How simplest attenuator!!! Does work?

[Willen]

How simplest attenuator!!! Does it work?

Look this schematic. I found it as simple attnuator in input stage to reduce 'over drive' in input.
-I think R3, R4, R5 and C1 acts as a attnuator, am I right?
- Why they didn't write clear Resistor value like xx ohm or xx Kilo-ohm?
What is mean by R3=150, R4=39? (I think that are SMD type resistor value)

 

[KJ6EAD]

R3, R4 and R5 form a -6dB pi attenuator. C1 is a coupling capacitor that isn't part of the attenuator.

The component values are assumed to be in Ohms. Did you think that a resistance would be in grams?

 

[Mikebits]

R3, R4 and R5 form a -6dB pi attenuator. C1 is a coupling capacitor that isn't part of the attenuator.

The component values are assumed to be in Ohms. Did you think that a resistance would be in grams?

OP, look up pI pad attenuator. your drawing shows two input injection points which will change impedance, but anyways, check out Pi pad attenuator. Basically a attenuator is an impedance matched voltage divider.

For starters here is a link. **broken link removed**
The cap just blocks DC component.

 

[Willen]

R3, R4 and R5 form a -6dB pi attenuator. C1 is a coupling capacitor that isn't part of the attenuator.

The component values are assumed to be in Ohms. Did you think that a resistance would be in grams?

when I am injecting 200mW RF, should I remove this attnuator stage or not?

 

[mvs sarma]

The sch has, and allows a low level input point. Thus, no need to remove the attenuator.

 

[Mikebits]

For optimal performance of the design, if it was designed properly is to use the attenuator as it functions as a impedance matcher. to bypass it would degrade the input match and make results unpredictable. If it was a crappy design to start with, it may not matter.

 

[Willen]

OP, look up pI pad attenuator. your drawing shows two input injection points which will change impedance, but anyways, check out Pi pad attenuator. Basically a attenuator is an impedance matched voltage divider.

For starters here is a link. **broken link removed**
The cap just blocks DC component.

asking a little basic question:- In this calculator (link), there are two type of result-
R1=150 ohm
R2=150 ohm
Zo=50 ohm
#Attenuation = 12.4 dB
#Return loss= -12.4 dB

''attenuation'' ''Return loss''. Actually what is that? I think, if I inject 40 dB RF into the attenuation, the output of this attenuator will be 28.6 dB, isn't it?

 

[Mikebits]

Not sure where you derived 12dB from the resistor values you listed. At any rate, the attenuation is a way to express insertion loss of a signal path ie. amount signal is decreased. So in the case of 6 dB insertion loss you have 40dB-6dB = 34dB.
Return loss is a bit more tricky to describe, return loss is a way to quantify impedance mismatch of a signal interface between 2 stages. I suggest you look up standing wave ratio to learn more.

 

[Willen]

Not sure where you derived 12dB from the resistor values you listed. At any rate, the attenuation is a way to express insertion loss of a signal path ie. amount signal is decreased. So in the case of 6 dB insertion loss you have 40dB-6dB = 34dB.
Return loss is a bit more tricky to describe, return loss is a way to quantify impedance mismatch of a signal interface between 2 stages. I suggest you look up standing wave ratio to learn more.

from listed (above) resistors, I obtained 12 dB attenuation and -12dB Returnloss by calculating PI or T version calculator from your link. I am little confuse because I am a little beginner, you are using different term ''Insertion loss =6 dB'' I don't know from where you derived this 6dB? How I can get this 6 dB insertion loss from this calculator? Help me in basic way plz

 

[davenn]

from listed (above) resistors, I obtained 12 dB attenuation and -12dB Returnloss by calculating PI or T version calculator from your link. I am little confuse because I am a little beginner, you are using different term ''Insertion loss =6 dB'' I don't know from where you derived this 6dB? How I can get this 6 dB insertion loss from this calculator? Help me in basic way plz

you obviously didnt use the attenuator correctly.....

here it is with the values stated above by Mikebits
what did you do differently ?



cheers
Dave

 

[Willen]

you obviously didnt use the attenuator correctly.....

here it is with the values stated above by Mikebits
what did you do differently ?



cheers
Dave

Oh now I understand the misunderstand between me ans mikebits.

You are so nice and clear speaker.

Hay Dave, I am waiting you for additional suggestion. Please see this my new thread (question) on 'Radio and communication' forum:- ''Large diameter of dipole antenna's rod....Can
I use?''

 

[audioguru]

Aren't resistor values measured in Dollars, not Ohms?
I have an 8 ohm/10W resistor that must have been worth $5.00 when new and maybe is worth about $1.00 today.

 

[Willen]

you obviously didnt use the attenuator correctly.....

here it is with the values stated above by Mikebits
what did you do differently ?



cheers
Dave

To get variable attenuation, which resistor (R1,R2 or R3) should i have change into Potentiometer? Is it possible?

 

[davenn]

you could change R1 to a variable, but you have to be aware that it would probably alter the input and output impedances
thats why in the above calculator it asks you for the circuit impedance
In very low power transmit stages ( tho we like/prefer to keep good impedance matching between stages) you could get away with a variable value attenuator, likewise in a receiver
The theory is somewhat more complex than that, but for experimenting, its ok

did you play with the calculator again and try some other values to make sure you understand how it works ?

Dave

 

[mvs sarma]

that attempt would perhaps amout a variable return loss pad!!!

 

[WTP Pepper]

Make sure your resistors are upto the job. The high power input will require decent specified resistor. Make sure they are not wirewound and are simple carbon composition or metal oxide ones.

 

[Willen]

Make sure your resistors are upto the job. The high power input will require decent specified resistor. Make sure they are not wirewound and are simple carbon composition or metal oxide ones.

Then, should I have to use high watt resistor like 1 watt too? Any idea to recognize wirewound resistor?
*OK i will use carbon or metal oxcide resistor. I think Wirewound Resitor has inductance in its wound, isn't it?

 

[WTP Pepper]

Wirewound resistors are usually mentioned as being just that in a catalogue. If you are sifting through a bargain bag then it's difficult to tell. You are correct in assuming they have additional inductance and that will cause the attenuation to be frequency dependant .

 

[everyone0]

i think its ok