I'm building RHCP crossed dipole for 137 MHz satellites reception (I'm using 137.5 as a central frequency). My calcs are:

  • frequency is 137.5 MHz
  • λ is 2.18 m
  • one dipole leg length equals to the λ/4 so 54.5 cm
  • phasing RG58 50 Ohm cable is of 36.0 cm
  • 28 to 50 Ohm transformer made of 2 parallel RG6 75 Ohm cables; each cable is of 36.0 cm

I've decided to solder second dipole to the one side of RG58 coax and join first dipole together with other end of RG58 coax and with RG6 feeder transformer by choc block (to ease possible future change of RHCP -> LHCP). I haven't faced phasing and transformer units earlier so I wonder how to perform right cut.

Right now I've cut RG58 and RG6 coaxes exactly at 36.0 cm. However for soldering and joining purposes I have stripped a part of external and internal insulation on all coaxes so actual length of untouched coax become smaller - about 30-32 centimeters. Also because of lack of space and to save coax length I've connected stripped parts of RG6 transformer to the choc block with small pieces of copper wire.

I'm not sure if I've done it in a right way. Should I cut coaxes a bit longer (let's say 42 cm) and strip insulation in a way that final untouched coax pieces would be 36.0 cm? What kind of side-effects this could render? Also I want to know if it is ok to use choc blocks and copper wires to interconnect all necessary parts because they increases effective length of dipole legs and/or signal path.

  • $\begingroup$ What velocity factors are you using for RG58 and RG6? RG6 should be much faster, as it has a light foam dielectric. $\endgroup$
    – tomnexus
    Commented Jun 17, 2020 at 6:28
  • $\begingroup$ I've used 0.66 factor for both cables so my calcs are length = λ / 4 * 0.66 = 36.0 cm $\endgroup$ Commented Jun 17, 2020 at 9:03
  • $\begingroup$ Ok, after some searching it seems there is a non-foam, solid PE dielectric RG6, so this would be correct. But if its foam it should be 0.81. $\endgroup$
    – tomnexus
    Commented Jun 17, 2020 at 12:25


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