Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Someone said I could be victim of transceiver agc

Status
Not open for further replies.

wtr

Full Member level 5
Joined
May 1, 2014
Messages
298
Helped
29
Reputation
58
Reaction score
25
Trophy points
1,308
Activity points
4,095
Hello all,

I'm trying to characterize a transceiver, see post here. I'm not sure if this is an RF or a DSP problem.

Setup is as follows
setup.jpg

Transmitter and Receiver are same. An AD9361, connected to an FPGA.

I'm setting a single tone transmit frequency. Then the receiver window to capture. The aim is the characterize the roll-off. To do this I'm moving the transmit frequency and recapturing the window. I believe I'm setting the gain(or attenuation) for transmit and receive AD9361s

The first 1024 or 2048 or even 4096 samples are fed into an FFT so I can get the max value at that frequency.

The receive window is exactly the same, all that is changed is the transmit has moved from 1902MHz to 1903MHz and the time the test is run.
Receive window, diff capture add1Mhz.png


The phasor diagram has some fuzz, which is why I plotted the magnitude on the left hand side above. The mean value for both frequencies is roughly the same, so I'm assuming the transmit isn't fluctuating the power. As you can see on the right hand side the FFT is looking different. Remember the exact same script and process is run. Only difference is I've moved the frequency 1MHz to the right.

If I plot all the different captures I end up with the following.

Screenshot from 2021-12-15 09-28-36.png


Playing around with Welch averaging can generate the following inverted nipple
welch.png


I'm at a lost for understanding whats happening from a first principles point of view.

If the signal I am capturing is out of phase on arrival, surely after so many samples it doesn't mater.
--- Updated ---

Here are some pretty pictures, that show magnitude fluctuation. Does this mean my transmitter if rubbish?
Fluxtuating_power_1903Mhz.png
 
Last edited:

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
50,778
Helped
14,600
Reputation
29,475
Reaction score
13,677
Trophy points
1,393
Location
Bochum, Germany
Activity points
290,811
You are asking about AD9361 AGC, you should know if you disabled it.

What's the used window type? What are the settings for decimation and sample rate?
 

wtr

Full Member level 5
Joined
May 1, 2014
Messages
298
Helped
29
Reputation
58
Reaction score
25
Trophy points
1,308
Activity points
4,095
I thought i was fixing the AGC. I've got a 2.4Ghz signal thats being decimated to a 61.44MHz. Pretty much standard SDR stuff.

The reason I mention the AGC is because the magnitude of IQ is fluctuating from 0.12 to 0.14.. On second thoughts i don't think its this.

I'm going to attempt this again with a signal generator. There problem may be my stimulus.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top