How to design the desired radio frequency detector for detecting the particular radio frequency

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Md Yusuf

Joined Jul 6, 2021
15
Hi, I am designing the radio frequency detector to detect the desired radio frequency which is between 200KHz to 5MHz so for that I need an antenna which can capture the signal in these frequency range after capturing the signal I have used band pass filter which will the desired frequency so the problem is that I am not getting the suitable antenna which can work in these range so if someone knows please let me know and give me any other idea through which this project can be done easily thank you.
 

Ya’akov

Joined Jan 27, 2019
5,659
The range you are trying to accommodate has wavelengths from 1500m to 50m. Making an effective antenna for that range is not practical. In order to make it work you will need to use a very poor antenna with an amplifier. Even then, it’s so broadband you are going to have trouble.
 

Audioguru again

Joined Oct 21, 2019
4,680
Your required frequency range is about from 1/3rd to 3 times the AM broadcast band. An ordinary AM radio uses a ferrite loopstick antenna tuned with a mechanical variable capacitor or with varactor diodes. Then it uses a variable oscillator and mixer to feed a permanently tuned Intermediate amplifier.
 

MrSalts

Joined Apr 2, 2020
1,762
The range you are trying to accommodate has wavelengths from 1500m to 50m. Making an effective antenna for that range is not practical. In order to make it work you will need to use a very poor antenna with an amplifier. Even then, it’s so broadband you are going to have trouble.
Please describe why it is not practical. AM radio works in part of this range and WWVB transmitted at 60kHz and received by small antennas on wall clocks. I'm not seeing the impractical part of the question.
 

bassbindevil

Joined Jan 23, 2014
422
As a rule, the longer the better for receiving antennas. It could be helpful to use a preselector or antenna tuner. Have a look at amateur radio books, particularly ARRL publications. Your frequency range is different, but the same principles apply.
 

Thread Starter

Md Yusuf

Joined Jul 6, 2021
15
What are you trying to accomplish? Is this, perhaps, to detect a listening device?

Bob
I am trying to detect the radio frequency within the range between 200KHz to 5MHz so for that I need an antenna which can work in these range and that is I am not getting
 

BobTPH

Joined Jun 5, 2013
4,899
I am trying to detect the radio frequency within the range between 200KHz to 5MHz so for that I need an antenna which can work in these range and that is I am not getting
Okay, let me try again. What is the source of this unknown frequency, and why are you trying to detect it?

We don’t like giving advice on secret projects. What are you hiding?

Bob
 

Ylli

Joined Nov 13, 2015
1,058
If you want a relatively efficient antenna to cover that large of a frequency range would require some form of log periodic antenna or a traveling wave antenna. Either of these would be huge to get down to 200 KHz. Alternately, you could use a 'voltage probe', (also called an E-Field Probe) antenna. This may be your most practical solution. An example: https://sites.google.com/site/g3xbmqrp3/antennas/efp
 

drjohsmith

Joined Dec 13, 2021
394
I am trying to detect the radio frequency within the range between 200KHz to 5MHz so for that I need an antenna which can work in these range and that is I am not getting
I think , there are a few points running here

a) antenna, Any conductor, is an antenna, stick your finger on a scope probe and you see the pickup as your body is an antenna
the question would be , so you need antenna gain, do you need directivity
If not, then just a bit of wire of any length meets your needs,
if you do want either of the above then your probably after an antenna with range switching,
and / or the use of ferrite coil antennas and tuning.

b) signal strength. Things like the 50 Hz mains are easy to detect, as the transmitter wires are so long,
and the signal strength is so high,
If you want to pick up a small signal, then you are going to need amplification
wide band amplification has two big problems
1) out of band signals over loading the input you want
2) feedback / oscillation
the answer normally used is filtering / frequency selection
as in a super het receiver

c) decoding : do you "just" want to detect you have a signal anywhere in the range,
or do you need to know what frequency
do you need to decode the signal
i.e. do you need to listen to an AM signal ?

All the above are points we are going to have to dive into to give you relevant advise,
 

Ya’akov

Joined Jan 27, 2019
5,659
I think the critical questions are:

What is generating the signals you want to detect?
What is the output power of those sources?
How far away will you be from them?

A resonant antenna covering the range you specified is going to be far too big and complex unless you intended to erect an antenna tower and have the budget to pay for a lot of wire, On the other hand, someting like a loopstick antenna will have gain figures measurable in negative dBi.

In either case, simultaneous resonance across the entire specified passband is not going to happen. Instead you will need to use something like varactor tuning and possibly multiple antennas/windings to sweep the range at some finite rate.

The question is: what are you trying to build?
Is is a handheld device? An intercept facility with an antenna farm? Something in-between?

[EDIT: fixed anomalies caused by on the fly editing and sub-optimal post activation time]
 
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BobTPH

Joined Jun 5, 2013
4,899
@Yaakov: I hope you can get more out of him than my two attempts, but my assessment is that he is purposely being evasive, and my guess is that he is trying to detect a listening device that “they” are using against him.

Bob
 

BobTPH

Joined Jun 5, 2013
4,899
Because we have seen similar requests before. And it makes sense that he would not know the frequency if this was the case.

Bob
 

Thread Starter

Md Yusuf

Joined Jul 6, 2021
15
Basically I want to detect the frequency on which the electrosurgery performs in hospitals so I want to make the device that can detect when electrosurgery is performed there is no to hide in this if someone knows the antenna which can capture this frequency please let me know otherwise let it be no problem thank you.
 

drjohsmith

Joined Dec 13, 2021
394
Basically I want to detect the frequency on which the electrosurgery performs in hospitals so I want to make the device that can detect when electrosurgery is performed there is no to hide in this if someone knows the antenna which can capture this frequency please let me know otherwise let it be no problem thank you.
How close to the surgery do you want to be ?
 
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