[Elecraft] K3 Sub-receiver use

[Joe Subich, W4TV]

 > 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.

I don't know that the requirement is for alternate sweep display -
just the ability to select main or sub-RX without the need to open
the K3 and make wholesale cable changes.

73,

    ... Joe, W4TV

On 5/31/2010 3:49 PM, Alan Bloom wrote:
> 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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