[Premium-Rx] What's in a WJ-8716 front end preselector?

[stephous]

Tim,

Having worked on a few of these radios I can tell you that there is nothing
of a mechanical nature inside the box. The filters are electronically
switched. I no longer have the manuals so I cannot tell you the specifics.
Let's just say that there are no user serviceable parts. For our purposes it
is a black box. The only problem I have ever seen was related to a loose
connector. Be careful if you must open it!

I open black boxes when I cannot locate spares. It is preferable to leave
them be. I am doing R&R on an 8617 HV can right now. Some black boxes are
more prone to failure and are in very limited supply. Those of us who have
spares tend to hoard them knowing what the future will hold.

There is very little inside the 8716/18 to fail. The MFP version is a
different story.

It is good to be curious and know your radio. Learning to repair it and how
to obtain repairs is also a good thing.

Steve


----- Original Message ----- 
From: "Brooke Clarke" <brooke at pacific.net>
To: "Tim Shoppa" <shoppa at trailing-edge.com>; <premium-rx at mailman.qth.net>
Sent: Wednesday, November 28, 2007 8:51 AM
Subject: Re: [Premium-Rx] What's in a WJ-8716 front end preselector?


> Hi Tim:
>
> How about opening the hood and take a photo of the engine?
> I doubt there's any motors in there.  More likely fixed L and C components
or
> filters that are switched in or out of the coax line.  My SDR-IR receiver
uses
> small mechanical relays to switch in or out different filter sections.
Each
> relay is in series with all the others so you can insert different
combinations
> of low pass and high pass filters.
>
> Have Fun,
>
> Brooke Clarke
> http://www.PRC68.com
> http://www.precisionclock.com
> http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam
>
>
> Tim Shoppa wrote:
> > I've got a WJ-8716 that has a front end preselector in it. It's a big
> > metal box with obvious coax in, coax out, and some presumably digital
> > and power wiring going into it too.
> >
> > I'm familiar with, say, the R-390A's front end preselection: a bunch
> > of octave-wide tunable LC narrow filters, with mechanical coupling
> > between the main tuning and the slugs that tune the L's. Pretty
> > nifty and perfectly obvious to me how iwoks.
> >
> > Is this how a WJ-8716 preselector works too? Are there little motors
> > moving slugs up and down inside as I tune, and banks of slugs
> > for each octave? Or does it work on some entirely different mechanism?
> >
> > Tim N3QE
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