What is a '67khz FM trap discriminator tap'? I think you mean a schematic for a discriminator tap with a 67 khz trap...
Anyway I played around with SCS (as it's more formally known) for a bit when I lived in Illinois some years back. I bought an external decoder which plugged into the Line Out of my old RF2900 Panasonic portable. Came up with a few things that were interesting...
One thing to keep in mind is that SCS has established several other offsets from the main carrier - if memory serves, they're on 47 and 92 khz or thereabouts. Therefore you need a way to tune the entire spectrum (up to 100 khz or so away) to find all the SCS and RDS services in your area.
Here's a kit from Ramsey...
SCA1C - SCA Decoder Kit - Ramsey Electronics
One problem with these decoders has to do with the structure of the FM signal itself - or rather, the strength of the main carrier. These subcarriers are often much lower signal levels than the main carrier, so it's important to be able to separate the two (sometimes more), or the main carrier might obliterate the subcarriers you want to hear. However these kits are an inexpensive way to get off the ground.
At one point, the late Dr. Bruce Elving (who passed away this past summer due to a major coronary) used to have an outfit that sold both kits and modified radios for SCS. He was the same one that published the FM Atlas year after year - widely considered to be the WRTH for the FM band. For more information, your best source would be the Worldwide TV FM DX Association - this club has a worldwide rep for being one of the best for this type of stuff. Their website, and some links from their club can be found in our wiki here...
DXing Above 30 Mhz - The RadioReference Wiki
I haven't touched base with these guys in years - I've even met Dr. Elving on more than one occasion during ANARC conventions. This guy knew his stuff down cold - oh and by the way, many of the tech folk at the WTFDA are hams as well...
best regards..Mike
