40m ECOCFD Antenna, VERSION 1
Feedpoint Split: 20% / 80%
Version 1.0-UN
ALL versions of Ver.1.x were made with the 4:1 Ruthroff 20% from the end with the 1:1 Guanella. This version was made intentionally too long, to eliminate the risk of having to extend the wire legs.
The 4:1 Ruthroff was wired as an UNUN (not a BALUN).
MEASUREMENTS:
These measurements were taken with a RigExpert Model AA-230 ZOOM antenna analyzer, connected directly to the 1:1 Guanella balun ( the beginning of the radiator). The analyzer was controlled using AntScope-2 running on a Google Pixel 6A cell phone (Android-13).
The data files (by band) for the measured data may be downloaded below:
DOWNLOAD Ver.1.0-UN data files:
Version 1.1-UN
The antenna was shortened for this version to bring the frequency of minimum SWR to (or near to) the low ends of the harmonic bands. As expected, 40m is still significantly below the bottom end of the band. The 4:1 Ruthroff was wired as an UNUN (not a BALUN).
After shortening the antenna, the harmonic bands are all still a little low. Minimum SWR (SWRmin) on 40m is, as expected, 100+ kHz below the bottom of the band.
The data files (by band) for the measured data may be downloaded below:
DOWNLOAD Ver.1.1-UN data files:
Version 1.2-BN
This version is exactly the same as Version 1.1, except the contacts between the coax and the Ruthroff were reversed. The 4:1 Ruthroff was wired as an BALUN (not an UNUN).
Recently friends and I discussed whether to connect the Ruthroff as a 4:1 BALUN or a 4:1 UNUN. It was concluded that the UNUN would produce more Common Mode Current than the BALUN.
I tried it both way to see what affect it might have on the SWR curve on each band.
I did not try to measure the difference in Common Mode Current.
The SWR curves for both versions are shown on the right. The UNUN is the green curve, the BALUN is the red curve.
The green curves were measured first, the red curves were measured second.
In most cases you can barely see the green curve because the red curve is nearly identical and covers most of the green curve.
DOWNLOAD Ver.1.1-UN data files:
CONCLUSION:
From an SWR aspect, it make no difference whether the 4:1 Ruthroff is connected as a BALUN or as an UNUN.
How much difference in Common Mode Current there is between the two, which affects how strong the short (coax) leg of the antenna radiates RF, remains to be determined in extensive field work.
