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[ Previously GW4ALG (QRT in February 2007) ]

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Doublet Antenna

In early December 2022, I replaced my 110 m perimeter horizontal loop with two antennas.  This inverted V doublet (shown in red and white) was one of them.  A 54 m longwire (shown in yellow) was the other.


This doublet has a top of 2 x 23 m. The centre feedpoint is supported at 11 m above ground by a copper beech tree.  Initial results are most encouraging, resulting in much better performance than the previous loop, with less local noise at the receiver.

The antenna is made of PVC insulated multi-strand tinned copper wire (19 strands of 0.4 mm diameter) fed with 30 m of 300 ohm twin 'ribbon' feeder. An MFJ balanced matching unit is used to do the transform to unbalanced 50 ohms.  Good results have also resulted from simply using a ferrite balun at the shack end of the feeder to an unbalanced Pi network antenna tuning unit.  The ferrite balun is switchable between 1:1 and 4:1 impedance transformation ratios.

Initial results (when tuned against a poor RF ground) indicate that the longwire is one to two S points down relative to the doublet on 80m. On 160, there appears to be no significant difference between the performance of the longwire and the doublet. On both 160 and 80, the received local noise (SMPS noise, etc.) is significantly stronger on the longwire relative to the doublet. On 40m, the longwire is often significantly better than the doublet when working UK and other European stations.