DTR Repeater Revisited

I know this topic has been kicked around for awhile. It seems that only the Cane company has offered a somewhat viable commercial DTR repeater.
With more Motorola DTR radios showing up on eBay it seems like interest is growing for a functional “Home Brew” repeater.
The fundamental problem of no repeater frequency split/shift in the programming of these radios is well known. So my question is, has anyone reading this come up with a reasonably functional solution to extend the useful range of the DTR handhelds?

It is just not practical to try to set up a repeater unless you have the version that uses internals from two radios. (Hence, the high cost.) The DTR cannot receive on one frequency and transmit on another because the “channels” are not individual frequencies, but are a pre-programmed algorithm of frequencies that it hops from one to another quickly.

Some users have tried cables that tie the headphone jacks of one to another, but they have never worked well. Most of those cables have been withdrawn from the market. The problem with using two radios tied to a cable is that you needed to block the signal coming to the transmitting radio or it would just not transmit. Some users have tried putting one radio very high up in a tree and the other very low down, tied together with the special cable. This only worked if the DTR was at its very limit of reception area, so that the high one would pick up the signal while the low one wouldn’t. As far as I know, no one has ever been able to resolve how to prevent the transmitting radio from also receiving the signal.

The other issue is that the DTR has about the best range of any two way radio on the market, and there has been less need for repeaters. It is not really designed for wide area coverage, because those radios would be licenced business radios. The DTR is a licence-free radio.

I am also interested in this, and perhaps I could help. Seems like the dtr radios are based on the iden 900MHz of Nextel. Perhaps one of these T6737A iden 900MHz quad base transceiver systems on eBay could be repurposed to significantly extend the range of the DTR systems on private internet networks?

I’m a wireless / network / systems architect (read: hobbyist) that has been interested in these dtr/iden PTT systems for some time now.

The DTR system really isn’t geared up for repeaters. It’s frequency hopping - picking the clear ones dynamically as required. This means that the fundamental operation of a repeater is compromised. They must have sharp filters that stop the output making the input desensitise. You can get smallish cavities that work fine with an 8Mhz split in frequencies, and you can get even sharper and more expensive cavities that can do less than a Megahertz split. With the Motorola system as far as I can see there’s no way to make the things NOT frequency hop. The analogue idea of linking two radios would still work, but as soon as one fired up, the other would be swamped by RF and even with frequency hopping, it wouldn’t cope.

You can do repeaters with two radios on DMR and while you can’t do it without opening the radios and using a discriminator feed, it works. I can’t see how a frequency hopping radio can work back to back.

The Cane Wireless DTR repeater is implemented using a pair of DTR radios running custom firmware. Using a pair of “normal” DTRs will NOT work. One thing I’ve read about the repeater is the digital audio delay between radios operating through the repeater is doubled.

Time domain duplex solves the desense problem without a duplexer. Analog cell phones years ago had a mini duplexer in them. Digital cell phones do not have a duplexer in them and use the time domain duplex technique. The DTRs in the repeater may do a similar thing.

The DTRs are required by FCC rules (15.247) to use a minimum hopset of 50 frequencies. The DTRs hop on 50 frequencies spaced 0.5MHz apart across the entire 902-928MHz band. Each hop spends no more than about 90 ms on each frequency at a time which works out to about 11 hops/sec.

The Cane Wireless DTR repeater will work with the DLR series and DTR600/700 models on public and private groups only. The repeater will not work when the Profile ID Number (PIN) feature is used to secure Profile ID mode channels. The repeater is built from a pair of legacy DTRs which don’t have the Profile ID features. The Profile ID features are new features which started with the DLRs and were carried forward to the DTR600/700 models. Cane Wireless needs to develop a new DTR repeater based on a pair of DTR700 radios to be able to work with the Profile ID features.