Hi Neal, Rich wb2dss responded (a big thank you Rich) to my last post and sent out some well lighted high-res pictures of his 2 meter GLB pre-selector. Another drum roll...
Yes, his pre-amplifier clearly shows an MRF-901 in place as the active device. So I'm working up the diagrams for the circuits to both the MRF-901 and the BF981 devices. Aria-GLB mentions in their current ads reportedly offers a Gasfet device option for the 220 and higher preamp models. I'll deal with a diagram for those models if and when I run across them. I've got a lot of data on the MRF-901 and now the BF981 so I'll run the relative numbers after I gather more information. A first glance and test of the BF981 indicates/measured a relative noise figure value of <.6dB to .7dB, which is actually a fair value better than I would have thought for an older Dual Gate Mosfet circuit. Although a Gasfet would have a lower (better) noise figure... would it really be practical to retro-fit (modify) an original GLB Preamp for the difference in noise figure performance. I don't yet plan to ramp up an MRF-901 preamp for noise figure comparisons.... but I might. Nothing wrong with all the Gasfet gain if you can keep a handle on it (tame the tiger). One ham out here on the left (west coast) gets away with series GasFet preamps separated only by a 1dB pad. It's red hot, seems to be stable and works like gang busters... not to mention the mountain top is not super clean. So I have seen nearly 30dB of preamplifier layout behind good enough generic T1500 type band pass filtering work fairly well in actual applied operation. Nice to have all that gain if you can get away with it... cheers, skipp > Neal Newman <cozy...@...> wrote: > Skipp I opened up My 2 meter GLB preamp pre-selector. it is > an MRF-901. Years ago there was an article in one of the > Ham radio handbooks that showed a 4 element UHF preamp/ > pre-selector that I built for ATV use. and it too was based > on an MRF-901. It worked great. GaSfets I feel have too much > gain, and introduce too much noise for repeater use. If I'm > not mistaken the Kendercom receivers use 2 MRF-901's in the > Front end. Other than Commercial Gear(motorola/GE) I felt > the Kendercoms were the best receivers out there. the newer > Maggiorees are not bad either. Depends on what else is on > your site that can create havic. > Neal
