Looking at this CB Radio antenna you may think I am crazy to use it for local and Skip!
BUT it is far better in operation than it looks!
I should make it clear at the start that my wife when I first met her was oblivious to all the various CB antennas I strung up or mounted on lattice towers all over her established home property in the outer suburbs. A massive tree in the back yard had many HF wire antennas and the house supported a tower with a HB9 Swiss Quad with a vertical above it that I was able to work the world on in the eighties.
Until we / she decided we should move to an new off the plan apartment in the inner city 10 years later. Well considering I made great friends with the owner builder of the apartment complex, it was no trouble to put three runs of heliax through the walls up to the flat iron roof four stories high from my designated radio room on the second floor. A high gain 12db 476MHz UHF CB coaxial colinear worked awesome.
But there was now way I could run the Swiss Quad and Vertical up there so another strategy was needed.
I had always been fascinated by unusual antennas across HF bands and the DDRR was always of interest to me. So simple to build just like a Quarter Wave Nine Foot mobile whip with a ground plane, but the added advantage of DC grounded, so low QRN noise! Also the height of the vertical part only needs to be twelve inches on 27MHz! The total length is a 1/4 Wave of the center operating frequency. The circular top hat is only a yard in diameter ending about eight inches from the vertical part giving a tunable capacitance.
The polarisation is both horizontal and vertical it seems.
Note that this is my redesign of the original DDRR that was designed for warships by the inventor. This has no tunable physical component of a capacitor, just the gap at the end of the top hat. This gives very high ‘Q’ of only five CB Channels each side of set resonant frequency which I tune with a Nano VNA H5 to 27.355. This usually occurs at about eight inches from the vertical part around the top hat.
As most SSB action happens between 30-40 it is fine and the VSWR less than 1.5:1, but i do peak with a tuner inline if I want to go further up or down the channels. It could be modified with a variable capacitor if you wanted to go to all the trouble for more band width.
From the Apartment after a few years we moved to a Townhouse on a hill five kilometers from the city, happily as someone had recently mounted airconditioning on the apartment roof five yards from my antennas! Unhappily I had lost a fortunes worth of heliax!
So had to go back to a nine foot stainless whip on top of a water air cooling metal box on top of the tile gable roof that worked ok because of the high location and the water plumbing earth. By now my wife made it clear that no obtrusive antennas would be welcome like they were on her older house.
So moving again to a Bayside town between two major cities across the water into a two storey house with a flat iron roof and no visible antennas allowed. So the DDRR seemed to be the only answer to my dilemma of wife approval. With only twelve inches height the DDRR was invisible, and if one is good two must be better! So I co-phased two and worked a lot of DX interstate and over seas.
Ten years later in mid 2021 we have moved again to a tree change home in the country over looking a large body of water with a gabled iron roof.
Luckily I have a flat iron roof on the garage rear shed I have turned into my radio shack so perfect for DDRR’s!
But the original DDRR’s I had were made of one inch copper stranded wire that was extremely heavy and did not make it onto the removal truck. But I had bought some copper tube for the purpose many years ago at a garage sale cheap so have what I need to build two more.
This is the first DDRR and I had to have a way to mount it on the iron roof easily so found an old rusted out CB base that with a bit of modification earthed out on the base and the roof as the radiating element has to be DC grounded for the low noise operation.
-1.1:1 SWR @ 56 Ohms impedance on 27.305 MHz – Prefered setup with Antenna Analyser or good SWR Meter in actual location.
D – USE Copper/Aluminium Tube or Coax – Heliax or EVEN RG213 would work I think! (But lower band width, maybe five channels with low SWR)
SP – 12 ” high
L – 108″ long Copper Tube or Coax cable
G – 8″ – 9″ gap from upright to radiator end. NO CAPACITOR!
FP – 8 – 9″ tap from upright along radiator. TO BE TESTED for LOWEST SWR on center of most used channels!
As you can see the NanoVNA is reporting a 1.05 VSWR on 27.390 MHz on the new DDRR!
What Is a DDRR Antenna?
DDRR stands for Directional Discontinuity Ring Radiator. The DDRR antenna was invented by Dr. J. M. Boyer. It is a short, vertical monopole antenna connected to a transmission line. The “monopole” antenna is bent into a nearly 360-degree ring. This is why they’ve long been known as hula hoop antennas, though the DDRR antenna is very different from the magnetic loop antenna. DDRR antennas may have one or two concentric rings.The Directional Discontinuity Ring Radiator or DDRR antenna was developed to meet the need for very low-frequency antennas on ships. In fact, the original design was classified. They didn’t become public knowledge until an article about “hula hoop antennas” came out in 1963. More importantly, they continue to be used in ELINT or Electronic Intelligence today.
The Advantages of DDRR Antennas
Perhaps the biggest advantage of DDRR antennas is their small size relative to the wavelength they receive. (They have a one-quarter wavelength element.) Given the low frequencies (2 to 30 MHz) they received, this makes them significantly smaller than half-wavelength antennas.They have a very simple design. According to Madjid Boukri, VE2GMI, the first versions of the DDRR antennas, were made out of four-inch diameter aluminum tubes mounted over a metallic structure like a ship. Rigid copper tubing can also be used. Doctor Boyer actually recommended four-inch wide (or wider) tubes if the pipe is more than 75 meters long. The first DDRR antennas were connected to the ship with several aluminum posts, while fiberglass posts supported the rest of the structure. However, they can work if you don’t have a purely metal ground plane beneath them. Yet you must fully isolate the DDRR antenna from the ground if you want it to work well.
This could be as simple as using fiberglass or PVC pipes as supports. A side benefit of this is that you can build a very large antenna out of generally low-cost materials.
Their low height makes them a good choice for ships or vehicles that need to literally maintain a low profile. For example, they’ve been used on heavy tanks and armored vehicles. It isn’t going to be knocked down or damaged when you pass under a bridge. Nor do you have to wait for it to fully extend to be able to communicate. A side benefit of the design is that they’re hard to damage, so they’ll often continue to operate if hit by shrapnel or falling debris. The low ring could also be protected by a cover on the roof of the vehicle if it isn’t built into the vehicle roof itself. Note that DDRR antennas are still used in water meters today.The metal loop design means it has low noise and very low impedance. This makes it almost immune to EMI from voltage spikes or lightning. It has a very high Q, too.Because it is a ring antenna, it is an omnidirectional antenna.
The Disadvantages of DDRR Antennas
They are lossy. This means they consume a lot of power relative to the signal they put out. Performance can be improved by adding radials.
It will only receive a very narrow frequency band. It is hardly better than wheel antennas in this regard.
Observations About DDRR Antennas
DDRR antennas are difficult to tune. In the original design, a high-voltage vacuum capacitor was used to tune the antenna. In later concentric circle DDRR antenna designs, additional posts were added that could be moved to adjust the standing wave ratio or SWR.