СраI listen to the sensitivity of the FM receiver Retekess V115 with car radio Daewoo AGC-1220RF-A, part code 2811 55052R, supplier code 269 779. Also, a way to improve VHF reception from Retekess is given.

To evaluate the sensitivity of a VHF radio receiver, you can use:
1) signal generator (which I don't have).
2) A-B comparison method. Turn on two receivers in turn at one point - compare the reception quality.
3) or find the reception boundary for the first and the other receiver, moving along the roads of the country. A more sensitive receiver has a longer range of reliable reception, so it provides high-quality reception at a greater distance from the transmitter.

The purpose of the trip on May 22, 2022 was to choose a repeater in Lyuban - along the M-10 St. Petersburg - Moscow highway you can directly approach the transmitter in Lyuban, which reduces testing time and gasoline costs.

The Lyuban transmitter, which retransmits Radio Vanya 96.7 MHz, is, I assume, located at coordinates 59.364029 31.251421 (KO59PI).
Height above sea level 45m, mast height 74 meters. Power 1 kW.

First point

The first point has been found where the Daewoo car radio receiver receives a radio station from Lyuban almost without hissing, but on the verge of crackling the FM detector, that is, with a score of 57.

КооGPS ordinates: 59.6701933 30.6402217. Heavy truck parking. Locator KO59HQ, height above sea level 47 meters.

Thus, the distance from the transmitter at the receiving point 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 an unsuccessful reception, I decided to drive closer to the transmitter in Lyuban and set the end point of the route in the village of Novolisino.
В НOvolisino I stopped at a bus stop. Retekess V115 received “Radio Vanya” with difficulty, but when connecting the counterweight to the case in the form of a USB cable (see photo), it also received it like a radio at the first point - on S7...S8. The radio was already receiving RDS and the level on its monitor 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 Novolisino to Lyuban is 35.2 km.

Retekess V115 FM sensitivity rating

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

Comparison table

Maximum range on car radio

On the way back I received the transmitter in Lyuban to Pavlovsk -54 km(hearing signal 5-6 points).
The presence of the station (2-4 points) "Radio Vanya" 96.7 MHz was observed near the Southern Cemetery -71 km!

Radiomobile calibration and sensitivity determination

The power of the Radio Vanya transmitter in Lyuban is 1 kW, the height of the transmitting antenna is 74 meters.
According to vcfm.ru.
The coordinates of the transmitter are supposedly 59.364029 31.251421.

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

Point 2.
To receive the S7 signal, in the Network parameters in Radiomobile the sensitivity on the VHF of the Retekess portable radio is indicated - 15 µV.
(Sensitivity 15 μV - with counterweight. Without counterweight - worse than 50 μV).

The lack of a normal “body” or “ground” affects it, and the antenna for FM is too short.

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

Coverage areas are shown on the same scale.

Calculation in Radiomobile: 7 µV. Car radio

Calculation in RadioMobile - 50 µV. Retekness without counterweight.

Fortunately, receivers cannot be compared, because... the price of the 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.

A way to improve VHF (FM) reception - a counterweight on the body

As a counterweight, I used the supplied USB - micro USB cable 1 m long.
The telescopic antenna and counterweight act as a single unit, improving matching and increasing the electromotive force at the receiver input.
Ultimately, the counterweight improves the low sensitivity of the Retekness V115 on VHF/FM and makes reception more confident.

During recording, I connect a counterweight (USB cable). A stronger technique is with a counterweight.

The composition is heard on the broadcast recording "Electric" group "Go Back To The Zoo",
received in Novolisino from Tosno on Retekness at frequency 70.8 (Radio Tosno-Plus).

Clarification

From the OFCOM recommendation I learned that a car antenna at a height of 2 meters has a gain of -12 to -10 dB. The reason, firstly, is diffraction losses (the antenna installation height is too low). Secondly, the antenna's radiation pattern is not parallel to the ground, but is angled upward.
0 dB gain begins only at an installation height of 10 meters above the ground. Below - the gain is negative!!!

Therefore, level calculations based on the assumption that mono reception begins at level S7 were carried out incorrectly. Since the incorrect value of the receiving antenna gain G=2 dbi was not entered instead of G=-10 dbi. This applies to the FM range around 96 MHz.

The updated data is given below:

First point (at antenna gain -10 dB)

At coordinate 59.6701933 30.6402217:
Receiving antenna gain -10 dB.
Daewoo car radio: receiver sensitivity - 1 µV
The calculation of 1 µV agreed with the passport data, because All car radios have a sensitivity of about 0.7-1.2 µV.

Correct network parameters:

Accordingly, poor reception of Retekess is also associated with an even more ineffective whip antenna (its gain is worse than -10 dB).

Source: annex-f.zip- see Figure 4.2 dependence of gain on height.

!!!!Conclusions: 1. Regarding the Daewoo car radio, theory coincided with practice.
2. The Retekess V-115 receiver works for its own money: it is not strong in VHF reception.
3. The method of improving reception using a counterweight - a USB cable, works.

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

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