Regardless, a proper working system requires some kind of complete circuit path to properly function. This means for our subject matter, an RF ground.
True one really does not need this if only attempting to send a signal to the other room. However having good ground can eliminate more problems such as inductive coupling into audio gear and audio lines, or causing unexpected interference to your own stuff in your own home.
There is very little that will radiate from a cold water pipe once connected to it, especially if you connect as close as possible to where the mains pipe comes up into the home. And keep the ground wire from the TX to that water pipe as short as possible, again to reduce the resistance along that return path for the RF for better ground, and to prevent unintended radiation.
Never thought I would see a day when ground was such a debated subject. Well I recall a time when it wasn't. Why so now?
Anyway, on with the research!!
RFB
I posted this before and I may even post it again.
'THE RULES" are not black and white. There is interpretation involved, and while it's interesting to see various people's interpretations of said rules, the ultimate authority is the FCC. No matter how technically adept those people view themselves to be.
A few years ago, it was considered compliant to have a transmitter high up in the air grounded to a metal structure. Now, it is not. Did the rules change? No, the FCC interpretations changed.
So my suggestion for anyone starting up a Part 15 transmitter, new or experienced, is to read "THE RULES", read threads such as this carefully, and then make informed interpretations of your own. After all, you have to live with them if the FCC comes calling.
And I suspect that intent plays a bigger factor than what some are willing to admit. But then, some think that everyone here goes out of their way to violate those rules.
Agitations and diversions aside, I will continue undaunted on the path of indoor antenna research.
I will not respond to phantasms about "rule violations" when that is totally off topic and I will not be prodded into mounting a defense against allusions.
If we have complex issues like narcissistic wound driven by guilt combined with remorse over not having become a recognized law enforcement hero for clamping down on ground lead violators, that should all be moved to a psychology discussion site.
Meanwhile, here in the wake of disruption, a Spectrum Analyzer is staring at me. I have no place to put it. Shall I change the subject yet again to that of "furniture for test gear?"
Sometimes confusion causes the brain to output unrelated products, like a bold scheme how someone could legally earn money building part 15 transmitter kits. It's a lesson from the alternative-health-care field, where a legally paid massage therapist may provide "side services" at no additional cost. What I'm saying is, it would be legal to charge $300 for a nicely built transmitter cabinet, which contains, at no additional charge, a fully built part 15 transmitter.
Maybe the new network should use that for fund raising.
Getting back on track so we don't loose our place here, have you thought of any antenna designs so that they are more eye relaxing in a home setting?
Example, standing lamps and lamp shades for top hats. Ceiling fan loop antennas, swamp cooler coils and maybe a c-pol patio table? 😉
Actually kidding aside, researching and developing indoor antennas that appear like a standing lamp with an actual working light, loop antennas above a ceiling fan assembly or other would be great!
RFB
Good, RFB, perfect! Floor lamp.
I go through floor lamp listings at shopping sites and watch for "antenna friendly" designs, or possible ways of converting generic floor lamps with a design that any wife would approve of.... that's the tricky part.
I almost have a space ready for the Spectrum Analyzer (SA). Clearing the space on my over-sized executive desk is taking all evening, because it has ten years of accumulation, at the very bottom of which are the N-scale train parts I never did anything with. I'm off-loading it all into a giant cardboard carton where it will be found by future generations.
Then the SA will be my companion there at the desk, so I can watch that spectrum for SETI (Sightings of Extra Terrestrial Intelligence).
What would they do if we set up a million Watter up on Mars, aimed toward earth?
"What would they do if we set up a million Watter up on Mars, aimed toward earth?"
Unfortunately, since NASA has established a line of communicating satellites and surface rovers with on-board communications systems, and although they cannot claim any authority on any part of Mars, the FCC will step in and say "nope" because you could cause interference to that established line of communication between NASA and its remote probes.
However it would be interesting to see how well RF will propagate on that planet's surface. It's nothing more than a ball of mud ice layers (conductive/excellent ground) and thin atmosphere and very very little other man made electric/electronic/RF noise.
How about we actually set foot on the planet first and then set up our megawatt monstrosity and turn Mars into our own version of Death Star. :p
RFB
It's a morning, probably Wednesday, here on earth, center of North America, an indoor antenna research station.
Upon advice from member RFB, a spectrum analyzer (SA)was obtained, arriving yesterday from all the way in China, and many hours were spent in simply making a location to install the device.
The hours from 11 PM to 1 AM were spent learning how to view the highly interesting picture of the RF spectrum obtainable on the device.
The first big find was the FM spectrum, 88 to 108mHz, with its many peaks and valleys; beaming signals and the slim spaces in between. I was unable to pick out our two operating transmitters at 101.9 and 107.1, but they are at legal part 15 power located a whole room away.
This new morning I went for the AM band, expecting little, because the antenna included with the SA is only about 12-inches telescopic.
But I did find evidence of AM activity. Most prominent was 1550kHz, a very tall spike coming from four feet away in the front window of the office. Next, I turned on 1680 AM and it produced a peak nearly as high coming from 37-feet away in the upper-management lounge.
