Complex Fan Dipole for Six Bands!

My complex fan dipole is now ready for me to work on six amateur radio bands: 40, 30, 20, 15, 10 and 6m. Initially the fan dipole had elements for 40, 20, and 10m bands. Later I added a couple of 122 microhenries loading coils to the 20m elements and extended the elements a bit beyond the loading coils. In its current configuration, it has 4.5m of wire beyond the initial 5m wire for the 20m elements. The aim was to make it work on 80m band. But somehow it has failed to work on 80m, but as a consolation prize I have been given the 30m band. Most probable reason why it has not worked on 80m band is because of low mounting, much below the ideal 20m height for an 80m antenna. Anyway I am happy about third harmonic resonances of the antenna which gives me tunable SWR on six bands from 40m to 6m. In addition it has SWR near 5 on 12m band, which might become tunable if I get an antenna tuner with higher range. The auto-tuner in my FT-710 radio covers only up to an SWR of 3:1.

Here is the current configuration of the complex fan dipole. 40m elements have 10m wire on either side. 20m elements had five meter wire on either side. After adding the loading coils, to bring back resonance to 20m band, I had to fold back and tie together 24cm of wire as shown in the previous picture. In effect there will be three layers of wire for the 12cm preceding the loading coils on either side. Extension segments on both sides beyond the coil are 4.5m long. Now it is a symmetric center fed loaded coil dipole antenna, mounted in inverted V fashion. Ten meter elements have 2.5m of wire on both sides. All the three sets of elements have a common feedpoint, connected to a 1:1 current balun. Coaxial feedline is a 15m long RG213 cable.

This is the NanoVNA tracing showing an SWR dip at 10.2 MHz, just above the 30m amateur radio band. That was tunable in my FT-710 radio for the 30m band.

Next we see two dips in SWR, one just above the 40m band another just below it. Together the SWR over the entire 40m amateur radio band is tunable with auto-tuner.

Here is the SWR dip on 80m band which I had aimed at, while adding the loading coils. Unfortunately it is at 3.8 MHz, above the VU band and with an SWR of 2.963. That makes it untunable between 3.5-3.7 MHz, the VU amateur radio band. I have placed an order for an automatic antenna tuner of ND7DDC design. I expect to get it next week or so and maybe then I will be able to use this complex antenna for 80m as well. Alternatively I could lengthen the wire beyond the coils and bring down the resonance to the VU amateur radio band. Then most likely I will lose access to the 30m band. Moreover, in the current mounting location, I do not have space to lengthen the loaded coil elements to both sides. It would also add another set of joints to those antenna elements.

For completion sake, I will go through the SWR pattern on other bands as well. This is the NanoVNA tracing showing SWR dip near 17m band, not tunable in my radio.

Here is the SWR dip near 20m band. That was tunable with auto-tuner on 20m amateur radio band.

SWR dip near 15m band made it tunable with auto-tuner as before.

There is an SWR dip near the 12m band as well, not tunable with auto-tuner in the radio.

SWR dip in 10m band is perfectly tunable with the built-in auto-tuner in FT-710. I did not check NanoVNA tracing on 6m as I had not calibrated the NanoVNA to that range. Instead I checked SWR in my FT-710 radio and it was in the tunable range for 6m as well. But I am yet to hear any station on 6m, the so called magic band. That may be because of lack of propagation or because of poor antenna gain on 6m. Earlier I had tried dedicated wire dipole for 6m. At that time I could not hear even my local VU ham at a distance of 10km. Hence 6m is an elusive band for me so far.