From: mcmurtrie@pixelmemory.us
In article ,
dplatt@coop.radagast.org (David Platt) wrote:
> >>Does anyone see an issue with mounting a pre-amp for a attic mounted
> >>antenna in
> >attic with the antenna ?
> >>
> >>Will the attic heat cook the pre-amp ?
> >>
> >>Thanks
> >
> >I design such equipment, and we life test it for a month at 85C. It
> >has to meet spec all through that - and down to -40C. It'll be ok
>
> I'd expect that there may be somewhat reduced long-term reliability
> due to the heat... continued high operating temperatures are
> notoriously bad for electrolytic capacitors. A preamp designed for
> commercial-grade service, and built with high-quality 105C capacitors
> would probably be less subject to trouble than designed-to-be-built-
> cheaply consumer-grade junk. You often get what you pay for :-)
>
> Some of those cheap "mount on the mast" preamps and "active antenna"
> systems have caused real problems in the past. There was an incident
> a few years ago in which one or two of these were installed on boats
> moored in a harbor here in Northern California. Under certain
> conditions they'd "go unstable" and break into spurious oscillation
> (always a risk for any amplifier) and they were squealing enough UHF
> noise back out through the antennas to saturate and blank out GPS
> receivers located within a mile or so of their location. This is a
> Very Bad Thing for captains who are trying to enter a fog-bound harbor
> safely!
Ceramics are in the hundreds of microfarads now so electrolytic caps are
becoming rare except for line power rectification. Ceramics are
smaller, more reliable, handle more current, and don't need special
soldering. There are even ceramic capacitors with resistive dampening
to prevent ringing.
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