IMBE repeater on the cheap.

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KC9UZB
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IMBE repeater on the cheap.

Post by KC9UZB » Mon Aug 13, 2007 10:47 am

I've heard it's possible with two mobile type radios hooked together.

Can anyone point me in the right direction of a URL or something..? Just trying to get an idea on how much it would cost, and the technicalities of it.

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Post by K2JLX » Mon Aug 13, 2007 10:59 am

Its two maxtracs, in'it. From what I have read its completely possible, but it will pass everything (EVERYTHING) that comes in on frequency.


There are discussions about this topic on bl.
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Post by KC9UZB » Mon Aug 13, 2007 11:20 am

Hmm. Will _any_ two radios work?

I have two hammy transceivers here (FT-8800). They have a discriminated audio out at the 9pin din at the back of the radios...

They also do crossband repeat, but I doubt if I fed imbe into the UHF side, repeated it onto VHF, received it on the other 8800 and crossbanded it back to UHF it would work :D

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Post by KC9UZB » Mon Aug 13, 2007 11:21 am

Eh... I meant:
The 8800's have discriminator tapped audio out (ie: unfiltered).

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Post by tvsjr » Mon Aug 13, 2007 11:21 am

Check out the ASTRO forum over on the Batboard... specs are in a sticky from The Pager Geek.

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Post by akardam » Mon Aug 13, 2007 11:27 am

r0f wrote:Ideally, you can recreate the simplex range of the radios, through the repeater...
I don't grok that. Are you talking about dynamic response, or distance?

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Post by akardam » Mon Aug 13, 2007 11:38 am

r0f wrote:
akardam wrote:
r0f wrote:Ideally, you can recreate the simplex range of the radios, through the repeater...
I don't grok that. Are you talking about dynamic response, or distance?
I'm talking about range...
OK, so you're talking about distance. I've never played with one of these back to back maxtrac jobs, did you mean it can double the simplex range of the radios? Vs. I suppose a Quantar or other P25 repeater (the Daniel's units come to mind) that could presumably do much better?

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Post by KC9UZB » Mon Aug 13, 2007 12:04 pm

Thanks...

Gives me an idea of the cost (and the fact I need some test equipment).

Compared to $500 for the cheap and dirty method, how much would a Quantar cost? :baby:

Just for S and G's.

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Post by motorola_otaku » Mon Aug 13, 2007 3:11 pm

r0f wrote:On the ebay market, they go for $2000-4000.
..plus another $200 or so for domestic shipping. I'd be scared to see what someone would want to send a complete one to the UK. :anus:

You're also right about the repeater passing everything it hears. I won't put one up for that reason alone.
And the sign says you got to have a membership card to get inside.

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Post by KC9UZB » Mon Aug 13, 2007 5:20 pm

Passing everything it hears = no access control?

Eek.

I'm going to take a look at that repeater builder site and look into making one... just to play around with, but over here its VERY hard to put a repeater up on the ham bands (red tape).

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Post by mancow » Mon Aug 13, 2007 6:09 pm

I made on using a B/K LPU handheld as the transmitter and an HT600 as the receiver. It worked but getting the modulation exactly right was damn near impossible. I never would settle down to a point I could trust it all to be shoved in a box together. But, when it was tuned up right it sounded great. I about fell off my chair when I heard the crisp clear digital transmission coming from the 2096 scanner.

I bet a couple of M1225s would be really easy to work with.

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Post by MattSR » Mon Aug 13, 2007 7:19 pm

r0f wrote:Turn ham-guard on.
aka DES-OFB?

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Post by KC8RYW » Mon Aug 13, 2007 7:35 pm

I had hammies 5 KHz up at a hamfest telling my over and over my radio was broken when I was transmitting P25. Heh. I think next time I'll turn off mixed mode so I don't have to hear the whining. :ham:

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Post by MattSR » Mon Aug 13, 2007 11:58 pm

r0f wrote:
MattSR wrote:
r0f wrote:Turn ham-guard on.
aka DES-OFB?
:baby: :ve4uo: :wacker:

And soon to be AES-256.
I would love to do the same, however, KVL3k+'s and XTS3000 AES modules are rare as buggery :cheeseandwhine:

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Post by mr.syntrx » Tue Aug 14, 2007 3:24 am

We've got the keyfill specs Matt, all that needs to be done is one of us to get off our arses and build such a device :baby:

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Post by Strike Team » Tue Aug 14, 2007 12:34 pm

M3ECM wrote:Passing everything it hears = no access control?

Eek.

I'm going to take a look at that repeater builder site and look into making one... just to play around with, but over here its VERY hard to put a repeater up on the ham bands (red tape).
Not so hard now. There's an amateur near me who's got a licenced repeater on his house. Not a brilliant repeater, but it works.

