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Harris PRC-152 VAA Project

aleigh

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Phoenix, AZ & Seattle, WA
For awhile now I've had a back-burner project to get a military radio setup working in my LMTV. The first phase of that was getting a VIC-3 system installed, which I mated to a Yaesu FT-857 by making a cable. I have all that mounted in one of the equipment racks that go behind the passenger seat. What I've really wanted to get working is a VAA with a removable PRC-152.

I happen to have two PRC-152 radios, so it was pretty straight-forward to purchase a VAA, they are on ebay and other places. What is harder is to find the mounting tray that has the intercom outputs; not all mounting trays do, and I think those were for fixed-station operation, like in the hardigg shock cases you see come up for sale from time to time.

In anticipation of someone getting twisted up about the PRC-152s, a bit of history. Harris developed the PRC-152 and a manpack radio on-spec (not for a contract) in the hopes they could sell them to various militaries, which became known as the Falcon II radios. This family has commercial encryption but it is non-CCI, non-Type1. The US bought a lot of them but decided that they needed a radio family which was SINCGARS compatible and usable for TS traffic. So, Harris produced the Falcon III, a Type-1, CCI controlled radio family. Since the F3 is CCI it has all the attendant legal/ownership issues. The F2 radios are commercial, off the shelf, and are legal, just rare.

When my VAA arrived I went to get it going and imagine my surprise to discover that the side connector (carrying the intercom lines, and PTT) was 32-pin instead of 18-pin. It turns out that the F2 family took the edge connector from the PRC-148 MBITR with a different pinout (and different key) and the F3 family uses a 32-pin edge connector. The VAA I had purchased was apparently a F3 VAA.

I sort of stupidly assumed that it was basically a broadband linear amplifier and so if I hooked up the antenna from the radio to the amp, it would work, and I would be missing the audio/ptt. I was wrong, the VAA did not work at all in this configuration. No rx, no tx. But it did draw about 25W at idle. I thought the amp might be broken so I took it all apart. Internally, it consists of a power supply, a motherboard with a Freescale microcontroller and a Spartan FPGA, and two RF boards. The amplifier and filter array looks like it's directly controlled by the computer. So, not simple. Around this time I also noticed that when I docked a radio it was saying "Connecting to VAA". So somehow from the battery pins it is able to deduce it's docked with a VAA.

To make a long story short, the radio interfaces with the amp, and by some miracle, the F2 firmware on the radio is willing to talk to the F3 amplifier that was produced many years later. The connection is established over the 2-wire RS-232 connection on the radio used for the remote control (the KDU). I used an o-scope to chase down all the pins. As soon as those were jumped between the VAA and the Radio it established a link, rx came alive, and it began working. If you interrupt the link during operation the radio displays a VAA fault.

There are some take-aways from this. The first is: Falcon 3 VAAs can be used with older Falcon 2 radios. The second is that they can ONLY be used with Harris radios. Anybody's hopes of getting a TRI radio or a random Ham radio to take advantage of these wideband 50W amps can probably stop right now. That said, I suppose it might be possible to decode the RS-232 and try to figure out what is going on between the VAA and the Radio. My guess is they handshake and then the radio passes the frequency information (keeping in mind they are frequency hopping) but that's a total guess. It might be possible to jerry rig an arduino or something to pretend to be the radio, but at that point, I am not sure it's a productive use of time just to get a 50W amp. Someone wanting that kind of a solution should take a look at Ultralife, they make broadband vehicle amps for these radios which do not appear to need a data-link or software-level support.

Draws well over 100W on TX.

For my part, I need to order or 3d-print a 18 pin connector, and then get my audio, ptt, and rs-232 lines wired up and it should be good to go in the truck.

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aleigh

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Phoenix, AZ & Seattle, WA
Printed up some prototype connector shells to work on the dimensions. Looks like I can get the spring loaded contacts off the shelf, so should have this all buttoned up once I get some of those in and finalize a design. I avoided getting a 3D printer for a long time but it turns out they are kind of like forklifts, once you get one you wonder how you ever lived without it. Useful for all manner of things.


IMG_1242.jpg
 

aleigh

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Phoenix, AZ & Seattle, WA
Someone PM'd me, I guess I forgot to mention:

VAA - solid red & solid black (at least on mine!). Sorry I don't remember which are which. The one pulled negative should be tx on the VAA. Harmless to try both ways. The pins are adjacent (same row).
Radio - 13 rx & 15 tx. Looking at the radio in its normal orientation 1 is the bottom left and 18 is the top right.
 

CallMeColt

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Wilson County, Texas
Someone on another website shared this thread with me. I was hoping to get SOME of the function for my TRI to work with the mount, but I guess not.

At least it will charge the battery and hold it while looking authentic.

I guess the best I can hope for is the gut the inside of the mount and use the inside of it for other stuff that might make it all a bit more useful for my goal of using Harris speakers around the cab of my M1078.
 

tgejesse

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Maryland
Someone on another website shared this thread with me. I was hoping to get SOME of the function for my TRI to work with the mount, but I guess not.

At least it will charge the battery and hold it while looking authentic.

