Randie Ohtsji [4555] wrote:

> Hi Paul,
>
> Actually, I wanted to have the capability to switch:
>
> 1) One antenna between two receivers
> 2) Two antennas between one receiver
> 3) One antenna between one transmitter and one receiver

> I took a look at the HP URL
> (http://hpcc923.external.hp.com/HP-COMP/rf/1n5719.html)
> which Clyde had suggested, but these appear to be only data sheets.

  Of course.  You're supposed to *know* the circuits!

  OK, I'll broadcast in part the reply I made to Dan Larson
<dlarson@citilink.com>.  Does this give you enough ideas?

> Hello Dan.

  <rending/ tearing noise>  (Can't find the snippers!  Never can when
you want them)

>  If your problem is in fact the one you mention; choosing between feed
> from a cable or a VCR, then it seems to me the job is done for you!
> Look for the module from a VCR which contains this function.  This
> item, I can assure you, is *very* available in the "pre-loved"
> department.  One minor theme on this list is "KISS" or "don't
> re-invent the wheel - except for fun/ education".
>
>   Now, if this *doesn't* suit, then go and make a switching unit with
> whatever diodes you have to hand.  I suggest using six diodes as
> follows:
>
>         Source 1 o--->I---+---I<---+--->I---+---I<---o Source 2
>                           |        |        |
>                           -        o        -
>                           ^     Output      ^
>                           |                 |
>         Switch   o---Do---+-------Do--------+
>                   (buffer)    (Inverter)
>
>   Not shown are the bias and bypass components at each source, output
> and each side of the inverter.  The two middle diodes may
> alternatively be exchanged for a balun transformer if you can figure
> out the biassing and such.  The principle is that you counteract the
> diode "off" capacitance by providing shunt paths with counter-switched
> diodes.  If you were tuning this for a specific frequency, you'd
> actually tune out these capacitances too.
>
>   But you are not limited to using diodes to do the switching.  The
> above assumes as you more-or-less implied, that you have plenty of
> signal and could stand a couple of dB loss.  If it is the other way
> about, just use broadband amplifier chips as the switching elements,
> parallel their outputs (or use a balun) and switch their respective
> supply lines.
>
>  This presumes you are not going into production, and "low cost" means
> $10 or so is OK but $50 is not.

  Cheers,
        Paul B.