Bob's radios : AM Transmitters
I have the misfortune of living in a market with no AM music stations. We have 2 all news (one french, one english), 2 news/talk (one french, one english), and in 2001 our oldies station switched to all sports talk. ICK! While rumours of the return of an oldies format continued to float about, I found myself surrounded with many radios I loved to look at, but couldn't stand to hear.
It became obvious to me that I would have to control my own airwaves, and broadcast material myself.
Click thumbnails to see full size images
This is my version of the AES wireless broadcaster. Based on a 1930's phono oscillator, it was a simple to assemble kit. It uses a 12SA7 tube. I dug through the junkbox for a switch and a light, and I opted for a project box instead of the pine board supplied with the kit. The antenna is an NOS car antenna.
If you're going to have it in the same room as the radio, it does an ok job, but the sound quality and range didn't do it for me.
Kit available from : Antique Electronic Supply (AES)
the thing looked idiotic sitting near the computer and I couldn't hide it well enough. Those bright "On Air" lights looked ridiculous.
It was very close to what I needed....
In the fall of 2002, I discovered (thanks to a discussion in rec.antiques.radio+phono ) the "Wild Planet Radio DJ". A small AM transmitter with tape player, microphone, sound effects and line inputs. It sells in toy stores for about cdn$30. I've seen it online for us$15. After much reading both in the discussions and websites dedicated to this thing, I went & picked one up. It's obviously a toy, but I was quite impressed with the sound quality & range. I was finally able to get a clear and usable signal all over the house.
(By the way, that's NOT me in the picture!)
The only problems I had with it were:
- It only broadcast on 1610 AM. a problem for old radios that only go to 1500. Also, we have a station on 1610.
With the help of the websites listed below, I found out that simply changing a crystal will solve my 1610 problem. So I swapped in a 6Mhz crystal ($.99) and it would now broadcast on 1500. With that solved, I set about making it look more worthy of the company it would keep. It's a well-known fact that you can't really expect to have a big purple toy DJ in the same room as an Atwater Kent and still expect people to take your hobby seriously...
So out came the Dremel and the soldering iron, and this is what I came up with. It's now 1500/1610MHz switchable, the "On Air" LED is a simpler indicator, and the Volume & power switches were replaced. The microphone, tape deck and sound effects are gone, since it's going to be fed by the computer or MP3 player all the time.
(By the way, that's still NOT me in the picture!)
The only thing left is to build a well regulated and filtered 6v power supply, and the batteries can go.
Helpful sites on the Wild Planet radio DJ:
Wild Planet Toys
Medium Wave Alliance (See engineering section)
Jonathan Smick's wonderful dissection page (gone, but the link gets the archived page)