Antenna No 60
Asymmetrical X-Dipole (AXD) for 6m and 4m
This is the same antenna described under Antenna No 23 but remodelled for 6m/4m frequencies and erected
in vertical polarisation.
This antenna was in use for several years for low-VHF (40-70Mhz) propagation
beacon reception. In 2014 I remodelled it for 6m and 4m frequencies
keeping horizontal polarisation so that it could be used for transmit on these
amateur radio bands. At the end of the 2015 Sporadic-E season I took down
the antenna as I needed the "antenna testing spot" on the gable wall.
Recently I had a requirement for a test on 6m FM using vertical polarisation
so I re-drilled the multiplex so that the antenna could be erected
vertically. I kept the 4m center-fed dipole in horizontal
polarisation. Running separate same spec coax (Ecoflex-10) to the shack
this gives me the possibility for simple A/B-switch polarisation checks on the
My new [test] antenna set-up on the gable wall: 4m/6m in VP and
4m in HP. Centre is about 8m above ground.
The SWR plot for this dual band dipole, in VP
Checking SWR with a network analyser, the 4m band dip appeared unchanged but
the 6m band dip had shifted up in frequency by about 1MHz. This was
unexpected, however, the antenna is still usable on 6m FM frequencies with a
slightly raised SWR of around 1:1.7. I believe the 6m resonance shifted up
because of a capacitive effect on the longer [6m] elements when the antenna was
mounted in HP.
The 70.400MHz check is the local frequency used for 4m FM.
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