Not sure where to park this but...

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AZScanner

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... I know "all the right people" haunt this particular sub-forum so here goes:

In the arduino thread here, someone mentioned using a radio modem to monitor the RD/LAP protocol. I've been all over google and batlabs looking for a "how-to" on setting this up, but coming up empty. Is this even possible? My thinking is that in order for this to work, you would need a way to put the modem in a test mode of some kind, where it would just decode any message that came along whether or not you were the intended recipient. Wouldn't I be better off using a 4 level slicer or a CML Micro EV9000 board? A quick ebay search revealed all sorts of RD/LAP modems but the last thing I need is another gizmo if I can't get it to do what I want.

Any info on this would be great, because monitoring RD/LAP is something I've wanted to do for years but just didn't have the know-how to pull it off. Mods, if this isn't the right forum feel free to move it to where it belongs.

Thanks,
-AZ
 

KA1RBI

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home (radiorausch) is one site to check - that guy used a USRP but I've had some luck using just a disc-tap. Definitely "some assembly required". If you have a radio equipped with a discriminator tap, and have a good strong site nearby, try capturing a sample signal (at least a 48K sampling rate sound file) and posting it somewhere where folks can analyze it... Might help to use a radio whose last IF is on the wide side, too...

73
 

AZScanner

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home (radiorausch) is one site to check - that guy used a USRP but I've had some luck using just a disc-tap. Definitely "some assembly required". If you have a radio equipped with a discriminator tap, and have a good strong site nearby, try capturing a sample signal (at least a 48K sampling rate sound file) and posting it somewhere where folks can analyze it... Might help to use a radio whose last IF is on the wide side, too...

73
Yep, seen that site. I've got my trusty old BC895 disc tapped and banging away on data channels 24/7, and I've even got an old thinkpad laptop I can toss Ubuntu on and play with the GNU software with (just haven't had the time to do so yet), so I think I'm covered there.

My question was specifically around the use of a radio modem for this purpose. Just curious if anyone has successfully attempted that before, and if so, how'd ya do it?

-AZ
 

rbrtklamp2

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you two seem to know alot about mdc and cad monitoring and i have wanted to get into that for years only problem is i do not know where to start if either of you would take some time and teach me the in and outs of th software and eqipment i would need i would be very greatful and compansate you for your time if needed please email me at robertklamp@aol.com i would be very very greatful for any information about getting stared in this area of law enforcement monitoring.

thanks again for any kind of help,

Bob
 

gary123

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you two seem to know alot about mdc and cad monitoring and i have wanted to get into that for years only problem is i do not know where to start if either of you would take some time and teach me the in and outs of th software and eqipment i would need i would be very greatful and compansate you for your time if needed please email me at robertklamp@aol.com i would be very very greatful for any information about getting stared in this area of law enforcement monitoring.

thanks again for any kind of help,

Bob
Im very interested in monitoring these systems too. Not only law enforcement uses mdts many taxi and couriers use them too.I can be pmed .

Maybe the mods can setup a new forum for discussions on this type of monitoring.
 

AZScanner

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It's a bit of a legal gray area guys, so I don't know if it will warrant it's own subforum. I'm sure the last thing Lindsay wants is more potential legal hassles.

Back in the day, you could monitor the older MCD4800 systems quite easily using a program called MDTMonitor. I used to monitor several of them in my area. Then, one by one, they transitioned to newer RDLAP 9600 and 19200 systems that employ a completely different protocol. Still the basis for decoding these systems remains the same:

Scanner ----> Discriminator Tap---->Computer----> Software to Decode the protocol----> Output (Display, File, etc)

What I'd like to get more info on would be a setup like this:

Radio Modem---->Computer----> Software to query modem and display data ----> Output.

I'm assuming that if you set the modem up correctly, you could use plain old Hyperterminal to read the output. From there, developing custom software to display the data would be simple.

In the meanwhile, if I ever get enough free time in one sitting, I'll have to fiddle with GNURadio and see what it can do.

-AZ
 
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