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Amateur Radio

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Antenna No 59
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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 4m band.



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 mount.



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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