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IF AMPLIFIER IN RADIO RECIEVER

R

RealInfo

Jan 1, 1970
0
Hi all
What is the "right" total amplification factor of an IF amplifiers chain in a radio receiver ?

For example a receiver employs 4 IF amps cascade , what is the proper total
voltage amplification of that IF cascade ?

Thanks in advance

EC
 
A

AndyS

Jan 1, 1970
0
Hi all
What is the "right" total amplification factor of an IF amplifiers chain in a radio receiver ?

For example a receiver employs 4 IF amps cascade , what is the proper total
voltage amplification of that IF cascade ?

Thanks in advance

EC

I liked putting the total gain of the RF, mixers, and IFs so that the
system would start AGC on noise. Then I could use the RF gain
or If gain control to back off on gain for specific applications.
I also liked to put a primary bandwidth filter as close to the
antenna as possible, usually at the IF input, in order to eliminate
adjacent channel signals, AND, if economics allowed, putting another
primary bandwidth filter at the IF output, to set the system noise
bandwidth.... If good Xtal filters are used, this is nearly always
too expensive for commercial production, so there is usual
a compromise position determined, depending on the system
requirememts....

So my answer to your question is that the IF gain should be
combined with the other gains/losses to develop an overall
response.
 
B

brent

Jan 1, 1970
0
Hi all
What is the "right" total amplification factor of an IF amplifiers chain in a radio receiver ?

For example a receiver employs 4 IF amps cascade , what is the proper total
 voltage amplification of that IF cascade ?

Thanks in advance

EC

As Jan said,

It can be next to nothing or a lot. It all depends on architecture.
If you are digitizing the signal you likely do not need a whole lot.

I was taught to build a table which tracked noise power through the
channel on one end and how close to compression the highest expected
signals got on the other end. Build a table which shows the
increases /decreases in noise power and also for the strongest
expected signal coming in. This table should get you started
 
B

brent

Jan 1, 1970
0
As Jan said,

It can be next to nothing or a lot.  It all depends on architecture.
If you are digitizing the signal you likely do not need a whole lot.

I was taught to build a table which tracked noise power through the
channel on one end and how close to compression the highest expected
signals got on the other end.  Build a table which shows the
increases /decreases in noise power and also for the strongest
expected signal coming in.  This table should get you started

I forgot to add, you need to also track the weakest expected signal
and keep track of S/N ratio degradation throughout.
 
F

Fred Abse

Jan 1, 1970
0
Hi all
What is the "right" total amplification factor of an IF amplifiers chain
in a radio receiver ?

For example a receiver employs 4 IF amps cascade , what is the proper
total
voltage amplification of that IF cascade ?

Depends on the required level at the demodulator, the gain (if any) at the
mixer, any pre-mixer (RF amplifier) gain, the available signal voltage. If
it's AM, AGC is usually used. FM receivers are usually designed to hard
limit (clip).
 
Hi all

What is the "right" total amplification factor of an IF amplifiers chain in a radio receiver ?



For example a receiver employs 4 IF amps cascade , what is the proper total

voltage amplification of that IF cascade ?



Thanks in advance



EC





What these guys are talking about is something called “gain line-up”.

It’s the system architecture design that balances the “large signal” distortion effects vs small signal s/n requirements.

As they've said, final “baseband” requirements will dictate overall specs.

I'd tell you to do a search, but you most likely already have; it's not a trivial exercise if you don't have any rf experience.

good luck
 
B

Bill Bowden

Jan 1, 1970
0
On a sunny day (Fri, 1 Feb 2013 03:05:43 -0800 (PST)) it happened RealInfo
<[email protected]>:
Hi all
What is the "right" total amplification factor of an IF amplifiers chainin a radio receiver ?
For example a receiver employs 4 IF amps cascade , what is the proper total
voltage amplification of that IF cascade ?
Thanks in advance

Just multiply the voltage gain of each stage, or add the db gain of each stage.

I reality IF gain will likely be under influence of some AGC[1], and vary
between 'next to nothing[2]' and 'a lot[3]'.

[1] Automatic Gain Control.
[2] Can be less than 1.
[3] Depends..

There are also limiting IF amplifiers, for example for FM,
so then output no longer increaes when the input increases,
you can than speak of a minimum signal level required for limiting.

duh

So, if the smallest signal input is 1 microvolt, and you want 1 volt
out, the gain is 120db? And that includes audio gain of maybe 20db?

