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 Yes, but the NF is unpublished & unknown.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
