RFI Identification on SDR

[pastian]

I have attached 3 images of my RFI problem

Image 1: Shows the RFI morphing into the alternating signal. This happens every 2.5 min and starts from a constant signal to a stronger signal for 5 sec then into the alternating signal for 5 sec.

Image 2: shows spacing of RFI

Image 3: What my washing machine looks like on SDR

Notes:
This is always here even with radio on battery power and different SDR dongles.
I have snapped on so many ferrite snaps my fingers hurt.
I have walked around outside with AM radio without my luck, other than obvious EMI
I have unplugged the house and it remains

This has been a real head scratcher any help is appreciated

Thanks

HP

 

[pastian]

Hmmm well the "experts" didn't weigh in, I guess I'm not surprised.

The "RFI" turns out to be simple SDR overload (mostly local AM Broadcast). Nothing several DB of attenuation and more than the average High pass filter for AM and FM broadcast.

The signals you see above have a RTL-SDR Blog FM AND AM "filters" perhaps someone at RTL-SDR Blog will read this and improve their products OR sell them by the dozen?

 

[krokus]

Hmmm well the "experts" didn't weigh in, I guess I'm not surprised.

The "RFI" turns out to be simple SDR overload (mostly local AM Broadcast). Nothing several DB of attenuation and more than the average High pass filter for AM and FM broadcast.

The signals you see above have a RTL-SDR Blog FM AND AM "filters" perhaps someone at RTL-SDR Blog will read this and improve their products OR sell them by the dozen?

I did not see your post until now. (Not that am an expert.)

The alternating nature made me think IMI, with the birdies.

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[pastian]

I wonder about IMI (Inter-modulation Interference) as well, The only thing I can come up with my limited resources is that:

Is it possible the Broadcast signals are so strong that even the harmonics have harmonics?

same results with another RTL-SDR (same model) HDSDR, SD# all show same pattern.

However it does seem to be attenuate-able (I had 3 old attenuater pads from cable modem days) without losing much signal. Notice in the pictures I was only using 7.7 DB of RF Gain

I actually have all I can possibly listen to if I set the RF gain at 1.7 DB

Thanks for the reply

 

[dave3825]

Is it possible the Broadcast signals are so strong that even the harmonics have harmonics?

https://en.wikipedia.org/wiki/Harmonic

I don't understand much of that but there is a chart towards the bottom the looks like it can.

 

[pastian]

Good eye!

I wonder if these Cheap Band Stop and High Pass filters cover the harmonics...actually no I don't wonder, get what ya pay for huh.

 

[krokus]

I wonder about IMI (Inter-modulation Interference) as well, The only thing I can come up with my limited resources is that:

Is it possible the Broadcast signals are so strong that even the harmonics have harmonics?

same results with another RTL-SDR (same model) HDSDR, SD# all show same pattern.

However it does seem to be attenuate-able (I had 3 old attenuater pads from cable modem days) without losing much signal. Notice in the pictures I was only using 7.7 DB of RF Gain

I actually have all I can possibly listen to if I set the RF gain at 1.7 DB

Thanks for the reply

Harmonics are infinite, theoretically, and are based on the original (fundamental) freq.

IMI product orders are the mixing of mixer results with fundamental freqs, and with other mixer results. These can be from any non-linear junction, not just semiconductors.

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