Booster and noise figure NF

It is not only ineffectual when the usage of the preamp for the reception of the booster and the amateur radio used to receive BS and CS is bad but also exists by not being and there is even a thing of goodness or more. It thinks about the booster and NF (It is said the noise figure or noise factor).

The loss occurs by the cable and the connector, etc. if the booster is not used when a weak signal is received, and the signal becomes small fast. NF worsens to the extent that it attenuates because the amount of the noise increases relatively when the signal becomes small, too.

When NF worsens once, NF is not improved no matter how it amplifies with the amplifier of the ideal. I think that an important thing to amplify before it attenuates is understood.

Definition of S/N ratio and NF

The ratio of the signal and the noise is called S/N ratio, and the ratio of S/N of the input and S/N of the output is called NF (noise figure).

There is no unit because the S/N ratio and NF are ratios. It shows by the decibel usually. Therefore, NF of the ideal amplifier is 0dB.

Computational method of synthesis NF

NF of the equipment such as boosters is written in ratings etc. , and NF of the loss and the attenuator is an amount of attenuation. The calculating formula of NF when these are combined with steps how many is as follows.

NF₁---NF_n : NF of unit of each steps

G₁---G_n : Gain of each steps

It calculates by a value that is not dB but true. The calculating formula by Excel is here.

I think that I can use it soon if Internet Explorer and Excel are installed. Please preserve in the file by right-clicking and use it by Excel when it doesn't go well.

Improvement of NF with amplifier (booster)

When there is no active element except the booster

Because the amplifier of the ideal doesn't exist in this world, it can be said that the noise is generated by amplifying without fail. Therefore, when the amplifier is used, it is necessary to use the amplifier that the amount of generation of the noise is a little, and the gain is large. An amount of generation of the noise little becomes an amplifier of noise figure NF small.

Example 1

It thinks about the case where only one booster (pre-amplifier) is installed in the antenna system that receives a weak signal as an example.

Loss amount =10dB from antenna to booster

NF=3dB   gain =30dB of booster

Loss amount =10dB from booster to receiver

NF=3dB of receiver

It becomes NF=13.04dB of the synthesis.

Example 2

When puts up the booster soon by the antenna the example above

Loss amount =0dB from antenna to booster

NF=3dB   gain =30dB of booster

Loss amount =20dB from booster to receiver

NF=3dB of receiver

It becomes NF=3.41dB of the synthesis.

If there is no booster, strength of the signal is -20 a dB of the output of the antenna (1/100 compared with the electric power), and NF=23dB. When the signal of the antenna is weak, a maybe satisfactory reception cannot be done. Strength of the signal is NF=13.04dB enough for example 1. If the signal of the antenna similarly is weak, I think that I cannot receive it good. It thinks with NF=3.41dB for example 2 in these comparisons in the condition similar to the ideal.

I do not think that I become a problem so much when the booster is put when there is a moderate signal strength even if of course, there is no booster.

When the signal of the antenna is weak, have you understood how it is important that NF put the booster of a good, moderate gain right under the antenna?

When you install the booster in the BS/CS antenna

Whether it was necessary to calculate by thinking about the BS/CS converter gain of the antenna when the booster was installed in the BS/CS antenna system was confirmed by the experiment.

It became a conclusion that it was necessary to calculate in consideration of the converter gain as a result of the following experiments.

This gets and is an experiment on the point of my mistake from Mr. Ichijo of the sun electrification service of Fukushima Prefecture. Thank you for Mr. Ichijo.

Example 3

NF=1dB   gain 50dB of BS/CS converter of antenna

NF=5dB   gain =30dB of booster

Loss amount =30dB from booster to receiver

It becomes NF=1.0001dB of the antenna system synthesis. Because strength of the signal has amplified the loss with the booster, the output of the BS/CS converter and the input of the receiver are the same.

Example 4

How do it become it this time when the booster is put up just before the receiver?

NF=1dB   gain 50dB of BS/CS converter of antenna

Loss amount =30dB from BS/CS converter to booster

NF=5dB   gain =30dB of booster

It becomes NF=1.108dB of the antenna system synthesis. Because strength of the signal has amplified the loss with the booster, the output of the BS/CS converter and the input of the receiver are the same.

There must not be problem if NF of the synthesis is 1.108dB though there are as much as 30dB of the amount of the loss from the BS/CS converter to the booster either. As for NF of the BS/CS antenna, the booster will not have the problem by a desk-top type either. NF of the BS/CS booster need not be also especially good.

I was surprised, too. The booster overturned common sense of putting it right under the antenna. Next, we will inform you of the outcome of an experiment that became the grounds.

C/N ratio measurement experiment when BS antenna output is attenuated

The output of the BS/CS converter was attenuated once, and the C/N ratio (* note) confirmed how to become it by the experiment when amplifying with the booster though it was common sense that the BS/CS converter installed the booster soon when the booster was installed in the BS/CS antenna system.

The result attenuates the output of the BS converter by 42dB, and it has been understood that the C/N ratio hardly changes even if it amplifies with the booster. The television reflected beautifully naturally.

(* note)  The C/N ratio is what looks like the S/N ratio in the ratio to the noise in the part without the signal and the signal.

Experimental methodology

The C/N ratio of the output of the booster of the BS converter was measured by inserting the attenuator (attenuator) soon, and installing the booster afterwards. The purpose of the reason to use the booster is to want to arrange doing that cannot measure both compared with C/N electric field strength and electric field strength as much as possible if there is no booster and to measure the C/N ratio.

Experiment date   2002.08.23   PM5 o'clock

Experiment machine parts

- BS antenna   National flat   TA-BS7A

Antenna gain   32dB NF 1.2dB   converter synthesis gain   49dB

- Current street type F type attenuator   4 pieces

Attenuation amount measurement value   Each of one dB 12dB 14dB 16dB   10

- Booster

Made of  DX antenna  GSM-301A BS  gain  30dB type

- Electric field strength measuring instrument

LEADER  952 type

Outcome of an experiment

The measurement channel It is broadcasting of BS9 NHK analog high-definition television.

The measurement put out the doing mean value twice because there was a change in the result of a measurement.

[DBμV] is the one that the voltage was shown in the ratio when 1μV is assumed to be 0dB.