DIY AM Transmitter for OEM Radio

[Ivan_B]

Since the OEM Philco tube radio was fixed, I was planning to install an AM transmitter, so that I can broadcast my own music into the radio. There are a few commercial solutions available for home and auto use but I don't like them. Inspired by this video, I've decided to make my own. The idea was very simple: make a small device which would work on 6 volt and broadcast MP3 from a USB stick.

 

Since I am not very electronically inclined, like the person in the aforementioned video, I've decided to rely upon readily available components. Here is what I came up with:

 

AMT-MW207 radio transmitter (these are available at various sources), bought my from E-Bay, from USA, for $27, shipped. A DIY assembly kit was ~$10 cheaper, but I figured that an already assembled version is better. You can order these even cheaper directly from China, but you'll have to wait for the delivery. Although, in my case, the postal service shipped it to Puerto Rico, by mistake, so I waited for an extra two weeks for it to return back to the mainland

 

MP3 player module, I've got this one for $6.49. There are plenty of different options available. I just needed something to play MP3 from a USB stick. Chose with this one because it runs on 5 volts USB power supply.

 

Power converter module. I chose this for $2.99. There are a lot of different options; I looked for two ports, high power output, and medium price. The plan was to power both MP3 player and the AM transmitter with the same power source (and preferably not directly to the car's battery), and it worked well!

 

Here is everything connected on the bench for testing:

 

And here is the final version, mounted inside a small metal box:

 

The sound quality is good! I am injecting the RF into the aerial antenna adapter to eliminate the unnecessary air gap. The transmitter is extremely close-range, so it would not work well otherwise, anyway. It seems that when I install the cover on, the sound quality gets worse. Not sure why, since I am transmitting the signal by wire. I suppose I just have no idea what I am doing here. I've left the cover off, for now, and will probably just cover it with cloth to keep the dust away. This way, it is also easier to change the USB stick, if I want to. I considered mounting it outside, but decided against that, so that I have everything inside a single box.

 

So, if you'd like to broadcast your own music into an old radio, this is very much doable.

[DJK]

This is what works for me using Spotify from my phone: MakerHawk Mini Amplifier Board Bluetooth Amplifier 2.0 2X50W 5V-24V Audio Power Amplifier Module for Store Home Theater Speakers $10.99 from amazon

[Ivan_B]

How do you get the signal into the radio, just connected it to the speaker? That is not what I wanted. Also, I don't like the necessity of playing around with the phone or other playback devices. My setup allows me to listen to the actual radio and, since I just uploaded 825 songs to the USB stick, it starts playing on its own as soon as I flip the switch

[vintage6t]

I was looking at the mp3 module you used. It looks like you're completely enclosing in an enclosure so no control of the tracks or volume?

 

If you do want track/volume control you can make a remote control panel very easily. The panel can be exposed or hidden within reach. Just get four momentary contact single pole switches of your choice. Mount them in a panel of some sort. 

 

Solder a two conductor cable on each of the switches. One wire on each side of the switch. When your done you'll have four lengths of cable to run back to your module enclosure. Solder each cable to a corresponding control switch on your module. One wire on each side of the switch. Alternatively you can do the same with a single eight conductor cable. Just keep the internal wires sorted by how you solder them to the remote switches.

[Ivan_B]

That's right, I am not using any controls, don't need to. The module seems to remember the volume settings, though, and the last track played. If you want controls and a display - there are slightly larger modules available with these, some have a touch-panel interface and a remote as well

 

I am still in the process of figuring-out why putting on the metal cover on the box slightly decreases the sound quality... Maybe I am tapping into my transmitter for wired signal at the wrong place? ?

 

Edited October 29, 2023 by Ivan_B

[FarmerJon]

Pretty cool, hope to do something similar down the road.

Does the volume knob on the radio alter the volume?

[Ivan_B]

Do it, do it now, you'll like it! ?

The volume on the OEM Philco? Of course! You can blow the speaker out with that thing. I am only listening at around 25-30% of the volume, right now. No alterations were done to the radio itself, what so ever, I am just feeding the radio signal by wire into the stock antenna.

 

Drove the car around town, today, the "radio" is working pretty cool. Although, I am picking some static from the running engine. Checked - appears to be unrelated to my setup because it is there even with the transmitter turned off, and it fluctuates with the engine RPM. This is probably the ignition system or the generator. I'll look into ways to get rid of it, over the week.

[FarmerJon]

I dont know the state of my radio- it was not wired up when car was car was rewired by Slob and Hack. Hoping to pull the dash this winter and get everything under there back to stock.

 

If you are running copper core spark plug wires and/or nonresistor plugs, they are likely to blame for your static. 

[DJK]

19 hours ago, Ivan_B said:

How do you get the signal into the radio, just connected it to the speaker? That is not what I wanted. Also, I don't like the necessity of playing around with the phone or other playback devices. My setup allows me to listen to the actual radio and, since I just uploaded 825 songs to the USB stick, it starts playing on its own as soon as I flip the switch

I use the Spotify app. My daughter down loads the music for me, I am electronically challenged. There is no radio in my car, just the amplifier, my phone and 4 speakers.

[Ivan_B]

2 hours ago, FarmerJon said:

I dont know the state of my radio- it was not wired up when car was car was rewired by Slob and Hack. Hoping to pull the dash this winter and get everything under there back to stock.

Sounds like a plan. Or, you can just take a look at your current radio to see whether or not it works... Basically, you need a working stock radio to go with the DIY AM transmitter route.

 

2 hours ago, FarmerJon said:

If you are running copper core spark plug wires and/or nonresistor plugs, they are likely to blame for your static. 

And this is exactly what's going on. Wires are copper core, plugs - non-resistor. I was sniffing around the car with another AM radio, I am getting the ticking/tapping noise from around the generator, voltage regulator, and the coil (sitting right next to my radio inside the cabin). I am still thinking about whether I should install shielded ignition wires, or try to put some filter caps on the coil, etc.

 

2 hours ago, DJK said:

There is no radio in my car, just the amplifier, my phone and 4 speakers.

Using a modern stereo setup is a good solution, especially if you do not have the radio in there. My car came equipped with the OEM radio (with a paper warranty tag), so the whole point was to get it working and then use it with my own music to enjoy the good-old warm tube sound

[Ivan_B]

Small update: I did some more tests with the ignition noise in the radio. Adding a filter condenser to the ignition coil power did not help. Neither did shielding the coil inside the car with some metal. Engine/body/exhaust grounds appear to be good. It seems I am getting the interference from the ignition wires, since my little digital AM radio goes dead if I bring it too close to the wires. I have to power-cycle it completely to get it to work again.

Edited October 31, 2023 by Ivan_B

[Dave72dt]

solid core or suppression wires?

[Woodie]

I added this device and it works great to blue tooth from. My phone.https://www.retroradioshop.com/products/am-transmitter-and-bluetooth-adapter-for-retro-vintage-or-antique-radios-1