Coax cable loss

Coax cable loss


Nov 22, 2016


Antenna receives the signal, receiver makes it understandable. Coax cable carries the signal between the two, which gets more and more tired the further it travels (coax length) and the bumpier the road (coax quality). 
Being tired means you lose energy, so poor signal cannot tell you all the information.
Less info is called signal loss, how much depends on coax cable length and quality. 




How to calculate signal loss



Online resources detail loss in decibels, which is logarithmic, so 3 dB is half the power  - transmitting or receiving makes no difference. 

Decibels and logarithmic stuff can be complicated, so measure length of coax cable, note the writing on it and google this plus "attenuation". Attenuation means weakening of signal in radio speak. So if writing says RG 6, google "RG 6 attenuation".
Get a decibel figure with this online calculator. Enter values on top - results in feet will be on the left, meters on the right, you get a figure in decibels.

Coax cable loss, attenuation, RTL-SDR, RTL, SDR, AIS, Marine, sdrformariners, SDRSharp, improve reception, VHF, marine, yacht, sailing



To understand decibels in a "this is how much percent of info reaches my receiver ", use this online calculator. It simply converts decibel to percentages, with 1 being 100 % of signal received at the antenna.

Coax cable loss, attenuation, RTL-SDR, RTL, SDR, AIS, Marine, sdrformariners, SDRSharp, improve reception, VHF, marine, yacht, sailing


Enter number to the left of dB with a minus sign, select energy size on the right, then press calculate. 
For example, common RG 58 in 20 metres loses 4.4 dB: only 36 percent of signal reaches the receiver.


Minimizing coax cable loss



1) Decrease the length of coax cable - shorter coax equals more signal.
2) Install better, higher quality coax coax, this can get really expensive real quick.

3) Get rid of coax cables altogether by using a Raspberry Pi 3 at the antenna as an rtl-tcp server.
4) Use a preamp at the antenna with longer coax lengths. This will help to overcome some coax loss, but will not completely eliminate it. Bias-T is easiest: receiver sends power down the coax cable.

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