8970b e27

i want to measure a x-band lna use the 8970a,i don't know whether the method that i used right or not.
i use the 1.3 mode,with a mixer and a LO source, then i calibrate the device,after that ,i connect the lna between the noise source and the mixer's rf port,the mixer's if port connect to 8970a.
that all.
the connector and the mixer giving me another error,isn't it? how much is it ?

Measurement mode 1.3 is wrong!

You must use 1.1 or 1.2 (it does depend on the type of oscillator you have, variable or fixed respectively).

If you have a variable local oscillator (meas mode 1.1), use SF 3.0 to set the IF frequency.
Use a LNA in front of the mixer to reduce the NF of the measurement system.
External filtering (after the LNA) is needed for SSB measurements.

Connect the IF port of the mixer to the input port of the 8970B.

Connect the noise source output to the input of your meas system (input of the LNA if you have , or input of the mixer) and then calibrate (ALL) the meas system.

Then, remove the source and insert the LNA and measure the corrected NF of the DUT.

p.s. the NF of the mixer is taken in account from the calibration

Thanks u very much.
i still have a question,you said i should connect a external filter after the LNA if i'm in SSB measurement.
what is the use of the filter?why don't connect the filter after the mixer?
and another one,when i can use the mode 1.3

The measurement mode 1.3 may be used when the DUT is a frequency traslating device (mixer).

The filter rejects the image frequency that otherwise goes into the mixer; if you have not the filter make a DSB (use special function 2.0) measurement and set the IF frequency as low as possible (15MHz for example).

Hi,I also want to know How to use HP 8970A to measure NF of my LNA at 2GHz.I have some questions to ask.

I use mode 1.2, I use RMS-25MH as mixer,A RF filter(BW:1920-1980MHz) placed at the RF port of the mixer. The CONVERSION LOSS of mixer is 7-9dB, and the CONVERSION LOSS of filter is about 3dB. I measured the filter and mixer, they do work properly.

I set the start,stop,step freq as 1920,1980,10. then 3.1 SF 1400, the freq of fixed LO is 1400MHz. But when I calibrate, E27 was apperaed, It's means overflow while calibration. Even sometimes, after calibration,no E27 was appeared, but the NF is still big, and is changing all the time.
What's the reason? what should I do in order to measure the NF? Need I add a amplifier in front of the mixer when do the calibration? If so, what kind of amplifier should I use? Low Noise, high Gain?

Waiting for your reply anxiously. Thanks very much.

Ok. FIrst af all, use SF 32.0 to set the input gain stage inside the instrument to the highest value (default value). You may obtain this also pushing on PRESET.

Probably this will not solve your problem because the losses in front of the instrument seem to be too much; use a LNA (low noise as much as possible, and at least 20 dB gain) and E27 will not appear anymore.


p.s. use the LNA in front of the filter, as first stage (better if you also add, in front of this last one, an isolator).

To reduce the jitter in the display reading increas the smoothing.


regards

To marcomdd:
Why the gain of the amplifier in front of the filter should be more than 20dB?
The loss of the filter and mixer is about 10-12dB. 20dB need two stages amplifier.

All I need to measure the NF of a amplifier at 2GHz is a amplifier with high gain and low noise, followed by a filter and then a mixer?
Is there anything should pay attention to?
Thanks very much!

With a 20dB gain amplifier you are able to reduce the noise of the passive blocks (filter and mixer) one hundred times, so that the noise factor of all the instrumentation is, more or less, equal to the noise factor of the (low noise) amplifier.
Low noise instrumentation means lower uncertainty !

Regards

p.s. if you have only 10dB gain .....better than nothing!

marcomdd,Thanks very much!
Now I can use mode 1.2 to measure the NF of LNA at 1.95GHz using HP 8970A.But Now I have another question to ask.Because of the diamatch between the LNA(DUT) and the mixer module, The Gain and NF measured by the Noise Figure Meter 8970A is not accurate.
The Gain of the mixer module is about 15dB. The gain of the DUT(LNA) is about 13dB, But when the LNA and mixer are connected together, the whole Gain is not 15+13=28dB, but only 22dB.
The measurement result of the Noise figure meter is 7dB(Gain)(not 13dB) and 2dB(NF).

I guess the gain and NF presented by 8970A are calculated(22-15~=7).
The output VSWR of LNA is 1.5 and the VSWR of mixer module is about 1.5.

So how can I make accurate measurement?

What do you mean with diamatch ? Perhaps mismatch ?

Please with only the mixer module in place , connect the noise source and measure the noise figure of the instrumentation. Say me the value.

Then , which is the noise source you have (model) ? More important, do you insert the exact ENR values in the noise figure meter ?

I need more informations to help you.

I think it's perhaps mismatch,as the gain of the LNA+mixer is not just 13+15dB.

I just used mode 1.4 to measure the mixer model, The LO freq is 2.2GHz,power is 12dBm.
The IF is 220-280MHz(So the RF is 1.92-1.98GHz), the result is
IF Freq(MHz) Gain(dB) NF(dB)
280 19.7 10
270 15.8 9.3
260 17.6 8
250 17.6 7.5
240 16.2 7.8
230 15.1 8.4
220 14.6 8.2


the Noise source is HP 346A,freq rang is 10MHz～18GHz,I do input the ENR correctly.

Do you need any more information about my measurement? Thanks very much.

To marcomdd:
first,thank you for all your reply very much.
and,i also want to know the maxim nf figure the Noise Figure Meter 8970A can measure.
for example,if i wanted to measure a device which nf figure was about 20db,8970A is ok?

when i set IF frequency lower than 30mhz , it display a wrong,do you konw what means it is ?

1- Repeat the measurement with an isolator at the input of the LNA+mixer . This will isolate the instrumentation from the change of the input reflection coefficient between the calibration step and the measurement one.

2- do you have a single block that aplifies and down converts the signal? How do you measure it ? With the NFM ? Being a translating device you have two use two different ENR values , the IF value for the calibration step and the RF value for the measurement step.

when i set IF frequency lower than 30mhz , it display a wrong,do you konw what means it is ?