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Thread: Dmd an/psg-2

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    Default Dmd an/psg-2

    Do you need 2 of these devices to digital message? I'm curious how it works. Are a computer and radio required? Seems any knowledge is pretty limited. I think they were used from the late 70's to ??. Can't find where they might be sold. Info about them is appreciated. Thanks

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    I did find this FM describing how to use various DMDs (Digital Messaging Devices), including the AN/PSG-2: https://www.globalsecurity.org/milit...30/f630_11.htm

    I'm still looking to see if any document describes what modulation this uses. If it's anything common, then you should be able to demodulate it using a computer-based modem rather easily, but the DMD may only be able to recognize messages coming back in a specific format. Section B-4, subsection C talks about this... "A DMD does not transmit messages as they appear to the operator. They are transmitted as a string containing 44 alphanumeric characters. Each DMD message is composed of two parts: the header and the body. The header uses six character positions. The first position of the body designates the message type, and the rest of the body can use up to 37 characters."

    You're definitely going to need some kind of military communication interface to make use of this at all. This can be a radio or it can be a field wire system, like the GRA-39. They key is that this produces a digital signal meant to be transmitted/received through a military communication system. The other side would either have another AN/PSG-2 or would have a compatible DMD.
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    4 Star General Wire Fox's Avatar
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    Quote Originally Posted by 2deuce View Post
    Do you need 2 of these devices to digital message? I'm curious how it works. Are a computer and radio required? Seems any knowledge is pretty limited. I think they were used from the late 70's to ??. Can't find where they might be sold. Info about them is appreciated. Thanks
    Quote Originally Posted by Wire Fox View Post
    I did find this FM describing how to use various DMDs (Digital Messaging Devices), including the AN/PSG-2: https://www.globalsecurity.org/milit...30/f630_11.htm

    I'm still looking to see if any document describes what modulation this uses. If it's anything common, then you should be able to demodulate it using a computer-based modem rather easily, but the DMD may only be able to recognize messages coming back in a specific format. Section B-4, subsection C talks about this... "A DMD does not transmit messages as they appear to the operator. They are transmitted as a string containing 44 alphanumeric characters. Each DMD message is composed of two parts: the header and the body. The header uses six character positions. The first position of the body designates the message type, and the rest of the body can use up to 37 characters."

    You're definitely going to need some kind of military communication interface to make use of this at all. This can be a radio or it can be a field wire system, like the GRA-39. They key is that this produces a digital signal meant to be transmitted/received through a military communication system. The other side would either have another AN/PSG-2 or would have a compatible DMD.
    As an update, everything I can find for similar fire-control systems looks like it uses FSK modulation. This is very common for military RTTY devices and a common world standard. For VHF use, you should be able to set the XMIT rate to 1200 (this is 1200 baud) and a preamble of 0.7. ...any amateur radio data modem computer interface should be able to match these settings and receive the message. The best reference guide I saw so far was a TB describing how to correctly connect the AN/PSG-2A to a SINCGARS radio. It's data configuration settings seem to line up with FSK settings.


    First up is TB 11-5820-890-10-9, page 3. http://radionerds.com/images/d/d5/TB...0-890-10-9.PDF

    Next up is TM 11-5820-890-20-1, 1.11, subsection c, which describes how analog data is received, modulated, and then transmitted. The above TB mentioned the SINCGARS radio needing to be in TF modes, which the below manual confirms as being "TACFIRE" mode, and older nomenclature confirms to cooperation of the TACFIRE system with various DMDs. As well, the below text confirms that signal the SINCGARS radio is expecting from an analog TF system is a FSK tone, which is then digitized before being retransmitted.


    "Analog Data Modulation. Data devices are connected in place of the handset on the VAA (AM-72398or earlier) or RT (AM-7239C or later). The handset is then connected to the RT AUD/FILL. A wide range of data signals can be transmitted. The data is frequency modulated on the RF carrier and transmitted.In AD1, all incoming FSK signals are treated the same as voice signals. In TF (TACFIRE) the FSK tones are changed to a 16 kbps signal. For RT-1523B and earlier, the RT needs a ground applied to pin F of the AUD/DATA connector for TFmode. The ground informs the RT to go to the analog data mode. Pin F is grounded by an FSK detector circuit in the VAA for the vehicular radio. Pin F is grounded by an adapter cable (CX-13308/VRC) for themanpack radio."
    http://radionerds.com/images/3/31/TM...0-890-20-1.PDF
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