Icom 627 Antenna Switch For Coax Stub Switching
Well lets talk about coax stubs. If you dont know anything about them I
suggest you visit K1TTT's site and read the coax stub article. (Do a search
Let me explain how they are used. I run a two radio single op station
(SO2R) with one radio as my CQ radio and the other (on another band) as my
multiplier radio. Hence I need to isolate one radio from another.
are two steps to perform. First I use bandpass filters (Dunestar 600)
between the radio and the AMP to cut down about 25-35 db of out of band
signals (incoming and outgoing). The filters are good for about 150 watts
Now since I run 1.5KW output on each amp, I need to attenuate the signal
more than 30 db since I can often hear the 7.0 Mhz cw signal in the other
radio when listening to 14.0 Mhz. So I use coax stubs (one set for each
band, two to a set), on the output of the amp. Here where the EX-627 comes
The 627 is plugged into ACC2 of the Icom and selects a band (coax stub set)
when the band info is generated by the Icom. My bandpass filter auto band
selector is plugged into the 627, so when the 627 selects 20 meters, it send
a signal to the bandpass filters to select 20 meters - so everybody is on
the same band.
The stubs provide an additional 25-30 db of attenuation so that 1.5KW coming
out of the CQ amp is attenuated enough that I don't even hear it on the
other radio even when the antennas are 6 feet apart! Pretty neat.
Now lets talk about the coax stubs. The 627 hooks up to the coax output of
the amp with a coax "T" connector (middle goes to 627 and other end
antenna switch. The 627 selects one of six sets of coax stubs each being
attached to the output of a single band with another "T" connector.
lengths of the stubs and which ones are used are described
on my website.
I use cox stubs on the CQ radio and the multiplier radio (12 sets
total) and the 627 selects each set depending upon the band needed. Since
the harmonic energy going thru the stubs is much less than 1KW, its rating
is sufficient. Works very nice.
BTW I select the antennas manually but will soon go to the WX0B 6X2 antenna
selector to select any of six antennas to two radios.