BCD996T Mods

Status
Not open for further replies.

n2nov

NYC/NNJ DB Admin
Database Admin
Joined
Dec 18, 2002
Messages
688
Location
Staten Island, NYC
I currently have the disciminator tap mod done. However, I am looking for guidance on where I can get information on the 67Khz FM trap discriminator tap so that I can investigate better the FM broadcast band subcarriers (RDBS, etc). Any help would be appreciated.
 

ka3jjz

Wiki Admin Emeritus
Joined
Jul 22, 2002
Messages
24,792
Location
Bowie, Md.
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
 

n2nov

NYC/NNJ DB Admin
Database Admin
Joined
Dec 18, 2002
Messages
688
Location
Staten Island, NYC
Thanks for answering, Mike. SCA/SCMO (in Canada) is on 67 or 92 Khz and RDBS is on 57 Khz. The IBOC OFDM carriers can take up anything from 50 to 200 Khz (that's right, the guard band is fair game per FCC). I am looking for the spot on the 996 circuit board to pick off the WFM demodulated signal before the non-FM broadcast stuff is scrubbed clean. Typically in a consumer FM radio this would be called a 67 Khz trap. Any ideas where I can pick off this raw WFM signal on the 996 for use with an external board like the Ramsey unit or similar? Thanks again.

BTW, Bruce Elving passed away about a year ago.
 

ka3jjz

Wiki Admin Emeritus
Joined
Jul 22, 2002
Messages
24,792
Location
Bowie, Md.
Re Bruce Elving - he died in July 2011 (see wikipedia).

No idea re the tap -but once again, unless UPMan comes up with it, your best bet would be the WTFDA. They have their own forums.

By the way, if you have a line out on your stereo, guess where that comes from? Aww, you peeked hi

best regards..Mike
 
Status
Not open for further replies.
Top