SWL GRUNGE-MASTER .625
The diagram for the $150 SIRIO Gain-Master 5/8 wave CB radio base station antenna is on the antenna's brochure. Inside the fiberglass shell of the Gain-Master 5/8 wave base antenna is a ham radio 'Flower Pot' like antenna design, that is constructed from high quality coaxial cable and wire.
I am going to build an antenna that is similar in design, using cheap coaxial cable and 14 gauge wire. I am going to disregard the matching section / coaxial cable stub that is normally used with this design, as this antenna will be used in an SWL / SDR Radio / receive only application.
THIS ANTENNA REQUIRES AN ANTENNA TUNER FOR TRANSMIT USE
: MATERIALS USED :
25 FEET RG-58 A/U COAX ($10)
15 FEET OF 14 GAUGE STRANDED COPPER WIRE ($5)
:DIRECTIONS: (THE DIRECTIONS CORRESPOND TO THE PICTURES BELOW)
1: RF Choke: Wrap coax 16 times around a 66mm plastic tube.
2: Measure 141.7 inches up from the top loop of the RF choke. Cut coax.
3: Measure 135.8 inches up from the top loop of the RF choke and mark that point. Then measure one inch higher and mark the point. Carefully remove the coax insulation and coax braid inside that 1 inch area of the coax, without cutting in to the center of the coax.
4: Measure 3.4 inches above the point where you have removed the coax insulation and braid. Whatever coax remains after that 3.4 inches, expose the coax outer braid and tin with solder. Insulate the center conductor of coax.
5: Solder 11 feet of wire to the coax braid on the end of the coax portion of the antenna.
Total length of antenna from top of RF choke to tip of antenna = 22.7 feet / 6.9 meters
SWL GRUNGE-MASTER .625 WAVE CB RADIO BASE STATION ANTENNA
AMAZING RECEPTION! With the base of the antenna only 3 feet above the ground, it performs like a 5/8 wave base station antenna that is mounted 15 feet above the ground. There is a logical explanation for this unexpected performance.
The SIRIO Gain-Master design is a center fed 5/8 vertical dipole. It is a balanced / decoupled antenna, therefore it does not require a counterpoise / ground plane. When the base of the antenna is sitting on the ground, the business end of the antenna is 11 feet above the ground.
This antenna has a very low noise floor, thus providing excellent signal to noise ratio. More desired signals and less noise. This dramatically improves the listening experience on the inherently noisy CB radio band.
Here is a video to showcase the antenna's local reception.
I connected this antenna to a MFJ desktop antenna tuner and made a few local contacts, using a stock CB radio with stock microphone. I received good reports all over town. That simple contraption made of coax and wire provides the true base station experience.
POWER HANDLING CAPABILITY
The SIRO Gain-Master has a power handling claim of 500 watts. Considering that this home brew antenna is made of cheap, lower grade materials, I personally would not load this antenna up with more than 100 watts.
Wavelength / gain far exceeds impedance match / VSWR. For example, the most primitive end fed or center fed 5/8 wave vertical antenna with a 4:1 SWR, has more gain than any 1/4 wave or 1/2 wave vertical antenna with a 1:1 SWR.
Vertical antenna gain = lower angle of radiation / reception. (good local & long DX)
THE SIRIO GAIN-MASTER IS WORTH BUYING
When I first saw the SIRO Gain-Master antenna's $150 price tag, I considered it to be a bunch of hype surrounding an overpriced product. My views on this matter have changed. With the price of an Antron 99 being $100, the Gain-Master's performance is worth the extra $50. Especially if you value features like low noise floor, improved local reception and high performance when mounting the antenna near the ground.
The SIRIO Gain-Master would make the world's best HOA / covert Flag Pole Antenna. With the base of the Gain-Master antenna sitting on the ground, inside of a 25 feet tall plastic flag pole, the antenna will perform like a base station antenna that is 11 feet above the ground.
Both ends of a vertical dipole radiate / receive, but, the top section is obviously doing most of the relative work.
(UPDATE) THIS ANTENNA WORKS UNUSUALLY WELL IN ODD POSITIONS
The tip of the wire antenna is hanging from a 30 feet tall tree branch, causing the RF choke to hang 6 feet above the ground. In an effort to tidy up this installation, I decided to test how the antenna would perform if I mounted the RF choke 7 feet high on the side of the house, thus bending the lower section of the antenna in to a partial fish hook shape.
RESULTS: Oddly, there was no noticeable change in performance. This is good to know, as it reveals that the lower section of the antenna can be angled for a cramped installation. As long as the top 11 feet of the antenna is reasonably straight, the antenna performs very well.
The design of this antenna continues to surprise me. It's like cheating the system. Commercial 5/8 base station antenna performance for fifteen dollars.
HOME MADE 5/8 WAVE CB RADIO BASE STATION ANTENNA
Here is a video to showcase the antenna's DX reception.