Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

[SOLVED] Spectrum analyzer measurements, suitable attenuator?

Status
Not open for further replies.

neazoi

Advanced Member level 6
Joined
Jan 5, 2008
Messages
4,119
Helped
13
Reputation
26
Reaction score
15
Trophy points
1,318
Location
Greece
Activity points
36,918
My spectrum analyzer's optimum input power is -90dBm to -30dBm. If I insert an input attenuator of 60dB (5W rated power), will I be able to feed to it signals as high as 1W ?

The analyzer can be damaged with signals as powerful as +15dBm, so I would like to make sure before I try this.

The setup will be: power amplifier under test, 1W output power max -> then attenuator 60dB -> then spectrum analyzer.
 

One watt is +30dBm; if that is applied to a 60dB attenuator the output will be +30 - 60 = -30dBm.

So it will be OK.

60dB is a lot of attenuation in one unit; I assume that you are using two or more attenuators.

Just to be sure, it's best to begin with a lot of attenuation and reduce it gradually; a variable attenuator or a string of fixed attenuators will do this.

For even better isolation a coupler is useful. This is a simple 30dB coupler that works up to about 100 MHz;

https://i42.tinypic.com/161dkwl.jpg

Higher frequencies would require a different kind of coupler.
 

This is for microwave 10GHz or so. I have used one of these coaxial attenuators made by companies. They may include two attenuators in series inside to reach 60dB, I do not know.
Ok so this is safe to feed 1W, that is fine
 

As long as the attenuator is rated to 10 GHz it should be fine. Aeroflex/Weinschel make attenuators of this kind; many others are only rated to 2 GHz or so and these may well allow through-leakage and less attenuation if used well above their frequency rating.

The -30 dBm rating would be the point where unwanted spurious products may appear on-screen, ie the response becomes non-linear.

Input power greater than this would not be harmful until the power reaches +15dBm which would be the level where damage to the mixer diodes is possible.

It's always good practice to always make measurements under -30 dBm and never allow more than 0 dBm into the input of this kind of instrument.
 

As long as the attenuator is rated to 10 GHz it should be fine. Aeroflex/Weinschel make attenuators of this kind; many others are only rated to 2 GHz or so and these may well allow through-leakage and less attenuation if used well above their frequency rating.

The -30 dBm rating would be the point where unwanted spurious products may appear on-screen, ie the response becomes non-linear.

Input power greater than this would not be harmful until the power reaches +15dBm which would be the level where damage to the mixer diodes is possible.

It's always good practice to always make measurements under -30 dBm and never allow more than 0 dBm into the input of this kind of instrument.

Yes that is exactly what the analyzer manual states. That is why I have chosen the Weinschel Model 44-60 60dB attenuator, do be able to measure directly powers ranging from very few 0.001mW up to 1W by having permanently the attenuator attached to the analyzer, and still be inside the linear (and safe) range of the analyzer. I hope I did the right choice...
 

Yes; a good choice.
 

You can check your attenuator for low power levels at 10 GHz before using it in a high power chain. I m not sure whether some new phenomenon arises when the input power is raised to 1 W but I think there will be no problem unless you exceed the rated power. Do not forget to keep your PA see 50 ohm load while operating. Otherwise, reflected power may damage your PA.
 

You can check your attenuator for low power levels at 10 GHz before using it in a high power chain. I m not sure whether some new phenomenon arises when the input power is raised to 1 W but I think there will be no problem unless you exceed the rated power. Do not forget to keep your PA see 50 ohm load while operating. Otherwise, reflected power may damage your PA.

An isolator (circulator with load) between the power amplifier ans the attenuator might compensate for any reflected power from the attenuator back to the amplifier.
By the way, do you know these standard small sized SMA circulators, how much power can they tolerate?
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top