Due to the accessibility of the balcony at my place of stay, I decided to install the Ground Plane antenna on all amateur bands 7-28 MHz, and, if I can tune it, then on 3.6 MHz. The design from the article was taken as a basis http://www.dk3red.homepage.t-online.de/de/s15_01.htm. The antenna is a fishing rod with wire wound around it, a tuner at the base, grounded on the railing or glazing frame of the balcony.

1. The first antenna option is a 4.5m wire and a manual tuner

In the first version, I placed the radio station and hand-held tuner on the balcony. This is an experimental option not for on-air operation, but for “proof of concept” and testing the possibility of working from a balcony.

As a mast, I used a carbon fiber rod 7 meters long. Along its entire length, with the exception of the handle, which is located indoors, a wire is wound with a large pitch of turns.

1. The antenna fabric is a wire 4.5 meters long.
2. The same as point 1 with an extension coil to ensure resonance at a frequency of 7 MHz.
3. The antenna fabric is a wire 6.8 meters long.

All antenna options were measured with a nanoVNA antenna analyzer without the use of a tuner.

1-A. The first antenna option is a 4.5 meter wire and an automatic tuner

An antenna without a tuner has an active resistance of 11...53 Ohms (reactivity does not exceed 100 in the range of 28.14 and 10 MHz).
In all bands except 3.5 MHz, the input impedance is convenient for matching with an automatic tuner.

Graph of short wire

The resonance of an antenna with a wire length of 4.5 meters lies at 12.5 MHz (between the amateur radio bands of 10 and 14 MHz).

It should be noted that the increase in the input resistance R of the antenna at low frequencies of 3.6 MHz is apparently due to the fact that:

• the tuner in the first version is connected to ground using a 2-meter long wire - it turns out to be a GP with a displaced power point, which increases Rin.

1-B. The first antenna option is a 4.5 meter wire + extension coil for the 7 MHz range (without tuner)

Graph: antenna with coil

The SWR in one low-frequency range of 7 MHz has improved (SWR = 1.8), while in the rest the antenna-cable matching has sharply deteriorated.

Impressions from the first version of the antenna (1, 1A, 1B) with a wire length of 4.5 m, a ground wire of 2 meters

In the high-frequency ranges 14-29 MHz, the antenna is little susceptible to interference (quiet), especially if you connect it to a hand-held tuner and when the transceiver is powered by a battery. For transmission, the antenna also works well in the ranges of 10-29 MHz.

2. The second antenna option is a 6.8 meter emitter, a minimum length ground wire (0.3m)

For operating in the 7 MHz band, the normal length of the emitter is 10 meters - which is 1/4. Nevertheless. a shorter wire of 6.8 meters is also workable: the length of the emitter is equal to 0.16 wavelengths in the range of 40 meters and 0.08 wavelengths in the 80 meter range. This antenna works best in the WARC bands of 30 meters (10 MHz) and 17 meters (18 MHz).

Graph of long wire 6.8 meters

In this version of the antenna, with a wire of 6.8 meters, the matching with the cable in the band of 40 meters has worsened compared to the first option (with a long grounding conductor). In the 3.5 MHz range, the antenna is built by a tuner (active part 53 Ohms plus capacitive component). In the 14 MHz band there is a high input impedance of 1 kOhm.

Impressions from the second version of the antenna - a wire of 6.8 meters and a short grounding conductor of 0.3 m

