--- In Repeater-Builder@yahoogroups.com, "skipp025" <[EMAIL PROTECTED]> wrote: > > > "ldgelectronics" <ldgyahoo@> wrote: > > Yes, the tower spacing is vertical (not horizontal), yes the > > tx/rx on the repeater is 443.3 and 448.3 (5 MHz split) > > Don't get sideways over the vert/horz terms. We would be concerned > with both the vertical and horizontal locations. Vertical distance > is an easy "best bang for the buck" option. But horizontal distance > and location per side of a tower is also quite handy. > > > Ok, now to fill in some of the blanks I left out. This is why the > > group is so coolÂ… things I thought were meaningless turned out to be > > important. The repeater power is 20 watts, the remote base is 10 > > watts. > > Relative to the grand scheme of things... your power output is not > that big of a problem to work with. > > > The repeater is an Exec II. The remote base is a Kenwood TK-805 > > (just because I have a stack of them). The broadness of the > > TK-805 is part of the problem and this could all go away by > > switching to another Exec II for the remote base. > > I've seen a lot of tk-805d radios used as links... and they are > very popular animals. It would be worth your while to include some > band pass selection (cavities typical) in series with the radio. > > > For the splits, we have both (high TX and low TX) here in Maryland. > > The overall plan is to connect the new repeater with the remote base > > to an existing hub repeater on 449.225 TX and 444.225 RX. > > Clint Eastwood called it a "cluster $%^&" in one of his movies. > > Keep in mind the closest frequency spacing from any transmitter > to any receiver is your largest gorilla in the room. > > > Skipp, I like the additional notch in the repeater duplexer trick. > > That alone may do it. > > I do a lot of close spaced in-band commercial radio repeating and > the notch in the reciver antenna path "is da dope" to take out the > unwanted visitor. If this is a fixed frequency remote used only > for repeater linking... then you should also include a notch or > "suck out" cavity on the remote radio, tuned to the repeater > transmitter frequency. We would "assume" the remote radio to > be operated half duplex? > > > I did the T-to-T thing with 2 and 4 band pass cans. The loss > > was in the 5-6 db range with 2 cans on each side. Not > > really worth it. If it were 2db per side, I would live with it. > > Something is wrong with your setup... you should be able to do > better than the 5-6 dB loss value. Since your power levels are > relatively modest (vs what they could be) you could actually > replace the band-pass cavities dual port-hole with simple suck > out notch cavities on the unwanted frequencies as long as > things don't get too crazy with choices of frequencies, power > level and a few other considerations. > > > Thanks again for all of the input. Sometimes just talking it through > > helps a bunch. > > Dwayne Kincaid > > WD8OYG > > Just think of the gas money you'll save by not having to drive to > the repeater site to disable a locked up link/remote base system. > > cheers, > skipp >
Dwayne, I am not sure what the actual setup is that you are trying to co- locate on the same tower. Maybe you could re list the frequencies? Here are a few facts about isolation that may help: Vertical separation of antennas on 450 Mhz of 10 feet gives almost 50 db of isolation. 20 feet vertical separation gives around 60 db of isolation. The spacing is figured from center to center of each antenna. Horizontal separation of 10 feet on 450 Mhz gives about 30 db of isolation. Horizontal separation of 100 feet on 450 Mhz gives about 50 db of isolation. It is much easier to get more isolation with a notch cavity than it is with a pass cavity. Combining with cavities will usually require an isolator on each transmitter in addition to the cavities. A pass cavity or a low pass filter is always required after an isolator to reduce 2nd harmonics generated by the isolator. When adding a second station on a tower you need to figure the isolation between each stations tx and rx the same as if you were building a repeater. With separate antennas the antenna isolation gets you the biggest part of that isolation. On a multiple stations tower also don't ignore tx to tx isolation as you can have intermod problems if proper isolation is not provided. Keep in mind just because a transmitter is low power that most of the same problems still exist as with high power. A 10 watt transmitter is only 10 db difference from a 100 watt transmitter when figuring isolation required. 73 Gary K4FMX
