[Elecraft] K3 Sub-receiver use

[Alan Bloom]

The K3's S-meter reads up to S9 + 60 dB, which is -13 dBm.  The noise
floor in 500 Hz bandwidth with preamp on is around -136 dBm.  So an IF
switch really needs more than 120 dB isolation to avoid cross-talk
between the main and sub-receivers.

That is certainly possible but it's not trivial either.  As Guy says,
you have to pay careful attention to grounding, power supply decoupling,
and other alternate paths in addition to the switch isolation.

If you want to switch in real time (say on alternate sweeps, so the P3
can display both main and sub "at the same time") then you'd need to use
solid-state switches.  Probably several sections to get the required
isolation. 

It should all be do-able.  A nice project for Wayne in his "spare
time."   :=)

Alan N1AL


On Mon, 2010-05-31 at 12:33 -0400, Guy Olinger K2AV wrote:
> I don't doubt for an instant what you say.
> 
> I'm thinking the common ground path issues and cable routing issues
> would get it, not that you couldn't do it with the relays
> "standalone".  And then the complaints would start about hearing
> signals move in one RX while tuning on the other, starting with 6m and
> moving down.
> 
> And parts are not the only cost.  After all you can't weigh software,
> worry or frustration.
> 
> 73, Guy.
> 
> On Mon, May 31, 2010 at 11:06 AM, Tom W8JI <w8ji at w8ji.com> wrote:
> > Others are asking for that to be switchable back and forth between the
> > two *dynamically*.  This involves both IF's and allows for signals in
> > the IF of one RX to be heard in the other.  This would a switch with
> > 100 dB isolation.  It would be an expensive option, plus some
> > significant new code.  Don't think this complexity is commercially
> > feasibility.>>
> >
> > I can get in that range in a 50 ohm system with a single relay at HF in a
> > proper layout using the right style of relay.
> >
> > I have not tried it with miniature relays, but I see no reason why it could
> > not be done. It would probably take three $2 SPDT relays the size of a
> > sixteen pin DIP package.
> >
> > 73 Tom
> >
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