I took the sensitivity test of the FM receiver Retekess V115 with compare to car radio Daewoo AGC-1220RF-A, part code 2811 55052R, supplier code 269 779. Also, in the article I gave a simple method for improving VHF reception at Retekess.

To evaluate the sensitivity, you can use:
1) the signal generator (which I do not have).
2) a A-B method of comparing. In turn, turn on two receivers at one point - compare the quality of the reception.
3) either find the boundary of the reception for the first and other receiver, moving along the roads of the country. A more sensitive receiver has a longer zone of confident reception, so it provides a high-quality technique at a greater distance from the transmitter.

The purpose of the trip on May 22, 2022 was chosen a relay in Lyuban - along the M-10 "St. Petersburg - Moscow" highway, you can straighten up to the transmitter in Lyuban, which reduces the time for testing and gas expenses.

Lyuban's transmitter, who retires Radio Vanya 96.7 MHz, I suppose, is in coordinates 59.364029 31.251421 (KO59PI).
The height above sea level is 45m, the height of the mast of the transmitter tower is 74 meters. Power is 1 kW.

First point

The first point was found where the Daewoo car radio receiver receives a radio station from Luban almost without hissing, but on the verge of crackling FM detector, i.e. with a rating of 57.

GPS coordinates: 59.6701933 30.6402217. Parking lot for heavy trucks. Locator KO59HQ, altitude 47 meters above sea level.

Thus, the distance from the transmitter to the reception point is 48.5 km.
https://gps-coordinates.org/distance-between-coordinates.php
According to the station service monitor signal=18 db, usn=45 mit=31 rds=0 q=0.

Second point

After unsuccessful reception, I decided to drive closer to the transmitter in Luban and set the final route point in the village of Novolizino.
In Novolizino, I stopped at a bus stop. Retekess V115 received "Radio Vanya" with difficulty, but when connecting a counterpose to the body in the form of a USB cable (see photo), it received it as well as a radio at the first point - on S7...S8. The radio already received in RDS and the level on its monitor was signal=47 db usn=2 mit=2 rds=100 q=22.

Coordinates 59.5709250, 30.7775515, locator KO59JN.

At this point, the distance to the transmitter from Novolizino to Lyuban is 35.2 km.

Estimation of RETEKESS V115 sensitivity on the FM band

By subtracting from 47 dB and 18 dB we get 29 dB - almost 30 dB of the difference (or 5 points by S-meter). Retekess V115 is inferior to the car radio Daewoo whole 30 dB of sensitivity, if used without a counterpose wire: 7*10^1.5 = 221 μV! With a counterpose, sensitivity can be estimated roughly at 15-20 μV.

Comparison table

Maximum receiveng range of car radio

On the way back, I took the transmitter in Lyuban to Pavlovsk - 54 km (a signal by ear 5-6 points).
The presence of the station (2-4 points) "Radio Vanya" 96.7 MHz observed near the Southern cemetery of St.Petersburg - 71 km!

Calibration of RadioMobile software and determinging of sensitivity

The power of the transmitter "Radio Vanya" in Lyuban is 1 kW, the height of the transmitting antenna is 74 meters.
According to data VCFm.ru.
The coordinates of the transmitter is presumably 59.364029 31.251421.

Point 1
To receive a signal S7, in the parameters of the "Network" in Radiomobile, the sensitivity of the car radio Daewoo is indicated at the level of 7...8 μV.

Point 2.
To receive a signal S7, in the parameters of the "Network" in Radiomobile , the sensitivity of the portable radio receiver Retekess - 15 μV.
( Sensitivity 15 μV - with a counterpose. Without a counterpose - worse than 50 μV!)

The absence of a normal counterpose or "ground" affects the receiver VHF performance, and the antenna for FM is too short.

Calculation of the transmitter coverage area in Lyuban for two cases of sensitivity

The coverage areas are given on one scale.

Calculation in RadioMobile: 7 μV. Car radio:

Calculation in RadioMobile - 50 mV. Retekess without a counterpose wire:

For good, the receivers cannot be compared, because The price of a car radio is 8-10 times higher than that of Retekess V115,
the antenna on the roof is resonant (0.84 m), the cable braid has reliable contact with the metal body of the car.

Method of improving the reception of VHF (FM) band - counterpose wire connected to the chasis

As a counterpose, I used a complete USB cable "Micro USB" 1 meter long.
The telescopic antenna and counterpose act as a whole system, improving impedance matching and increasing the electric motion force at the input circuit of the receiver.
Ultimately, the counterpose improves low sensitivity of Retekness V115 on the VHF/FM band, making the reception more confident.

On the record I connect a counterpose (USB cable). A stronger technique is with a counterpose.

On the record from the air sounds the composition "Electric" of the music band "Go Back To The Zoo",
accepted in Novolisino from Tosno on Retekness at a frequency of 70.8 (urban radio "Tosno-Plus").

Clarification

From the recommendation, OFCOM found out that the car antenna at a height of 2 meters has gain from -12 to -10 dB. The reason, firstly, in diffraction losses (too low the height of the antenna installation for band 87-108 MHz, in which wavelength is 3 meters). Secondly, the antenna diagram is not parallel to the Earth, but is rejected at some angle up.
Strengthening 0 dB begins only with an installation height of 10 meters above the ground (3 wavelengths). Below - the Gain is negative !!!
Therefore, the calculations of the level from the assumption that the reception in mono begins with the level of S7 is carried out incorrectly. Since the incorrect value of the G (Gain parameter), reception of the antenna with G = 2 dbi is not introduced instead of G = -10 dbi. This applies to the FM range in the region of 96 MHz.

The specified data are given below:

The first point (with the amplification of the antenna -10 dB)

In coordinate 59.6701933 30.6402217:
Strengthening the receiving antenna -10 dB.
Daewoo car radio: Sensitivity of the receiver - 1 μV
The calculation of 1 MKV agreed with passport data, because All car radio tape recorders sensitivity about 0.7-1.2 μV.

The correct network parameters:

Accordingly, a poor reception RETEKESS is also associated with an even more ineffective rod antenna (its Gain is worse than -10 dB).

Source: Annex-f.zip - For relation "Gain versus Height" see Figure 4.2 in the document compreeed in ZIP-file.

Link:
*Radiomobile - website of the developer Roger Coudé, PE1MEW (Netherlands).

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