Noise in E4438C vector signal generator

[Djaferbey]

Hello,

I'm currently working with an ADC for SDR applications and conducting a blocker test.

Blocking is a measure of the receiver's capability to receive a modulated desired input signal amidst the presence of an unwanted unmodulated input signal, without this unwanted signal causing degradation of the receiver's performance beyond a specified limit.

The issue arises when I apply a blocker signal at a power level of 8.64 dBm; the noise floor of the ADC increases by 13 dB. How can I determine the noise generated by the E4438C signal generator? I aim to discern whether the 13 dB increase in the noise floor is attributable to the signal generator or the imperfections in the ADC quantization process.

 

[BigBoss]

I believe that this comes from poor combining conditions. The generator is influenced by jamming/blocker signal.

 

[Djaferbey]

I believe that this comes from poor combining conditions. The generator is influenced by jamming/blocker signal.

can you elaborate on that?. Im using a power splitter to combine the two signal generators one producing the wanted signal and the other a 90dB larger signal unwanted signal

 

[D.A.(Tony)Stewart]

> How can I determine the noise generated by the E4438C signal generator?

I would plot the SNR vs the dBm of interference at different frequencies for both CW and different modulation types.

The SNR can be correlated with BER using CRC/ECC. The results will be non-linear but much better with ECC.

 

[BigBoss]

can you elaborate on that?. Im using a power splitter to combine the two signal generators one producing the wanted signal and the other a 90dB larger signal unwanted signal

Yep, a Power Combiner should be used but how about the Isolation between the ports of this combiner.?
If it's poor, jamming signal "might" disturb the generator. This is what I thought.

 

[albbg]

The two generator have to be isolated one each other to avoid intermodulation. To combine them you could use a directional coupler with high isolation and low coupling factor.
The blocking signal has to be connected to the main line and the wanted signal to the coupled port.
In any case I think the noise could be due, instead, to the blocker generator itself. In this case you should use a very narrow bandpass filter.