- Posts
Some may consider the net radiation from a conductor connecting the ground pin receptable of an a-c power line outlet to an earth ground to be low/negligible, due to field cancellation caused by the other a-c wires in the house.
However the physical separation of such wires is a very small fraction of a wavelength in the AM broadcast band, and their radiated fields have almost no cancellation.
Practical examples of this are the tapered towers used by some AM broadcast stations. They consist of 3 or 4 essentially vertical legs along with numerous horizontal and diagonal braces along its height. These configurations may have their legs separated by 30 feet or more at the base of the tower. Yet this structure produces almost the identical radiation pattern as that of a single conductor of the same height.
The “ground” conductors of a-c house wiring are effective radiators of r-f energy along their entire length/height from the a-c outlet to the point where they connect to the buried ground rod at the a-c service entrance.
Total posts : 45366We agree on that point. But there are more circumstances encountered in house wiring than taken into account in previous post.
Instances where AC ground drops vertically straight down to the electric panel the AC ground wire becomes the negative side of a dipole and very likely radiates RF that will increase the field strength of the signal. Agreed.
But here in the internet building the AC wiring is run from the electric panel up into the attic, across the attic, and is dropped from above to the room outlets.
Therefore if we were to attach RF ground to AC ground the upward wire in the wall would be out of phase with the transmitting antenna and actually attenuate our RF field strength.
Another example.
A real life case of poor performance from attaching to “house ground” exists right here where we have an AMT3000, loading coil and ground clamped to one end of a 60′ steel I-beam below the floor. As it crosses the basement the I-beam comes in contact with metal ductwork and a heavy copper bonding wire connecting the electric panel ground and ground rod to a cold water pipe on opossite sides of the basement.
One would expect so much metal attached to RF ground would comprise a veritable ground plane that would send my signal flying throught the air but not so.
In fact our signal is strong ONLY within the building and fades out rapidly as little as 15-feet around the exterior.
My argument says that wiring schemes in buildings vary to the extent that some AC ground points add to RF radiation while others may actually diminish it.
Total posts : 45366But it makes a pretty good, radiating antenna component. It is not an effective r-f ground, at all.
…Instances where AC ground drops vertically straight down to the electric panel the AC ground wire becomes the negative side of a dipole …
Note that both sides of a dipole antenna carry r-f (alternating) current. Neither side of the dipole has a single polarity such as “positive,” or “negative.” Both sides become either positive or negative during each 1/2-cycle alternation of the r-f energy applied to it.
In fact, if either side of the dipole is long enough, it can be both positive and negative at various locations along its length.
…Therefore if we were to attach RF ground to AC ground the upward wire in the wall would be out of phase with the transmitting antenna and actually attenuate our RF field strength …
Note than an r-f ground does not exist at the “ground” pin receptacle of an a-c power socket located a finite distance away from the buried ground rod it connects to as a ground reference.
Total posts : 45366when the first phono oscillators hit the market…
Hooking a record player into a phono oscillator
“transmitter” and transmitting through an
existing radio saved money in those days.
One did not then have to buy a record player
with it’s own expensive audio amp. There was
already one in the radio. (I may not be
stating this quite correctly but you
guys know what I mean.)
The FCC (or the Federal Radio Commission –
whatever they were then) figured out the
first Part 15 rules, I guess. It seems to
me that they might have been aware of
oscillator injection into the AC line and
reradiating ground wires. Perhaps
they factored this into the rules.
(??????) That was 80 years ago.
Was it even called “Part 15” then?
Brooce, Hartford CT
Total posts : 45366—
Total posts : 45366The “ground” conductors of a-c house wiring are effective radiators of r-f energy along their entire length/height from the a-c outlet to the point where they connect to the buried ground rod at the a-c service entrance.
In light of the factual information you dished out above, there is something which has alway puzzled me.. How is it that the most plentiful and commonly used manufactured part15AM transmitter in history was/is certified compliant with it’s connection to the ground pin receptable of an a-c power line outlet? They have been legally manufactured like that for almost 40 years.. Is there something I’m not taking into consideration?
The Talking House
- You must be logged in to reply to this topic.