I guess the best I can hope for is the gut the inside of the mount and use the inside of it for other stuff that might make it all a bit more useful for my goal of using Harris speakers around the cab of my M1078.
did you have any luck? About to go through this set up myself!
 

NVAM998

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Steel Soldiers Supporter
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Virginia
If you want an amplifier that SOCOM uses in the FOSOV, get one from Tricom Research, not ULBI. Nice setup. And yes Harris made both exportable and Type I 152's. They may still be exporting 152's, IDK. Harris uses a high speed bus for control of their VAA.
 

tgejesse

Well-known member
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63
Location
Maryland
If you want an amplifier that SOCOM uses in the FOSOV, get one from Tricom Research, not ULBI. Nice setup. And yes Harris made both exportable and Type I 152's. They may still be exporting 152's, IDK. Harris uses a high speed bus for control of their VAA.
In English-ish for someone newer to radios? Lol
 

CallMeColt

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Location
Wilson County, Texas
I'm drown back to this thread...

I got myself in the same situation as OP now. Got some Falcon II I'm wanting to work in the Falcon III VAA.

@aleigh , did you perfect your 3D printed adapter there? I'm my head, I thought this would be ideal. I'd like to make my VAA able to go back to the Falcon III easily as well, since I may be getting one soon.
 

aleigh

Well-known member
1,040
49
48
Location
Phoenix, AZ & Seattle, WA
So in the end I did get all this working. I did two things: In order to conclusively figure out the pinouts between the different connectors, I got a 5935-01-587-7966 which if you look on the bay which is e some people are selling. It's like a rosetta stone for this problem. These were intended as a retrofit kit of some kind, I forget the details, to mate some new and old equipment together. By using a multimeter I just figured out which pins were connected to which and then made a map. Unfortunately the gender is wrong to just use it as an adapter for the VAA.

Then, separately, I ended up just coming into a PRC152 serial/data cable and I ended up using that, so I have a real connector.

I did follow through on the 3d printed connector and it did work, once I got the right size spring contacts (they are not that hard to find), so that concept is not a bad one. A variation would be to just take a block of delrin and drill holes in it, solder the wires to the spring pins and then glue them into the holes, then figure out something to do for the backshell.

Just like my earlier tests had established, once the radio (with new enough firmware) has the serial data link to the VAA, it works.
 

CallMeColt

Well-known member
Supporting Vendor
900
1,256
93
Location
Wilson County, Texas
So in the end I did get all this working. I did two things: In order to conclusively figure out the pinouts between the different connectors, I got a 5935-01-587-7966 which if you look on the bay which is e some people are selling. It's like a rosetta stone for this problem. These were intended as a retrofit kit of some kind, I forget the details, to mate some new and old equipment together. By using a multimeter I just figured out which pins were connected to which and then made a map. Unfortunately the gender is wrong to just use it as an adapter for the VAA.

Then, separately, I ended up just coming into a PRC152 serial/data cable and I ended up using that, so I have a real connector.

I did follow through on the 3d printed connector and it did work, once I got the right size spring contacts (they are not that hard to find), so that concept is not a bad one. A variation would be to just take a block of delrin and drill holes in it, solder the wires to the spring pins and then glue them into the holes, then figure out something to do for the backshell.

Just like my earlier tests had established, once the radio (with new enough firmware) has the serial data link to the VAA, it works.
I have a few of those adapters already. When I see things cheap, like wires & what not, I grab them. Seems our minds were on the same track. In my head, I was thinking of going cannibalizing a serial connection for the radios I have... got a few. My challenge is the mapping. Guess I'll need to take the time to do that unless you by chance still have it written down.
 

aleigh

Well-known member
1,040
49
48
Location
Phoenix, AZ & Seattle, WA
I have a few of those adapters already. When I see things cheap, like wires & what not, I grab them. Seems our minds were on the same track. In my head, I was thinking of going cannibalizing a serial connection for the radios I have... got a few. My challenge is the mapping. Guess I'll need to take the time to do that unless you by chance still have it written down.
Sorry I don't have the pinouts handy. In some notebook from that year somewhere.
 

tgejesse

Well-known member
264
283
63
Location
Maryland
So in the end I did get all this working. I did two things: In order to conclusively figure out the pinouts between the different connectors, I got a 5935-01-587-7966 which if you look on the bay which is e some people are selling. It's like a rosetta stone for this problem. These were intended as a retrofit kit of some kind, I forget the details, to mate some new and old equipment together. By using a multimeter I just figured out which pins were connected to which and then made a map. Unfortunately the gender is wrong to just use it as an adapter for the VAA.

Then, separately, I ended up just coming into a PRC152 serial/data cable and I ended up using that, so I have a real connector.

I did follow through on the 3d printed connector and it did work, once I got the right size spring contacts (they are not that hard to find), so that concept is not a bad one. A variation would be to just take a block of delrin and drill holes in it, solder the wires to the spring pins and then glue them into the holes, then figure out something to do for the backshell.

Just like my earlier tests had established, once the radio (with new enough firmware) has the serial data link to the VAA, it works.
Great minds think alike I picked up these three items to get it all together.
I have a TCA PRC-152 clone coming… was hoping to get it to play nice but it sounds like that’s gonna be a no go.
This may be a dumb question but this VAA is for F2 or F3 originally?
 

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