On Sun, Sep 4, 2022 at 04:30 PM, Tish wrote:
Does separate RF choke have big impact on SWR measurements?
It all depends on the antenna. If you have a dipole, which is a balanced antenna, and you connect it directly to an unbalanced transmission line (like coax) the outer surface of the coax shield is connected to one leg of the antenna. So it becomes part of the antenna and radiates. When you change the length of the coax or ground it at the radio end this will affect the SWR and the resonant frequency. If a current balun is installed at the feedpoint it will "choke" the current flow on the coax outer shield and considerably reduce this effect.
The J-pole which is a common VHF antenna will also radiate on the coax and the SWR will change as you hold the coax or change the length. Once again a choke is required.
Any decent book on ham antennas will discuss this issue. The ARRL Antenna Book is a good reference.
Roger
Roger Need