-------- Original Message -------- Subject: Velocith factor further explained List-Post: krnet@list.krnet.org Date: Fri, 21 Oct 2011 17:45:28 -0500 From: Glenn Martin <rep...@martekmississippi.com> To: Lance McBride <lance_mcbr...@yahoo.com>, KRnet <kr...@mylist.net>
On 10/21/2011 4:27 PM, Lance McBride wrote: > It's unique to the cable that you would use for the antenna construction. It also is a factor in the antenna itself (being that AIR is the dielectric that it propagates into, and the antenna is mathematically modeled as a transmission line). The velocity factor generally used for antennas is .93-.95 (the speed of propagation is 93 to 95 percent the speed of light). Thus at 126 MHZ the calculated wavelength (in free space) is 93.7", the 1/4 wavelength is 23.4", and the target length taking into account velocity factor is (23.4 * .94) = 22.01". Once coated with fiberglass, the antenna velocity factor decreases to an even lower percentage. The 20.3 inch length Mark gave you would equate to a velocity factor of 87%, which off the cuff seems about right. For comparison, the velocity factor of the RG-58 coaxial cable connecting your radio to the antenna is 66% the speed of light (.66). I'm glad you all are interested in this. If the purpose of building an experimental aircraft is to learn, I hope this discussion contributed! -- Glenn Martin, 2Lt Director Of Communications, CAP Squadron MS-066
