Best SWR for Radiowavz DX 40 OCF Short wire dipole antenna?

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Trying to tune the antenna with the balun about 20 fee up off the ground. The antenna is advertised to be resonant on 40, 20, and 10 meters and is shortened on one end with a coil. The total length of the antenna is only 37 feet. The two wire ends are suspended with ropes which can be adjusted as necessary to shorten the antenna on each end.

Initially the only dip shown on my Nano VNA was around 30 MHz. Although this dip showed almost a 1:1 SWR, there was nothing else below 3:1 shown for other bands. Shortening the wires created a second dip but this was still never below 2:1 SWR and was not a useful frequency. 40 and 20 meters have much higher SWR, around 5 or 6:1.

Any ideas? I am using a choke. Shortening the antenna on each end does not seem to improve the SWR. Are off center dipoles tuned with high SWR or is there a way to tune each band?

I also tried to set up this antenna vertically hanging it from the short wire end, and would like to do so if there is a way for this setup to function with low SWR, but the high SWR reading is making the antenna an impractical choice for a vertical at this point.

Richard

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@Richard_Evans that it is an off-center-fed antenna. These antennas need to be at least 35 feet above the ground to perform, and there is no need to shorten the ends either. These types of antennas are NOT self-resonant, so an antenna tuner must be used to tune them across all bands.

Also, hanging it vertically isn’t a good idea. An off-center-fed antenna is not like an end-fed wire, which requires a high-impedance transformer.

Using a choke is a great idea, but its main purpose is to reduce RF feedback and not lower SWR on the antenna. Some off-center-fed antennas can exhibit SWR as high as 6:1. Most would prefer to use an external antenna tuner, such as an LDG, as it is far more forgiving than the radio’s internal tuners.