Hi Daniel I'll be looking forward to your single antenna split result- just a T piece on a BNC will do the job (costs 6dB rather than 3dB) I think you will find a higher diversity gain compared with two antennas.
Now, you need to set up a test course etc, that you always drive in order to compare apples with apples day after day. Adding another carrier is a nice demonstration but likely to provide the great gain for the effort. It is pretty obvious by visual inspection how good it is. I think that TDMA duplexorless repeaters should be avoided because they do not enforce good filtering . But maybe that is like bad government policy from an old guy like me. Now, the next thing is, how to do two TX frequency , two RX frequency 2m repeater duplexor ! hmmm that is harder. I wouldnt recommend it at 600kHz offsets. 5 megs 70cm is a bit easier. Let's put aside the 2nd diversity channel for the moment. The issues with single frequency TDD (time division duplex) are a sharing the frequency with other users. All current comms hardware is two frequency duplex, that is there is a transmit band and a receive band, and they are separated enough to make filtering easy. Therefore operating single frequency TDD on a comms site is very unfriendly , and therefore because you will NOT be able to be in any existing repeater frequency plan, a new bandplan will be required that gets you out on your own away from TX and RX repeater pairs, and far enough to have practical filtering. At 2m, for same antenna, for 600kHz offset, about 100dB rejection is needed of the TX noise. You will need to have the TDD operation at least 600-1000 kHz away from any other repeater input/output (otherwise you will not get the rejection from an affordable set of filters) So, sounds easy in theory, not in practice. Filtering is not that hard, so I would suggest sticking with two frequency duplex. How would you integrate the diversity system into a standard 2m bandplan. Not easily and it would require extra cavity filters. ef the existing was RX 146.3, TX 146.9, might become RXA146.1, RXB 146.3, TXA 146.9, TXB 147.1 but... whatever you come up with is going to have to fit in the bandplane, and with other users, and their egacy expectations. certainly 70cm there is more room and scope, and also 70cm benefits even more form diversity because the nulls are much much deeper than 2m. Compatibility with existing bandplans and users etc is harder than the technology. with TDD, then there is the problem of multiple users in the one area. Because multiple users may be transmitting while others are receiveing just a few tens of kHz apart, the system performance will be heavily degraded by desense between the users. At least with two frequency duplex, there is a decent frequency sep between those trying to listen and those talking.... glen. ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=190641631&iu=/4140/ostg.clktrk _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
