Motorola VPA (Simple Voice Inversion)

[radiorepair]

Just wondering if anybody has a pinout sheet for an old Motorola VPA unit. I picked one up but can seem to find anything on the net regarding the pinout (screw terminals). Any help would be appreciated. Thanks, PHIL

[jcobb]

Phil,

Now you've done it - I had to dig thru 2 Motrac manuals (with reading glasses and a flashlight no less!) and my VPA manual. I hope you are talking about a T1490A Voice Privacy Adapter.

This should be a shortened-L shaped beige unit, with an orange lite on the left of the faceplate, MOTOROLA and under that Voice Privacy Adapter in the center of the faceplate, and a CODED/CLEAR labeled switch on the right of the faceplate.

It should have 5 "holes" for wires with pins to be inserted on the left short side of the L (looking at it facing away from you), labeled 1, 2, 11, 12, 13. It should have 6 wires coming out of the right short side of the L, numbered (on the wires):

Nbr. COLOR
1 - Red
2 - shield for the Red wire
11 - Orange
12 - Black/red
13 - Black/orange
28 - Green/orange
30 - Red
31 - Black
32 - Yellow


Are you familiar with the Motrac/Motran line? It would help if you were.

Is this the unit you have?

Jack

[radiorepair]

Jack, Thanks for the quick reply. The actual model number is D1021A which of course is pretty old! It's a rectangular box with 2 knobs (vol, pot), and clear/coded SW with orange lamps to indicate if in clear/ coded mode. The rear of the unit has barrier terminals numbered 1 - 20. I was trying to figure out how to connect this to a Maxtrac. Thanks for the help, I'll try to reverse engineer the Motrac/Motran wiring to figure it out 73! Phil

[jcobb]

Phil,

I have the manual on the T1490A but not the one you have. If you want to try the T1490A ( I don't know what your project is), I could probably scare one of my old units up out of the basement.

Jack

[Big Blue TO/\/\]

Not tooooo far off topic, I was told way back that you could "descramble" this type of privacy by running your audio thru an old dial-type TV tuner as a pot, until it cleared to be useable.
Is this true? Is this 'basically' what the VPA is inside?

[radiorepair]

The project is to mate this old VPA to a Maxtrac. I thought it would be cool to enable voice inversion so that I could use the VPA with some Vertex VX10's that I have. I have tried the Transcrypt SC-460 rolling code stuff and also the Motorola DES equipped radios but for simple coded comms the single voice inversion seems to work the best for me. I guess I could always buy an MX-Com chip and wire it up to the Maxtrac, but the VPA looked too cool to pass up! As for using a TV tuner I don't know if that would work (possibly for decode) but I'm trying to use it for TX. Thanks for all your help guys! Phil

[Jonathan KC8RYW]

[quote="Big Blue TO/\/\"]Not tooooo far off topic, I was told way back that you could "descramble" this type of privacy by running your audio thru an old dial-type TV tuner as a pot, until it cleared to be useable.
[/quote]
Wait... I thought the old dial-type TV's were for listening in on cell phones on channels 70 - 82? With a little touch of the fine tuning dial, and some patience...


Seriously though, I am pretty sure there are programs out there for Windows that descramble "donald duck" radio transmittions using your sound card. Not that I've ever used these programs, since I've actually never come across any Tx that wasn't in the clear.

radiorepair: what do you think of the vx-10? I am considering buying a few of these. What do you think of them? What about the "weird" PTT button?

[radiorepair]

Hmmn, What do I think of the VX10's? Well to be quite honest I think the Vertex line of Land Mobile stuff is just beefed up "ham" radio gear. I work for a shop in NY that sells and services all types of land mobile gear and the Vertex radios that I see most often are the VX10 and the VX400. Even though they give the VX10 a Mil-Spec rating it has some serious problems. The reason I use them is because they are self programmable and small, but for any serious use I would only go with Motorola.
As for the PTT watch out for the rubber cap that covers the PTT and side buttons (first thing that goes bad).

Although the NYPD is in the process of switching over to the Vertex radios so go figure! Phil

[Glen W Christen]

This sounds like the scramblers that we installed a few months after I started in this business in 1969. The Cedar Rapids, IA PD had them built SP (Special Purpose) to work with Motracs and T41G (tube and vibrator) radios. The permise was good but it didn't work too well because of lack of test equipment to tune them properly. Also, CR is the home of Collins Radio and there were enough engineers to easily defeat the inverted code and build decoders for sale. Oh, the good old days.

[radiorepair]

Those wonderful days are long gone, and so are the easy fixes for todays current high tiered Moto's. Most of my time is spent sending stuff back to /\/\ (Rockford) for repair. I have found that it's far more cost effective letting /\/\ "dope" out the repair than sit at a bench trying to remove micro SMT stuff off boards (especially Visars and Professional series).

As far as the VPA, well I figured out how to connect and adjust it for several mutually recognized scrambler codes however it was not a pretty project with the amount of reverse engineering. Currently it's connected to a CDM 1250, sort of like having an old Willys Jeep alternator connected to the new H2 Hummer! Thanks all for your responses! Give me some Transcrypt rolling code boards any day! Phil