The essence of the experiment: find out which antenna will create the maximum field strength at a distance of 5 km.

The essence of the problem

To work both through a repeater and in a direct channel with correspondents, it is necessary to ensure the highest possible field strength. There are two options here - raise the antenna to the roof and put up with losses in the cable and connectors, or place the antenna on the balcony or mount it near the window. If the antenna is placed near the transmitter, the loss in the cable does not exceed 1 dB.

Description of the experiment

Antenna No. 1- two elements at 144 MHz, directly at the transmitter, installed at a height of 4 meters, antenna gain 6 dBi, loss less than 1 dB (RG58 3 meters long - loss 0.2 dB).

Dimensions of a two-element antenna:

Antenna No. 2-Comet GP3 installed at a height of 14 meters, gain 5/8 - 2dBi loss 3 dBi (cable 25 meters long).

Signal level in dB was measured on WebSDR (http://websdr.78dx.ru:8901/)5 km from my house.

The first antenna has a resonance at a frequency of 145.100 MHz - checked using a nanoVNA device, with SWR = 1.2, Rin = 60 Ohms.
The second antenna on the roof is set at the factory to the 144-146 MHz range.

Cable loss- antenna No. 1 (on the roof) - a feeder of two sections: 4 meters RG8X for passing through the frame and 25 meters analogue RG213 to the antenna. The RG8X cable has a loss of 11 dB/100 m, and RG213 has a linear attenuation of 8 dB/100 m. I take the loss to be 5*11/100+25*8/100 6dB=3dB. To these you need to add the signal attenuation on the connectors - 2 connections of 1 dB each, for a total total loss of 5 dB.

Antenna No. 2 - one piece of RG-58 cable 1.5 meters long with PL connectors, there is practically no loss.

Select antennas #1 and #2 using an industrial-type antenna switch.

Comparison of transmission power to remote WebSDR receiver

At a distance of 5 km from the receiver, an antenna located at a lower altitude can outperform a higher one.

With a short cable, if the antenna is outside the window, you need to pay attention to the SWR - at 1.3-1.5 the transmitter seems to reduce ("throw off") the power, but at SWR 1.0-1.2 this does not happen and the power output is full. Thus, it is necessary to rebuild antenna No. 1 (outside the window) higher in frequency.

Interference with reception from an antenna installed outside the window. Reception quality comparison

If the antenna is installed outside the window, it receives “electrical smog” from electrical appliances in the house. At the same time, the magnitude of the interference depends on the type of wiring - old houses have wiring with an insulated neutral without a grounding wire, the interference is significant up to 8 points. Houses of new series - more attention is paid to grounding, interference on HF and VHF is much weaker.

Although an antenna at a height of 4 meters creates a high field strength, in terms of reception it is significantly (more than 5 points) inferior to an antenna on the roof. For example, on the S-meter scale, interference of the “50 Hz harmonics” type on a low antenna is up to 8 points, while on the roof the noise is 2-3 points. Also, the purity of reception is higher with an antenna installed on top of the building. The long-range repeater R1 (145.625) is not received at the first antenna at a height of 4 meters on the opposite side of the house (only presence), while at antenna No. 2 in the center of the roof there is a signal of 8 points with a little white noise.

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