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 Yes, but the NF is unpublished & unknown.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. >>> 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. The Angle, ARR, Telewave, Hamtronics, yadda-yadda brand Pre-amplifiers are just Pre-amplifiers. The Simrex / GLB box is an RF Amplifier with both Pre and Post filters. The lower realized gain of the Simrex / GLB unit is directly related to the additional filtering included inside the box. >>> The Simrex unit makes a nice solution if you don't have >>> the physical space for a 1/4 wave bottle. But it's not the primary reason why I like them. >>> Then again, I know someone who just ordered an even >>> smaller MtronPTI front-end crystal filter to solve >>> a front-end overload problem from a TX over 1 MHz >>> away from his RX. Crystal filters can be very helpful but people tend to depend on them to cure a Symptom. >>> Not the best solution (higher loss, can't be re-tuned >>> if he ever has to change freq.), but I guess it works >>> for him. Sometimes you need a large brick wall with only a small doorway so they obviously have their usefulness. >> If you picked the UHF Simrex unit with less gain, more >> selectivity than the standard model, then the noise >> factor should be better? The less gain is related to the internal filtering "stages", not the device. I would expect the version with the GasFet to have the typical expected NF for that device. Any other available active devices to have Noise Figures commensurate with their typical expected values (for those devices). > I doubt it. But without any real NF numbers, it's all > guesswork. I have measured all the original GLB Pre-selectors and their performance values are very realistic (no surprises). I wouldn't expect a surprise/difference if I ordered the GasFet equipped Simrex Pre-selector. >> I guess it comes back to price too, a 1/4 wave can plus >> pre-amp will cost more money....... No, your selection should be based on your needs. Do you need a bare RF-Pre-amplifier or do you need an integrated, amplified RF Pre-selector box? >> 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... 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. s.