I fancy putting up a 70CM FM repeater in my area, as Glasgow's only 70CM repeater is on the other side of town from me.

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Post by KC9UZB » Tue Aug 14, 2007 2:09 pm

:anus: :anus:

who cares if its redneck... that would "own"

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Post by Wowbagger » Tue Aug 14, 2007 2:10 pm

The key fill physical layer isn't RS-232, but a synchronously clocked protocol with one common data line, driven by open collector outputs on both ends.

The logical layer is either a subset of APCO-25 OTAR, or a proprietary protocol developed by Motorola - so unless you have the TIA/EIA specs for the OTAR protocol or the documentation from Motorola you are going to have a devil of a time reverse engineering the protocol.

And no, I will not violate my NDA and jeopardize my job telling you how to do it.

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Post by tvsjr » Tue Aug 14, 2007 2:10 pm

Syntrx is already working on this particular project.

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Post by mancow » Tue Aug 14, 2007 8:30 pm

Do you have a KVL service manual available? They break down the system in pretty good detail with descriptions of the data packets and such.

If no, I have one you can eye.

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Post by MattSR » Tue Aug 14, 2007 8:43 pm

mr.syntrx and myself have done some work already in this area - what wowbagger has said is correct.

We have given up on Advanced Securenet protocol (ASN) as its proprietary and very difficult to obtain the specs. P25 (aka CKR mode) is much easier to obtain the specs for. I'm mostly a software guy so the protocol itself is straight-forward - its the hardware interface that I am having trouble figuring out.

The other spanner thats in the works is the baud rate - its 4000 symbols/second which can't be done via a RS232 port. Sort sort of AVR based interface is required, which is a whole new game for me to learn also :)

mancow - I would be interesting in viewing the KVL manual also :)

Cheers,
Matt

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Post by MattSR » Tue Aug 14, 2007 8:45 pm

Wowbagger wrote:T...unless you have the TIA/EIA specs for the OTAR protocol or...
I do. They're available for sale through the TIA website for a cost.

Still doesn't give you any real clues on the hardware design though.

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Post by mancow » Tue Aug 14, 2007 9:17 pm

I had to dig for it but I found it.

It's a T3020AX instruction manual but it has a theory of operation, parts list, and full schematics. Part # 68P81060E40-O 09/14/1981

(RETRO Huh? )

I wonder if the 3020 is similar enough to the 3011?

excerpt...

The inserter first tests its own DES device. This is done by loading a test key (in HEX, 1010101010101010) into the DES device. Then 64 bits of encryped output are compared to a reference table of 64 bits previously previously computed and stored in the inserter's ROM. If all bits match, the inserter loads its DES device with the correct key. It also loads a pseudorandom bit sequence called an initialization vector; this vector is used by the DES device as a starting point for encryption.

The inserter then begins signalling the radio by sending synchronizing information (a combination of the 6 kHz end-of-message (EOM) signal and a pseudorandom bit stream) so that the radio's clock circuitry becomes phase-locked to the inserter's clock. Three separate types of tests are then performed; these are detailed below....

The first is parity checking. Each of the eight bytes in the 64 bit has to have odd parity...........

S-box testing................

Checkword testing..........

After all tests are passed and encrypted 1.5 kHz tone is sent to the radio...............




.............denote portions abbreviated.



That's the type of language and material that is covered in this manual. It goes into quite a bit more detail about what lines are asserted during different phases of the operation etc........

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Post by MattSR » Tue Aug 14, 2007 9:42 pm

r0f wrote:....Keep in mind what we're trying to accomplish here is pretty simple. ...
Yes, I agree with this - but if you think its as simple as soldering a few wires from your COM port to to your radio and writing a bit of software to fire some characters out that port then you are kidding yourself..

No offence intended here r0f, I'm just putting a realistic point of view forward..

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Post by K2JLX » Tue Aug 14, 2007 10:13 pm

If you do, buy a mega millions lotto ticket, quickly.
:baby:
Homophobe....... I'd hit it like a fucking screen door in a Goddamn tornado. When you get all old and sickly my round arsed friend, you will learn to take advantage of situations as they arise or do without. Does that make me a fag? Dunno.....don't care........but it means I am not going to do without....... -- FatherJack - 3/29/2012

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Post by n3jfw » Tue Aug 14, 2007 10:17 pm

or a barcode scanner
N3JFW 4:29 pm
(4:29:48 PM): so he's gay huh
(nameless ham) 4:30 pm
(4:30:02 PM): haha no, but he is a music major
N3JFW 4:30 pm
(4:30:15 PM): so he's still in the closet

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