--- In [email protected], "ldgelectronics" <[EMAIL PROTECTED]> wrote: > > Hi all, > > We've added a preamp to our local repeater and found that it had too > much gain. It started picking up lots of garbage.
Elaborate on the term <garbage>. Intermod? Users from distant repeaters? If intermod, it may be produced in the preamp or receiver if not protected enough with selectivity ahead of the preamp. If users, you've achieved your goal of increasing the sensitivity of your system. Adding attenuation ahead of the preamp very effectively removes much of the sensitivity you've gained with the preamp. I'd deal with that kind of garbage in other ways. Reducing the gain > by about 6db seems to put it in a good operating place. > > We also found that by putting the 6db attenuator on the input of the > preamp (right after the band pass can), it's real easy to add in the > system. If we mount it after the preamp, we'll need an adapter on > each side of the preamp to make it all connect up. Obviously it would > be best if we could put the attenuator after the pre and have no > adapters, but it's not convenient. Attenuation placed ahead of the preamp is nowhere near the same as placing it behind. Placing it behind reduces the gain of the preamp while retaining the noise figure of the preamp. In my experiments on 2m with an ARR preamp and Motrac receiver, up to about 10db of attenuation after the preamp did not reduce system sensitivity. > > The question is how much trouble will be getting into by putting the > 6db attenuator on the input side of the preamp? Would it still be > better to put it after the preamp even though it would add two > adapters? In most cases yes. I've read about cases on this group where attenuation ahead of the preamp is the proper thing to do, but the reasons escape me. Laryn K8TVZ > > Thanks, > > Dwayne Kincaid > WD8OYG >
