[K3] KRX3 Antenna Flexibility

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[K3] KRX3 Antenna Flexibility

Bill W4ZV
I believe many are now receiving their KRX3s and are about to discover the amazing benefits of True Diversity with the K3.  As some of you know, I love to chase DX on 160 and will only say Diversity is something I will never be without.  I typically use a directional 3-el vertical array on transmit and a Beverage in the same direction on receive.  In Diversity mode, I use my TX antenna on Main and the Beverage on Sub.  Sometimes it's absolutely amazing to hear signals switching back and forth between ears in <1 second!  I'm sure these signals would exhibit extreme QSB if listening on one antenna by itself.

Although the K3 has an effective switching system for most use, there's one situation which I've run across which needs an external solution.  This is the (somewhat unusual) case when a signal will be present on only one of the antennas being used in Diversity.  I found I wanted a quick way to switch out of Diversity, so that either the TX or RX antenna alone would be applied to both ears.  Otherwise I'm feeding extraneous noise with no signal to one of my ears.

A simple solution to this is to use an external splitter for the Beverage input.  This should be a Magic-T splitter (not just a T-connector) which preserves impedance and isolation between the two receiver channels.  You can either build one yourself (using two ferrite cores and a resistor) or buy a commercial unit (Mini-Circuits ZSC-2-2 or DXE RSC-2 are both ~$50).  The Mini-Circuits unit is available in either 50-50 ohm or 75-75 ohm versions and the DXE is 75-75 only.  If you make it yourself, you can make one which will match a 75 ohm antenna to the 50 ohm RX inputs of the K3.  See W8JI's website for details to roll your own:

http://www.w8ji.com/combiner_and_splitters.htm

So how does this work?  I feed my Beverage to the splitter and then connect its two outputs to RX ANT and AUX RF.  When I want Diversity, I use my TX antenna (ANT1) on Main and the Beverage on AUX RF (the KRX3 allows you to choose either the same antenna as Main or AUX RF).  Here are the two cases to switch from Diversity to either the TX array or RX antenna using a splitter.

1.  When I want my Beverage on both ears, I simply "tap" RX ANT.  To go back to Diversity Mode, I "tap" RX ANT again.

2.  When I want my TX array on both ears, I "hold" RX ANT which switches the KRX3 to the same antenna as Main.  When I want to return to Diversity, I "hold" RX ANT again.

One tap or hold and you instantly can go out of (or back into) Diversity with either your TX or RX antenna in those rare cases when a weak signal may be on only one antenna.

There's of course a ~3 dB loss when you use a splitter, but this isn't significant on the low bands since the external noise floor is so far above the noise floor of the K3 (...even if ATT is on).

True Diversity in the K3 is a remarkable achievement compared to other rigs costing much more (neither the IC-7800 or Orion has True Diversity).  In my configuration, I have it in a rig which cost me ~$2.8k including 6 filters (2 of which are unnecessary for non-contesters, i.e. a 1.8k and 200).

If you want to hear some recordings using Diversity, listen to EI6IZ's CW and SSB pileups here:

http://ei6iz.com/  (Audio links at the bottom of his KRX3 article, and you really need stereo headphones for the full effect.  BTW, I never use anything but headphones for DXing or contesting.)

73,  Bill  W4ZV

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Re: [K3] KRX3 Antenna Flexibility

Bill W4ZV
Reposting this since the Elecraft list on qth.net was down earlier:

Bill W4ZV wrote
I believe many are now receiving their KRX3s and are about to discover the amazing benefits of True Diversity with the K3.  As some of you know, I love to chase DX on 160 and will only say Diversity is something I will never be without.  I typically use a directional 3-el vertical array on transmit and a Beverage in the same direction on receive.  In Diversity mode, I use my TX antenna on Main and the Beverage on Sub.  Sometimes it's absolutely amazing to hear signals switching back and forth between ears in <1 second!  I'm sure these signals would exhibit extreme QSB if listening on one antenna by itself.

Although the K3 has an effective switching system for most use, there's one situation which I've run across which needs an external solution.  This is the (somewhat unusual) case when a signal will be present on only one of the antennas being used in Diversity.  I found I wanted a quick way to switch out of Diversity, so that either the TX or RX antenna alone would be applied to both ears.  Otherwise I'm feeding extraneous noise with no signal to one of my ears.

A simple solution to this is to use an external splitter for the Beverage input.  This should be a Magic-T splitter (not just a T-connector) which preserves impedance and isolation between the two receiver channels.  You can either build one yourself (using two ferrite cores and a resistor) or buy a commercial unit (Mini-Circuits ZSC-2-2 or DXE RSC-2 are both ~$50).  The Mini-Circuits unit is available in either 50-50 ohm or 75-75 ohm versions and the DXE is 75-75 only.  If you make it yourself, you can make one which will match a 75 ohm antenna to the 50 ohm RX inputs of the K3.  See W8JI's website for details to roll your own:

http://www.w8ji.com/combiner_and_splitters.htm

So how does this work?  I feed my Beverage to the splitter and then connect its two outputs to RX ANT and AUX RF.  When I want Diversity, I use my TX antenna (ANT1) on Main and the Beverage on AUX RF (the KRX3 allows you to choose either the same antenna as Main or AUX RF).  Here are the two cases to switch from Diversity to either the TX array or RX antenna using a splitter.

1.  When I want my Beverage on both ears, I simply "tap" RX ANT.  To go back to Diversity Mode, I "tap" RX ANT again.

2.  When I want my TX array on both ears, I "hold" RX ANT which switches the KRX3 to the same antenna as Main.  When I want to return to Diversity, I "hold" RX ANT again.

One tap or hold and you instantly can go out of (or back into) Diversity with either your TX or RX antenna in those rare cases when a weak signal may be on only one antenna.

There's of course a ~3 dB loss when you use a splitter, but this isn't significant on the low bands since the external noise floor is so far above the noise floor of the K3 (...even if ATT is on).

True Diversity in the K3 is a remarkable achievement compared to other rigs costing much more (neither the IC-7800 or Orion has True Diversity).  In my configuration, I have it in a rig which cost me ~$2.8k including 6 filters (2 of which are unnecessary for non-contesters, i.e. a 1.8k and 200).

If you want to hear some recordings using Diversity, listen to EI6IZ's CW and SSB pileups here:

http://ei6iz.com/  (Audio links at the bottom of his KRX3 article, and you really need stereo headphones for the full effect.  BTW, I never use anything but headphones for DXing or contesting.)

73,  Bill  W4ZV