Bob, Some of us are geographically disadvantaged when it comes to availability of equipment. Here in rural Australia, anything secondhand for Amateur Repeater construction is rare, shipping of anything is expensive. From what I read on the group, the U.S. Is overloaded with surplus equipment, sometimes at bargain prices. For me to buy and ship that "cheap" 1/4 wave can and pre-amp would be more expensive than buying a new Simrex Pre-Selector :-) Since this is a hobby for me.......not a paid commercial "day job" I will take the chance on the NF aspect and have my fun experimenting and testing :-) IF the Simrex-GLB product did not perform..........the word would spread faster than the Black Plague and no one would buy them........
73, Jack. VK4JRC Sent from my Apple iPad Tablet PC On Jul 31, 2010, at 11:30 PM, n...@no6b.com wrote: > At 7/30/2010 08:31, you wrote: > > >Re: Simrex - GLB Pre-Selector Pre-Amplifier > > > > >>> Yes, but the NF is unpublished & unknown. I therefore > > >>> assume it's poor, maybe 3 dB? > > > >Once again, the NF depends on what device arrives in your > >specific Simrex (aka GLB) Pre-Selector. It wouldn't hurt > >or be impossible to ask. > > Nothing new here - same goes for different versions of preamps, i.e. ARR > bipolar vs. GaAsFET. > > > >>> A Chip Angle GaAsFET @ UHF has 0.5 dB NF. Put a 1/4 > > >>> wave pass cavity with 0.5 dB loops in front of it & > > >>> you have a narrow 1 dB NF front-end. I'll take 1 dB > > >>> NF over 3 dB NF any day. > > > >You're actually comparing two different boxes. > > Nope - comparing GLB vs. GaAsFET/pass cavity combo. > > >I have measured all the original GLB Pre-selectors and their > >performance values are very realistic (no surprises). > > Care to publish your results here? > > > >> I guess it comes back to price too, a 1/4 wave can plus > > >> pre-amp will cost more money....... > > > >> GaAsFET preamp is ~$130. I don't think I've ever paid more > > >> than $50 for a pass cavity, so the total is ~$100 less than > > >> the GLB unit. > > > >Reads like you're comparing a new Preamp with a used cavity > >against the price of a new Simrex (GLB) Pre-selector. That's > >not really fair... > > Perfectly fair. Used pass cavities in good condition are plentiful. Can't > remember the last time I saw a used GLB or equivalent unit for sale, so I'm > simply comparing what's readily available. > > >One of the really nice (and mostly overlooked) items about > >the Simrex (GLB) unit construction (and operation) is the > >Post (active) Amplifier Filtering (tuned circuits). For more > >than one real reason they can be one of the most under > >reported "bacon saver" in your fry pan. > > A single pass cavity usually has enough out-of-band rejection to be totally > adequate on its own - no post-preamp filtering needed. > > Then again, the fact that post-device filtering is used in the GLB makes me > worry about the actual selectivity ahead of that device. If there's only 1 > or 2 resonators ahead of it, that's not much protection. A 1/4 wave bottle > will provide much more rejection ahead of that first amp, and with less > loss hence lower NF. > > IMO the Simrex amplified preselector is a space-saving compromise, nothing > more. > > Bob NO6B > >
