you may reduce the audio input level by managing the Volume control.of your mp3 player.thsignal strength or streo lamp would be an indication of signal tuned. the attached mods have specific ref to siliconchip's micromitter schematic. I thanks the originator of these mods.
Sarma,
Thanks for the document. There is a lot of good info in there. Unfortunatly, for me to take advantage of most of it, I would have to had known about it before I built the PCB. If I have to go back to square one and start over, I'll be sure to make some changes. I attached to this post a zip file with the .sch, .brd, and all the .lbr files in the project. I also included a few datasheets for components used in the circuit. I actually compressed everything with Winrar but I had to rename it zip because rar is not a valid file type for upload on this board. If I forgot a library and you get errors, just let me know and I'll upload it.
Glad your making progress. One thing to consider, going to an air core inductor may reduce your Q of the inductor, this could result in instability in your VCO. You might need a scope to see this on the VCO control voltage TP1. One other thing you might try is to remove one winding on the cored inductor.
Mike,
Well you were certainly right about the air coil instability. If I even sneezed within 5 feet of it TP2 would go off by 300-400 mV. Because of that, I went back to the adjustable coil with the ferrite core. I couldn't modify the existing one but I improvised one. I had some nylon spacers that I drilled out and tapped to make the coil form. I then used 1.5 turns of magnet wire and I was able to get the voltage at TP2 pretty darn close to 2V and it's stable. I haven't seen the voltage at TP2 drift more than 50 mV at any point. I secured everything down with some hot glue so I hope that part of the circuit is good to go now. I did have to use a thinner gauge of magnet wire than what was called out in the article but I hope this won't be a problem. Please tell me if you think otherwise.
So, TP2 is now a stable 2V but I'm still getting the annoying warbling tone. I made a discovery sort of by accident. I don't usually troubleshoot this way but I found out that if I place my finger in the vecinity of R15 and R6 (as shown on my schematic), the warbling went away and I could hear a very faint music coming through the radio. It was a little staticy but mostly OK. I adjusted R12(once again as shown on my schematic) and the music got slightly louder but was still pretty faint. If I removed my finger, the warbling returned and I could no longer hear the music.
I'm not sure if my finger there added capacitance or what but I hope that little clue might help you zero in on what's going on here.
- Does the stereo receiver pilot light turn on when your testing?
I don't have a radio in the house that has a pilot light so I had to go out to my car to test this out. The short answer is no, the stereo indicator is not present on my car radio. I was able to get it to flicker for a short while by holding my finger near R6 & R15 and adjusting R12. I also noticed if I grabbed the antenna, it flickered on and off a few times. Maybe part of the problem is I need a longer antenna. What do you think? Currently, my antenna is about 2.5 ft of 20 AWG stranded copper wire.
- Have you tried the unit with no audio in. Should get silence
I have tried it with no audio input but I do not get silence. I get the same repeadative warbling tone.
- Do you have access to a scope?
Yes, I do. I have an old Tektronix T922 that I bought at the surplus electronics shop for $40. It's certainly seen better days and not all the time and voltage divisions work but it would probably do the trick for some basic troubleshooting. What should I be checking for with my scope?
We keep making slow but steady progress here and it seems the end is in sight. Thank you very much for all the help. It's greatly appreciated.
P.S. This is my first RF project in case you couldn't tell.