I kept an eye on the 850kHz spot because a 5kW station was due to turn on only a mile from here, and right on time there it was. I could even watch their spike shoot up and down as it followed the Amplitude Modulations of the announcers voice.
Smaller spikes included 1120kHz, 1320kHz, 1430kHz and 1600kHz, owing to their power level and relative proximity to this location.
The next project will be the building of a loop antenna for the medium wave band, and that may not take long since it can be built from parts on hand.
Let's head over to the cafe.
What do we want to do with an indoor antenna design? First and foremost we want the thing to radiate the maximum possible signal though constrained by physical limitations of indoor space.
The following are ideas which have not been tested by me but are offered to those who wish to do so.
Install a linear ground conductor with the transmitter "ground" connected to the center. In principle, this would provide for the necessary return current path to the transmitter and the net radiation from this "ground" should be zero.
Is it possible to build an antenna system which radiates the signal and doesn't require a ground at all? Yes, but it may not be the most efficient approach. How about two 1.5 meter conductors arranged as a dipole with the transmitter in the center and each with a resonating loading coil?
Neither of these suggested systems may compete well with an outdoor system with radials but it may be that this is the best that can be done indoors and they just might give a decent signal range.
I would like to see this topic approached with a sense of adventure rather than a listing of reasons why it would not work.
Neil
Dear Neil:
No indoor antenna design will be left behind.
As these experiments unfold, we will try everything.
The resulting documentation will be available as it's written at the link given above, and will be made available in the public domain for inclusion in the part15.us library.
Your mention of twin loading coils is very techno and will be fun to implement.
I just put my 2nd self-loaded coil to work on the Wintenna at 1550kHz, and my first self-loaded coil on the Quacker Oat box is stored with the Ramsey AM 25B.
"I would like to see this topic approached with a sense of adventure rather than a listing of reasons why it would not work."
....I
RFB
Neil's # 1 Idea a few jumps back is reprinted here:
"Install a linear ground conductor with the transmitter "ground" connected to the center. In principle, this would provide for the necessary return current path to the transmitter and the net radiation from this "ground" should be zero."
Aha! Yes sir! And that indeed is a "secret ingredient" that I recently learned on this website, in things said by Neil, rich and perhaps MRAM.
That is exactly what I now have on AM 1680, the AMT5000, serving bird bath and back fence.
It was the key to finally getting the signal up the hill to the mulch pile. But it is also an indoor antenna!
Half of my linear ground conductor leaves the building at foundation level and travels underground uphill, while the counter-portion runs through the basement, tie-wrapped with the I-beam.
Fuller details on these designs will be forth coming.
The first full day with Spectrum Analysis has been very part 15. Now the radio station has become real. It doesn't need listeners, it needs that peak on the scope.
Finally I know what the radio engineers were doing with their interesting scopes while I served as a mere announcer.
I always thought they knew a special way to use an oscilloscope, and when I built a recording studio I had a scope used for aligning stereo tape heads on tape decks. I was sure that I could use the scope in a radio station some day.
I wonder if this spectrum analyzer would impress a lady. "Would you care to stop in to see some medium waves? It's like etchings, only more wiggly."
Finally I know what the radio engineers were doing with their interesting scopes while I served as a mere announcer.
Both the disciplines of distribution and program content are needed to create a superior, or even a viable audience base with respect to contemporary, competitive sources. Even more so now, considering all of those sources available these days.
But probably _first_ come the program distribution channels (science), and then come the programs that they convey (art) -- as first was shown by the dramatic development/growth of MW broadcast station audiences back in the 1920s and 1930s.
The radio horse did definitely come before the program cart, mixing a metaphor with a fact, as the technical radio instrument was first demonstrated, followed by the artistic minds who saw the chance for "theater in the air."
No one invented a radio program prior to the development of radio transmission.
Commercial sales were done door-to-door and the musicians on phonograph records competed with their own hotel ballroom dance orchestras until they were saved by occasional movie jobs.
Pre-radio announcers accounted for the large number of railroad bums.
This may be on the slate for tomorrow, since the FM STL path down one-floor to the LPB CC transmitter is still in the multipath.....
As several of you have said, the vertical FM antenna above the CC transmitter is putting a null downward, so we need some horizontal signal, but need to keep a vertical signal for a 2nd path located on the same floor which does not have multipath.
I would like advance opinions about what to expect, but I'm going to find a piece of metal strong enough to bend into an "L-shape", with equal legs.
One leg will point vertically, the other will face horizontally.
There are two ways to try it.
1.) Series fed -- where the RF goes into the tip of the horizontal leg and flows up the L to the tip of the vertical section;
2.) Parallel fed - with the RF injected at the elbow of the "L", putting the horizontal 180-degrees out of phase with the vertical.
I'm not sure how the phasing is done on a professional vertical/horizontal antenna, but I will watch this on the Spectrum Analyzer and compare both methods.