Static on 150mhz Scanner

[Clay_Lowery]

I have Tram 1411 run through KMR 400 coax split through pigtail to 3 RTL-SDR dongles, and every transmission that comes through has crackles throughout; the modulation is NFM. I am just wondering because of the mess of pigtails, interference, or other?

 

[buddrousa]

#1 you need a Combiner not T splices.
#2 a combiner has Isolation between the ports.

 

[n1ofj]

#1 you need a Combiner not T splices.
#2 a combiner has Isolation between the ports.

believe you mean a multicoupler. Combiners are for TX.

 

[buddrousa]

Yes multicouplers just twisting the center leads together or keep adding T's to make the number of ports you need is not the answer.

 

[Ubbe]

I am just wondering because of the mess of pigtails, interference, or other?

To rule out any pigtail mess, just connect one single dongle using one single coax directly to the KMR400 coax.
To rule out the SDR dongle you probably have another receiver you can use, that will be of a better quality of reception than a SDR dongle. Even if you only can receive analog with that other receiver/scanner you can verify what reception you get from the dongle at the same frequency in the VHF band.

Never use automatic gain settings with SDR dongles, always set manual gain values.

At VHF you might have interference issues that will require some type of extra filtering, maybe an expensive notch filter from PAR electronics to reduce a strong transmitters signal level. It is the sum of all signals that makes the cup overflow, so using a cheap FM broadcast filter might also help.

/Ubbe