I hope that I'm not the only one getting a working transmitter out of this.
I kept the non working ones, hoping to modify them (based on what was done to make one work). Who knows if I'll ever get around to doing that.
I still haven't done much with the transmitter. I have the appropriate crystals but haven't had the time to solder one in (see the new thread I started on moving).
The last one sent, finally, did not have audio distortion issues. Instead what I got was a transmitter without a functioning 12MHz crystal and the audio level (at 17MHz) being way too low. Being as it was never disputed formally on eBay, because I dealt with the guy in good faith and just as I was about to give up he did send another one, it's just going to have to be another 'back of the junk closet' project for some point in the future if I ever get bored.
I'm not sure if 'luck' is the term but anything to do with amplitude modulation has just never really worked out all that well for me.
Cheers everyone and hopefully, happier broadcasting to you all.
This was mentioned earlier, I think, but if a schematic of that ISM SW transmitter could be drawn and posted, a few of us would love to pick it apart.
Drawing up a schematic of this Turkey transmitter (pun intended!) is way beyond me, but my offer to send the actual transmitter to someone who'd like to "pick it apart" still stands. Lemme know!
I was litterally within hours of sending my Turkish SW transmitter to a member of this forum who agreed to take a look at it ---- when I thought of one more thing to try. I remember 45 years ago when, as a high school kid, I was building a pirate radio station. We were trying to figure a cheap way to feed multiple audio inputs into a single microphone input on the transmitter. ( a mic, 2 tape decks and a turntable with preamp) I was a kid with no money, so a Lafayette 4 pot mic mixer that ran off a 9v battery became our "board" for $5.95. I don't know how, but that setup worked great back then on the 1st try! Well I still have the mixer, so I said "What the heck -- I've tried everything else". I hooked my portable cd player to the mixer, the mixer to the transmitter and fired everything up, and Praise the Lord IT WORKS!! I have good fidelity, a nice high modulation percentage, and NO DISTORTION!! (unless I purposely overload it) The input knob of the Xmtr is all the way up, and the knobs on the mixer run about 2/3rds open.
Anyone have any ideas as to WHY this works when everything else would not? Is it because the antique mixer's output is much closer to mic level than line level? If so, why wouldn't just turning way down a line level mixer's output work? Or why wouldn't this xmtr fed directly from the portable cd player with the volume turned way down work, like it was designed to accept?
I'm glad to have found a way to make this thing work, but why did I have to go back to a 45 year old mixer to do it?
Thanks to everyone for keeping this Pt 15 SW idea alive. Gimme a couple of weeks to string up a dipole and/or my Isotron, and I should FINALLY be on the air. And if nothing else has worked for you, (seems to be the case for most...) get one of those antique mike mixers from e-bay and go for it! See you on the air!
rlkocher it is so wonderful that you came up with the idea to try that old mixer!
Whatever you found can be duplicated for others with this transmitter, and we even have a chance now to solve the mystery by carefully going over the details of what worked and what didn't.
This has been a topsy turvy thread, but with more than one good outcome!
The distortion of the audio when connected to some sources and not others, considering that the input volume control was adjusted from min to max, would lead to suspicion that some other attribute of the audio connection is the cause. One might be that if the input to the transmitter is DC coupled and this is connected to a source with the output at DC ground (such as a low Z speaker output) then the bias for the amplifier in the transmitter will be changed which could cause distortion.
Not all audio outputs are isolated from DC ground but all audio inputs should be. This is done with a series capacitor and maybe the transmitter designer left this out. The Lafayette mixer probably has a series capacitor in the output lead which serves the isolation purpose.
It might be worth while to try the transmitter again with a source which did not work with a series cap of 2 to 10 uF added in series with the input with the + lead connected to the transmitter input.
Neil
Perhaps the transmitter audio input stage level control is POST input stage. Meaning, the audio signal goes directly into the amplifier and the output of the amplifier feeds the level contol.
If that's the case, the level control would have no effect on how much signal is fed into the amplifier, only what's coming out. To much signal in would overload the stage regardless of where the output level control is set.
Have you tried an attenuator at the transmitter audio input?
I didn't try attenuating the output of the line level mixers 'cause I thought I was doing that when I was bringing the faders down to almost nothing. Maybe not. I'll try that next. Will also try the cap in series route. Some good ideas coming out now. At this rate, we'll soon have everybody's transmitter working right. Thanks guys!