1. This antenna option is interesting because reception in the 14 MHz range is much superior to transmission.
2. The 14 MHz antenna does not need counterweights - high input impedance of 1000 Ohms (voltage resonance). However, the antenna is built by a tuner - several radio communications in the 14 MHz range were carried out on an antenna with a wire length of 6.8 meters.
3. The antenna, despite its decent height, is much inferior to the directional ones (I can hear who other radio amateurs in St. Petersburg hear) - in the 14 MHz range, districts 6 and 9 (Krasnodar, Ural) are good, but district 0 (Siberia) is not even present, there are not even signs of stations from Siberia. FT-8 shows only traces of stations from China. This may be due to the house shielding from the north-east direction. At the same time, Europe passes through with high levels; at distances of 2000-3000 km everything is fine.
4. When placing the antenna fabric wire, although it is insulated, it should not touch the balcony railing, because the capacitance to ground increases. Also, the extension reel in the base and the helical antenna on the fishing rod should be kept away from the metal fence. Otherwise, the extension coil behaves not as a pure inductance L, but as an L-link made of L and C, with unpredictable resonances and a decrease in efficiency.

The third antenna option is a 6.8 m wire with an automatic tuner on the balcony

The purpose of the third option is to move the transceiver to the radio room for operation from more comfortable conditions. Naturally, a solution with a remote automatic matching device CG-3000 made in Belgium (for power up to 100 W), which was purchased earlier, suggested itself. The automatic tuner is tuned remotely to any frequency based on a signal from the transceiver. It does not have any control cables, except for the 12 Volt supply voltage from the power supply for operating the relay electrical circuit. The tuner is tuned to the frequency of the input high-frequency signal.

Impressions from the third option - with an automatic tuner

1. Compared to the manual tuner, the reports I received (estimates of my signal) deteriorated somewhat (from 1 to 10 dB). This is most likely due to inaccurate matching up to SWR=1.5, while the manual tuner made it possible to achieve SWR=1.0. But for the FT-8 mode this is not significant, the price is for convenience (setup speed, multi-band).
2. In the 14 MHz band, air noise increased to S7 with an automatic tuner on the balcony compared to S1-S3 using a manual tuner. The reason for poor reception is common mode interference.
3. Household interference from the AC mains to the tuner power cable has been detected. In the range of 80 meters (3.5-3.8 MHz), the loudest stations were heard against the background of the characteristic “growling” of interference from the electrical network - a consequence of common-mode interference and a current loop along the braid of the coaxial cable - transceiver - tuner - control cable.

The fourth version of the antenna (final) is based on option No. 3 with an automatic tuner. Added shut-off chokes to all cables and a common mode filter for the 220 Volt power supply

Since the source of interference was precisely identified - common mode interference, high frequency isolation from the 220 Volt network and from the room (in which interference is induced on all wires) was required:

1. To prevent common-mode interference along the outer braid of the coaxial cable, a large balun is installed in front of the automatic tuner in the form of winding 8 turns on a plastic cylinder with a diameter of 10 cm - the so-called “Ugly balun”.
2. To minimize interference along the tuner power cable, the wire near the matching device is passed through 7 ferrite rings - each with 3 turns. The “garland” of filters was put away together with the tuner in a plastic suitcase (bought for 500 rubles).
3. On the 220-volt network side, the transceiver's power supply is connected through an interference filter (EMI Filter) from AliExpress to a voltage of 220 volts and a current of 30 amperes. The interference filter is installed in a plastic mounting box purchased at a hardware store. There is a socket on top of the case, the filter has a wire with a plug for connecting to a 220 volt electrical network.
4. To reduce internal interference from the building to the antenna surface, the wire loop from the fishing rod to the matching device has been removed. To do this, the tuner is raised up and tied to the balcony railing. The grounding wire to the balcony railing is shortened to a minimum.

The use of these measures made it possible to reduce interference from 8 to 4 points in the range of 80 meters (using the S-meter with the “IPO” button turned on, bypassing the preamplifier), that is, the interference level was reduced by 24 dB! As a result, I can hear at 80 meters better than they can hear me. I receive all local 80 meter stations from St. Petersburg and the Leningrad region. The presenter of the round table at 3630 kHz scores 9+ points. They also answer me (of course, not 9 points, but “up to 9”).

The antenna connection diagram is shown below:

Appearance of a 220 volt interference filter

Click to enlarge:

The power filter is installed in the radio room. The transceiver's power supply is connected through this filter.

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