For outdoor and dxpedition, for sure is the basic and easiest Antenna to build ! 100% efficiency !

The only “bad things” is that you can use for one band only, but at the end this Antenna makes his band reallllly goooood ! I have tested this kind of antenna and succesully used for QSO on 15 and 20 meter making qso’s with a qrb of 8000km, and was very consistency along a period of one week…. and allowed me some DX with QRB of over 16.000 km !!

The GP (Ground Plane) is a simple 1/4 wave lenght Resonant Antenna, with 3 or 4 radials …. his winning point is really the efficiency, as is build exaclty for the frequency you going to use… no trap, no coil, just the perfect phisic lenght for the band you will build.

Here below you can see my Setup for 10-15-20 meters…. I have done one for each band from 10 to 30meters, and I mount all of them on a 10 meters Spiderbeam Mast; the spiderbeam is perfet for this purpose, and using this lenght allow the antenna to be setup in the perfect height from the ground, another important parameter to let the antenna works properly; as these antennas are used for Outdoor Operation, everything is done with wire for an easy transport.

I have made for each antenna a proper Coaxial Current Choke, to eliminate the Common Mode Current, and to eliminate all potentially noise in the antenna; it is an easy construction, that can be built direclty with the same coaxial you will feed the antenna.

Here below how I did for each band:

Air Choke for 10 Meter Band: 8 coils wound on a 5cm diameter

Air Choke for 15 Meter Band: 8 coils wound on a 7cm diameter

Air Choke for 20 Meter Band: 8 coild wound on a 10cm diameter

Let’s see now the measure to build the antenna.. I used copper wier 1.5mm, to cover the possibility to use also with an amplifier. I have considered a Center Band for general use (cw/ssb)… it can be adjusted but will vary of very few…. see here below the scheme:

GP Mono Band Antenna RADIATOR

The main reason is that the antenna is “electrically” longer due to the diameter of the wire and the insulation: to maintain the resonance at 28.3 MHz, the physical length must be shorter. This is normal and well known in radio practice.

If you want to calculate the length more precisely, you can use:

where k is the shortening factor (typically 0.93 to 0.96 for thick insulated wire)

GP Mono Band Antenna RADIALS

About Radial, as my radial will be not Horizontal but 45° inclined, to keep the 50 Ohm I will use the formula of 5% less then real lenght of radiator. This rules can be avoided if the Radial are Horizontal

Theoric Height to keep between radials and ground

For keeping always the 50Ohm, also the radial can interacts with gournd, so the best perfomance of Antenna you should observe these minimum height betwenn the lowest point of the radiales and the ground; using the 10 meter Spiderbeam mast fir perfect, becasue when you hang the wire antenna from the top of 10 meters, none of them will arrive on the ground.