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Two K3 Rigs: How to wire a Mute Connection to one K3 while the Second K3 is Transmitting. Field Day.


Mark W2OR
 

A K3 Wiring Question - - How to easily mute one K3 while a Second co-located K3 is transmitting: 

 

We need to know how best to (easily) hard-wire a connection between two K3 radios, a connection that will mute a second, receive-only K3 automatically when a co-located 'main' K3 is transmitting with a KPA500-watt amp.  Both are tuned to the same band (HF and VHF).  Each has its own separate, nearby antenna.  The intention is to fully protect the circuitry in the second receive-only K3 from RF overload or damage.

The K3 units will be used in a multi-op environment, and so we hope to keep this mute connection as simple as possible.  
There are probably two or more ways to do this, so am open to suggestions on all. 

GL on Field Day, everyone.
73 de Mark
.. w2or ..
(( The responses to this question should be very 'interesting' ...))
 


Tom Doligalski W4KX
 

I think you need to do more than simply “muting” the second K3 to protect its front end. 

W4KX

 

On Jun 20, 2020, at 8:48 AM, Mark W2OR via groups.io <reston2010mm-orders@...> wrote:



A K3 Wiring Question - - How to easily mute one K3 while a Second co-located K3 is transmitting: 

 

We need to know how best to (easily) hard-wire a connection between two K3 radios, a connection that will mute a second, receive-only K3 automatically when a co-located 'main' K3 is transmitting with a KPA500-watt amp.  Both are tuned to the same band (HF and VHF).  Each has its own separate, nearby antenna.  The intention is to fully protect the circuitry in the second receive-only K3 from RF overload or damage.

The K3 units will be used in a multi-op environment, and so we hope to keep this mute connection as simple as possible.  
There are probably two or more ways to do this, so am open to suggestions on all. 

GL on Field Day, everyone.
73 de Mark
.. w2or ..
(( The responses to this question should be very 'interesting' ...))
 


Michael Foerster
 
Edited

You Would need to use the PTT output from the transmitting K3/KPA500 to drive a 12v relay which would disconnect the antenna and short the second K3 input to ground.  You can drive multiple devices from the PTT.

 If you’re not transmitting from the second K3 then the relay type doesn’t matter, other than it being a SPDT.  If it will be transmitting, then you might want to use a heavier relay.  These are quite commonly used for antenna relay switching.

Mike, W0IH


Bob Evans
 

Mark,

 

That requirement has been solved several ways depending on how deep your pockets are.  Tom is exactly right; this is NOT simply a mute issue alone.  A K3S has an automatic overload relay built in (assuming your K3 is a K3S or a K3 with this feature added.  I don’t believe the early ones had it).  When that feature kicks in, a warning pops up on your K3S that says “reduce overload” or something along those lines.  It is reassuring to know it is there to help but it is not meant to handle overload repeatedly during a contest so another method of protection is needed.

 

The most expensive way is to use extremely tight (say 5 KHz) external bandpass filters on BOTH rigs that “move” with the frequency of each rig.  This takes quite a bit of engineering to get right.  You would also have to make sure both rigs are never within each other’s bandpass so a frequency watch/control facility would be needed as well.  There isn’t enough time to engineer this option if you are talking FD 2020….maybe 2021 if you work fast.

 

The second method that can make sense for a FD type operation is to have a second receive antenna, preferably of a different polarization, mounted a couple of hundred feet away from the transmitting antenna.  Assuming the transmitting antenna is some kind of beam, the receiving antenna would be a vertical antenna (approx. 30db natural cross polarization attenuation).  Placing the vertical off the back of the beam would help too.  Since your second receive only K3 is secondary to the primary K3, it won’t hurt to have loss from a couple hundred feet of coax (even inexpensive RG-6 would work) running to the vertical.  An old vertical (even a mobile whip mounted on a car) is easy to erect for a weekend.  If you didn’t have 200 feet of separation available, then the antenna could be a receive only loop mounted vertically but still mounted as far from the transmit antenna as possible.  Yes, there would be quite a bit of coax loss but your S/N ratio would be better and you could hear everything you wanted…even listening to your transmitting K3 which would probably be 60 over 9.  Experiment with this at 5-10 watts until you are sure your setup works.  Then gradually work the power up on the KPA500 to validate. 

 

A third method that truly is a mute solution is to use a rig protector relay which removes the receive K3 antenna and grounds it during transmit of the main K3.  There is a pin in the AUX connector on the back of the transmit K3 which could trigger that relay connected to the antenna port of the receive K3.  You could also buy a box (I think MFJ makes an inexpensive one  https://mfjenterprises.com/collections/mfj-enterprises/products/mfj-1708b-sdrs) which would do something similar.  Both of these ideas have the severe drawback of not letting you listen while the other rig is transmitting.  Depending on how serious you are about FD and the actual purpose of a receive only K3, this could be a deal breaker.

 

Good luck in FD!

 

Bob K5WA


OZ1BZJ
 

Hi 

Maybe crazzy idea 

Connect the key output from the main K3 to the key input of the secondary.  Set the power out on the secondary as low as possible. 

In that case when the  main station are in TX the Secondary  are as well in this way protecting the RX.  How much that will effect the return power on the secondary I am not sure.  

Not sure if that work, but it is easy. 

73 de OZ1BZJ, Michael



Den 20. jun. 2020 kl. 15.18 skrev Michael Foerster <mcfroston@...>:



[Edited Message Follows]

You Would need to use the PTT output from the transmitting K3/KPA500 to drive a 12v relay which would disconnect the antenna and short the second K3 input to ground.  You can drive multiple devices from the PTT.

 If you’re not transmitting from the second K3 then the relay type doesn’t matter, other than it being a SPDT.  If it will be transmitting, then you might want to use a heavier relay.  These are quite commonly used for antenna relay switching.

Mike, W0IH


Wes Stewart
 

I haven't done this but I think the following will work assuming a KXV3 is installed:

1)  Put a dummy load on the receive only K3(S) antenna port.  Crank the TX power to zero.

2)  Put the receive only K3(S) in "Test" mode.  Caution, this does not survive a power cycle and there is some low level garbage garbage generated.

3)  Connect the receiving antenna to the RX Antenna Input.

4)  Connect the transmitting K3(s)'s Key Out line to the receive only K3(S)'s PTT input.

So you will be "transmitting" on both radios, just with no power out of the receive only one, but it will be muted and its input protected.

Wes  N7WS


On Sat, Jun 20, 2020 at 05:47 AM, Mark W2OR wrote:

A K3 Wiring Question - - How to easily mute one K3 while a Second co-located K3 is transmitting: 


Mark W2OR
 

Thank you, Michael, and thank you, Wes.  Likewise thanks to the others - Thomas, Mike and Bob.

All workable and interesting approaches here.  We'll probably go with that suggested by Michael and Wes, as outlined in their replies, utilizing the PTT link between the two K3 units, etc.  (Yes, these are older K3 units, and not K3s units.)  

73 73 at FD ...  You guys all get an extra 500 points in the FD log book here.
// Mark