a MS-110A modem running in ASYNC mode

This is a sample of MIL-STD 188-110A Serial 75bps/L modem working in ASCII ASYNC mode and transporting a Citadel encrypted file. The transmission was heard on 7413.0 KHz/USB following a 188-141A handshake between two Algerian Air Force nodes: CM2 (Algerian Air Force Base - Oran, 2nd Regional Command Centre) and COF (Algerian Air Force HQ - Cheraga). 

In ASCII Asynchronous mode the bitstream consists of a 8N1 structure: one start-bit (0), 8 data-bits and at least one stop-bit (1). Each character is transmitted using a total of 10 bits and the 8 data bits are transmitted with the LSB first.

Fig. 1

Working in the ASYNC part, after removed both the start and the stop bits we get the clean 8-bit data where the characterstic pattern of the Harris "Citadel" encryption is easy to identify (Fig. 2).

Fig. 2

A similar example but related to Asynchronous STANAG-4285 can be read here:
http://i56578-swl.blogspot.it/search/label/Stanag-4285%20Async

You may use the MIL-STD Data Modem Terminal (MS-DMT) [1] to verify how the MS-110A works in ASYNC mode (Figs. 3,4)

Fig. 3 - MS-DMT settings for ASYNC mode

Fig. 4

[1]
http://www.n2ckh.com/MARS_ALE_FORUM/MSDMT.html
The latest MS-DMT test build is available at:  
www.n2ckh.com/MARS_ALE_FORUM/MSDMT32v200B1000TB1002_FI.zip

Thanks to  Steve Hajducek for the update, I suggest to subscribe his group at
https://www.facebook.com/groups/MARS.MIL.STD.TOOLS.LIB/

https://yadi.sk/d/1rw59Z0K3QuToC 
(MS-110 Async from Algerian AF)