-Bill
 
On a sunny day (Fri, 1 Feb 2013 03:05:43 -0800 (PST)) it happened RealInfo
<[email protected]>:
Hi all
What is the "right" total amplification factor of an IF amplifiers chain in a radio receiver ?
For example a receiver employs 4 IF amps cascade , what is the proper total
voltage amplification of that IF cascade ?
Thanks in advance

Just multiply the voltage gain of each stage, or add the db gain of each stage.

I reality IF gain will likely be under influence of some AGC[1], and vary
between 'next to nothing[2]' and 'a lot[3]'.

[1] Automatic Gain Control.
[2] Can be less than 1.
[3] Depends..

There are also limiting IF amplifiers, for example for FM,
so then output no longer increaes when the input increases,
you can than speak of a minimum signal level required for limiting.

duh

So, if the smallest signal input is 1 microvolt, and you want 1 volt
out, the gain is 120db? And that includes audio gain of maybe 20db?
But, but, but dB only refers to power, right? ;-)
 
On a sunny day (Fri, 1 Feb 2013 03:05:43 -0800 (PST)) it happened RealInfo
<[email protected]>:
Hi all
What is the "right" total amplification factor of an IF amplifiers chain in a radio receiver ?

For example a receiver employs 4 IF amps cascade , what is the propertotal
voltage amplification of that IF cascade ?

Thanks in advance

EC
Just multiply the voltage gain of each stage, or add the db gain of each stage.

I reality IF gain will likely be under influence of some AGC[1], and vary
between 'next to nothing[2]' and 'a lot[3]'.

[1] Automatic Gain Control.
[2] Can be less than 1.
[3] Depends..

There are also limiting IF amplifiers, for example for FM,
so then output no longer increaes when the input increases,
you can than speak of a minimum signal level required for limiting.

duh
So, if the smallest signal input is 1 microvolt, and you want 1 volt
out, the gain is 120db? And that includes audio gain of maybe 20db?

But, but, but dB only refers to power, right? ;-)



it's just a conversion, note the reference in the following;

dBm,dB(W),dB(uV),dB(V),etc.

also note rf systems generally are 50 ohms, cable 75 ohm.

take that into account when doing the conversion.
 
J

Jeroen

Jan 1, 1970
0
On a sunny day (Fri, 1 Feb 2013 03:05:43 -0800 (PST)) it happened RealInfo
<[email protected]>:
Hi all
What is the "right" total amplification factor of an IF amplifiers chain in a radio receiver ?

For example a receiver employs 4 IF amps cascade , what is the proper total
voltage amplification of that IF cascade ?

Thanks in advance

EC
Just multiply the voltage gain of each stage, or add the db gain of each stage.

I reality IF gain will likely be under influence of some AGC[1], and vary
between 'next to nothing[2]' and 'a lot[3]'.

[1] Automatic Gain Control.
[2] Can be less than 1.
[3] Depends..

There are also limiting IF amplifiers, for example for FM,
so then output no longer increaes when the input increases,
you can than speak of a minimum signal level required for limiting.

duh

So, if the smallest signal input is 1 microvolt, and you want 1 volt
out, the gain is 120db? And that includes audio gain of maybe 20db?
But, but, but dB only refers to power, right? ;-)

Decibels are fertile ground for confusion, much like percentages are
for bankers. The basic definition is 10*log10(P1/P2). _If_ both are
electrical signals working into the same impedance, this is the
same as 20*log10(V1/V2). The trouble is that not everyone is equally
careful with this.

For example, control system engineers employ 20*log10(V1/V2) and
totally ignore impedance. They even use dB to express ratios between
different units, e.g., as the ratio between say, voltage and pressure
of a transducer. (I once got into an argument over that with Dr.
Middlebrook.) RF engineers will usually, but not systematically,
take the impedance into account. For example again, my Rohde &
Schwartz 50<->75 matching pads are marked as having the same
attenuation in both directions, while my Radiall matching pads
have two different values, despite doing exactly the same thing in
the same way.

Then there is the jungle of reference levels, with an abundant number
of definitions, sometimes conflicting, often illogical. For example,
dBm is dB referred to 1 mW, but dBu is referred to 1uV. I wouldn't
be at all surprised if with some digging, we could come up with over
a hundred different definitions of reference levels that are in
common use in one corner or another.

Jeroen Belleman
 
On a sunny day (Fri, 1 Feb 2013 03:05:43 -0800 (PST)) it happened RealInfo
<[email protected]>:


Hi all
What is the "right" total amplification factor of an IF amplifiers chain in a radio receiver ?

