Mention was made in another thread (about FM transmit systems) about the effects of connecting a conductor from the r-f ground terminal of an elevated Part 15 transmitter to a basement cold water pipe. However such conductors don't even need to connect to an r-f ground to produce a significant effect on radiated fields.
This seems worthy of a new forum topic, so it might be found easier in the future.
The NEC study below shows an elevated Part 15 transmittter with 3m whip attached, with and without an 8m vertical conductor connected to the r-f ground terminal of the transmitter. The base of the 8m conductor is open (no metallic path to an earth ground).
This antenna configuration with the 8m conductor is that of an off-center-fed vertical dipole, which is a semi-balanced radiator that needs no reference to a physical r-f ground for quite good system radiation efficency.
The fields radiated for the system with an ungrounded, 8m conductor are compared in the NEC graphic to those when that conductor is not present. There is a very substantial difference between the two fields, as shown (a difference of about 5.85X in favor of the system with the 8m conductor).
A transmit system in the AM broadcast band using only a 3m conductor and no path to an r-f ground or counterpoise wire(s) has a very high antenna system input impedance, and very poor radiation efficiency.
OTOH, if that 8m conductor connected to earth ground, then currrent distribution along it would be uniform instead of dropping to zero at the base (open end). That would increase system radiation efficiency even more.
Possibly all of this is the reason for FCC §15.219(b).
Maybe something to think about, for the technically inclined 🙂
as i stated in the other thread, rangemasters and procasters, currently the two most popular part 15 am transmitters on the market will radiate from the power and audio leads, especially the negative power lead, and the audio ground leads because at some point they do connect to a earth ground. this is why timinbovey is getting the range he is getting from a procaster placed 30 ft in the air regardless of it being over a piece of pvc piping on the mast with no gorund connection attached.
there is some filtering iirc on the power and audio leads on both transmitters but as you stated in so many threads over the years that filtering, especially the small board mounted filtering they use, goes only so far to supress radiation from power audio and ground leads.
i can only assume as many have discovered this is the same for fm transmit system which use an electrically short radiator as most of them do.
Good Info for my New AM TX. Jeff and I will have to try and see if we can come up with a great indoor antenna based on this Information.
Addendum: It would be interesting to know how the FCC reacted or would react to an inspection case where any/all conductors other than a ~ 3m whip connected to an elevated Part 15 AM transmitter setup produced much greater fields than possible from that system installed with its base a few inches above the earth -- a configuration clearly permitted by §15.219 (other things equal).
it apperently has happened to Gerry Gaule using a unmodified talking house v5 with it's OEM 3m wire antenna and plugged into a electrical outlet indoors and i would assume a audio cable connected from his processing to the talking house on his 2nd or 3rd floor apartment.
everything done completely consistent with manufacturers instructions and within it's certification perameters.
still resulted in a NOUO levied against him. this is the most oddest thing i have ever heard of a field inspector citing someone for. most of them who come across that type of situation would likely just instruct the person on what they see wrong with the install and make a recommendation on how to bring it in compliance.
which in the Gaule case i just simply could not see what could be done to bring it in compliance or why the agent cited him in the first place. Gaule wasn't even using the external ATU unit, just the straigt V5, oem 3m wire tacked to his ceiling, and the unit plugged into the wall.
exactly as it was certified for.
this one has boggled the mond of everyone, broadcast engineers, part 15 enthusiasts, and i am knd of wondering if fellow agents didn't quietly question this agents action in the case.
Not so sure of the conclusions/statements posted in Reply 5 of this thread, but I'm willing to be convinced otherwise by documented fact.
Does the author of Reply 5 above believe his knowledge/assessment of the conditions leading to any FCC NOUO action shows that such an FCC action was undeserved?
If so, then for his sake I hope he posts such factual/provable bases.
The author of Post # 5 is Robert kc8gpd. I thought you two had previously met.
