New SDR Users FAQ: Why is there a mountain of noise on MW?

[sunwave]

Is your SDR near your internet gateway and the computer power supply?

Short demonstration of how severe switching power supplies totally wipe out reception on the medium wave broadcast band. I had the surge protector turned off when you can see all the pretty local and distant MW signals until I turned the surge protector back on. Internet gateway and laptop power brick is on the same surge protector.

(Sorry but no audio)

 

[ka3jjz]

Another very common issue is overloading. I see way too many folks using 100 foot or more as an antenna. Particularly with these little stick SDRs like the RTL, their front ends simply can't handle this without adding some filters or a passive preselector. This is also a possible cause if you live near a major city with lots of MW (or FM) stations, even with a smaller antenna. SDRs are wonderful but their front ends aren't very good yet at rejecting out of band stuff and handling a large amount of RF.

 

[sunwave]

Another very common issue is overloading. I see way too many folks using 100 foot or more as an antenna. Particularly with these little stick SDRs like the RTL, their front ends simply can't handle this without adding some filters or a passive preselector. This is also a possible cause if you live near a major city with lots of MW (or FM) stations, even with a smaller antenna. SDRs are wonderful but their front ends aren't very good yet at rejecting out of band stuff and handling a large amount of RF.

I have RTL-SDR dongles. Every single one of them overload and image. Strong signals like this one on the RSP1a and other RSP's doesn't overload. What we see here is an overmodulated transmitter on CB Channel 6 (27.025MHz) with splatter. This is what we should see from an SDR.

 

[PDXh0b0]

It's quest...lol..after my experience, when someone asks which dongle to get, if they want hf/mw/sw get an rsp1a or hf discovery, because once you buy a dongle than an upconvertor your already close to the cost of one of those. That said , fm broadcast on up, can't beat the $30 dongle in software compatibility

 

[sunwave]

I just received my Nooelec Balun 1:9 v2 with metal case and new RG-58 coax. I tried medium wave band with everything turned on. I can hear all the local medium wave broadcasters now. I don't know what it is about the balun but it seemed to work really well. I have disabled the bias-T in SDRuno on the RSP1a to prevent accidental voltage burning out the balun.

Will someone explain how it is that that little balun cleared up a lot of noise and now able to hear all the local MW broadcasters please?

 

[rabbit108]

I just received my Nooelec Balun 1:9 v2 with metal case and new RG-58 coax. I tried medium wave band with everything turned on. I can hear all the local medium wave broadcasters now. I don't know what it is about the balun but it seemed to work really well. I have disabled the bias-T in SDRuno on the RSP1a to prevent accidental voltage burning out the balun.

Will someone explain how it is that that little balun cleared up a lot of noise and now able to hear all the local MW broadcasters please?

I will try.

The balun lets the signals pass through because they are the differential current (opposite directions) in the coax. The noise pickup on the coax is common mode current (same direction), which is attenuated by the balun. The 9:1 transformer is a conventional RF transformer with two separate windings, rather than the less effective (for this application) autotransformer type.

The NooElec Balun 1:9 v2

Thank you for calling my attention to that Nooelec device.