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Filters & Antenna Switching
In a basic ham station you connect the coax from your antenna to the back of your radio and get out there and call CQ.  As your station grows you add additional antennas.  Now you need a switch to select the correct antenna when change bands.  Later you might get into DXing and/or contesting.  Now you will want some automation that switches your antenna switching for faster band changes with fewer mistakes.  Life gets more complex.

But as long as you are a one radio/one amplifier it is all pretty straight forward.  Once you decide to get into SO2R (single operator two radio) contesting your antenna switching architecture gets much more complex. 

Now you need a 100%  sure method to make sure that you can't have both radios on the same band. 




The first challenge is to make sure that I can not transmit with both radios tuned to the same band.   The Flex 6700 handles that internally.   I was able to get rid of a number of accessories (such as the MicroHam MK2R+) that I needed to use before I got the Flex.  That has simplified my shack considerably.

For filtering, I use two kinds of filters.  One set comprises two W3NQN band-pass filters.  These filters connect between the transceiver and its amplifier to severely attenuate any signals other than those for the selected band.  These are switched by a USB connection directly from the Flex radio.

The second set of filters are coaxial stubs, lengths of coaxial cable, cut in very strictly determined lengths, to attenuate harmonics.  The stubs are pretty large and are installed in heavy duty equipment enclosures.  There is one set of stubs for each contest band between 160 and 10 meters - six in all.  These connect in between the amplifier and its chosen antenna for the band you are operating on.  Here's where it gets complicated.

I use a set of relays to switch the appropriate antenna and stubs to the Flex Radio and amplifiers.  The relay switching apparatus gets its input via USB connection to the Flex radio. 

An Antenna Genius antenna switch from Ranko, 4O3A sitches the appropriate antenna for each Slice (think radio) from the Flex radio.  The radio and the Antenna Genius communication via the Local Area Network (LAN) in my shack.  The switch reads the frequency of each Flex Slice and switches the antennas accordingly.    The Antenna Genius has inputs for  the coaxial transmission line from six antennas after filtering and outputs for two Flex Slices and their amplifiers. 

From there, the antenna transmission lines go outside through conduits to a connection both with lightning protection devices and grounded to yet another ground rods.  And from there out to the antennas.

Bill Axelrod  11 April 2017

And you need filters to help ensure that your transmissions on one band won't hurt the front end of your second receiver on another band.  And, of course, a you need a way to switch those filters and perhaps automate all of that. 

These filters also are critical in minimizing intra-station interference when doing SO2R.

Here's how I dealt with it at K3WA.  Now that I have updated my station with a Flex 6700 radio I am back to a single software defined radio (SDR).    The Flex 6700 does SO2R with just one radio.  I had to re-do my filter and antenna switching to match.