Issue with SA44 + TG44 scalar network analyzer on low frequencies

Hello,
I’m trying to make some measurements with SA44 + TG44. The scalar network analyzer in Spike works well, but when I set frequency < 16MHz it stops working at all (for example I want to scan range 10..20MHz), Spike counts measurements, but the graph is not updating at all.

Can it be fixed?

And a second question,
what “store through 20db” button does? I do “store through” and I see visible changes in graph, then add 20dB attenuator and do “store through 20db” – and now I don’t see any changes.

Hello Ivan,

Thanks for the heads up. I was able to quickly find the issue with the low frequency network analyzer sweeps. I am planning on releasing an update to the software within the next couple weeks. I can have this fix included. Is this adequate for you?

Regarding your other question, the 20dB store through enables more accurate measurements below -45 dB. Without the 20dB store through, we can only calibrate 0 -> -45dB. Check out the user manual, section 4.4 for more information.
https://signalhound.com/sigdownloads/Spike/Spike-User-Manual.pdf

Regards,
A.J.

1. Thank you, that will be great!

2. I see that 20db pad shows me perfect -20dB line in 0-2GHz region and rolls off slightly to -21..-22dB in 3-4GHz range. This is so before and after “store 20db” button (no visible changes). Is that correct? I thought it should make flat 0dB line after “store thru”, and then make perfect -20dB line after “store 20db”. Am I wrong here?

Regards, Ivan

Hello Ivan,

The 20dB store through is just being used internally to calibrate high gain measurements. You will not see the effect you mentioned. It will only affect measurements below -45dB.

Regards,
A.J.

Ivan,
The actual value of the 20 dB pad is not important. It is measured and nulled as part of the store 20 dB procedure. We just need enough attenuation so we don’t overdrive the ADC when setting it to the high gain state. This is usually 12-16 dB minimum. A 30 dB pad would even work, but the readings would be noisier.

Thank you for the explanation!

Let me tell some other personal impressions on network analyzer mode.
1. It would be very useful to save \ load “Store Thru” calibration (and other parameters – freq range, number of points, gain…). Now every time I run Spike, I have to plug-unplug connectors, make calibration again.
May be the easiest thing would be to add “Store Thru” data to Presets.

The most annoying thing is accidental lost of calibration, it’s not so obvious why some parameters change involves calibration lost and some others don’t.

2. Second cool thing would be to have a logarithmic frequency scale in network analysis mode, to make a wideband amplifer test (10-100 points in every decade from KHz up to GHz). To easily see a rise\fall lines with 6 (12 or 18)dB/octave.

3. Third useful thing would be a kind of power sweep mode, to do 2-4 plots on one screen with different attenuation of tracking generator output (0dB, -10dB, -20dB, -30dB). That mode can show an amplifier dynamic range and possible saturation or compression of the signal.

Regards, Ivan

[Author]

Posts