Warning!
High Voltage!
Use extreme caution in building and operating.
EMAIL FROM CameramanLink
Hi Rick
I have a few questions about the transmitter I wanted to clear up before I start building. I checked out the schematic and pictures, and they didn't seem to match up exactly.
1. One side of the audio input looks like it's connected to the chassis in the photo, but it's not referenced to ground in any way on the schematic. Should I connect one side (ground side) of the audio input to the chassis?
2. The 4.7mfd cap on the audio input transformer looks like its positive side is connected to the transformer while the negative side is grounded. However the picture above the schematic shows it the other way. Does it just look like that in the photo?
3. Why is there a red wire coiled around the input transformer's capacitor? Is this necessary for proper operation?
4. Do I need to use a shielded wire to connect the oscillator to the grid of the 6L6?
5. Is the capacitor inside the Quaker Oats box connected to the antenna through the screw?
6. Can I use a regular FM receiving antenna for the radiating antenna? This is what the antenna looks like in the photo.
I was also wondering how I could connect audio devices with a higher impedance output to the transmitter (such as a tape deck or preamp). The audio output transformer you used as an input transformer looks like the 3W 2.5K to 8 ohm surplus one they sell at AES. Would it be possible to add a modulation amplifier before the RF power amplifier? I appreciate you taking the time to read this. I just wanted to find out this kind of information so I don't have to try to fix something after it's too late. Thanks!
My reply
CameramanLink Yes you’re right.
1. It is connected to earth ground. I think I ran out of three lug terminal strips and just use what I had. I would recommend not grounding either side of the audio input.
2. The 4.7 is in backward in my transmitter. It is at least a 250 working volt capacitor so it does not matter. However please observe the polarity in the update drawing if you use 50 working volts or less.
3. That was a shielding experiment. I don’t remember why I did that but it had no effect and I was too lazy to remove it.
4. Try it with out the shield. I think that was another experiment that did not matter.
5. Yes the capacitor inside the Quaker Oats box is connected to the antenna through the screw.
6. Yes you can use a regular FM receiving antenna for the radiating antenna or a length of wire.
Sure you can add an amplifier for high impedance equipment, we’ll have to work something up.
Thanks for your questions,
Rick
