Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Help with Sleeve Dipole
I am a little confused with calculation of appropriate length of metal
tubing used in a sleeve antenna design (the 1/4 wave section). I understand that as RF travels through various mediums, Velocity of the wave slows down relative to Er of the material. So for coax the wavelength would be say 0.66 Lambda. With the tubing over a coaxial cable though it seems there is Vp related to the dielectric formed between the sleeve and the outer sheath of the coax cable but also the Metal has an Er value. 1. Do you need to count for both these when calculate how the tube should be. 2. Is there relationship that needs to be considered between sleeve length and distance between sleeve and coax (ie. If the sleeve is made larger diameter does it effect the length required for the tube or is this still defined strictly by Er) also, Does the diameter of the tube effect the impedance ? The specific example is RG174 Coax cable vertical dipole. The top radiating element is 1/4 long. At the bottom of this element is a length of RG174 Coax. 1/4 wave length of this coax has a 5/32 Brass sleeve. The sleeve is soldered to the RG174 coax at the point where the coax meets the top 1/4 wave element. I need to understand what needs to be used to calculate the length of Brass tubing sleeve given the tubing diameter is 5/32 and besides air, the outer sheath of the RG174 is also between the sleeve and Earth braid. Is the diameter of the tubing critical (will it impact adversely on SWR looking into this antenna). The final point would be if I place some ferrite rings across the coax below the sleeve, will this improve SWR ? Thanks Regards David |
Thread Tools | Search this Thread |
Display Modes | |
|
|