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Post by Admin on Mar 17, 2020 14:23:11 GMT
Using Electronics by Harry Zarchy
The publication linked above is full of simple electronic circuits you can build.
This was my favorite book when I was 12 years old, talk about way back.
Checkout circuit number 20, an AM broadcaster. This was the first Part 15 transmitter I ever built.
Constructed on a piece of wood, using little nails for the tie-points.
I only had to buy the loopstick antenna coil as the rest came from old radios and TVs.
Great fun...
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Post by Boomer on Mar 19, 2020 6:46:07 GMT
Let's OscillateThat's about the simplest of broadcasters you could build, just a one transistor oscillator, and a classic circuit in its many forms. I built a few of this type from junked parts, and one used antenna bar and tuner cap from a transistor radio I must have trashed. I also built on pieces of wood with penny nails, dad had a pickle jar full in the garage. Just wrapping the component wires around the nails didn't give a good connection, so I tried soldering them, but the solder didn't stick the wires to the steel nails, though it melted into the wires underneath the head of the nail, and the connection was fine. Radio Shack came out with something that's probably a similar circuit, with a tunable loopstick and a fixed capacitor. It was part of their early P-Box kits around 1970. I built the fancy 'AM broadcaster' version that came out later, when I guess Radio Shack realized all kids wanted to be DJs. It says the P-Box version went 20 feet, and the Broadcaster I got was supposed to go 40 feet, but it barely went outside of the house, just one room coverage. What kind of signal did you get on your build?  Boomer
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Post by station8 on Mar 19, 2020 13:48:25 GMT
Howdy y'all:
I had both of the of the radio shack kits
I had the p- kit 28- 103 am wireless microphone ( boomer the picture of ).
Do not have the kit anymore but still have the original instructions little ruff.
I also had 28-209 am radio broadcasting kit for $7.95. ( Science fair kit )
I still have three of the original 28-209 kits two in there complete boxes.,
I also made this tx cover 1 to 1 and 3/4 mile range with my own antenna design.
And this tx held up great in all kind of weather for me ( snow & electrical storms ).
Fun kits to play with and i enjoyed them
The good old days i wish they would come back for good!.
Enjoy and have fun
Station8
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Post by Admin on Mar 19, 2020 14:56:38 GMT
My Harry Zarchy home built covered maybe a 300 foot radius. It was tied to my outdoor crystal radio antenna, 30 foot wire up about 15 feet.
My buddy lived across the street, 3 doors up, and he could hear it.
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Post by station8 on Mar 19, 2020 20:36:20 GMT
Howdy y'all:
That's neat mram.
I also have a graymark 533 am tx it was a 1980 kit
I think i have four of them around in kit form
These where also nice kits as well.
Metal case top and bottom used four transistors 2sc1815y
Very good audio quality
Was a dial to tune freq like on old portable am radios.
Enjoy
Station8
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Post by Boomer on Mar 20, 2020 2:37:33 GMT
Pre-teen powerhouseCool about the range Dr. Bob, I would have been happy to get that after being disappointed that my kit's signal was almost nil just outside of my house. I only got more range when I wrapped the transmitter's antenna wire around our rotary phone, and the signal followed the phone line a bit down the street. Not sure if I tried picking up my AM broadcaster with a crystal receiver at that time, but that probably would have sounded real good! Those simple AM transmitters have incidental FM going along for the ride, making the bandwidth wider, so it stands to reason that a crystal radio, being wide band could pick up all of the oscillator's signal. I found that highly selective radios sounded bad on oscillator transmitters, muffled. Antique Radio Forums (ARF) has something on the Greymark that Section 8 is talking about: www.antiqueradios.com/forums/viewtopic.php?f=4&t=362107That has something I hadn't seen in a P-15 AM band transmitter before, a double-tuned output circuit! Two AM oscillator coils coupled together, through a 10 ohm resistor. That's novel, but those oscillator coils (red screw cans) were probably cheap and that circuit would have lowered harmonics a good bit, and made the signal more stable. Old tube-type Greymark, model 515. www.smecc.org/graymark_transmiter.htmNo more 'fatal', than a tube-type table radio with phono input. I would have liked to see the circuit have a separate oscillator driving the final for more stability, lowering FM and antenna tuning effects. That would have required more parts, and a 9 pin tube socket for a dual triode like a 12AU7, and maybe a shielded oscillator coil, but that might have been good for a deluxe model that sold for a few dollars more. Boomer
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