection in your simulation for an elevated antenna mounted to an ATU fed by coax, i.e., is it the coax that's radiating, or the ground?
The NEC model has no separate conductor between the ATU and the earth. The conducting path to earth is via the outside surface of the outer conductor of a 50-ft coax cable to a 3-m, buried ground rod.
The r-f ground terminal of an ATU normally connects to the "circuit ground" used by the components of the ATU. The shield of the incoming coax cable also connects to that circuit ground. At the transmitter end of that coax cable, the shield connects through the circuit ground of the transmitter chassis to the a-c neutral, via the power supply. But as pointed out above, the neutral conductor does not provide an r-f ground until it reaches the buried ground rod.
I also am confused by your posting, rich, which clearly says there's a 20-foot conductor from the raised transmitter down to earth ground. What is confusing is that this is a reversal of your long standing and oft repeated advisory that such lengthy grounds are not compliant.
The purpose of that posting was to show the reason why long conductors radiate, not as a suggestion to use them.
Could it be possible that the two units (ATU/iAM) are a balanced circuit through the coax? I mean, IF they are loaded correctly on both ends, no R.F. should emit from the coax, correct?
A coaxial cable consists of a pair of conductors, arranged concentrically. Zero radiation from the coax shield requires equal current flowing in opposite directions on the outer surface of the inner conductor and the inner surface of the outer conductor -- where they are confined by "skin effect."
The cable termination provided by an ATU essentially is an unbalanced load. The r-f on the coax cable center conductor passes through a loading coil to a ~3-m whip, which is an unbalanced radiator (a monopole). The "circuit ground" in the ATU provides a conducting path for the currents on the inside of the coax outer conductor, which then can flow to the outer surface of the outer conductor of the coax at the coax connector of the ATU.
This path along the outside of the coax shield unbalances the currents flowing on the inner and outer conductors of the coax, which causes the shield to radiate.
...unit has a tuning mechanism built-in to tune the circuit between the xmtr and the ATU.
The on-line manual for the ATU shows that the coax cable connects to a separate r-f output connector on the transmitter labeled "Outdoor Antenna Connect," and there is a "Antenna Select" slide switch to select between Basic and Outdoor. This tends to indicate that the auto-tuning used for an indoor antenna is not active when using the ATU.
If the ground from the ATU and the shield of the coax is isolated via R.F. chokes or whatever at the ATU, then the shield wouldn't be active with the ATU. Hence, not part of the antenna.
However if r-f current is prevented from flowing on the outside of the coax shield, and on any separate conductor between the r-f ground terminal of the ATU and the earth, then the fields radiated by the system using the ATU probably would not be as great as when using the basic (indoor) antenna.
I believe I understood that part of the certification mentioned that the ATU was a seperate R.F. amp. Could it be possible that the coax just feeds R.F. and D.C. to the ATU...
Some have claimed that the ATU is the final stage defined in §15.219(a). However from patent information available on the web and believed to apply to such an ATU, it can be seen that no d-c power is supplied to it -- only r-f power. If so then the ATU is a passive device, and not a final stage amplifier in the conventional use of that term in the electronics industry.
I haven't studied the Talking House skimmy enough to know what goes where at the R.F. output section so maybe someone who has can chime in..
Most ATU units are placed near the xmtr in the feedline, not at the antenna. This fact alone makes me wonder..
I must question why the Talking House has provision for a ground connection at the ATU if the coax is used as the return, beyond static discharge or lightining protection. The ATU must be isolated from the mount. They highly suggest to not change the length of the connecting coax or alter it in any way, including the addition of a ground connection. Adding a ground connection to the shield between the two units, Like in a normal TX'r/ATU situation, would change things and throw the "calculated" properties out of balance, I'd figure. There's a delicate balance in that circuit for a reason..
This leads me to believe that this unit isn't a typical ATU like most understand..
BTW.. Happy Holiday, ya'll..
The ATU is a passive circuit consisting of a toroid input transformer, two separate, adjustable loading coils selectable with a band switch, and a meter circuit to indicate peak voltage applied to the whip antenna.
It is referred to as the "final RF output" of the Talking house system when used as stated in the OET test data supplied by Radio Systems.
It is basically just an adjustable loading coil with a signal meter.
Yes, most Hams put their antenna tuner in the shack where it is easy to access for adjustment. But, the best place for any antenna tuner is at the antenna.
When a tuner is placed at the transmitter and separated from the antenna by coax, the coax becomes part the the equation and will have standing waves on it and radiate.
When a tuner is placed at the antenna, if the tuner input impedance matches the coax and transmitter impedance, very little radiation will occur from the coax. It would be the same as connecting a transmitter to an antenna where all the impedances match, i.e. a CB ground plane antenna or FM ground plane antenna.
