Tuesday, 16 April 2013

2 Element V-Quad for 27mhz


This is my first article, and I am a keen 27 mhz CB operator. I started out in the 70's during CB's most popular time, when it was legalized. While absent from the scene for many years with family life, I've been back into it for a few years now and really enjoying it. There is something about the 11m band that brings operators back, and brings in new operators for the first time. It's low cost and simplicity could be a factor, and also it's lack of pretense. Doesn't matter what equipment or experience you have, someone will always say G'day and have a chat with you. There are a few clowns out there like anywhere in life, but most just enjoy the hobby. My call is 361, or BSB361, as I'm a member of the Bendigo Sideband Club.
To the subject. I was looking for a beam antenna a couple of years back, as I enjoy DXing or chasing skip. There isn't much else, as local operators are thin on the ground. My needs included a tight budget, limited space and a low mounting position. After looking at a 3 element yagi, I decided that wasn't an option due to space and the need to have it at an elevated position to maximise it's potential. I then looked at a cubical quad, but again mounting would be a problem for me because of the height needed. The boom is central in the antenna and a high supported mast or tower would be required. Then I hit pay dirt, the V-Quad or Delta Loop. It has the boom at the base of the antenna, perfect for my low mounting requirements. It's low angle of radiation makes it ideal for this type of install, whereas a yagi needs height to perform at the same level. After looking into it, and costing, I decided on a 2 element V-Quad made by Shockwave Antennas in Melbourne. The price was right, and construction is very robust.
After picking up the antenna and getting it home, I quickly put it together, very easy and made sure the metallic jointing paste was used for conductivity and corrosion prevention. I bolted it to the pole and clamped it to my pergola. Connected coax and excitedly checked SWR, which was 1.3, good enough. Radio check, and working beautifully. Rotating the antenna is easy, via the armstrong method, and the noise level was very low compared to my vertical. Signal strength is about 2 'S' points higher compared to the vertical, and similar on transmit. Couldn't be happier with the 'V' performance.
SWR is easy to adjust, via the gamma match. I had to adjust SWR after a big storm passed through here, which caused some damage around the area. A tree in my backyard broke in half and had blown onto my garage roof, making a large hole through the tin roof. My vertical bent like a banana, but didn't snap thankfully. The 'V' looked in perfect condition, no bends or breaks, but I was worried watching it in the wind. Checking the SWR the next morning and it was at 3, which confused me a bit because it was still in the correct shape after the storm. Thinking about this for a while, I figured the only possible way the SWR had changed is by the gamma match moving. I adjusted the gamma match out and SWR dropped to 1.5.  Bingo, I found the cause of high SWR. The flexing and bending of the driven element in the storm had caused the gamma to close about an inch. Another adjustment and the SWR was flat, no movement on the meter at all. The first time ever I've had an antenna achieve this, I was very happy. I will note also that Pete from Shockwave Antennas advised against sealing the gamma with silicone, and said vaseline is better because it waterproofs and allows for future adjustment. Great advice which I followed.
I've had countless contacts on the CB with the V-Quad, and rarely use the vertical these days. Being only 2 element, it has a good range of coverage to the front, I would say 120 degrees is about right. Though for weak signals a better directional adjustment is needed to boost the signal. By and large, if skip is running into Victoria, I can point it NE and get Eastern Australia, New Zealand, Hawaii and mainland USA without needing to move the antenna. If channels 35 and 38 are clogged with overseas and local skip, a flick to the official call channel, 16, can bring surprising results as quite a few still operate there. Also many Pacific Islands use 30-33usb, so always worth checking.  I have read recently there are some trying to push 27.255usb as an international call frequency, as opposed to the 27.555 which is outside the Australian, and most countries, legal operating band. I encourage operators to support 27.255usb, or channel 23, to avoid crossing paths with the ACMA and staying within the legal band.
Enjoy the hobby and good DXing,
Mick 361.   

1 comment:

  1. Nice article and photo mate. No doubt the V is great looking and performing antenna.