In general, the Marconi antenna is a well-known type of antennas widely used by hams, and, in fact, is a Ground Plane antenna. In comparison to the regular Marconi antenna, the twin-lead modification is a short-circuited one.
Figure 1. Marconi antenna. Can be vertical, sloped or folded. You need to fold it in case of using it on lower bands, where its length is quite high to be hard to hold it vertically. The coax shield is connected to the grounded rod. Addition of some number of counterpoises should bring more effectiveness because of the increased conductivity of the ground plane.
Figure 2. Twin-lead Marconi antenna. This type of the Marconi antenna is a better implementation because of its short-circuited nature - it does not collect static electricity as its predecessor. The jumper on the top of the antenna can be used to change the electric length of the antenna which changes the frequency of resonance. But the easier and proper way to achieve this is to use the coil. But don't forget about the high current flowing in the feeder connection point. Addition of counterpoises increases the effectiveness of this kind of antenna as well.
Below is a couple of models grabbed from the MMana-gal application. I have provided them for demonstration purposes to show how small is the difference between them.
Figure 3. The view of the GP and distribution of currents. Noting unexpected - maximal current is located in the feed point. In order to make the antenna 50 Ohms the counterpoises have to be sloped.
Figure 4. The same for twin-led GP. The current is maximal on the feed point as well. But as far as the opposite part is connected to counterpoises, the current is quite asymmetric. This causes small changes in the radiation pattern (see below).
Figure 5. The radiation pattern of the quarter wave GP. It is quite low-angled like every GP we built already.
Figure 6. The radiation pattern of the twin-lead GP. It is almost the same as the one above. The lowest angle it can radiate the waves is less, though.
Antennas shown above are relatively short Marconi antennas, which do not allow to see how long folded and sloped twin-led Marconi antenna looks. I created a model of such an antenna and played a little to make it resonant and 50 Ohms compatible. It has four pretty short counterpoises and the long body. The body has 11 meters long vertical part and 35 meters long sloped part. The highest point is on 23 meters above the ground. The feed point is 1 meter above the ground. To eliminate the reactance the coil (40 uH) was used at the feed point.
Pictures below display the view, radiation pattern and SWR plot. By the way, the antenna is rather narrow - it is as wide as 25 kHz by SWR 2:1.
Figure 7. The overall view of the antenna. Distribution of currents is shown as well.
Figure 8. The radiation pattern. Most of the energy is being emitted to the zenith. Very good for local connections.
Figure 9. The SWR plot. The antenna is very narrow, which made it almost unusable. Although changing the length and number of counterpoises should improve the situation, the antenna still remains ineffective.
To sum up. This antenna is very simple and easy to build. The disadvantages are a zenith radiation pattern and a very narrow band. Therefore, the presence of some kind of tuner at the feeding point should be a good solution to have this antenna to be resonant on the whole band.
The model of the antenna (for mmana-gal) is shown below.
Folded twin-lead Marconi antenna for 80m (50 Ohm)
*
3.55
***Wires***
11
0.0, 0.0, 0.0, -2.8, 3.0, 0.0, 0.001, -1
0.0, 0.0, 0.0, 3.2, 3.0, 0.0, 0.001, -1
0.0, 0.0, 0.0, 3.0, -3.0, 0.0, 0.001, -1
0.0, 0.0, 0.0, -2.8, -3.0, 0.0, 0.001, -1
0.0, 0.0, 0.0, -0.02, 0.0, 0.1, 0.001, -1
0.0, 0.0, 0.0, 0.02, 0.0, 0.1, 0.001, -1
0.02, 0.0, 0.1, 0.02, 0.0, 11.0, 0.01, -1
-0.02, 0.0, 0.1, -0.02, 0.0, 11.0, 0.001, -1
0.02, 0.0, 11.0, 0.02, 33.1, 23.54, 0.001, -1
-0.02, 0.0, 11.0, -0.02, 33.1, 23.54, 0.001, -1
-0.02, 33.1, 23.54, 0.02, 33.1, 23.54, 0.001, -1
***Source***
1, 0
w6c, 0.0, 1.0
***Load***
1, 1
w6c, 0, 40.0, 0.0, 0.0
***Segmentation***
400, 40, 2.0, 2
***G/H/M/R/AzEl/X***
2, 1.0, 1, 50.0, 120, 60, 0.0
Figure 1. Marconi antenna. Can be vertical, sloped or folded. You need to fold it in case of using it on lower bands, where its length is quite high to be hard to hold it vertically. The coax shield is connected to the grounded rod. Addition of some number of counterpoises should bring more effectiveness because of the increased conductivity of the ground plane.
