On Jul 30, 2010, at 9:31 AM, n...@no6b.com wrote:
> At 7/29/2010 14:59, you wrote:
> >Re: Simrex - GLB Pre-Selector Pre-Amplifier
> >
> >The Simrex (aka GLB) units are actually amplified pre-selector
> >assemblies, not just plain wide-band Receive Pre-Amplifiers.
> >
> >There's a reason why these units offer/spec 8dB Gain versus
> >the others "un-protected" preamps. The less obvious gain
> >when compared to traditional GasFet and BiPolar RF Preamplifiers
> >is due to the internal integrated pre and post filtering.
> >
> >What does it all mean...
> >
> >If you have some types of IMD "grunge problems" when trying
> >a regular GasFet/BiPolar Preamplifier, chances are your results
> >using the Simrex/GLB pre-selector might be better. The pre and
> >post filtering inside the Pre-Selector is a big deal.
>
> Yes, but the NF is unpublished & unknown. I therefore assume it's poor,
> maybe 3 dB?
>
> 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.
>
> The Simrex unit makes a nice solution if you don't have the physical space
> for a 1/4 wave bottle. 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. Not the best solution
> (higher loss, can't be retuned if he ever has to change freq.), but I guess
> it works for him.
>
> Bob NO6B
>
>
If you picked the UHF Simrex unit with less gain, more selectivity than the
standard model, then the noise factor should be better? I guess it comes back
to price too, a 1/4 wave can plus pre-amp will cost more money.......
No such thing as a free lunch :-)
73,
Jack VK4JRC
