[Elecraft] KPA500 and KAT500 Ports

[Jim Wiley]

Here's a thought.  I was faced with the problem of having a fairly large 
selection of HF antennas, and 3 operating stations.  What to do?    
After some thought, I decided to create a matrix-type switch that could 
control 10 different antennas into any of 5 rigs, in any combination.  
That equates to 50 different setups, not counting multiple feeds. 


The controller also allows multiples, in that any antenna can be 
connected to more than one rig, and any rig can be connected to more 
than one antenna.   This is occasionally useful for special receiving 
situations or experimentation.


The controller features a locking function that works with my station 
controller (the gadget that manages which rig is allowed to be "on air" 
and which audio or keying source is delivered where, as well as audio 
outputs from the associated receivers).   The lockout function makes it 
impossible to transmit into another rig, or cause any other similar 
problem.   If I could have my 'druthers, I would have integrated the 
lockout function directly with the rigs themselves, but when it was 
being built,  very few rigs (if any) were available that could do this.  
Modern rigs, such as the K3 could accommodate this, I think.   I do have 
to be careful and not key up a rig "internally" (using it's own transmit 
function button).  But there is a BIG red light that comes on to help 
remind me.  Only did that once, years ago, with a Kenwood TS-940S, but 
that rig's input overload protector handled the fault with no other 
apparent damage.


My version does have a small amount of cross-talk (about -50 dB) that a 
somewhat better design could reduce further.  Overall, the project was 
extremely successful, and works better than I could have envisioned.  It 
uses a control-head + switch unit architecture (the actual matrix switch 
is mounted away from the operating position).   It was NOT cheap, but 20 
years later is still performing flawlessly, so the cost per year 
continues to decline.  I was able to recoup some of the expense by 
selling a hat-full of other coax switches - which by the way would drive 
me crazy to operate as there never seemed to be the right combination 
for all the different setups I wanted to use.


I did NOT attempt to create something that would perform at VHF and 
above.   My switch is strictly a HF/MF device.   The insertion loss is 
on the order of 0.5 dB or less, depending on band.  Measured VSWR, last 
time I looked, tends to stay below 1.25:1 on any frequency or equipment 
combination, except of course for multiple connections.   Not perfect, 
but good enough.   An antenna coupler makes what minor corrections are 
needed, if I were to care about such things, which usually I don't.  
Getting that last little bit of SWR out is not worth the trouble, 
usually, particularly at HF.  VHF and above is different.   Handles 1500 
watts with ease.


- Jim, KL7CC

.

Eric Swartz - WA6HHQ, Elecraft wrote:
> I'd like to redirect this discussion to what is be desired for an 
> external antenna / rig switching add-on box for the K3/KPA500 and/or 
> KAT500.  
>