How can I enter high frequencies from a receiving antenna to a PC for analysis?

[patrickian01]

I am going to do two antennas, one for transmitting and the other for receiving. I will be transmitting a simple sine wave at around 600MHz and for the receiving side, I will be using an equivalent antenna, same as the one used for transmitting along with filters and amplifiers to capture the signal and amplify it so i can analyze it using a software. The problem is, How can i get this 600MHz signal to enter a computer using a program like matlab or anything that you could suggest. I have tried using an audio generator and attaching it to a 3.5mm stereo jack connected to the mic port of the PC and using audacity to record the signals but audacity can only effectively record up to ~20kHz and beyond that, the signal is barely usable. Any ideas on how i can get this 600MHz from the receiving antenna to the PC? any suggestions would be much appreciated.

 

[chuckey]

One way would be to use an amplitude modulated TX signal and a suitable receiver (no AGC). This will give you amplitude information as the demodulated audio will be in direct proportion to the received carrier amplitude.
Frank

 

[patrickian01]

Wow thanks. I haven't thought of that. Will give it a try once I get to school. Any other ideas are welcome thanks in advance.

 

[upand_at_them]

You can do what software defined radios do: Mix the incoming signal with an offset to produce a result in the audio range. You can then use the sound card to digitize it.

 

[patrickian01]

how can i do this offset? do i need to do a circuit? and if so, what components do i need? sorry if i sound like a noob.

 

[vfone]

If is just about a sine wave signal, you can build a simple A/D converter and place it at the demodulated output of your receiver.
The data can be send digitally to the computer using an RS232 interface.

**broken link removed**

 

[biff44]

you have not provided sufficient information for a correct answer. WHAT are you trying to do with the 600 MHz signal. Send music along it? Send digital data along it? Measure its amplitude and phase? Compute the distance between transmit and receive antennas??? That information will allow us to tell you how to generate and receive the signal.

 

[patrickian01]

If is just about a sine wave signal, you can build a simple A/D converter and place it at the demodulated output of your receiver.
The data can be send digitally to the computer using an RS232 interface.

**broken link removed**

Thanks, one of my initial options was to actually convert it to digital.

- - - Updated - - -

you have not provided sufficient information for a correct answer. WHAT are you trying to do with the 600 MHz signal. Send music along it? Send digital data along it? Measure its amplitude and phase? Compute the distance between transmit and receive antennas??? That information will allow us to tell you how to generate and receive the signal.

i will just transmit a simple 600MHz sine wave with no information and modulation, just a sine wave. At the receiver side, I would just like to see the 600MHz sine wave that i transmitted, just to verify that i received it. I would like however, to input this received sine wave in a computer software such as matlab.

 

[upand_at_them]

Well, if you're expecting to input the 600MHz signal into the computer you're out of luck.

If you're using it as a carrier frequency and want to input the modulated signal that rides on top of the carrier then you can mix the signal with a frequency that brings it down to what your sound card can process.

That process is called mixing. Two signals mixed together produce the sum and difference of their frequencies.

 

[biff44]

well, it is not so simple. the world is full of RF signals, and a simple detector that just says there is RF power present may detect your 600 MHz sine wave, along with wireless burglar alarms, wireless phones, key fobs, etc etc. If the detector goes off, how do you know it is because of your 600 MHz tone, or some other spurious signal?

A crude detector can be tuned to a specific frequency. either an amplifier/bandpass filter/diode detector...or a regenerative receiver tuned to 600 MHz. That is more likely to only pick up your signal, but no guarantees.

You could have a superheterodyne receiver, say an antenna/low noise amplifier/600 MHz bandpass filter/mixer/IF amplifier with a phase locked local oscillator. If the local oscillator was tuned to maybe 600.02 MHz, then when your 600 MHz is present, and IF tone of 20 KHz will be generated. You could input that low frequency tone into your computer's analog input. Unfortunately, if there were a 599.98 MHz sine wave present, it would also generate a 20 KHz tone, to you would have to maybe tune your desired signal around a little until there was no unwanted interferer signal

But if you did some modulation to your 600 MHz carrier, say on/off modulating it at 1 KHz rate, you could use a simple AM detector, find that 1 KHz modulating tone, and then deduce that the 600 MHz carrier had to be present also.

 

[FvM]

Talking about realistic ways to implement a simple 600 MHz receiver, a wideband ISM transceiver chip that covers the 600 MHz range, e.g. SiLabs Si4431 could be used as RF frontend. It's designed to decode digital modulation schemes like ASK and FSK, but can also make simple signal strength measurements.

 

[patrickian01]

Talking about realistic ways to implement a simple 600 MHz receiver, a wideband ISM transceiver chip that covers the 600 MHz range, e.g. SiLabs Si4431 could be used as RF frontend. It's designed to decode digital modulation schemes like ASK and FSK, but can also make simple signal strength measurements.

thanks for the suggestion. I will be definately looking for this chip, although I am kinda skeptical since we don't have much components in here.

 

[FvM]

The intended sensitivity and selectivity matters for a real design. You didn't tell about it yet.

In other words, what's the level of the 600 MHz signal, do you expect other signals of similar or even higher level around it?

 

[patrickian01]

The intended sensitivity and selectivity matters for a real design. You didn't tell about it yet.

In other words, what's the level of the 600 MHz signal, do you expect other signals of similar or even higher level around it?

Well, the reason I chose this frequency is because I don't think there will be much devices that use the same frequency that could greatly affect the experiment. There could be stray signals however, I expect it to be very weak and barely noticeable. As for the signal level, I will still have to look into it, since i'm having a difficult time obtaining the materials for the oscillator.