Lionel 455 kHz signal choice for Legacy/TMCC?

Jeffrey Fikes posted:

I just noticed after reading the article about how TMCC/Legacy works that Lionel uses frequency shift keying with a center frequency of 455 kHz. If memory serves me correctly-- that is the IF frequency of Superhet AM radio receivers in the U.S. I was just curious as to why that frequency was selected?  AM radio has significantly declined in the U.S.-- but maybe world wide- these components (coils in particular) were readily and cheaply available-- or maybe in this day and age there are chip-sets that function at that frequency? Or maybe that frequency allowed them an easier path to FCC approval?

????

Jeffrey in Alabama

 

At the time the components were conveniently available.  There was a very specific Japanese Radio Corporation radio receiver IC that made this all work nicely.  It is of course obsolete now.  

Lou N

Lionel is still building TMCC/Legacy equipment, they must be using something.

Jon Z figured out a replacement but at the time the radio board was still patent protected; hence no interest in determining what it is.

It is however used on the ERR boards.  If you have one, I don't, take a close look.  The old chip was JRC3376.

Lou N

Apparently, it's the Lansdale MLE3372-5P, here's the datasheet.  This is on the MiniCommander II.

Lansdale ML3372 Narrowband FM IF.pdf

gunrunnerjohn posted:

Apparently, it's the Lansdale MLE3372-5P, here's the datasheet.  This is on the MiniCommander II.

Lansdale ML3372 Narrowband FM IF.pdf

 

Thanks for the datasheet.  That must be it.

Lou N

I can't pretend to understand how all this works, my experience with AM sets dates back to the 5 Vacuum Tube AC/DC sets sold long ago. I just remember they had 455 kHz coils in cans with a screw adjustment on the top for peaking/alignment. That they have been able to incorporate all the necessary circuitry into an IC is quite amazing. Thanks for all this information. --learn something every few minutes.

Lou, that's the only possible IC that would be the receiver part, it's right next to the LT455U ceramic filter.  There's also the PIC, four diodes, a couple of opto isolators, and a pair of 8 pin mystery IR parts that I can't find, they must be the drivers.

gunrunnerjohn posted:

Lou, that's the only possible IC that would be the receiver part, it's right next to the LT455U ceramic filter.  There's also the PIC, four diodes, a couple of opto isolators, and a pair of 8 pin mystery IR parts that I can't find, they must be the drivers.

John,  My guess on the mystery parts is IRF7319, a P-N power mosfet half bridge.  I've used them in DCC decoders.  They did show up on Digi-key.

Lou N

They were IR P138T, but that number is a mystery, so maybe there's just a code.

Old thread, but I cracked the code.   I was looking up what is apparently the date code, DUH!  The part is the F7343, and it's readily available.