I have taken on a project (involving mini quads if you know anything about them) and I have come up with a half baked solution that would involve measuring the RSSI of a signal of a giving frequency. These frequencies would be in the 5.8GHz range. I've read it may be possible to just use a piece of wire as an antenna etc however I don't know of a way of tuning the circuit to the given frequencies. Maybe using a transistors to connect some capacitors of different values? I don't have a clue.

Thank you

 

Hello,

I assume that you are using the therm RSSI for Received Signal Strenght Indication.
http://encyclopedia.thefreedictionary.com/Received+Signal+Strength+Indication
For 5.8Ghz, the circuit will be quite a challenge to make.
Also how will you make the dBm scale, that is used for RSSI.

Bertus

 

Hello,

I assume that you are using the therm RSSI for Received Signal Strenght Indication.
http://encyclopedia.thefreedictionary.com/Received+Signal+Strength+Indication
For 5.8Ghz, the circuit will be quite a challenge to make.
Also how will you make the dBm scale, that is used for RSSI.

Bertus

Yes I am, I'm not interested in giving the signal strength a unit. I'm just interested in relative signal strength essentially.
So why would that be a challenge to make? I assume it's easier to build circuits for a lower frequency.

Jack

 

Yes I am, I'm not interested in giving the signal strength a unit. I'm just interested in relative signal strength essentially.
So why would that be a challenge to make? I assume it's easier to build circuits for a lower frequency.

Jack

It is difficult because the wavelength of the signals is the same order of magnitude as the dimensions of the circuit. This means that ordinary lumped circuit components are no longer what you think they are. Inductors turn into distributed capacitors, capacitors turn into distributed inductors and active devices are unable to provide much in the way of gain. You can't design with pencil and paper and you can't debug without instruments that cost more than a house in a middle class neighborhood. So knock yourself out.

 

PapaBravo gave you the straight scoop.

When you are working in the GHz range, parasitic capacitance in inductors and particularly parasitic inductance in capacitors can make your life difficult.

For example, in the 5GHz range, small 0402 size MLC's (multilayer ceramic capacitors, about the size of a lowercase "o") have too much inductance due to how the conducting layers inside the cap meander around; you have to use SLCs (single layer ceramic capacitors) and custom trim them using a $30,000 material analyzer to get the capacitance you need.

The inductors would look about like "_n_", and you would need a $40,000 network analyzer to ensure you had it properly tuned.

 

Is a mini quad a R/C craft? Does it currently use a 5.8 GHz link?

 

Is a mini quad a R/C craft? Does it currently use a 5.8 GHz link?

Yes

 

It is difficult because the wavelength of the signals is the same order of magnitude as the dimensions of the circuit. This means that ordinary lumped circuit components are no longer what you think they are. Inductors turn into distributed capacitors, capacitors turn into distributed inductors and active devices are unable to provide much in the way of gain. You can't design with pencil and paper and you can't debug without instruments that cost more than a house in a middle class neighborhood. So knock yourself out.

Would it possible to use an op amp to amplify the signal a little. Then I could compare the input signal to the op amp and its output signal's voltage to determine the gain. Then could I determine the frequency right?

 

Would it possible to use an op amp to amplify the signal a little. Then I could compare the input signal to the op amp and its output signal's voltage to determine the gain. Then could I determine the frequency right?

Take a typical opamp, look at the datsheet, find a parameter called GBW (Gain Bandwidth Product). If you can find an opamp that will produce a gain of greater than 1 at 5.8 GHz then be my guest at creating a circuit. All the stuff I mentioned before still applies.

 

Hello,

There are apmplifers for the given frequency:
https://www.xmicrowave.com/product/XM-A266-0804D/
https://www.xmicrowave.com/product/XM-A2A5-0404D/
Just have a look how complicated the PCB is on that page.
And have a look at the indicated price.

Bertus

 

If you are determined to pursue using an amplifier, I recommend you look at Mini-circuits offerrings:
https://www.minicircuits.com

Their SMA modules make it simple and remarkably affordable to prototype a system.