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800MHz to VHF crossband

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70cutlass442

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Hello all,

Can you guys recommend a simple full duplex option to cross 800 MHZ simplex to VHF simplex? I am familiar with motorola maxtrac, CDM, GM, ect.... but need something that will do 800mhz narrow and i think my radio options are limited... I am not opposed to going to kenwood
 

mmckenna

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Kenwood NX-920 might be an inexpensive way to get a new 800MHz radio that will do narrow band. I'm running a bunch of the NX-900's for my trunked system. I've got an zone set up for back up systems, including a narrow band 800MHz repeater we have at a second site. Works just fine.

I think most of the newer 800MHz radios out there will do the 12.5KHz channels, so maybe finding a used one would be a cheap option.
 
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Kenwood NX-920 might be an inexpensive way to get a new 800MHz radio that will do narrow band. I'm running a bunch of the NX-900's for my trunked system. I've got an zone set up for back up systems, including a narrow band 800MHz repeater we have at a second site. Works just fine.

I think most of the newer 800MHz radios out there will do the 12.5KHz channels, so maybe finding a used one would be a cheap option.

I'm a bit off subject but what system do you use those Kenwood radios with?? do you think they can be programmed to receive only a Motorola type 2 system?
 

Thunderknight

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What do you mean by 800 MHz narrowband? 800 was not subject to the 1/1/13 narrowbanding deadline.
Do you mean 800 NPSPAC?
 

photoguy2

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Wait, full duplex? Why? A basic 800MHz radio and a Pyramid vehicular repeater might be a good option, but not sure how you'll do full duplex on a simplex system.
(I think) by full duplex he means vhf to 800, and 800 to vhf, not just one direction like in-band.
 

mmckenna

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I'm a bit off subject but what system do you use those Kenwood radios with?? do you think they can be programmed to receive only a Motorola type 2 system?
I replaced my old SmartNet (Type 2) Motorola system with the Kenwood NexEdge (NXDN) 5 channel trunked system.

The Kenwood radios won't do Type 2. If you need to do Motorola Type 2 trunking, you need either a Motorola or EF Johnson radio.
 

70cutlass442

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Thanks for the replies...

I am aware NB was not a mandate for 800MHZ, but i believe our public safety system still NB the simplex channels... and by duplex, I mean bi-directional. We are using this for mutual aid with area departments that are both VHF, and UHF. I do have some TK940s here, but am not familiar with the different types of interfaces available for KW.
 

70cutlass442

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Are you sure they narrow banded and not re-banded? Many 800 Mhz systems had to re-band for the Nextel/Public Safety frequency changes.
BB
I am checking on this today... Lets say I can use a WB radio... had anyone successfully used a GTX and a CDM or better yet, a MCS series radio for this?
 

WA0CBW

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Our /\/\ shop designed and built VHF/UHF/800 cross band (bi-directional) repeaters using any of the professional series Motorola radios. We used commercial RDL modules for audio mixing and distribution and a custom designed switched selected controller. We sold several hundred of them but discontinued it last year due to lack of demand.
BB
 

70cutlass442

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Just my luck!! we have an immediate need for two of them, with the possibility of several more. How much was that unit and what are the chances any of them are left on the shelf?
 

WA0CBW

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They were custom built for each customer. None "on-the-shelf". All of the chassis, parts, controllers and cases were used. Cost was about $5000 not including the radios. They were designed so customer could use their existing radios. They had to be programmed to low power (to keep the intermod down). We had two versions, one was a stand-alone box and the other was a custom console that could be mounted between the seats in a vehicle. Motorola's new digital radios would require a re-design of the controller (the new radios don't have the same in/out signals).
BB
 

70cutlass442

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They were custom built for each customer. None "on-the-shelf". All of the chassis, parts, controllers and cases were used. Cost was about $5000 not including the radios. They were designed so customer could use their existing radios. They had to be programmed to low power (to keep the intermod down). We had two versions, one was a stand-alone box and the other was a custom console that could be mounted between the seats in a vehicle. Motorola's new digital radios would require a re-design of the controller (the new radios don't have the same in/out signals).
BB
That would exceed our budget a bit. My hopes was to just a Maxtrac with a 16 pin logic board and cross to a CDM... $14 cable and it's done. The problem I'm having is we need a "A6" Maxtrac with more than 2 channels. Tracking one down is not an easy task. The GTX series appear to not have a carrier detect on pin 8 however :/
 

70cutlass442

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/\ still waiting on a response as to whether they plan to NB our simplex channels ( I assume they wont, but not 100%)
 

902

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That would exceed our budget a bit. My hopes was to just a Maxtrac with a 16 pin logic board and cross to a CDM... $14 cable and it's done. The problem I'm having is we need a "A6" Maxtrac with more than 2 channels. Tracking one down is not an easy task. The GTX series appear to not have a carrier detect on pin 8 however :/
Carrier detect or some other kind of logic isn't usually a big deal in microprocessor equipment. The audio circuitry is usually provided with some kind of logical unmute signal when the proper decode is detected. Find the signal with a scope, then maybe build a buffer or inverter with a transistor and some resistors if you have to, and you should be set.
 

70cutlass442

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Carrier detect or some other kind of logic isn't usually a big deal in microprocessor equipment. The audio circuitry is usually provided with some kind of logical unmute signal when the proper decode is detected. Find the signal with a scope, then maybe build a buffer or inverter with a transistor and some resistors if you have to, and you should be set.
I wish I had those resources available to me, unfortunately I don't. I understand the basic theory behind an inverter, but I know just enough to ruin a radio. I was hoping someone has done exactly what I am trying to do but it appears as if it's not as common as I thought it was. I have heard some GTX series have the output on pin 8, and some do not, some also have it on pin 15 but until i have one, or several in front of me, its a shot in the dark. Has anyone used a TK940 for this type of project?
 
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