[hpsdr] PING ALEX / Preselector

[Henry Vredegoor]

Hi All, Graham,

Exiting news!

I think just the kind of response Eric was hoping for with his PING...?!
;-)

Sorry, English being not my native language, I cannot relate too good to the
phrase "bottom inductor coupled....." :-(

So if possible I would sure like to see some diagram just showing the
principle of the circuit!?
Or a pointer to some more info?

One other remark is that the increased use of Hittite switches (8 X) as
indicated on the 01-APR-2007 revised Mercury block diagram, seems to
increase the Noise Figure of Mercury already from 23.5 to 27.5
(Theoretically, please correct me if I'm wrong...)

So one more good reason to keep insertion losses as low as possible on ALEX
by using relays.


73's,

Henry.


> -----Original Message-----
> From: hpsdr-bounces at hpsdr.org 
> [mailto:hpsdr-bounces at hpsdr.org] On Behalf Of Graham Haddock
> Sent: dinsdag 17 april 2007 1:21
> To: George Medakovich
> Cc: 'High Performance Software Defined Radio Discussion List'
> Subject: Re: [hpsdr] PING Preselector
> 
> 
> ***** High Performance Software Defined Radio Discussion List *****
> 
> George Medakovich wrote:
> > I'm not complaining at all.
> > It was just an expression of curiosity.
> > I thought maybe somebody would chime in with the specifics ;-)
> >
> > George
> George:
> Current status of ALEX is block level diagram on the ALEX wiki page.
> All (50 Ohm) RF switches shown are solid state.
> 
> 1.8 to 30 MHz tunable filter being evaluated is two resonator,
> capacitor tuned, bottom inductor coupled.  Phil H. is preparing to
> evaluate the size inductor needed to get the IP3 of the filter up
> where the filter won't degrade Mercury's IP3 performance.
> 
> Most likely topology has solid state switching of the two 
> sets of tuning
> capacitors in some kind of binary value tree.  Multi-tapped
> (tuning) inductor switched by relays, and bottom coupling
> inductors switched by relays.  The reason for using the
> relays is that the ON resistance of either the Hittite switches
> or the alternate FETs we will evaluate is in the 1.5 Ohm range,
> and that is too high for the coupling inductors, and the max
> voltage of the Hittite switches is not high enough for some
> of the voltages that might be seen in a multi-tapped
> tuning inductor when it works as an auto-transformer when
> certain taps are selected, at maximum signal level.  So,
> for tuning, something like 16 solid state switches and
> 12 relays.  I promise that we won't use a relay where
> a solid state switch can be made to work.
> 
> Depending on the thickness of the toroids chosen to meet
> IP3, we still may be able to fit into the ATLAS card spacing.
> Lots of things still to learn.
> 
> I'll post some sample filter passband shapes and schematics 
> as soon as we
> choose the filter inductors, and switches for the capacitors, 
> and things
> are a little less fluid.
> 
> --- Graham


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