Micro Power AM Transmitter Redux

Some clarification on what I’m looking into on these part 15 radio transmitters. No crystal clarity for me. Think more late night 1970’s sound under good propagation conditions, Like when the pirate stations were coming in clear for the few hours of night as was possible.
I’m after that sound and trying to recapture the feel of the moment, A good DX capture on a station 3 states away kind of sound.
Not any of this new digital AM  crap. Stuff the over forty and over fifty somethings can relate to.  Suzi Quatro belting out “The Can Can“, The Bay City Rollers ” Saturday Night“, or The Sweet’s “Fox on the Run“. (Also those musical choices are a good measure of your AM transmitters capabilities.)
I ran some serious radios back in the day with some real serious antenna wire.  All of it allowed me to hear some sounds not heard on my “Top Forty” stations nearer to home.
For me the “70’s were the last hurrah’s for AM listening, It was dying by the mid “80’s”. All of that said, Here’s Some ones  efforts at AM modulation on a mighty mite.


Not Bad at all.
In the next vid Is a pretty good explanation of AM or Amplitude Modulation.
Though they use chips in their transmitter design. I avoid almost all op amp chips unless I’m in a hurry.
I would rather rather use an old school discrete transistor design to replace the LM386 amplification in my radio.

Cool.

Right now I’m waiting on a parts order so I can move the radio off the bread board an into a finished state. I need a better variable capacitor for it. The old one from a cheap transistor radio is too noisy.
That will add another $15.00 or so to the cost of the transmitter, but will be worth it in the end. I may be able to find something to work at the flea markets tomorrow.
Though I assembled the prototype from salvaged components, I’m going to use all new when it gets put into the case. It will be worth it.

Lessons:

Small value capacitors are your friend.

I had to put a new sound card (PCI) on the computer as the onboard sound was noisy going into the amplifier stage. Found out when I used a portable mp3 player instead as a source.

Heat is the enemy. Use a good heat sink and thermal grease on the transmitter stage transistor.

Put a ferrite bead on the patch cord to minimize stray interference at that area. (1 turn)

I haven’t decided whether or not to drop the transmitter crystal as of yet, as the circuit will produce a carrier with it jumpered out. I’m trying to figure out which config will realize the “Retro sound” best.

Future Mods:

Drop the LM386 chip for an old school built op amp for the buffer amp stage.
Remember to install RF shields through out.
Multiple audio source with mini mixer with faders.
Keep it simple.
Keep it modular.

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About theelderdragon15601

Bleh.
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2 Responses to Micro Power AM Transmitter Redux

  1. Thomas Icom says:
  2. Elder Dragon says:

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