The problem of creating an effective antenna for the bands 160, 80 and 40 meters for working in confined spaces concern to many hams, including me. Previously used LW, Dipole and Inverted Vee'm not satisfied. On my roof yet somehow can fit dual band variant IV 3.5 and 7 MHz, but the third antenna at 1.8 MHz, nowhere to set. In April 1995 I made a GP antenna with capacitive load on 7 MHz. After two years of successful operation, I was convinced of its sufficient efficiency. Its height - 11.9 m, plus four wire 5 m, secured to the top of the antenna and stretched nylon ropes at an angle of 90° to each other. Efficient operation of this antenna was suggested about remaking her in-band option.

After a long study of various publications about vertical antennas [1...3] I settled on a design [3], which was not a very great height and gave me the opportunity to work successfully not only with DX-mi, but also effectively close the connection.

Design

In my case the mast has a height of 16.8 m and collected from the four pipes with a diameter of 55 mm (antenna mast radio station R-401), three pipes with a diameter of 40 mm and one with a diameter of 32 mm. All pipes are well connected to each other. Used four layers of nylon stretch marks. The mast is lifted by the lift of the P-401. The lift together with the mast installed on insulator (plate of thick fiberglass). Insulator with reinforced steel corners on a concrete slab sizes HH cm (these plates lined walking paths). This plate rests on the flat roof of the house and around the perimeter of the filled resin. Two wires capacitive load is made of steel wire with a diameter of 2.5 mm and a length of 8.5 mm and stretch marks are a part of the upper tier. The counterweights are made of aluminum wire with a diameter of 2...2.5 mm (was taken semilly wire from overhead transmission lines and disheveled). At 7 MHz is used 6 resonance balances in the ranges of 3.5 and 1.8 MHz - 4 counterweight. It is best if all of the counterweights are located at equal angles to each other, but due to the fact that the width of the house is just 10... 11 meters and he arched, had to place the counterweights just putting them on the roof. In my case the antenna power cable is 75 Ohm.

Vertical antenna for LF ranges

Setting. Setting of 7 MHz I have any difficulty, apparently, was affected by the proximity of the antenna 2el QUAD on the HF bands. When measuring RF bridge input resistance at resonance was 38...40 Ohms, respectively, and the SWR was about 2. So I had to modify the schema matching device (see figure), adding a third relay circuit, which through the normally closed contacts short-circuits on the housing of the outlet of the coil L1 in the range of 7 MHz. When using any of the relays K1, K2, i.e. the ranges of 1.8 and 3.5 MHz, the relay circuit is actuated, its contacts open, and it does not affect the operation in the range of 1.8 and 3.5 MHz. Now the antenna can be configured perfectly. In fact, in [3], in the range of 7 MHz is only adjustable resonance frequency and input resistance Rin - no, so to achieve the CWS is exactly equal to 1, because Rin is determined not only by the height of the mast and the angle of the capacitive loads, but also surrounding objects. In the present embodiment matching device (SU), moving average allotment of the coil L1, establish a resonant frequency, and then moving the top outlet, regulate bits, i.e. achieve the CWS= 1. If the SWR at resonance >1, it says only that the setup is not thoroughly produced. Setting the resonance frequency UAH 7,050 kHz moving average allotment, it is necessary to simultaneously move the upper and - so that between them there was always 2...3 coils.

The ranges of 1.8 and 3.5 MHz without problems tuned in accordance with the methodology described in [3], i.e. the resonance at 1.8 MHz was achieved by changing the total number of turns of the coil L1, and the CWS=1 - moving it lower outlet.

In the range of 3.5 MHz, the selection of capacitor C1 has reached the minimum SWR in the middle of the range. Better when you configure solder KPE air-dielectric from broadcast receivers capacity 12/495 pF, adjust the antenna and then by measuring the capacitance of the capacitor, solder the capacitor capacitance constant.

After presetting is completed, a matching unit lid and, if necessary, adjust everything again. Due to changes in the schema SU, relay switching ranges are powered by a separate control line. In my case the relays are controlled by the voltage of +15 V. the Coil L1 is wound around a copper wire with a diameter of 2.5 mm on a ceramic frame with a diameter of 55 mm with step 2...2.5 mm It contains 33 turns, bends from - 8, 22 and 25 turns, counting from the grounded end. Exact numbers of turns and the position of the taps is determined during configuration. Capacitors: C1 - type CSR for a voltage of 500 V, C2 C4...any locking. Diodes VD1 and VD2 can use any rectifier enduring current of the relay. Relays are used on high frequency ceramics, the distance between the contacts is about 1.5 mm For relay switching thepolished two-wire line, which is on the roof shunted by capacitors C2 and C3, and the other end when you enter the radio station is passed through the ferrite ring permeability NN (5...10 turns).

Results.
In the range of 1.8 MHz VSWR at resonance=1, the edges of the range VSWR=1,8 (1810 1930...kHz).
In the range of 3.5 MHz SWR of 1.1, the edges of the range of 1.4 (3,5 3,8...MHz).
On the 7 MHz on the resonance of the CWS=1, the edges of the range is 1.2.

I use this antenna while only two summer months and use RA capacity 250... 300 watts. 40-meter range freely get any DX-a, which you hear. With the first or second attempt manages to break through almost any pile up. Spent a lot of links to all the continents. However, unlike a regular GP, this antenna gives you the ability to work confidently with others and correspondents. Working day, 40-meter range, I almost never get a report lower than 59+20dB.

For the 80-meter band, I immediately began to hear, and I heard the station I on Dipole and IV never been able to get an answer. In General the call come LU, ZP, XIE, PY, UAO, VK, JA, Africa, Antarctica. A great example of operation of the antenna is the relationship with Carlos (TI4CF) that I always come greeting, a report from him never below 58. When there is at least a weak distant passing even with my not very large output power manages to keep the frequency of the General call in DX-window (3790...kg) for quite a long time. Those who worked on CQ in this phase, you'll understand what that means. Those who are preparing to try their hand in DX-window 80-meter band, it should be borne in mind that if your calls within a few minutes no one DX station, so even when your signals are audible in Europe is not very loud, then at best you are politely asked not to take in vain narrow DX-OKHO, and at worst is just the frequency, ignoring your presence on it. When working in the evening with neighbors correspondents report 59+10 dB and more than I get from stations having antennas with vertical polarization. If the correspondent has a horizontal antenna, a report is usually below - 58, 59.

On the 160-meter band during the two months spent many connections at distances of 2000...5000 km For short links (up to 1000 km) antenna didn't work so well on 40 and 80 meters from the stations of the Baltic States, Poland report is rarely more than 57. However, on longer routes - DL, G, F, UA9, UN - hear me much better, and rarely report below 59. Hopefully, in the winter, the results will be more impressive, because in summer the passage of low frequencies are noticeably worse.

Literature

1. Bieńkowski 3., Lipinski, E. Amateur antenna LW and УSW. - M.: Radio and communication, 1983.
2. Zeldin I. LW antenna with vertical polarization. - Kharkov, 1991.
3. Goncharenko I./ Hams. LW and УSW. - 1997. - N1. P. 30.

Author: G. Tsymbal (EU1AI), Minsk; Publication: N. Bolshakov, rf.atnn.ru

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