"We will often remind the reader that indoor antennas will always be inefficient, we are simply trying to improve on the result available."
Well, the 'locals' in this group have said loop antennas (magnetic rather than electric) won't work with the low power we have to work with, but I think with a properly-designed matching network and coupler, and large diameter copper refrigeration pipe attached right to the TX at its antenna connection (no loss, the coupled antenna 3' in diameter)..
It will take a fair chunk more engineering and running formulas, especially for skin effect on the matching network, but I really believe an indoor system like that should work quite well.
It will be relatively directional compared to an electric stick, so it will need to be oriented to serve the target audience.
Also, I really want to experiment with the "loop that isn't a loop" antenna idea ... i.e., a 1" copper pipe bent to approx 3' diameter, with a loading coil inductor att'd AND connected to the pipe at one end, but att'd and NOT connected at the other end.
An apartment-dweller could set up one of these as an art-object if done right. I've had some visions of what it might look like.
I like your loop antenna vision, Ken Norris, and that it could be made to look attractive as an art work makes it very desirable for indoors.
I have the unproven and perhaps mistaken thought that loop antennas for transmission have been found undesirable by experimenters at medium and high power, and not by low power experimentation.
The directional factor might prove useful so long as the antenna can be placed in a best location.
"The tree is a natural example of a Fractal design"
There are literally hundreds of papers written on this subject. Both the military and cell phone makers are very interested in them
The problem is one of time and materials. I worked out a scaled design for a circular fractal antenna for LP AM radio. However, the sizes I needed for AM BCB would be prohibitively expensive, and involved a heckuvva lot of work to make the parts, lots of soldering, etc.
The primary use of fractal antennas is in wideband microwave areas, which is why cellphone mfrs and military are interested. E.g., "smart" phones have to work on several different frequency bands ... obviously you don't want to put multiple antenna systems in them, so the wideband characteristics of fractal antennas are a good solution, especially as one can be made using industry-standard PCBs.
A very huge difference between fractal antennas used in Ghz compared to Khz.
RFB
....tried fractal ground arrays?
You could bury one heck of a "tree" pattern made from wire.
I certainly don't want to throw water on any antenna experiments, but an indoor antenna is a real unpredictable beast.
An indoor antenna is surrounded by aliens! Electrical wiring, plumbing, possible metal studs, possible metallic siding, etc. are MAJOR obstacles to the RF signal.
Additionally, the RF ground path is almost totally unpredictable, and probably will be poor in relation to the goal of providing a low loss RF ground counterpoise.
A long baseboard ground wire may provide a good counterpoise, much in the fashion of elevated radials for an outdoor antenna, but you are still contending with the huge effect of the shielding cage of the house.
It would be a welcome event to hear from anyone who has had meaningful success with an indoor antenna that ranges a significant amount beyond the house.
"It would be a welcome event to hear from anyone who has had meaningful success with an indoor antenna that ranges a significant amount beyond the house."
In another thread somewhere (which I can't seem to find at the moment ... I'll try later if I remember), I told of using a TH v.5 tx with the stock wire antenna tucked into an arched wood window frame from inside, The darned thing was quite listenable at 500 ft. from the house, and in one direction over a block behind the house and down that street to the high school, about 350 yards, and could be heard all the way down to Spring St. (our "Main St.") ... and that just after sunset ... but it got pretty noisy a little later.
"It would be a welcome event to hear from anyone who has had meaningful success with an indoor antenna that ranges a significant amount beyond the house."
As Ken noted, a TH using the supplied 3 meter long wire strung vertically along a wall, by itself can cover 500+ feet from the home easily. And that is with the TH and wire antenna INSIDE the house.
Even your 5K unit with a simple wire can shoot the signal 6 houses down the block and over into the next block, all with the 5k set up indoors with that simple wire.
But I think you know that already.
RFB
The Indoor Antenna page linked at the start of this thread has yet to be updated from its very undone blankness, but there is now something to add to the page.
In various other threads we have discussed ground radials and other aspects, and there's now enough information to document one of our indoor antennas.
Using the internal AMT3000 inductors and a baseboard floating ground we achieved 69 dBm, up from something in the 50 dBm range from earlier.
But tonight we installed and tuned our truangular hand-wound loading coil and have achieved a record 71 dBm on the Spectrum Analyzer.
All the details about this experimental antenna will be written up and published as time goes by.
Right away we move to the next indoor antenna, different in many ways from the one just completed.
"Right away we move to the next indoor antenna, different in many ways from the one just completed."
Looking forward to it!
RFB