Hi all,
A bit off the subject of part 15 stuff since radio and RF energy are not involved but I thought some would find this interesting.
Hi all,
A bit off the subject of part 15 stuff since radio and RF energy are not involved but I thought some would find this interesting.
On Thanksgiving day I was accused by a family member of "being older than dirt". My response was "yes, but you should have seen the new dirt before time turned it to dirt. All you see now is dirt that has turned to dirt". I think he is still trying to figure out that one. Anyway, for those of us who are older than old dirt (which was once new) here's my recollection of something I tried back when kids had to build their own neat electronic stuff.
I had read in a magazine (PopTronics or Radio-TV or some such thing) where one could build an inductive headphone system for wireless transmission of programming. The idea was to build a giant transformer in a room with the secondary worn on a headband and feeding earphones. So, I tried it. Copper wire was free to me since when the phone company replaced or repaired service drops they left the wire in the drainage ditches so I had an almost unlimited source. (They also discarded working No.6 cells removed from the wall crank phones so I never was short of DC power.) I wound several turns of this wire around the perimeter of my basement laboratory and connected it to my tube type car radio (bought it for a quarter at a junk yard) which was adapted to be my "home entertainment center". So much for the primary.
The secondary was built on a coil form salvaged from the lid of a waxed cardboard gallon ice cream container. I used some 40 gauge magnet wire left over from a Tesla coil project (first place at the science fair) to wind a multi-turn secondary. My headphones were WW2 leftovers. These were incredibly sensitive. They had a mica diaphragm and were driven by a coil with an armature connected by a stiff wire to the center of the mica. They were so sensitive that if I touched one of the phone tips I could hear 60 cycle hum (back then there were no Hertz, just cycles per second). So my receiver was superbly sensitive, yet it didn't pick up any interference..
It worked and I was pleased with my technical skills which allowed me to pull this off. But, since I had a part 15 AM transmitter (KnightKit) and one of the first transistor radios of the era it turned out to be only an interesting physics experiment since I could have my wireless experience by more elegant means. The article even mentioned using coils in quadrature to achieve stereo but I didn't go that far.
Things such as this used to excite my imagination and had to be tried even though there was very little practical use for them. I hope you found this interesting and thanks for indulging the ramblings of a long time experimenter who is arguably older than dirt.
Neil
Neil, you've fired up my old dirt imagination (not dirty imagination).
Let's just say you loop your primary around the attic, fed from the audio source downstairs. The secondary coil would feed the Part 15 transmitter by the chimney antenna, and you'd have a wireless studio-transmitter link (STL).
After all, long runs of unbalanced audio lines are inadvisable and converting and un-converting to balanced audio line might be more trouble than driving a loop of wire with a 3-watt 8-ohm amplifier.
It certainly would be an interesting installation.
I remember a similar PopElec article using a step up transformer and a couple of ground rods to broadcast in the dirt! I was able to pick it up at the neighbors house 100 feet away,but with some hum and every kind of appliance motor screaming away. It got a little better when we used the electrical ground on one side of the groundrods. Then we upped the power to a 300 watt PA amp and a bigger transformer putting 6 or 700 vac in to the ground rods,worked pretty good until we started coming through neighbors stereos,intercoms and the neighbors sink!!!
Lee,
I tried to try that. My plan was to use the house water pipes as a ground and a buried electrode as the active element. I went to the back of the property and dug a huge hole, filled it with aluminum foil and salt and several ground stakes. I waited a few days for it to settle and was ready to give it a try with a 48 watt audio amplifier but it was not to be. Turns out that my electrode was placed in an easement and the stars aligned such that a trencher ripped through my electrode while doing the install on a new gas distribution line just days after my installation. The workers probably thought they had plowed through a trash dump!
I never got a chance to try it for real. If I recall this method was used by hams during WW2 when on the air transmission was banned.
I also experimented with part 15 fuses for pyrotechnics, homemade and store bought. Things such as this would probably result in the young experimenter washing police cars these days. Back then, no one cared...it was part of growing up.
Neil