I was fiddling with this transmitter sometime last year, but it performed more like a jammer than anything else. Moreover, it wasn't stable either.

Yeah I more or less had the same issue, can promise you this MK-XI version will blow your socks off...

Here's a quick & dirty recording of the audio taken by camera mic then converted to a Mp3, remember mic response is limited, so it has a hollow sound that isn't really there... This is using a 10ft antenna hanging inside my garage out back, approx 125ft from receiver(my TV tube radio)...

http://amradio.freeiz.com/transmitter/lm386aud.mp3

Tom

Sounds very good to me, great job as always...Alan

Well, it sounds really good, and it's remarkably better than what I had.

Really nice work Tom. Remember I said "Tom, you're going to be pleasantly surprised." I was pissed too at how well it worked, and mine was bare bones. You have perfected it.

Thanks guys, I doubt anyone is going to be disappointed with this one...

Mike you were correct, build it right and it'll perform better than is imaginable... By right I mean lead length is important, overly long leads especially at the input will possibly pick up stray RF and cause a major howl...


Tom

Tom,

It seems that anytime in the past I built something from a diagram that came from a magazine, or book, it didn't work at first. Usually it was an error or omission in the diagram. I always expect that I will have to go through and spend a great deal of time to figure out the problem. I have to say, the little tube transmitter that you designed worked perfectly the first time and it still does. Good work !!

Ed

Tom and Bill,
Thank you for the design and this kit, hope to be able to return the favor sometime.
I had laid the parts out on a solderless breadboard and all I got out was some motorboating - set it aside but came back to it today.
I had connected the output choke from the LM386N to pin 1 of the oscillator versus #14 - a senior moment.
So the transmitter is working very well now on the breadboard, strong and clear after some adjustment of the antenna trimmer.

I intend to marry this one with an MP3 player in a suitable enclosure w/power supply... I'll update with photos when that's done.

Thanks again,
-Sam T.

Glad to hear it's operating...

One thing not mentioned is antenna tuning, unlike the tube units that dip, this unit's current draw will be highest when properly tuned... Should get a reading of approx 11ma at 9v... This is for the 1000Kc osc, I'm assuming the 1.228 will be similar but I haven't actually monitored the current for that version...

Tom

K4YDO said: "It seems that anytime in the past I built something from a diagram that came from a magazine, or book, it didn't work at first. Usually it was an error or omission in the diagram. I always expect that I will have to go through and spend a great deal of time to figure out the problem."


Yes, I know the feeling. I don't know of anything that came from a Radio-Electronics magazine that actually worked for me.

35Z5 said: "Yeah I more or less had the same issue, can promise you this MK-XI version will blow your socks off...

Here's a quick & dirty recording of the audio taken by camera mic then converted to a Mp3, remember mic response is limited, so it has a hollow sound that isn't really there... This is using a 10ft antenna hanging inside my garage out back, approx 125ft from receiver(my TV tube radio)..."




This sounds like something that came straight out of a recording studio! Are you sure that you didn't have the microphone lying next to some CD player? It sounds totally awesome! Drool!!!

Awesome sound.

Makes me want to build one, but I don't really need another AM transmitter, but would be a good backup in case my two tube unit ever develops a problem.

25v caps OK for this?

Larry

Except for the antenna coupling, 25v is OK, at that position I used a 100v but a 200v is probably best... The Tx will work just fine without it but if antenna is grounded, you can kiss the osc goodbye(yeah one gave it's life in testing)... Voltage on antenna is fairly high so use at least a 100v, I have checked the 100v in the breadboard several times, no problem at roughly 500hrs...

Tom

Thanks Tom.

Larry

Hey I got this pieced together on the breadboard.
The MP3 player needs five volts, so I tried running the transmitter at 5V too.
Seems to work fine, drawing ~35ma running a 4GB SD card.
Of this, only about 8ma is being drawn by the transmitter itself.
Does that sound right?

Thanks,
-Sam T.

Not to hi-jack the thread.. but I just have a brief question about the 4gb-SD card.

I was using a 2gb SD card on the same kind of mp3 player.... and tried to copy a bunch of my Mp3 files from my computer to the SD card... but after about .... maybe 80 (wild guess) or so files were loaded on it, it gave me error message saying "could not create file"
So I checked to make sure it was not getting FULL and it was not... only about 1/8 used space.

So I tried re-formating the SD card and the same thing happened at the same point.

It seems to have a limit on the number of files or file names it can make.

Are you familiar with this problem?
Edit update;
Googling around I may have found the solution.
They say the root directory has a limit ... but creating a sub-directory and loading all files in the sub-directory should work...
I'll try it and report back.

Update-2:
Yes that works. Making a sub-directory allows seemingly unlimited file count.

In the ball park for sure...

At one time I'd have said 5v was too low, but recent testing proved those osc are stable at 1.8v or less... At 5v, voltage out of the LM386 should be around 2.5v...

Tom

Here's something to make tuning easier, install LED in B+ feed to LM386... Led will be brightest when antenna tuning is peaked(which is opposite the tube transmitters that we dip current)... Causes no issue but does drop approx 1.5v depending on color of diode, for battery operation a AA in series with your 9v is a good solution...

Another option is install the LED in place of the 150uh coil... This also works fine but due to the output of the LM386 being approx half of input voltage, B+needs to be raised closer to 12V...

Additionally unless one is using a very high impedance source, the input resistors can be as low as 1K and the gain pot 5K... That's what being used on the breadboard, performs just as well if not better than the higher values...



Tom

A bit late to the party, sorry. Pardon my ignorance but can somebody tell me how far away from the frequency of a local station would this would need to be to avoid problems. I have a powerhouse at 980.
thanks,
Sandy