Optimizing SISO System with BPF vs Cavity Filter for Interference Protection

In summary, the conversation is about a SISO system with microwaves devices using 16-QAM information at 20KHz, upconverted at 30 MHz and then at 2462MHz. At the receiver, the same procedure is done to downconvert. However, the system is experiencing problems with interference signals despite using a BPF with a large bandwidth of 200MHz. A purchase of a cavity filter with a center frequency at 2462MHz and BW=25MHz was made, but it resulted in a worse BER of 10-3 or 10-4. Suggestions were made to check the tuning and bandwidth of the filter, as well as input and output matching. The use of a directional coupler or
  • #1
Fovakis
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[/URL]Hi to all,

i have a SISO system with microwaves devices. The 16-QAM information is about 20KHz , upconverted at 30 MHz and then at 2462MHz.At the receiver the same procedure, downconverting. After the first LNA i have a BPF fc=2430MHz which has large Bandwidth so it does not protect me from interferense signals. It has 200MHz BW. Although, i have a BER about 10-4 maybe 10-5 if the channels is clear (more often at evening).I did this setup in a Laboratory and behind us there are a lot of with WiFis transmitting all day etc...

i did a purchase of Cavity Filters with center freq at 2462MHz and BW=25MHz. i replace the BPF with the cavity and...the result is worse!:cry::confused: i have 10-3 maybe 10-4 BER Can you please tell me some ideas to fix this problem?
 
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  • #2
Have a look with a spectrum analyzer at your 2462 signal before and after the cavity filter to be sure the filter is correctly tuned and has adequate bandwidth.
 
  • #3
Not much that can be said other than
1. Probably you have incorrect input or output matching
2. Maybe you are "using it wrong".
 
  • #4
With the original setup you will have both mixer products at the output of the mixer - 2462 and 2522. Generally the LO frequency is such that it puts the unwanted mixer product outside the input bandpass.

What are the insertion losses of the BPF and the cavity? The Electrician has a good suggestion. Compare the output level of the BPF with the output of the cavity with a spectrum analyzer. If the output of the cavity is lower, you might try using a directional coupler between the LNA and the cavity to see how much reflection you're getting from the cavity. As meBigGuy suggests, it may be a matching problem.
 
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  • #5
The Electrician said:
Have a look with a spectrum analyzer at your 2462 signal before and after the cavity filter to be sure the filter is correctly tuned and has adequate bandwidth.

Yes it is tuned in the right no prob with that.
 
  • #6
meBigGuy said:
Not much that can be said other than
1. Probably you have incorrect input or output matching
2. Maybe you are "using it wrong".

Thanks for the reply.

1.First i don't understand what is the input and what is the output port!There is no label that explain me what is each port (!). Is there any difference? About the matching i will check it with
a network analyser better, maybe?

2. What do you mean is this way?What can it be wrong?
 
  • #7
skeptic2 said:
With the original setup you will have both mixer products at the output of the mixer - 2462 and 2522. Generally the LO frequency is such that it puts the unwanted mixer product outside the input bandpass.

What are the insertion losses of the BPF and the cavity? The Electrician has a good suggestion. Compare the output level of the BPF with the output of the cavity with a spectrum analyzer. If the output of the cavity is lower, you might try using a directional coupler between the LNA and the cavity to see how much reflection you're getting from the cavity. As meBigGuy suggests, it may be a matching problem.

Yes you have right.The 2462 and 2522 (image freq) are going into my filter (from the TX_). The image freq is about 20dB Lower that the desired in my case. But in both senarios this image freq exists.

i don't have a directional coupler in my lab, but i have a network analyser, so i can see the reflected.

Also the cavity has two ports. I don't understand which one is the input and which one is output?Is there any difference with that?
 

1. What is the difference between a simple BPF and a cavity filter?

A simple BPF (bandpass filter) is a type of electronic filter that allows only signals within a certain frequency range to pass through, while blocking all others. On the other hand, a cavity filter is a type of resonant filter that uses a series of cavities to select a specific frequency or range of frequencies. The main difference between the two is that a simple BPF is a single-stage filter, while a cavity filter is a multi-stage filter.

2. Which type of filter is more commonly used in practical applications?

It depends on the specific application and requirements. In general, simple BPFs are more commonly used in electronic devices where space and cost are limited, while cavity filters are more commonly used in high-power and high-frequency applications due to their better performance and higher power handling capabilities.

3. What are the advantages of a simple BPF over a cavity filter?

Simple BPFs are typically smaller, lighter, and less expensive than cavity filters. They also have a wider bandwidth and can be easily designed for specific frequency requirements. In addition, simple BPFs have a simpler construction and are easier to tune and maintain.

4. What are the advantages of a cavity filter over a simple BPF?

Cavity filters have better selectivity and rejection, meaning they can better filter out unwanted signals and noise. They also have a higher power handling capability and can operate at higher frequencies. In addition, cavity filters have better temperature stability and can maintain their performance over a wider temperature range.

5. How do I choose between a simple BPF and a cavity filter for my project?

The choice between a simple BPF and a cavity filter depends on your specific application and requirements. Consider factors such as size, cost, frequency range, selectivity, power handling, and temperature stability. Consult with a filter design expert to determine the best option for your project.

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