Tuning a Radiowavz 40 OCD Short. What is the best SWR to expect?

Questions & Answers
1

Trying to tune the antenna with the balun about 20 feet 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, 9 inches. The shortened side, which appears to be the “long” end of the antenna is shortened with a coil, measures 14 feet. The other end is 23 feet 9 inches.
My understanding is that a 40 meter dipole (not shortened) is a total of 66 feet long. Moving the balun to make the dipole an OCF usually means that the shorter wire is one third of the total length or 22 feet and the longer wire is 44 feet, therefore, on the Radiowavz shortened antenna the wire without the coil, being 23 feet 9 inches long must be the short wire.

In order to tune the antenna, the balun was raised about 20 feet and the two wire ends were set up to be adjusted.

Initially the only dip shown on a Nano VNA was around 30 MHz. This dip showed almost a 1:1 SWR, but the SWR for other bands was very high. Shortening the wires created a second dip but not on a useful frequency.
In the end, no dip was obtained on 40, 20 or 10 meters as advertised for this antenna. Instead these frequencies 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

2

@Richard_Evans Here is what I have been able to find out: That it is an off-center-fed antenna suggests it might be a Windom 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. I would prefer to use an external antenna tuner, such as an LDG, as it is far more forgiving than the radio’s internal tuners.

The radiation patterns on thethe Windom off-center fed design are substantially different from those of other popular designs, such as the G5RV, which are center-fed.

I hope this info is helpful! Sorry for the delay in the answer.

3

Sue, thank you so much for your response. All of this makes sense. I can indeed get the antenna balun up 35 feet and test it again with an external antenna tuner. Thanks for your help. Unfortunately Radiowavz has not responded to my emails.

4

@Richard_Evans you are very welcome! Thank you for shopping with us!