[EMAIL PROTECTED] wrote: > I was told by our local techs. half duplex is OK on links. > Their Vhf link system uses half duplex link equipment to a 442 > repeater. > Is full duplex better? Why?
Depends on what you want to do. We implement some full-duplex links, others half duplex... but the half duplex links have a "full break in" type of setup going the direction AWAY from the main site. The reason? Control. If the remote (far away) site has an open squelch/CTCSS problem and we want to control it, we need that link to "turn around" and go the other direction so we can send commands to it. (We typically have more than one method of control, but for a "last ditch effort" we want the RF side to be able to get there. If a link is half-duplex and the receiver at the remote site is open causing the link to transmit back to the hub/main system, we HAVE to have a way to turn that link around. Having to go look up control codes to do it is annoying... we build 'em so that they ALWAYS give the main site priority over anything of the outlying repeaters at the "edge" of the topology. > We have three Uhf repeaters which can be linked. Each end tx is > on 444. Were the center tx is on 448. So, the ends could have > link equipment to the center repeater. With properly done filtering, yes. You can even share antennas with the right setup. > Or should the link equipment be added to all three sites using a > link simplex frequency? See above... we won't ever do simplex if we can avoid it. If NOTHING else, we can always put a transmitter of our own on the air on the receive frequency of the remote site and over-ride whatever's locking up the system... etc. Think about the failure modes and engineer them out. > With only two Uhf sites, can/should the equipment be on set to > use the opposite frequency pair, with one being the repeater and > the other the link, or should a simplex link frequency and equipment > be installed and used at each site? Another very good option is to get away from UHF links altogether. Go down to 220 MHz, or up to 900 MHz, 1.2 GHz, etc. Utilize the low-usage bands, and you'll have oceans of spectrum to utilize if you find a particular link frequency is noisy, etc. (Unless you live somewhere where 220 MHz is busy like SoCal.) Nate WY0X
