Low power mono FM transmitter distortion

Bob D. · 2010-07-21T00:53:58Z

I have a modest collection of vintage FM radios/tuners. I home brewed a low power mono transmitter to play my mp3s on them. Up to now I've been just ecstatic with the fidelity of results. But I've run into ONE song that produces substantial distortion. This is a beautiful tune by Julie London called "Cry Me a River". Played directly into my HiFi system, the sound is fantastic. Played through my little transmitter, the S's and T's are distorted unless I turn the modulation level way down. (BTW, I tried one of those Ipod type car modulators with this song, and the distortion is even worse!) The only theory I have is that the recording must have a lot of energy beyond 15 KHz on the S's and T's of Julie's voice. Perhaps this is blowing up the bandwidth beyond what the radio can handle? I have a single pole roll off at 15 KHz that counter acts the boost from the pre-emphasis circuit above 15 KHz, so above 15 KHz the response flattens out but does not fall. Maybe I need more substantial filtering above 15 KHz? Does anyone have a good brick wall filter design for this application? Or maybe a better theory of what's causing this distortion? BTW, how do the commercial stereo kits filter the L+R audio source before adding in the pilot and subcarrier? Bob D.

Page 2 / 2 Prev

temp

Last Post by Anonymous 16 years ago

16 Posts

2 Users

0 Reactions

2,147 Views

RSS

Anonymous

(@Anonymous)

Posts: 0

For our operation Winamp is set to mono mode, which therefore supplies only mono to Stereotool plugin, and because I want to process for AM transmission I use the selectable and changeable Bandpass Filter to allow 88 to 11,530 Hz. I also believe that Stereotool can be set to process mono within itself, because the Stereo Processing section can be turned off.

Because Winamp can be run in multiple instances, a second running of Winamp would allow a totally different Stereotool config, maybe for stereo FM.

There are probably even more creative arrangements than I have discovered.

Posted : 23/07/2010 6:21 pm

Page 2 / 2 Prev

13 Forums
7,740 Topics
63.5 K Posts
65 Online
2,249 Members

Forum Icons: Forum contains no unread posts Forum contains unread posts

Topic Icons: Not Replied Replied Active Hot Sticky Unapproved Solved Private Closed