AnsweredAssumed Answered

Question about N8973A NFA

Question asked by RAVONCAPD on Oct 12, 2009
Latest reply on Oct 30, 2009 by Fhahim987

Like • Show 0 Likes0
Comment • 8

We are using the N8973A NFA (with N-TYPE connector) with a SNS series 4001A noise source.
Our D.U.T has SMA female connector.
Does the loss of the N-Type to SMA adaptor needed to connect the Noise source to the NFA input get added to the loss of the Noise reciever as part of the 'after D.U.T' losses or to the Noise Source as part of the 'before D.U.T' losses and is there a way to change the setting?

Thanks in advance

No one else has this question

Outcomes

8 Replies

Dr_joel Oct 12, 2009 7:32 AM
Mark Correct
Correct Answer
If you connect the noise source to the DUT directly, then presumably the sma-to-N must be left on the NFA so the SMA dut can connect to the NFA. Thus, it must be loss after DUT.
Like • Show 0 Likes0
Actions
RAVONCAPD Oct 12, 2009 11:50 PM
Mark Correct
Correct Answer
Sorry I wasn't clear, the question is does the NFA calibration algorithem assume any additional losses after the Noise Source output are losses after the D.U.T or does it assume some are before? and if the Later is there any way to change the settings so the calibration assumptions will match the reality (i.e all losses after the Noise source are after the D.U.T)
Like • Show 0 Likes0
Actions
Dr_joel Oct 13, 2009 9:21 AM
Mark Correct
Correct Answer
I'm not sure, but I believe that any losses before the DUT must be added to the ENR of the noise source, thus, any loss compensation is always applied to "loss after DUT". It should not really affect noise figure, but would affect gain.

If you have more questions, could you be a little more clear on the setup...

I think you mean: I connect the noise source to a SMA-to-N adapter, and connect that to the NFA for cal.

Then, I connect the SMA noise source to my SMA amplifier, and connect the SMA amplfiier to the sma-to-n adapter to the NFA for measurment.

If above is your situation, then the adapter should be applied only to the gain, and the NF will remain essentially unchanged.
Like • Show 0 Likes0
Actions
RAVONCAPD Oct 14, 2009 12:13 AM
Mark Correct
Correct Answer
Thanks, and yes that is the setup we use. Our concern was that since we're dealing with low noise, (under 1dB) if the adapter loss was erroneously added before the D.U.T it would add a significant error to the measurment.
Like • Show 0 Likes0
Actions
Dr_joel Oct 14, 2009 1:53 PM
Mark Correct
Correct Answer
Less than 1 dB is tough to do unless you can connect the Noise Source directly to the amplifier. Even so, if your DUT is not isolated, depending upon the Rn, you would exect about +-.5 dB variation due to differences in the hot/cold impedance and error from 50 ohms. You should use a low ENR source (6 dB) to reduce this error. Or use a PNA-X.
Like • Show 0 Likes0
Actions
RAVONCAPD Oct 15, 2009 7:38 AM
Mark Correct
Correct Answer
What do you mean by "if your DUT is not isolated"? How do you isolate an amplifier?
We haven't seen errors as bad as 0.5dB despite using high ENR noise source, I think the worst variation was ~0.3dB.
Like • Show 0 Likes0
Actions
Dr_joel Oct 15, 2009 9:08 AM
Mark Correct
Correct Answer
Isolated means with an isolator between the noise source and the amplifier under test. But of course this depends upon the match of the noise source and the NF sensitivity to input match on the amplifier.

One good way to test this sensitivity is to use a precision airline on the input of the amplifier, like one out of a verification kit. The airline should have very little loss (such as 0.02 dB) and very good match (maybe 50 dB), so adding it to the input of an amplifier should have very little effect on the NF of the amplifier. But, it will change the phase of the mismatch between the noise source and the amplifier, and if the NF changes, you can assume that this change is due to mismatch effects. On well matched amplifiers, this can be small (0.3 dB as you say) but some low noise amplifiers are not well matched and the effects are larger.
Like • Show 0 Likes0
Actions
Fhahim987 Oct 30, 2009 12:54 AM
Mark Correct
Correct Answer
If you have more questions, could you be a little more clear on the setup...

I think you mean: I connect the noise source to a SMA-to-N adapter, and connect that to the NFA for cal.

Then, I connect the SMA noise source to my SMA amplifier, and connect the SMA amplfiier to the sma-to-n adapter to the NFA for measurment.

If above is your situation, then the adapter should be applied only to the gain, and the NF will remain essentially unchanged.

magic jack
buy magic jack
magic jack review
Like • Show 0 Likes0
Actions

Question about N8973A NFA

Outcomes

Related Content

Recommended Content