LNA degradation

Here I need some comments regarding what, I suppose, it’s a “LNA degradation” over time. That station hasn’t had any modification over that period ( 25 feb --> 25 apr --> 26may ), the waterfall is fixed regarding the range, the satellite is know to be a “reference”, at least for me
From the oldest to the most recent it’s quite evident the noise rising and the presence of birdies over the passband…
Anybody had same experience???

de I3VFJ, Vittorio

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Yes, and most of the time it is not the LNA put local RFI, that being said it can be the LNA but that wouldn’t be first choice.

As an example: I had a terrible RFI in the UHF range and couldn’t find the reason, at the end after many weeks of searching I found out it was both the two Sony TV’s that are in use.

So now every time I make sure they are both switched off or even better unplugged from the wall outlet when nobody is watching.

Two example from the same setup, one in the middle of the night and the other during daytime.

2021-05-05 02:18:56 https://network.satnogs.org/observations/4058740/

2021-05-27 16:57:45 https://network.satnogs.org/observations/4174664/

All the best.


Tnx Jan,
you are right, but in my case I’m quite sure abt LNA; the obsevation shown are (almost) time alligned…
So, next week I’ll be there on the station with another LNA if I’m able to find it in my messy shack, or I’ll try without LNA cause the feeder there it’s only 7 m and with gud quality coax.
Tnx anyway, I’ll report further news :slightly_smiling_face:


… and this is the results, second image from a passage under 18° elevation, thus very distant:

No LNA, pushed the RTL gain to 44dB (just a bit under compression point); all the birdies and background noise gone!
Obviously S/N it’s worst, but at last, the LNA shows clearly some degradation, as supposed.
Now I’ve it on the table to do some measurement but I’m quite sure to change this block to a tuned one.
Vittorio I3VFJ

Could it be power supply or LNA capacitors degradation instead, causing inadequate filtering?

Uhm… could be, but there isnt much components into this kind LNA:

I’ve the LNA under test on my workbench but “apparently” it’s ok.
So, to replicate the stuff, I’m going to leave powered the LNA for looong time, as it was installed into the node, and see if it’ll be something strange.
As usual, my reports here :wink:

Vittorio, I3VFJ

I can see a capacitor on the power terminals. Did you try replacing it?

Nope, but it seems that I have wrongly accused the wrong component …
After 2 days of continuos stressing ( heating / cooling / overdriving / mismatching ) test the LNA, nor the capacitor, is not guilty.
So I should look at the power supply of the system, or to an external cause… working in progress!!!
Stay tuned :wink:

Vittorio I3VFJ