There's no reason to challenge Robert to "prove" anything, the Jerry Gaule incident is exactly as he describes it... shrouded in mystery over why an NOUO was issued, especially giving no mention of Part 15.219.
As I recall from the time when that NOUO was fresh news you, Rich, expressed perplexity as to the nature of the written document, which you never seem to have tracked to a final resolution.
but I am much more interested in the response of kc8gpd to my post than I am in yours - assuming he hasn't authorized you as his legitimate spokesperson.
Normally rhetorical questions go unanswered.
I do believe Station8 and I discussed this when we talked about how AM is going to get me more listeners than part 15 FM even if I ran a 500mW FM station. He told me that a legal part 15 AM station will beat the tar out of a 500mW FM transmitter. After which we talked about the only NOUO he knew of and it was caused by a jealous licensed broadcaster near where the part 15 operator lived. The agent from the FCC stated his Talking House V5 was 125 mW to the final. The legal limit is 100mW to the final. When Station8 tested his V5 it was only 92 mW. So with that said and this just a theory can't back it up but do the math. Someone has paid that agent to shut down that operator at any cost. On a wire antenna unless you connect a watt meter to the transmitter you could not differentiate between 100mW and 120 mW. My question is how can the long wire give you better field strength than a 10 foot whip. And if I'm on the first floor and use a tapered helix antenna as long as it is no bigger than 3 meters it should be legal. Even if it were scientifically possible to have a 500Db gain inside antenna as long as it does not exceed 10 Ft (3 meters) and the ground rule is not broken it would not matter. Now I know there is no way of a 500Db gain inside antenna I'm just making a case. Imagine if it was invented.
There's a rather simple and inexpensive way to minimize the effect of power/signal cables acting as conduits for an RF ground which I used successfully in my "High Efficiency AM Transmitter" design.
Simply place a RF transformer at the output of the final amplifier with the secondary not connected to the transmitter circuit ground. One secondary lead goes to the radiator, the other to the RF ground (if used). Since there is no current path between the transformer secondary and the circuit ground there is no RF present on the power/audio lines (except for that which may be induced). This provides for a well defined RF antenna system circuit separate from the transmitter circuitry.
This has the added advantage of breaking a ground loop from the power/audio circuits and the RF ground used for the antenna system.
With this method, chokes and other RF suppression components are not needed on the power/audio lines to control radiation.
Neil
Neil, you came along with the perfect resolution to the problem at exactly the right time. Yours is the page on this subject that should be printed and kept in the engineering file.
It was just last May when Rich took us on this same tour, which makes interesting reading as well.
Elevated or not, an AM Part 15 transmitter is going to need audio and power. Whether it's on the ground or in the air you still have to get power to it and audio. Unless there will be a new requirement that they must be mounted on the ground with a built in audio source and the whole outfit runs on internal batteries.
Assuming my power/audio cables are providing a counterpoise (it makes no difference it they reach "ground" in some way, as I did tests runing it on a 12V battery and providing sound from a small portalbe mp3 player -- nothing connected to power, powered mixer, computer, etc and the field strength did not change on an actual FIM as I too was perplexed by the coverage with no ground) any transmitter would benefit from the SAME counterpoise. You gotta get sound and power into it.
I would imagine that any transmitter tested by a lab of the FCC would show increased output RF with power cables or audio connected. Difference is, ones with built in batteries, like the WH 3.0 can be tested in a lab with NO cables and show lower output.
TIB
Is Rich on a mission to further restrict Part 15 broadcasting?
It seems like it to me each time he persistently twists the conversation to this matter of interconnecting audio & power wires possibly adding some minute amount of radiation.
The fellow is routinely about reminding us of the limits of the hobby.
Audio and power cables have been and remain a recognized part of the hobby, it is foolish to bring them under suspicion.
- I don't have time for political correctness. - Donald Trump, 2015
Why do you guys always come up with ideas like poking the FCC in the eyes with a stick?