How does the RoomCap antenna work?
The RoomCap antenna works by using the capacitance between the tube element and the surrounding space to create a resonant circuit with the RFA. The RFA is a variable capacitor that can be controlled remotely by a small motor. By changing the capacitance of the RFA, the resonant frequency of the antenna can be adjusted to any desired value within the band. The RFA also acts as a matching device to provide a 50 Ohm feed impedance for the coaxial cable.
The tube element is mounted vertically on a non-conductive support and has a diameter of 5 cm and a length of 50 to 170 cm, depending on the frequency. The length of the tube element determines the bandwidth of the antenna. For example, a 50 cm tube element can cover the entire 10 m band, while a 170 cm tube element can cover only part of the 80 m band. The tube element can be made of any conductive material, such as aluminum, copper, or steel.
What are the advantages of the RoomCap antenna?
The RoomCap antenna has several advantages over other types of HF antennas, such as:
It is small and easy to install. It does not require any supporting poles, wires, or radials. It can be mounted on any vehicle, balcony, roof, or mast.
It has a low SWR on all bands without the need of a tuner. It can be tuned to any frequency within the band by using the RFA.
It has a low radiation angle and a circular radiation pattern in the horizontal plane. It can reach distant stations with low power and low noise.
It has a high efficiency and a low loss. It does not waste power in heating up the ground or nearby objects. It radiates most of the power into free space.
How to build the RoomCap antenna?
The RoomCap antenna can be built as a monoband or multiband antenna. The construction details are explained in the construction guide that can be ordered from [HB9ABX's website]. The construction guide includes diagrams, photos, parts lists, and instructions for building and testing the antenna. The construction guide also provides tips and tricks for optimizing the performance of the antenna.
The main components of the RoomCap antenna are:
The tube element: A conductive tube with a diameter of 5 cm and a length of 50 to 170 cm, depending on the frequency.
The RFA: A variable capacitor that can be controlled remotely by a small motor. The RFA is mounted inside the tube element and connected to the coaxial cable.
The control unit: A device that sends signals to the motor to adjust the capacitance of the RFA. The control unit can be manual or automatic.
The support: A non-conductive material that holds the tube element vertically. The support can be PVC pipe, fiberglass rod, or wooden pole.
The coaxial cable: A 50 Ohm cable that connects the RFA to the transceiver. The cable should be as short and as good quality as possible.
The construction guide also provides information on how to measure and adjust the SWR of the antenna, how to install and mount the antenna, and how to operate and maintain the antenna.
What are some examples of contacts made with the RoomCap antenna?
The RoomCap antenna has been tested and used by many amateur radio operators around the world. Some examples of contacts made with the RoomCap antenna are:
HB9ABX worked VK9NS on 80 m with 100 W and received a 59 report.
HB9ABX worked ZL1AMO on 160 m with 100 W and received a 57 report.
HB9ABX worked ZS6EZ on 40 m with 100 W and received a 59+ report.
HB9ABX worked JA1BK on 20 m with 100 W and received a 59+ report.
HB9ABX worked VP8LP on 15 m with 100 W and received a 59+ report.
HB9ABX worked PY2XB on 10 m with 100 W and received a 59+ report.
IN3ECI worked VK6HD on 40 m with 100 W and received a 57 report.
IN3ECI worked ZL3CW on 40 m with 100 W and received a 55 report.
IN3ECI worked VK2APG on 20 m with 100 W and received a 59 report.
IN3ECI worked ZL2AGY on 20 m with 100 W and received a 59 report.
IN3ECI worked VK4EMM on 15 m with 100 W and received a 59 report.
IN3ECI worked ZL1BYZ on 15 m with 100 W and received a 59 report.
These are just some of the many contacts made with the RoomCap antenna. The antenna has proven to be very effective for DXing and contesting on HF bands.
Conclusion
The RoomCap antenna is a new type of HF antenna that uses a capacitive sky radiator to achieve high efficiency and low SWR on multiple bands. The antenna is small, easy to install, and suitable for mobile, portable, or fixed use. The antenna has a low radiation angle and a circular radiation pattern for DX contacts. The antenna can be built as a monoband or multiband antenna by following the construction guide provided by HB9ABX. The antenna has been tested and used by many amateur radio operators around the world and has shown excellent results.
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