The ProMini Air Transmitter and Receiver are now Compatible with Stanton Cab (S-Cab)

Introduction

The Stanton Cab (or S-Cab) is a series of dead-rail transmitters and receivers developed and sold by dead-rail pioneer Neil Stanton, Ph.D. S-Cab products are available at this site.

Stanton offers a hand-held transmitter, the S-Cab Throttle, specifically designed to transmit to S-Cab RF receivers. These receivers include the S-CAB Radio Receiver (LXR-DCC) and Loco Receivers for HO, On3, On30, and some S-scale installations. Also, Stanton will provide an S-Cab receiver coupled with decoders for larger scales. The available options are discussed on the S-Cab website here.

The S-Cab Throttle and receivers operate at 916.48MHz or 918.12MHz (single frequency only!). The former frequency is close to Airwire Channel 16 (916.36MHz), and the latter is the same frequency as Airwire Channel 11. However, Airwire hand-held transmitters WILL NOT WORK with S-Cab receivers at either Channel 16 or 11. And Airwire receivers WILL NOT WORK with the S-Cab Throttle.

I successfully determined RF settings that allow the ProMini Air transmitter (PMA Tx) to operate with the S-Cab receivers (such as the LXR-DCC). So I have now added an S-Cab compatible Channel 17, and this addition required moving the European Channel 17 to Channel 18.

The specialized RF settings for Channel 17 also allow the S-Cab Throttle to transmit to the ProMini Air receiver (PMA Rx) with just a tiny wrinkle to establish communication (more about this below).

You should note that the ProMini Air interoperability is with S-Cab products operating at 916.48MHz. Contact the author should you need this interoperability at 918.12MHz.

General Discussion

Stanton designed his products to operate with intermittent transmissions from the S-Cab Throttle to the S-Cab receivers. This practice is at variance with other transmitters such as Airwire hand-held throttles, the Tam Valley Depot DRS1 transmitter, the NCE Gwire Cab, and the ProMini Air transmitter.

S-Cab Receiver Interoperability with the ProMini Air Transmitter

I used the S-Cab LXR-DCC receiver for interoperability testing with the PMA Tx. See the photo below.

The S-Cab LXR-DCC receiver

[Warning: Technical, you can skip this paragraph.] Since the LXR-DCC would NOT operate on Airwire Channel 16 (916.36MHz), I devised more specialized RF settings that allow the PMA Tx to transmit to the LXR-DCC receiver successfully. The new “S-Cab Channel 17” transmits at 916.48MHz with a reduced “deviation” frequency FDEV of 25kHz instead of the Airwire channels’ value of 50kHz. Shifting the RF transmission from the “center frequency” FC (916.48MHz in our case) by FDEV indicates a logic transition. Thus a series of pulse transitions are generated by the timing of transmitter frequency shifts: FC -> FC+FDEV -> FC -> FC+FDEV -> … This encoding technique is called Frequency Shift Keying (FSK).

The photo below shows the DCC transmissions from the PMA Tx on Channel 17 and the DCC output from the LXR-DCC. The waveforms clearly show that the PMA Tx successfully transmits to the LXR-DCC.

Demonstration that the ProMini Air transmitter (yellow waveform) successfully transmits to the LXR-DCC receiver (blue waveform) on Channel 17. Note the very slight time delay of the LXR-DCC’s waveform.

There’s not much more to say about using the ProMini Air transmitter with S-Cab receivers: set the PMA Tx to channel 17!

As a parenthetical note, Channel 17 will also work with the older Tam Valley Depot (TVD) Mk III receiver/amp and the NCE D13DJR wireless decoder. Both use the now-discontinued Linx ES Series receiver operating at 916.48MHz. Unlike the S-Cab LXR-DCC, they will also work on Airwire Channel 16.

S-Cab Throttle Interoperability with the ProMini Air Receiver

So now, let’s turn to operating the S-Cab Throttle with the PMA Rx. Since the S-Cab Throttle transmits at 916.48MHz, the PMA Rx must use its automatic “channel search” capability to “find” the intermittent transmissions at 916.48MHz with an FSK deviation frequency of 25kHz.

The S-Cab Throttle’s intermittent transmissions are where the “wrinkle” occurs. The PMA Rx’s channel search after power on quickly searches for transmissions in the following channel sequence: 0(A), 18(E), 17 (S-Cab), 1(A), 2(A), 3(A), …, 16(A), where (A) mean Airwire channel, (E) means European ISM frequency 869.85MHz, and (S-Cab) means for S-Cab at 916.48MHz.

Since the S-Cab Throttle’s transmissions are intermittent, if the operator does nothing, the S-Cab Throttle might not be transmitting in the short time window when the PMA Rx is looking for transmissions on Channel 17. So, to force the S-Cab Throttle into nearly continuous transmissions, slide the speed control up and down continuously for several seconds while the PMA Tx is powering up to guarantee the PMA Tx has transmissions on Channel 17. If the PMA Tx does not “sync up” with the S-Cab Throttle, try again by turning the PMA Tx off and then back on while sliding the S-Cab’s speed control up and down.

The video below demonstrates that the PMA is successfully receiving S-Cab transmission since the DCC address displayed by the PMA Rx matches the S-Cab’s loco address (4), and the PMA Rx auto-selected Channel 17.

Video demonstration of syncing the S-Cab Throttle with the ProMini Air receiver. Note the following: 1) sliding the speed control back and forth at PMA Tx power-on, 2) the PMA Rx’s finding transmissions on Channel 17, 3) the PMA Rx displays the correct loco address (4) with a valid DCC command, and 5) with no action (and transmissions) from the S-Cab Throttle, the PMA Rx outputs a DCC idle.

Conclusion

I have updated the ProMini Air transmitter and receiver firmware with a new Channel 17 to allow interoperability with the S-Cab throttle and S-Cab receivers. This new channel will also work with the Tam Valley Depot Mk III receiver and NCE D13DJS wireless decoder, although Airwire Channel 16 will also work with them. To make “room” for this new channel, the European channel (at 869.85MHz) has been moved to Channel 18.

Author: Darrell Lamm

I earned my Doctorate in Physics from the Georgia Institute of Technology in 1982, and before retiring in 2019 I worked for 37 years at the Georgia Tech Research Institute. My last position was Chief Scientist of the Electro-Optical Systems Laboratory. Like many people, my love for model railroading began at an early age, and I rekindled that interest starting in 2017.

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