Fig. 1
One of the best GP designs on the low-frequency bands 1.8 ... 10.1 MHz (fig. 1) has been widely used by radio amateurs for more than a quarter century.
This article describes a new matching unit for this antenna. The 60 and 20 meter bands have been added. The matching bandwidth is increased in the 160, 80 and 40 meter bands.
With this matching unit the antenna operates in the following bands/sub-bands: 160m CW, 160m SSB, 80m CW, 80m SSB, 60m, 40m CW, 40m SSB, 30m, 20m.
The matching circuits in each of these bands/sub-bands are shown in Fig. 2
The antenna parameters by band are shown in the following six screenshots. The calculations are made for average losses in the radial system and/or the ground.
The zenith patterns in the 160-40 m bands are equivalent to a vertical with an electrical length of 23 meters.
In the 30 m band, the electrical length of the antenna is long and the radiation is raised upward. Nevertheless, the gain at low angles <100 remains higher, a single quarter-wave GP of this band.
In the 20-meter band, the effect of the excess electrical length is compensated for by tilting the top wires. Therefore, the antenna radiates in this band as a vertical with lambda 5/8, i.e. a vertical with maximum gain.
Fig. 3 shows a switchable matching unit that realizes all the bands circuits of Fig. 2.
Table of relay states by bands and circuit diagram of the control unit are shown in Fig. 4. The control unit and matching unit are connected by an low-cost STP-4 LAN cable. The colors of the wires in Fig. 4 correspond to the colors of the STP-4 LAN cable wires. Any diodes that can withstand the current of the relay winding.
The following screenshots show graphs of VSWR versus frequency by bands.
160m. Antenna model files with matching unit in 160m CW and 160m SSB (in MMANA-GAL program format).
80m. Antenna model files with matching unit in 80m CW and 80m SSB (in MMANA-GAL program format).
60m. Antenna model files with matching unit in 60m (in MMANA-GAL program format).
40m. Antenna model files with matching unit in 40m CW and 40m SSB (in MMANA-GAL program format).
30m. Antenna model files with matching unit in 30m (in MMANA-GAL program format).
20m. Antenna model files with matching unit in 20m (in MMANA-GAL program format).
All coils are wound with thick wire with a diameter of 2 ... 3 mm with a pitch equal to the wire diameter. The number of coils should be calculated depending on the diameter of your existing frame. This can be done in the MMANA-GAL program > Tools > HF components > Coil.
Three frames are used. One has L1 wound on it, another has L4 wound on it, and the third has L2 + L3 wound on it (actually it is one ~12 µH coil with a tap). Take care to design the coils so you can adjust their inductance + 10% and solder taps when tuning.
Capacitors C1...C3 should be rated to RF current up to 5 amperes at a TX power of 1 kW. Also, the capacitances of C1 and C2 should change slightly during tuning. Therefore, it is convenient to make C1 and C2 each of two parallel capacitors. One of them of constant capacitance is ~10...20 pF less, than the calculated value. The second one is adjustable 10 ....40 pF for the tuning time. After tuning the tuning capacitors are changed corresponding short open sections of RG213 coaxial (capacitance of most 50 Ohm cables ~1 pF/cm).
In principle, it is possible to do all C1 ... C3 from several parallel connected short open-circuited sections (15...25 cm each) of RG213 (or same) and not to look for powerful ceramic RF capacitors.
HF current through the relay contacts does not exceed 5 Amperes at TX 1 kW. And the voltage between contacts can reach 400 V on K1, K2, K9; 1 kV on K7, K8 and 2 kV on K3, K4, K5, K6.
I used RT314 as a relay K1, K2 and K9; old electrical relay with a 1 mm gap between open contacts as K7; and vacuum relays as K3, K4, K5, K6.
The tuning is done in the following sequence step-by-step:
25.09.2024