rtl-sdr multi dongle trunking hardware - 800Mhz

[kc3ajv]

I'm very new to all this and need some help.

I want to set up a scanning system to listen to my local public safety. I'm near Ocean City, MD but commute 45-50 minutes up rt113 through DE. I would like the system to operate mobile for my commute.

I've read the tutorials on rtl-sdr trunking systems. I have one knock off dongle and have successfully set up SDR#, but that's about as far as I've gone. I'm comfortable installing and setting up the other software pieces to the puzzle, but I'd like to focus on hardware first.

Here are links to the public safety frequencies I'm interested in:

https://www.radioreference.com/apps/db/?sid=411
https://www.radioreference.com/apps/db/?ctid=314
https://www.radioreference.com/apps/db/?sid=7214
https://www.radioreference.com/apps/db/?sid=386
https://www.radioreference.com/apps/db/?sid=9339
https://www.radioreference.com/apps/db/?ctid=1211

DE is all Motorolla type II project 16 and Maryland looks like mostly EDACS project 25. The one question I haven't been able to answer is what the Maryland State Police are using to transmit on 39.6? Maybe a question for a different forum....

I would like to note that I currently have an Icom 2720h installed in my car hooked to a Tram 1265r NMO magnetic base and a Tram 1180 144/440 antenna. I'm just as new to ham radio as I am to scanning/sdr so I'm not sure if I can operate the Icom and a scanning system at the same time.


I would appreciate input/comments/suggestions on my planned scanning hardware below.

-Two rtl-sdr dongles
-Powered USB OTG hub with at least 2 full sized USB inputs
-Larsen tri-band 150/450/800 NMO antenna
-another NMO magnetic base (or use existing Tram 1265r if I can't run Icom 2720 at same time)

Here is where I'm hung up:
I would like system to run on semi-small form factor hardware such as a Windows tablet. I've seen older threads praising the 8" Winbook tablets but those are no longer available. Amazon has cheap generic brand 8" tablets but I am not sure of required ram/CPU speed to run a trunking system. I would ideally like to know if any of these generic tablets have been used by others with success to run trunking SDR systems...

Also, I'm unsure of the type of splitter to run two dongles off 1 antenna. I've looked up sma-y splitter-to-SO239 adapters, but want to know if there are any specific requirements for a mobile installation?

I summary:

-Can I operate (rx and tx) a ham 144/440 radio while scanning?
-From my links above, am I right that DE is Motorolla Type II and MD is EDACS?
-Will a Larsen 150/450/800 cover my local public service frequencies?
-Suggestions/requirements for mobile system antenna splitter to dongles (SMAx2 to SO239)?
-Suggestions for mobile hardware to run Windows (tablet or other) close to 8"

Thanks!

 

[boatbod]

MSP are mostly moving to FiRST, which is a P25 Phase 2 system.

 

[dlwtrunked]

I'm very new to all this and need some help.
...
-Two rtl-sdr dongles
-Powered USB OTG hub with at least 2 full sized USB inputs
-Larsen tri-band 150/450/800 NMO antenna
-another NMO magnetic base (or use existing Tram 1265r if I can't run Icom 2720 at same time)
...
Also, I'm unsure of the type of splitter to run two dongles off 1 antenna. I've looked up sma-y splitter-to-SO239 adapters, but want to know if there are any specific requirements for a mobile installation?
...
I summary:
-...
-Suggestions/requirements for mobile system antenna splitter to dongles (SMAx2 to SO239)?
...
QUOTE]

A couple comments. Using SO239/PL259 for higher frequencies is a bad idea and using small coax like RG-174 is not good (primarily not because of the loss at higher frequencies but because it always fails/breaks at connection points eventually). And eventually, even if not now, you may want to use your setup for ADS-B at even higher (1090 MHz). Personally, I would use BNC for your project, and if you do not want to spend money for Stridsberg multi-couplers, I would get a cheap TV 2-way splitter and put adapters on it for BNC. Or you could use Type-F connectors with compression connectors for whatever cable (not RG-174) that you use--using Type-F might be easier and may be fewer adapters. Do not worry about 50 vs. 75 ohms as that makes little difference. Try to keep the number adapters though to a minimum as each adds a little loss. I would re-think this through with the above comments.

 

[troymail]

Reading your post/question, my question is why, given all the things you are trying to monitor, would you want to make it so complicated? I know doggles are cheap but the setup will be a bit complex and combersome.

I find make this stuff work while stationary (on the road) or even at home can be a bit of a challenge.

For your area, with exception of Maryland FiRST and until Worcester County (and maybe Ocean City) switches over to their new P25 Phase 2 system, you'd be much better served with a low end scanner.

Maybe I'm missing something.

 

[M105]

You can't hook your transmitter and scanner to the same antenna. Keying the transmitter will blow the front end out of your scanner. Technically it can be done with a diplexor if you transmit and receive on different bands but not practical for a wide band scanner setup. It also is not a good idea to do it with two antennas in close proximity to each other as in a mobile setup. I have destroyed the pre-amp transistors in a scanner with my 2 meter radio running mobile with two separate antennas. It is fine to listen to both the ham and scanner but if you pick up that microphone either disconnect the scanner antenna or use very low power on the 2m/440 radio.
---
I can't answer the computer question but am very interested in the answers you get. I have wondered about using some kind of small windows computer mobile for SDR myself.

 

[SteveSimpkin]

I'll add my concerns that this setup is not well suited for operating in a vehicle that you are driving. Unlike a scanner which has physical buttons (or large touch screen controls), these software packages would not be easy to see and operate while driving. Added to the complexity of setting this all up and the problems you will likely run into trying to make this work on a low end Windows tablet computer, I think this is the wrong tool for the job. Save yourself a lot of frustration and buy a scanner.

You will need a separate antenna for the scanner and you should separate them from each other as far as possible to reduce the chance of damage to the scanner's front end when you transmit. This question comes up frequently. Here is a recent example. Search the forum for other examples.
http://forums.radioreference.com/sc...-transmit-antenna-separation.html#post2732797