Reason 1. is that my wife has lost her sense of humor regarding? “UGLY CB ARIELS!”? for CB radio since I first met her over 25 years ago.
I must admit I pushed the boundaries of antennas in her small suburban home backyard that had the gift of some very high gum trees right at the back fence line and the front nature strip. Did not need a DDRR then!
PERFECT for CB Radio antennas and plenty of clear space in the middle for my tower on the back of the house with the Directional Swiss Quad Beam and Avanti AstroPlane Verticle above it with heliax on HF as I had picked up 100’s of meters at a govt utility auction for next to nothing. Obviously was worth it for UHF CB as well to my 12db Co-axial Colinear UHF ariel above the Avanti Astroplane. It all lead into the alcove off the lounge room so I could play radios and watch TV in the lounge as well. She has always been big on TV’s and I made sure her TV antenna worked well without interference or my life was not worth living.
It was when we bought an apartment near the city for some reason that she come home and looked at the house roof as if for the first time in ten years and said “Oh my god, look at all those ugly antennas!” ?Oh well I ten good years of operation there so could not complain too much.
But I did get our off the plan builder to integrate three runs of heliax from our apartment on the second floor up through the walls to the roof above the third floor of the block. A huge “U” shaped complex that had a flat iron roof that loaded up on all the ham bands awesomely for SWLing. ?With my UHF 12db Colinear and Astroplane up there they worked to my satisfaction for two years until some rich dicks moved into the upper floor and installed Airconditioning equipment on the roof. That was the end of the radio in that building but luckily we were looking to move anyway as Pauline was sick all the time there and we always had black soot building up on surfaces that seemed to be from car pollution in the inner city area.
So we moved to northern suburbs on top of a large hill. Of course, you dont think I would live in a bad radio spot do you? Highest point close to the city with views in all directions from the roof, and I could open my eyes in the morning and see the Dandenong Mountains. The only problem was I was only able to put up a 27MHz 9′ Stainless Steel whip on top of the metal ground-plane that was the evaporative air-conditioning cooler we installed for that very reason! HAH. Everything else had to go inside the tall gable tile covered roof but about six different ariels worked well in there for SWL ham bands and scanning. I did manage to erect a 2meter long UHF CB coaxial co-linear antenna on the neighbours TV antenna when the adjoing house was sold and no-one noticed or cared which solved that problem.
Well that all went OK for ten years until we decided to move.
So we bought a house that we fell in love with on the internet. Damn, lucky it was up reasonably high close to the water with some natural salty ground plane to the North, East & West.
Problem is it has a flat iron roof that most Ariels stand out on like dogsballs! So problem number one is how to get out on DX with 12 watts as I am running legal! (and also advertising my location on this website!) And my full call Ham brother is a pain about doing the right thing!
Solution 1. STEALTH!
With a flat iron roof this was the catalyst that got me to do something about building a DDRR.
I had always wanted to play with these strange antennas and now I had a valid reason as they only stand at 27MHz about 15″ high on the roof! But are able to radiate omnidirectional in the vertical polarisation mode. This is also with a grounded centre conductor that eliminates most noise. (EXCEPT the DAMN PLASMA TV that QRN NOISE peaks on CB Channel # 35 LSB!!) Now my wife interferes with my CB radio with her TV! Probably Karma payback for when I used to run a Linear back in the old days! Hell I wonder if anyone will read this.
The DDRR does not look pretty, but it matches at 53 Ohms on 27.335!
BEWARE!! THE FEED POINTS MUST BE TUNED WITH AN ANTENNA ANALYSER or a SWR Meter at low power!!
CB Radio 11 Metre DDRR measured & TUNED to FREQUENCY with a SARK Antenna Analyser ?MORE on building a CB DDRR antenna on CQDX11.net
You can visualise the size by the house bricks that are holding the insulated upright supports.
They are just cardboard tubes but have been replaced with plastic plumbing pipe that I have tested in a microwave that dont get hot so are non conductive.
It is virtually the 9 ft whip just bent over and turned into circle with the tip at eight inches from the bend start so its only a metre ?across.
Yes I know it looks pretty agricultural in its construction, but it makes up for that with a great “low noise interference” signal on any radio I use it with.
I should note that I have the House roof GROUNDED also but this is not necessary for a DDRR to operate as it was designed originally.
This is because the centre conductor is earthed which makes the whole array very low noise on any band. Yes any band – I have just started to test it on my Icom R71A RX on all the ham bands cause my VK Full Call brother wants me to get a VK F call and it works much better than a massive wire loop 40 meters around the roof edges. You can just see it going past the front of the DDRR and behind the 9 foot Stainless. Also this wire loop seems to have brought the SWR on the DDRR & 9′ array to 1:1 for some reason. I dont understand or really care how or why! I thought it would cause problems when I first put it up being so close to the both antennas, but it has been a fantastic fix to having to use the antenna matcher/tuner prior to putting it up. Unfortunately it is only about 12 inches off the roof metal so that is probably why it does not work so well on RX ham bands.
More information to follow on DDRR’s