[hpsdr] preselectors

[Graham Haddock]

Henry:

Besides the ones you already mentioned, some additional things to think
about are the series resistance of a solid state switch.  The "switch" 
is usually
a FET of some kind, which will have a series on-resistance of a fraction
of an ohm to several ohms.  This series resistance causes losses,
or can reduce the "Q" of a resonator if used for tuning.

The on-resistance can be a function of applied voltage, thereby introducing
additional distortion/mixing not associated with relays.

Price - solid state switches can be cheaper than relays these days, in 
addition
to much smaller and faster.

The parasitic capacitance and inductance of a relay is quite different than
a solid state switch.  Unless the relay is a specifically designed to be an
RF relay, the parasitics are usually less with the solid state switch, 
and it
is easier to go higher in frequency with the solid state switch due to 
smaller
size, and ability to get the controlled impedance transmission line
much closer to the switch element.

--- Graham

==

Henry Vredegoor wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
>   
>
> ------------------------------------------------------------------------
>
> Hi All,
>  
> What would be the advantages/disadvantages of having the preselector 
> switched by relays or some sort of semiconductor switches?
> (Besides the obvious ones like e.g. mechanical size, power handling, 
> switch-over times to name a few)
>  
> ??
>  
> Henry.
>  
>
>     -----Original Message-----
>     *From:* hpsdr-bounces at hpsdr.org [mailto:hpsdr-bounces at hpsdr.org]
>     *On Behalf Of *FRANCIS CARCIA
>     *Sent:* maandag 12 maart 2007 14:43
>     *To:* hpsdr at hpsdr.org
>     *Subject:* [hpsdr] preselectors
>
>     Hi all,
>     I looked at the schematic of my Cubic prepost selector and it is
>     quite complicated. It has an 8035 processor to select the relays
>     controlling Silver mica caps and 3/4 inch square package
>     adjustable inductors. The board is about 10 by 12 inches packed
>     with 1/4 crystal can relays and control parts. This is well above
>     the scope of out board profile.
>     A good preselector to check out is the Cubic R3030. You can
>     download the manual from bama or premium RX. It uses pin diodes
>     for higher bands and relays for low. Also has a CP640 grounded
>     gate fet amplifier. The R3030 MDS is about -136 dBM.
>     I think it has about 10 filters to cover 15 KHz to 30 mhz. It
>     takes 4 bits to a local decoder to select the correct filter.  The
>     can inductors could be replaced with torroids. The L vales are on
>     the schematic. The board is about 4 by 6 inches.  fc
>
> ------------------------------------------------------------------------
>
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