REQUEST->FINDING MW FREQ USING SPECTRUM ANALYZER

[charommel]

Hi friends,
I'm not really familiar with Transmission, can anyone provide me a step by step procedure on how to conduct a frequency sweep to determine the actual frequency used in a MICROWAVE transmission using Spectrum Analyzer? please help .

[charommel]

Transmission Experts PLEASE HELP!

Hi friends,
I'm not really familiar with Transmission, can anyone provide me a step by step procedure on how to conduct a frequency sweep to determine the actual frequency used in a MICROWAVE transmission using Spectrum Analyzer? please help .

[nextgenius]

May be this would help you

http://www.home.agilent.com/agilent/...|S||2923820296

[ANTRF]

Go here.
You'll find everything you need.

http://www.home.agilent.com/agilent/...US&lc=eng&sm=g

B.R.

ANTRF

[byja]

First, you need to be more specific and tell us what your goal is. Is it to determine channels used on one route, or perhaps to determine which is the actual frequency of a MW system under observation, if you're unsure of it's output signal?

Either way, working with spectrum analyzer is a bit tricky. I suggest you read some of the application notes from Agilent or Anritsu website before you do something like this.

Here are few examples of measurements I did.

1. Measuring center frequency of a MW radio unit

Connect output port of a radio unit to a transition (from waveguide to coaxial, if necessary), then to attenuator (make sure it has sufficient attenuation at operating band, and make sure it can handle such power load). After attenuator use coaxial cable to connect to a SA. There's no need for some high quality coax cable since you measure only frequency.

Based on output signal type, you can get results such as


or

In first case I've disabled modulation on radio unit, so I get only signal from Tx + IF LO. In second case I have modulated signal, so I can measure central frequency by placing markers on 3 dB points left and right, and calculating average value.

2. Scanning the freq range for used channels

In this case, you need some easy to use antenna, preferably horn antenna which is good for the range you're about to scan. You also need good coax cables and preferably a LNA (low noise amplifier). Place the antenna on a stand, mind the polarisation, and do a freq sweep. You can get something like:



As you can see, this particular route has a lot of traffic. You only get to see one polarisation, cause channels on opposite polarisation have been masked by thermal noise. Now simply move the marker on SA and measure frequencies for used channels.

[charommel]

Hello byja,

I really appreciate your support. What we intend to do is to conduct a Frequency Survey Audit without initially knowing the actual frequency being used by the different Microwave radios. So we need to get the EIRP, Center Frequency (TX & RX), Bandwidth, Polarization & ITU channel #. Can I get all these data from the Spectrum Analyzer? Also, where do I make the meaurement, is it on the receiver side of the radio? thank you for your help.

[byja]

You intend to do a Frequency Survey Audit on site itself, or...?

First of all, don't do anything with MW radios that are not yours. So, the only measuring you can do is outside, using your own antenna with known parameters for measurement.

EIRP - AFAIK, you can't measure EIRP of a microwave link. Only way to measure EIRP is to measure power into the antenna and then calculate EIRP based on antenna gain, by finding out which antenna type is used. Any measurements made outside of system would be within near field of the antenna and/or off antenna axis, which would give bad results. You could measure power to the antenna but that would require breaking the link and outage of the system.

Tx Center Frequency you can easily measure simply by using horn antenna. Problem is, if there are many MW radios you might end up confused about which frequency goes where.
Rx Center Frequency you can't measure directly (unless you break the link and connect directly to the antenna port). But knowing Tx Freq, and duplex spacing used in your country for particular band, you can calculate Rx Center Freq.
Bandwidth - No problem. Even easier if you have a modern Spectrum Analyzer with such functionality:


Polarization - Can be "measured" simply by climbing the tower and looking how the unit is mounted or where the waveguide ends.
If that fails, you can always use horn antenna, twist it and see where you get better signal.

ITU Channel No. - Well, if you have Tx Center Freq, you know what channel no. that is.

[charommel]

Hi byja,

You really made my day and yes, we intend to do a Frequency Survey Audit for the regulatory body in one country. So basically, we shall start from scratch without any data on hand except the coordinates. then we need to give to them the results of the audit. Some additional clarifications below:

1.) For determining the TX Center Freq in a site with many radios, is there a way to avoid confusion on the frequency assignement? do I simply base it on the strongest received level?
2.) How do configure the use of LNA? is it SPECTRUM ANALYZER->LNA->HORN ANTENNA?

Again, thanks you for your help. more power!

[byja]

Couple of more interersting posts, before I start writing again...

http://www.finetopix.com/showpost.ph...55&postcount=9

http://www.finetopix.com/showpost.ph...20&postcount=2

[arban]

Hi friends,
I'm not really familiar with Transmission, can anyone provide me a step by step procedure on how to conduct a frequency sweep to determine the actual frequency used in a MICROWAVE transmission using Spectrum Analyzer? please help .

Very easy. The objective of frequency scanning is to find vacant frequency spectrum, so that we can know what Tx/Rx frequency we can utilize when doing hop commissioning.

First, you need to know what is your MW equipment signal threshold. This is the minimum value that your equipment can detect as a signal. So any value that is lower than this value will not be regarded as signal. By knowing this value you will know what is the value to set as "reference" at your spectrum analyzer. So whatever signal that is higher than this is considered as "signal" and have potential to interfere your signal if you transmit or receive at the same frequency. Normally the value can be from -80 dBm to -90 dBm.

Then using spectrum analyzer and horn antenna, sweep the frequency according to intended sub-bands. You perform this activity at the place where you want to install your antenna and make a 360 degree rotation with 30 degree interval. (this depends on your client requirement)

At the same time mark all the peak and transfer this information to a frequency table to clearly display which band is occupied. Any free sub band is for you to use. Hope this will help.