Figure 2. Twin-lead Marconi antenna. This type of the Marconi antenna is a better implementation because of its short-circuited nature - it does not collect static electricity as its predecessor. The jumper on the top of the antenna can be used to change the electric length of the antenna which changes the frequency of resonance. But the easier and proper way to achieve this is to use the coil. But don't forget about the high current flowing in the feeder connection point. Addition of counterpoises increases the effectiveness of this kind of antenna as well.
Figure 3. The view of the GP and distribution of currents. Noting unexpected - maximal current is located in the feed point. In order to make the antenna 50 Ohms the counterpoises have to be sloped.
Figure 4. The same for twin-led GP. The current is maximal on the feed point as well. But as far as the opposite part is connected to counterpoises, the current is quite asymmetric. This causes small changes in the radiation pattern (see below).
Figure 5. The radiation pattern of the quarter wave GP. It is quite low-angled like every GP we built already.
Figure 6. The radiation pattern of the twin-lead GP. It is almost the same as the one above. The lowest angle it can radiate the waves is less, though.
Antennas shown above are relatively short Marconi antennas, which do not allow to see how long folded and sloped twin-led Marconi antenna looks. I created a model of such an antenna and played a little to make it resonant and 50 Ohms compatible. It has four pretty short counterpoises and the long body. The body has 11 meters long vertical part and 35 meters long sloped part. The highest point is on 23 meters above the ground. The feed point is 1 meter above the ground. To eliminate the reactance the coil (40 uH) was used at the feed point.
Pictures below display the view, radiation pattern and SWR plot. By the way, the antenna is rather narrow - it is as wide as 25 kHz by SWR 2:1.
Figure 7. The overall view of the antenna. Distribution of currents is shown as well.
Figure 8. The radiation pattern. Most of the energy is being emitted to the zenith. Very good for local connections.
Figure 9. The SWR plot. The antenna is very narrow, which made it almost unusable. Although changing the length and number of counterpoises should improve the situation, the antenna still remains ineffective.
To sum up. This antenna is very simple and easy to build. The disadvantages are a zenith radiation pattern and a very narrow band. Therefore, the presence of some kind of tuner at the feeding point should be a good solution to have this antenna to be resonant on the whole band.
The model of the antenna (for mmana-gal) is shown below.
Folded twin-lead Marconi antenna for 80m (50 Ohm)
*
3.55
***Wires***
11
0.0, 0.0, 0.0, -2.8, 3.0, 0.0, 0.001, -1
0.0, 0.0, 0.0, 3.2, 3.0, 0.0, 0.001, -1
0.0, 0.0, 0.0, 3.0, -3.0, 0.0, 0.001, -1
0.0, 0.0, 0.0, -2.8, -3.0, 0.0, 0.001, -1
0.0, 0.0, 0.0, -0.02, 0.0, 0.1, 0.001, -1
0.0, 0.0, 0.0, 0.02, 0.0, 0.1, 0.001, -1
0.02, 0.0, 0.1, 0.02, 0.0, 11.0, 0.01, -1
-0.02, 0.0, 0.1, -0.02, 0.0, 11.0, 0.001, -1
0.02, 0.0, 11.0, 0.02, 33.1, 23.54, 0.001, -1
-0.02, 0.0, 11.0, -0.02, 33.1, 23.54, 0.001, -1
-0.02, 33.1, 23.54, 0.02, 33.1, 23.54, 0.001, -1
***Source***
1, 0
w6c, 0.0, 1.0
***Load***
1, 1
w6c, 0, 40.0, 0.0, 0.0
***Segmentation***
400, 40, 2.0, 2
***G/H/M/R/AzEl/X***
2, 1.0, 1, 50.0, 120, 60, 0.0
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