Introduction:

An antenna is a metallic structure that captures and/or transmits radio electromagnetic waves. Antennas come in all shapes and sizes from little ones that can be found on your roof to watch TV to really big ones that capture signals from satellites millions of miles away.

                  

Antenna design:

          Range is the antenna design. If the antenna design and it’s placement is optimized, then it will complement the conductive performance of the wireless MCU reference design. The optimum range and system performance can only be achieved when the reference design is followed and the antenna if optimized.

Construction:

  • Generally, a dipole for 160 meters requires minimum of 260 feet of horizontal space and supporting ropes at each end.
  • It is usually installed near to the ground, relative to its operating wavelength, which turns it into a NVIS (Near Vertical Incidence Sky wave) antenna, only good for very short-range communications.

Fitting a resonant antenna on the 160 meter band in less space than required:

It is a ‘hybrid‘ design because, depending on how we look at it. These antennas are not a dipole with huge loading inductors. And not a grounded quarter wave vertical (containing a huge loading inductor at its base and a whip, with lots of buried wire radials either).

A true inverted ‘L’ is a 5/16 vertical antenna worked against ground  

This design looks like an inverted ‘L’ antenna. Its vertical portion is bent to form an inverted ‘L’ (a vertical portion followed up by a horizontal portion).

It’s long leg going up vertically, then away horizontally – and with its short leg lying flat on the ground and insulated from ground electrically!

It could also be viewed as a 160m off-center fed dipole antenna

  • It looks like an end-fed 1/4 wave 160 meter antenna (130 ft or 39.624 m long) which goes up some 25 feet (7-8 m), then over horizontally, at an average of 25 feet (7-8 m) above ground, to a tree at the far end of my property. It is worked against a counterpoise which is connected to the shielded side of the coaxial feed point.

                         The hybrid 160 meter antenna layout diagram

Counterpoise: 130-foot (39.624 m) length of insulated antenna wire. The antenna was resonant way below the 160 meter band and was too long. Its resonant frequency was around 1.7 MHz!

Tuning of 160m Antenna Counterpoise:

Active part of antenna was ¼ wave of wire in the air then in order to bring the resonant frequency above 1.8 MHz, the counterpoise was shortened. And then the end of the counterpoise back on itself was wound in a coil having 6inches in diameter. After few attempts, resonance was obtained as 1.841 which is within the lower part of band. The counterpoise ended up measuring 62 feet overall, with the roughly coiled up portion at its end

An orange electrical wire connector on the end of the counterpoise wire to prevent the ‘live’ inner conductor from making contact with the wet grass, wet leaves .Since it could damage your transceiver if it happened during transmission.

Supply to 160 Meter Antenna:

               RG-8X coaxial cable was used to feed the antenna which was connected directly to the antenna. The connections are protected by a weatherproof outdoor electrical junction box, installed outside, about four feet above ground. The center conductor of the coax cable is connected to the aerial portion of the antenna while the coaxial shield is connected to the counterpoise portion.

Preset condition:

  1. The  antenna was feed through a homemade RF choke made of 22 turns of RG-58X on a plastic form cut out of a Folgers coffee container

RF feedback could also be coming from two other antennas:

  • An off-center-fed 80 meter dipole that was used on all HF bands – from 80 to ten, sometimes even on the 6-meter band!
  • A 40-meter dipole that also sometimes used on the 15-meter band.
  • When there is no protection from common mode RF feedback, the coaxial feed line from the antenna pick up some of the RF radiated if it was transmitted by other two antennas.  

160 meter antenna can cover at least half the 160 meter band within a 2:1 SWR. Any antenna tuner should be able to easily handle the higher SWR over the other half of the band.


Dimensions for construction:

The above-mentioned dimensions of the aerial part, and its counterpoise depend on:

  • the height above ground of the horizontal portion of the aerial;
  • the length of the vertical portion;
  • the conductivity and dielectric properties of the ground below the antenna – both its aerial part and its counterpoise;
  • Not to mention surrounding structures within 1/2 wavelength (273 feet or 83.33 meters) of the antenna.

Anyway, one should be able to ‘tune‘ the antenna to resonance easily enough by simply adjusting the length of the counterpoise adapt it to its given environment.

Weather conditions:

The counterpoise was laid on the ground, in its final ‘tuned‘ state, late in the month of October.

Remark:

It is a “single band” antenna. The 160 meter band is not harmonically related to higher HF bands

Conclusion:

    In this construction, if we want to use this antenna with different HF bands, we need to use a wide range antenna tuner for handling the unpredictable values.

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