Connect two DMR mobiles to one antenna.

[Quasar_A]

Greetings

I have two DMR mobiles (DM-3400), first radio transmits at F1 TS1, second radio at F1 TS2, they works with repeater, RX frequency at F2. I need to install this two radios in same place and connect to the same antenna. Can I use combiner for this application? I have doubts, due TX frequency for both radio is same.

 

[mmckenna]

No.

A transmit combiner needs to have the frequencies separated by a certain amount. If both radios are on the same frequency, but different timeslots, there would be no way to provide enough separation between the two radios to keep the RF from one radio getting into the other.

You could use two separate antennas, but you would need a fair amount of separation between them.

 

[jonwienke]

You'd have better luck modifying the radio firmware so that one radio transmitted both TS1 and TS2. Or using an actual repeater instead of 2 mobiles.

 

[KC8ESL]

You'd have better luck modifying the radio firmware so that one radio transmitted both TS1 and TS2. Or using an actual repeater instead of 2 mobiles.

Ehm, er, no.

The only reason a repeater can transmit on both timeslots is because it occupies both timeslots at any given time. It can't interfere with itself as it intends on setting the benchmark for a time base on the DMR system that you're on.

Why can't you just use the 1 DMR mobile radio and set to scan and set the TX designated channel as "Last Active Channel"?

 

[Quasar_A]

Ehm, er, no.
Why can't you just use the 1 DMR mobile radio and set to scan and set the TX designated channel as "Last Active Channel"?

First radio for first dispatcher, second radio for second dispatcher. They should work independently.

Maybe someone have experience with RX/TX switches on pin diodes?

I can not believe that there is no solution for connecting the TDMA devices to a single antenna.

 

[Project25_MASTR]

First radio for first dispatcher, second radio for second dispatcher. They should work independently.

Maybe someone have experience with RX/TX switches on pin diodes?

I can not believe that there is no solution for connecting the TDMA devices to a single antenna.

Their is as long as they aren't on the same frequency. Best way to go about what you are trying to go about would either be to use IP dispatching direct to the repeater or utilize a hardware console design (which can also be done with IP based interfaces) and separate the radio's location in the building to minimize feedline loss.

 

[Ubbe]

If you can accept to loose more than half the power then use a hybrid combiner, it doesn't care what frequencies you use. But if one transmitter should transmit in one time slot and the other transmitter in the other time slot, then you will need them to be synced to not interfere in each others time slot.

/Ubbe

 

[prcguy]

You can use a hybrid combiner for two transmitters on the same frequency or in the same band, but these are transceivers and the combiner does not address the receiver side. If you were to use a hybrid combiner with two transceivers on the same frequency you will damage the receivers. You would need to separate the receiver inputs and run them to a second receive only antenna.
prcguy

If you can accept to loose more than half the power then use a hybrid combiner, it doesn't care what frequencies you use. But if one transmitter should transmit in one time slot and the other transmitter in the other time slot, then you will need them to be synced to not interfere in each others time slot.

/Ubbe

 

[jonwienke]

There are 2 separate issues here:

1. Dealing with 2 radios on the same frequency.

2. Dealing with the TDMA timing/sync issue so that both radios are not transmitting at the same time.

It is not practical to address issue #1 with filters, and no filter will address issue #2. What you need is a repeater that allows direct transmit inputs for TS1 and TS2. You can't have 2 radios with separate clocks transmit on TS1 and TS2 and stay in sync. It has to be one radio with a single sync clock. With a repeater, you have one master clock that all the client radios sync to. To do what you need, you have to either have a repeater, or a standard radio with modified firmware to act as a repeater (provide the sync function of a repeater).

 

[Ubbe]

You would need to separate the receiver inputs and run them to a second receive only antenna.
prcguy

Yes. It is switching diods connected to the TX and RX modules and you lift the RX one and solder a coax there connected to a duplex filter, or to a sepearate RX antenna using a filter.

I have looked in a Motorola DMR basestation and it looks like two mobile transceivers, one act as RX and the other as TX, with special firmware and a network control module.

Looking at the moderate pricing of the basestations it doesn't seem to be any point of trying to do a homebuilt solution.

/Ubbe