Re: Agilent 346A and N9069A reading high?

John Quarmby

Hi Conrad

I have also seen abnormally high NF readings on an example of the HA8ET preamp. This preamp includes narrow band filtering, and it could be that the noise bandwidth of the preamp is narrower than the Agilent test set bandwidth. I recollect that you might be able to configure the Agilent box for a narrower measurement bandwidth, but I don't have the manual to check. The 8970A will suffer from the same problem and is not configurable, the only way to test such preamps with the 8970 series boxes is to build a low loss narrow band 144MHz filter, then calibrate the instrument with the filter in circuit and then test the preamp via the filter (bear in mind that the filter won't look like a flat 50 ohm source so there will be errors due to changes in the impedance seen by the preamp input unless you include an isolator after the filter).


John G3XDY

On 18/07/2013 13:44, Conrad Farlow wrote:
I have access to an Agilent 346A head with an N9069A noise figure
measurement application running on an EXA series spectrum analyser. It
seems to have number of issues.

1. After calibration the noise figure and gain are never truly zero, the
noise figure normally reads -0.1 or similar and the gain will be -0.15
or thereabouts, these are just typical figures.

2.When I measure noise figure I see good results on the gain but the
noise figure seems high. For instance my HA8ET Extra 2 LNA reads about
1.4dB whereas I am pretty sure that it is much better than this.

I have Tcold set to the temperature on the surface of the device as
measured by a thermocouple. I have used some loss compensation before
the device, I have generously allowed 0.1 dB for a high quality
female-female N type.

Does anyone have any advice as to what is going wrong? I do have an 8970
that I could use for a reference check but it hasn't been switched on
for a while, shocking I know.......

Bit puzzled..

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