<< NumericalMath`BesselZeros`
<< Graphics`Graphics`

ρa := 1.5; ρb := 2;

DisplayTogether[
      Plot[BesselJ[0, ρb knl] BesselY[0, ρa knl], {knl, 0, 10}, 
        PlotStyle -> Hue[ .3]], 
      Plot[ BesselJ[0, ρa knl] BesselY[0, ρb knl], {knl, 0, 
          10}, PlotStyle -> Hue[ .6]], ImageSize -> 550]

l = 1;

DisplayTogether[
      Plot[BesselJ[l, ρb knl] BesselY[l, ρa knl], {knl, 0, 10}, 
        PlotStyle -> Hue[ .3]], 
      Plot[ BesselJ[l, ρa knl] BesselY[l, ρb knl], {knl, 0, 
          10}, PlotStyle -> Hue[ .6]], ImageSize -> 550]