Originally the TX-472 had both the C31XR and XM-240 yagis installed. The C31XR was at 74 feet and the XM-240 at 80 feet. Not only was this configuration taxing to the point of concern due to windload, there was considerable interaction between 40m and 15m antennas.
To the left the TX-472 is tipped over to make adjustments to the C31XR in the process of changing the single-feed system to three independent feeds for SO2R (2016)
Antennas are interfaced to radios via a 2×8 RatPak from Array Solutions. Tuned stubs provided additional isolation initially but were later replaced by K∅ZR-designed 2 KW bandpass filters. In most cases the respective filter affords 50 dB or more additional isolation from neighboring frequency bands.
A DX Engineering 80/40, 53 foot vertical with 90 radials was in use for 80m for some time. In 2019 this was changed to a full quarter-wave for 80m with the same 90 radials as its ground plane. To the left is the base of the 80 m vertical antenna. Each radial extends a minimum of 60 feet. It has the “CW Optimizer” from DX Engineering allowing the height to be somewhat less than a full quarter-wave.
Somewhat due to COVID in 2020 and the absence of flying to Los Angeles “too often” for work, three more yagis made their way to the Rohn 45 tower. Each of the additional antennas are side-mounted to the tower facing the Caribbean. Homebrew 1×2 RF transfer blocks enable remote controlled switching from the larger, rotatable arrays to the Caribbean-facing antennas in a split second. Bias-tees are incorporated into the K∅ZR-designed 2 KW BPFs and near the towers, the complement function of bias tees and 20 amp relays are located. A short write-up on these switching blocks is in the “Writings” section of this site.
As of November 2020 the directional antenna complement includes:
- C31XR @ 74 feet Tower #1
- XM-240 at 90 feet Tower #2
- Homebrew (w4RN) 3-element 20m at 67 feet fixed on Caribbean
- HyGain 153 at 57 feet fixed on Caribbean
- M2 4 element OWA for 10m at 32 feet fixed on Caribbean
In October 2020, the azimuth of the new Caribbean-facing yagis was checked and found to be considerably more south than desired. In order to correct this additional hardware was added to each of the mounting plates.
Each (Caribbean) yagi has its boom mounted to a 6″ x 20″ x 3/8″ thick aluminum plate. Originally two legs of the tower were U-bolted to this plate, two on a side. In order to make the azimuth change, an additional “push-off” plate made of 12″ x 4″ x 3/8″ aluminum was installed with a 1 1/4″ OD aluminum tube serving as a hinge point. The picture below is that of the 20m modification; both 15m and 10m have the same modifications.
Although rather difficult to see, the 6″ wide aluminum plate holding the boom has two U-bolts to the 1 1/4″ OD tubing and the 4″ wide aluminum plate has two U-bolts connecting to the same 1 1/4″ OD tube. Together they act as a hinge allowing the azimuth to be changed to ~ 155 degrees. A vertical 3 foot aluminum pipe is mounted to the backside of the boom plate to serve as a connection point for the phillystran truss cables.
C31XR Users Employing Separate Feeds
Since going into SO2R I have never been happy with the VSWR attainable on the 15m band, no matter how much adjustment was applied to the hairpin match and radiator element length. In August 2021 I came across an entry by 5B4AGN wherein he described his comparable difficulty AND a solution for it. He found that if the 20m feed was open-circuited while using the 15m feed, the VSWR was improved considerably. Although there are filters for each band at K0ZR, the 20m filter looks like a DC short at 15m, not an “open”. So, a parallel L-C, anti-resonant across the 15m band, was placed in a small box after the 20m filter. The minimum VSWR had been around 1.4:1 and now it is 1:1.