Unusual spectrum pl...
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Unusual spectrum plot with the lowest RBWs

Active Member
Joined: 3 years ago
Posts: 11
Topic starter  

Hello people, I got the spectrum plots which are shown in the images with an Spectrum HF-60105 V4 X device. This device was bought with the options 020 (preamp) and 002 (0,5ppm TCXO Time Base). I connected a 50ohm load at the input to see the sensitivity I can get with the lowest RBW (200 Hz with option 002). The difference among the images is the span and RBW. I cannot understand why a band with a lower power appears in the middle of the plot when I choose the lowest RBWs, 200 Hz to 1 KHz, with a span bigger than 200 KHz. The band's lenght is 200 KHz when RBW is 200 Hz, and a little bit more when RBW is 1KHz. In one of the images I changed the RBW to 10 KHz and the band dissappeared. And in another image I changed the span to 200 KHz (with RBW 200Hz), to only see that band, but a peak appeared in the middle of the plot.
Have someone got the same results? Is it something normal? Can you help me to understand this phenomenon?

Member Admin
Joined: 11 years ago
Posts: 321

Certain frequencies that are multiples of 10/20 MHz are sensitive to internal interference from the device as you can see in your third image. The MCS has a feature called "Peak Suppression" to eliminate those fake signals. As different combinations of sweep parameters influence the amount of interference this can sometimes look a bit strange like in your second and fourth picture as the generated fake noise doesn't match the real surrounding noise.

You can disable the "Peak Suppression" feature in the Extras menu.

New Member
Joined: 3 years ago
Posts: 2


I have an identical unit to this.

Sometime I see "strange" things like you and w/o having any reference to what "normal" is I end up wondering if my unit works 100%.

I would be very interested to connect directly with someone like you to exchange information / compare notes.

I think that it would be a time saver.

my email [email protected] if anyone would like to respond.

New Member
Joined: 2 years ago
Posts: 2

I find similar problem with MCS.