## Monday, November 9, 2020

### Antenna for SOTA, POTA, and DXpeditions

Initial Prototype:  The initial prototype had a turns ratio of 14:2 (14 secondary and 2 primary).  It used a single 100 pF capacitor across the center conductor to ground.  The tests of this initial prototype after pruning for a best compromise resulted in:

2:1 SWR Bandwidth on 40 meters is 6.730 -> 7.530 MHz with a dip to 1.3:1 SWR at 7.060 MHz

2:1 SWR Bandwidth on 20 meters is 13.910 -> 14.806 MHz with a dip to 1:1 SWR at 14.360 MHz

2:1 SWR Bandwidth on 15 meters is 21.010 -> 22.070 MHz with a dip to 1.6:1 SWR at 21.610 MHz

2:1 SWR Bandwidth on 10 meters is 29.1 -> 30.8 MHz with a dip to 1.8:1 SWR at 29.900 MHz

On 10m it is not very usable unless one has an ATU.

The second prototype (photo below) used two 220 pF capacitors in series which technically by the numbers should be 110 pF.  My measurements of the capacitance was closer to 130 - 140 pF.  This had a substantial effect on making 10 meters usable without a tuner.   The results are as follows:

2:1 SWR Bandwidth on 40 meters is 6.820 -> 7.510 MHz with a dip to 1.3:1 SWR at 7.150 MHz

2:1 SWR Bandwidth on 20 meters is 13.990 -> 14.840 MHz with a dip to 1:1 SWR at 14.430 MHz

2:1 SWR Bandwidth on 15 meters is 20.950 -> 22.270 MHz with a dip to 1.1:1 SWR at 21.650 MHz

2:1 SWR Bandwidth on 10 meters is 29.1 -> 30.8 MHz with a dip to 1.3:1 SWR at 29.900 MHz

Being a link dipole for 30m - here are the results for 30m:

2:1 SWR Bandwidth on 30 meters is 9.730 -> 10.880 MHz with a dip to 1.0:1 SWR at 10.280 MHz with a SWR between 1.3 and 1.2:1 from 10.100 to 10.150 MHz

A third prototype had the following results (identical in construction to the second one) with the following results.

2:1 SWR Bandwidth on 40 meters is 6.820 -> 7.500 MHz with a dip to 1.3:1 SWR at 7.150 MHz

2:1 SWR Bandwidth on 20 meters is 13.980 -> 14.850 MHz with a dip to 1:1 SWR at 14.440 MHz

2:1 SWR Bandwidth on 15 meters is 20.780 -> 22.280 MHz with a dip to 1.2:1 SWR at 21.600 MHz

2:1 SWR Bandwidth on 10 meters is 24.5 -> 29.9 MHz (which actually overlaps into 12 meters) with a dip to 1.1:1 SWR which is wide - 28.0 to 28.5 MHz so 10 meters is now perfectly usable without a tuner and so is 12m which is a very narrow band.

This is one heck of an antenna - requiring no tuner on 40m, 20m, 15m, 12m and 10m and power handling ability as follows SSB 60w, CW - 40w and Digital (key down) - 30w.

The final product: