On 9/8/2011 10:43 PM, Dave Platt wrote:
You could build a very nice full duplex repeater on a single
frequency that way.

Yes, except that the ARRL has decided to only petition for a waver for
single time slot TDMA, which can't be used for a repeater.

You're scheme would certainly work, and I too am wondering why nobody
has bothered to do it. Possibly because nobody really wants full
duplex (with echo, reverb, feedback, etc).
Not so much full duplex, but single frequency half duplex, with
negligible time delay (implying 100ms frame time) between Rx and Tx.



I wonder whether you may not also have to be really careful with your
transceiver/receiver switching design. You'll really need to be able
to trust (and drive) those PIN diodes properly... goof up on even a
single time-slice and you could put enough TX power into your receiver
to turn its front end into a pile of smouldering char in a millisecond.

This isn't a problem with normal split-frequency repeaters, thanks to
the isolation in the duplexer cans.

Do any of the commercial TDMA systems use the same frequencies for
base-mobile and mobile-base? My recollection is that TDMA cellphone
systems operate with split uplink/downlink frequencies.


Sure.. 802.11 is half duplex on a single channel, for instance.

Lots and lots of radars have fast and reliable T/R switching at pretty
much any frequency you care to name from DC to light.

TDMA cellphone uses split bands probably because it was on top of
existing AMPS systems. There is also a frequency allocation issue (e.g.
no need for new licensing). Having separate forward and reverse bands
also helps with frequency reuse and near-far issues. I hardly think
that hams are going to carpet the country with repeaters to the extent
that cell sites do.