Kent Chong wrote: > Good day everybody, > > For an off-air repeater, we normal use bi-direction amplifier (BDA). > A BDA is constructed using two amplifiers for uplink and downlink, > interconnected with two duplexers (or circulators) at the front end. > In order to prevent the BDA from looping oscillation, the duplexer > (circulators) must provide sufficient isolation. > > We have built such BDA; however, we face the oscillation problem. We > are thinking of breaking the BDA into two parts: uplink and downlink. > And we amplify uplink and downlink separately. In this way, we need > four duplexers (or circulators). Would this method work? Anybody > could advise?
If you're having oscillation problems, either there is not enough isolation between the antennas, ie, too close, or the gain of the amps is too high, or a combination of both. Measure the isolation between the two antennas. It should be at least 12 dB MORE then the gain of the BDA. TX-RX and EMR are two major BDA manufacturers, also check out <http://www.rfsolutions.com/> There's several cheap BDA companies out there that make junk. If you see a BDA with a price tag of only $1000 or so (new), run away! Also, a good BDA will occupy more space then, say, an external modem, by a factor of at least 10. (Yes, it's bigger then a bread box!) -- Jim Barbour WD8CHL
