14MHz Coil Shortened Dipole

 After a multitude of antenna builds using other people's designs, I thought it was time I designed my own from scratch. I decided a single frequency would be best to start with so I chose 14MHz because of the amount of traffic on this band. I think it's so popular because the antenna size is not too large to construct especially in a confined area. I looked at trap dipoles and the like and the art of shortening using coils. My final design would be a 6 metre long dipole so that it could be formed into an Inverted V to join my nest of dipoles in the loft. The coils were calculated for a 20mm former and came out at 6.68uH - 25 turns of 1.13mm diameter insulated solid copper wire, at 14.15MHz centre frequency. I decided to centre load the elements.

Testing

14MHz = 1.1:1

Bonus: 50MHz = 1.7:1(ATU) 

I had to add about 100mm to each end to get the SWR down. This means the calculations, or the interpretation of them, was in error. The measurements were made to the centre of the coils which is probably incorrect. When tested at 50Mhz, it was found that the SWR was a useable 1.7:1. I suppose the antenna has a tuneable harmonic.

Contacts made:

Croatia -6dB    Poland -15dB    Germany -11dB    Belarus -12dB    France -12dB

Hungary -17dB    Croatia(2) -13dB    Hungary(2) -11dB  (All on FT8)

Spot Reports for 14.074MHz FT8:

Conclusions

The SWR readings achieved were to be expected. This is a single frequency antenna with a comparatively narrow bandwidth. The Inverted V angle was very large, probably greater than 120 degrees. If this antenna was erected outdoors, the performance would be much better. Loft antennas tend to perform a lot worse. It seems to be working very well though and I will keep this antenna on-line for using on a regular basis.