coax Its an urban legend. The best length to use is one that reaches from the radio to the antenna. There are some exceptions if you are counting on the feedline to act as an impedance transformer..
WRONG! Ignoring cable losses, the VSWR is independent the length of the cable. What changes with length are the complex components of the impedance, while the absolute value (VSWR) remains constant.
TT: I found this URL (among others) with a Yahoo search for Smith Chart: http://www.web-ee.com/primers/files/SmithCharts/smith_charts.htm . Look at Fig. 8 to see an example of a constant VSWR circle
I haven't run any experiments, but I'll concede that some methods of measuring VSWR are less than perfect, in which case that is a definite possibility. Bob, N7XY -- Bob Nielsen, N7XY n7xy (at) n7xy.
ANY feedline repeats the Load Z (Impedance) every 1/2wavelength..remember that must take into account the velocity factor of the feedline...for normal coax its about 66% so 0.66 x 468/freq in MHZ = l
Ok...what I should have said was "apparent" SWR changes according to the metering..... If the cable length changes and the antenna is NOT a resistive only component, the coax will cause an apparent c
factor is wl NOT wrong. The swr in the coax doesn't change with length, except for small losses that always reduce it. The problem is cheap meters or installations that have rf on the outside of the
as its 1/2 wl 50ohm +0j antenna is NOT WRONG SWR Sorry Chris, but that's neither correct or helpful. SWR is constant except for a small change from line loss, and reactance doesn't "fool" a properly
according to the resistive only reactance, thus That's incorrect also unless the meter is improperly calibrated. If the meter is that bad, you probably should not be using it. 73 Tom _______________
The sweet length is infinity or zero. --Original Message-- From: towertalk-bounces@contesting.com [mailto:towertalk-bounces@contesting.com]On Behalf Of Tom Rauch Sent: Monday, October 11, 2004 10:22
Thanks Tom, I like that plain language description with the examples. I've known it works that way for years, but I never bothered to put any figures with it. Roger (K8RI) Tom Rauch wrote: <snip> SWR
All true ... however, if one is using 75 Ohm cable in a 50 Ohm system (e.g., CATV hardline) then the multiple of 1/2 wavelength shows a 1:1 SWR on a 50 Ohm bridge - exactly what is desired. The 75 O