For example a receiver employs 4 IF amps cascade , what is the proper total
voltage amplification of that IF cascade ?

Thanks in advance

EC


Just multiply the voltage gain of each stage, or add the db gain of each stage.

I reality IF gain will likely be under influence of some AGC[1], and vary
between 'next to nothing[2]' and 'a lot[3]'.

[1] Automatic Gain Control.
[2] Can be less than 1.
[3] Depends..

There are also limiting IF amplifiers, for example for FM,
so then output no longer increaes when the input increases,
you can than speak of a minimum signal level required for limiting.

duh

So, if the smallest signal input is 1 microvolt, and you want 1 volt
out, the gain is 120db? And that includes audio gain of maybe 20db?
But, but, but dB only refers to power, right? ;-)



Decibels are fertile ground for confusion, much like percentages are

for bankers. The basic definition is 10*log10(P1/P2). _If_ both are

electrical signals working into the same impedance, this is the

same as 20*log10(V1/V2). The trouble is that not everyone is equally

careful with this.



For example, control system engineers employ 20*log10(V1/V2) and

totally ignore impedance. They even use dB to express ratios between

different units, e.g., as the ratio between say, voltage and pressure

of a transducer. (I once got into an argument over that with Dr.

Middlebrook.) RF engineers will usually, but not systematically,

take the impedance into account. For example again, my Rohde &

Schwartz 50<->75 matching pads are marked as having the same

attenuation in both directions, while my Radiall matching pads

have two different values, despite doing exactly the same thing in

the same way.



Then there is the jungle of reference levels, with an abundant number

of definitions, sometimes conflicting, often illogical. For example,

dBm is dB referred to 1 mW, but dBu is referred to 1uV. I wouldn't

be at all surprised if with some digging, we could come up with over

a hundred different definitions of reference levels that are in

common use in one corner or another.



Jeroen Belleman



it's pretty straight forward if people are clear when they use the terms.

gain = dB.

input and output ports should always have an absolute value referenced to them.

keep the impedance straight and it becomes simple arithmetic.

btw, it's virtually impossible to do a gain line-up correctly if you don't keep this stuff straight when using mixed impedances and equiv nf and IM specs.
 
B

Bill Bowden

Jan 1, 1970
0
On a sunny day (Fri, 1 Feb 2013 03:05:43 -0800 (PST)) it happened RealInfo
<[email protected]>:
Hi all
What is the "right" total amplification factor of an IF amplifiers chain in a radio receiver ?
For example a receiver employs 4 IF amps cascade , what is the propertotal
voltage amplification of that IF cascade ?
Thanks in advance
EC
Just multiply the voltage gain of each stage, or add the db gain of each stage.
I reality IF gain will likely be under influence of some AGC[1], and vary
between 'next to nothing[2]' and 'a lot[3]'.
[1] Automatic Gain Control.
[2] Can be less than 1.
[3] Depends..
There are also limiting IF amplifiers, for example for FM,
so then output no longer increaes when the input increases,
you can than speak of a minimum signal level required for limiting.
duh
So, if the smallest signal input is 1 microvolt, and you want 1 volt
out, the gain is 120db? And that includes audio gain of maybe 20db?

But, but, but dB only refers to power, right?  ;-)

The original question was about voltage gain. 20dB is a factor of 10
times the voltage. 20dB=10 , 120dB= 1 million.

-Bill
 
On a sunny day (Fri, 1 Feb 2013 03:05:43 -0800 (PST)) it happened RealInfo
<[email protected]>:
Hi all
What is the "right" total amplification factor of an IF amplifiers chain in a radio receiver ?
For example a receiver employs 4 IF amps cascade , what is the proper total
voltage amplification of that IF cascade ?
Thanks in advance
Just multiply the voltage gain of each stage, or add the db gain of each stage.
I reality IF gain will likely be under influence of some AGC[1], and vary
between 'next to nothing[2]' and 'a lot[3]'.
[1] Automatic Gain Control.
[2] Can be less than 1.
[3] Depends..
There are also limiting IF amplifiers, for example for FM,
so then output no longer increaes when the input increases,
you can than speak of a minimum signal level required for limiting.
So, if the smallest signal input is 1 microvolt, and you want 1 volt
out, the gain is 120db? And that includes audio gain of maybe 20db?

But, but, but dB only refers to power, right?  ;-)

The original question was about voltage gain. 20dB is a factor of 10
times the voltage. 20dB=10 , 120dB= 1 million.

I understand that it's late. Go back to bed.
 
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