Re: [amsat-bb] follow-up: GaAsFET part help

[Alfred Green <nu8i@xxxxxxxx>]

Scott Townley wrote:
> 
> Last week I wrote regarding my dysfunctional Mirage mast-mount preamp,
> and mentioned in passing my dysfunctional TE Systems preamp that uses
> the same active device.
> 
[snippy]

> 1a.  I've always wondered...how do we/manufacturers "get away" with
> using generic power relays like that for RF (even VHF) applications?
> How would one translate "power" ratings to RF?  There surely is some
> performance tradeoff between cheap(er) power relays and going coaxial.
> The Mirage preamps at least use an RF-rated Aromat relay, 

As the contact length is a small part of a wavelength even at 144MHz the
impedance bump is low enough not to be a factor. The downside is that
the isolation is fairly poor. I have used the miniature SPST PC mount
relays in several projects up to 2m with no problems. As they are
smaller they perform better than the open-frame types. Even better ones
are available now; for instance the Omrom G5Y is rated to over 900MHz
with better than 60dB isolation and negligible loss and SWR. Digi-Key
has them for around 6 bucks. I've used them up to 1296.

The quoted power ratings are usually for hot switching. You can get away
with a lot more if you sequence it properly.

73  Alf  NU8I
Scottsdale AZ DM43an
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