I believe the coax connecting the ATU to the Talking House transmitter could radiate if the mismatch is great enough. However, connecting a separate ground wire would certainly radiate and both Radio Systems and Information Station Specialists warn of this.
These facts had to be known and were accepted when the OET test data was submitted and the certification granted.
That answers many of my questions and reinforces the thought of a balance circuit between the two..
I wonder how much loss there is going through 50-100' of RG-6? Obviously not much..
I believe the coax connecting the ATU to the Talking House transmitter could radiate if the mismatch is great enough.
Coax can radiate even with a near-perfect match of the coax to the feedpoint of the antenna.
Consider a 1/2-wave, center-fed dipole, which at resonance has a feedpoint impedance of about 72 ohms. and a reactance of zero ohms (it is resonant).
That impedance mismatch at the feedpoint when using 75-ohm coax would result in an SWR of less than 1.03:1, which is very good for an antenna system.
But regardless, the r-f current carried by the inside of the outer conductor will cross to the outside of the outer conductor where the coax shield connects to one side of the dipole. This will unbalance the currents in the coax, causing the shield to radiate.
This is the same scenario as with a Part 15 AM remote ATU, except one side of the dipole is very short -- just the ground circuit buss of the ATU.
However the coax shield also connects to that ATU ground buss, adding radiating length to that side of the dipole.
Wouldn't the signals (input-output) be 180 degrees out of phase because of the transformer? This would null out the small amount of radiation emitted from the coax shield..
A normal resonate wire dipole doesn't have a matching transformer. The dipole isn't isolated from the coax shield..
The r-f currents on the OD of the inner and the ID of the outer coax conductors are already 180 degrees out of phase. The shield connects directly to the ground bus of the ATU, where the shield current crosses to the OD of the shield, which can produce radiation from the coax.
The coax inner conductor is connected to a transformer primary whose secondary feeds the loading coil and 3-m whip. The cold side of both transformer windings connects to the ground bus. I would guess that this transformer provides an approximate match to the coax used in the system, when the loading coil is resonating the 3-m whip.
It would be useful if the manufacturer publicly offered his description of how this ATU and system are designed to operate with respect to Part 15. There may be something not identified about it, so far.
It would be useful if the manufacturer publicly offered his description of how this ATU and system are designed to operate with respect to Part 15. There may be something not identified about it, so far.
THANK YOU!!!
me and RFB have been trying for a week to make this point.
contact radio systems rich in relation to the iAM.
maybe you will have better luck prying that out of them than me and RFB did.
A dipole antenna is a balanced antenna. When connected directly to unbalanced coax, the shield of the coax skews the radiation pattern and will radiate even though a near proper impedance match is at hand.
This is why a proper installation, when using a dipole antenna, employs a balun to stop common mode currents from running along the outside of the coax shield.
This could be a transformer balun or a stack of ferite rings at the connection point.
So yes, when not connected properly to a dipole antenna there will be some radiation from the shield of the coax.
There are far more larger concerns now than some ATU flung up in the air.
I beg to differ with mram's statement of the OET declaring the ATU as a "final RF stage". No where does any OET source document state that, only "copies" of a page or two from the company's records, and it is not complete.
However there is a much BIGGER problem than the ATU.
Part 15.2.1043 clearly defines the permissible changes that can take place to an already certified device. It also states clearly what CANNOT be modified without re-application for new grant of certification.
Right now you got this iAM running with a modified modulator circuit, totally different from its "basic" circuit design that WAS certified. However there is no record at the OET of any new application for retesting with the new modified modulator circuit. The final's bias has also been changed, which 15.2.1043 specifically says no modifications can be done to the basic modulator circuit, OR the finals.
Now how can a company continue to market a unit modified which is NOT documented, under the old certification that applies to an un-modified unit?
They can't.
I've been given contact information to the OET and have already started the process in finding out what's going on with this thing.
Forget elevated ATU's and coaxes, because right now, the evidence so far indicates that the non-compliance is right there inside the transmitter itself, a modified modulator and final circuit.
And there is no evidence of those updated circuits being tested to comply under the existing certification, or that any new testing was done with the modified unit to be granted a new certification, or if those modifications kept the specs within the old certification.
Take it as you will. This is for my own research and protection. I don't care what everyone else want's to do or not. That's your own situation to deal with.
But I won't take non official answers or copies out of some manual when there is far more missing and they know it.
Push me and I push back...with a vengeance.
The investigation continues.
RFB
Good for you, RFB. I admire a person that sticks to their guns. Maybe you can sell yours to some sucker.
I'm sure glad my stock is in the older, unmodified Talking House units.
Yes siree bob.
problem is when they revoke certification, it gets yanked for all units including the ones using original certification design as well as the modified ones.
so if/when fcc pulls certification anything sporting the original THIIv5 certification number is no longer valid.