Towertalk
[Top] [All Lists]

## [Towertalk] Newbie Question

 To: [Towertalk] Newbie Question n4zr@contesting.com (Pete Smith) Fri, 19 Jul 2002 08:02:44 -0400
 ```At 11:16 AM 7/18/02 -0700, Troy Flowers wrote: >Ok I'm a relative newbie so I'll ask also. I ran 1/2" Heliax up my tower >for HF. But 75 ohm CATV line can be used also? Being a cheapskate I'd much >rather spend nothing so explain. My radio/amp wants 50 ohm but the feed >line is 75 ohm and the antenna is some range also based upon freq. Are you >supposed to do a complex analysis of this or is it safe to take a simplistic >view of it (in terms of station performance)? Well, here's what I did. RG-213 from the antennas to the antenna switch. At the antenna switch (at the bottom of the tower) I switched to 75-ohm CATV, using a multiple of a half wavelength at the lowest frequency of interest, measured at the highest frequency of interest, using an antenna analyzer. A pigtail of RG-11 at the tower bottom was used to make trimming easier. At the house end, where the prescribed length of CATV hardline ended, I connected 50-ohm cable to go the rest of the way into the shack. I was warned that the 1/2-wavelength rule is good theory but wouldn't hold up well at higher frequencies, particularly 10 meters. It is true that there are all sorts of minor impedance transformations going on along the transmission line, which produce some odd results (for example the 20m resonance moves up 200 kHz as measured in the shack compared to at the bottom of the tower), the bottom line(s) are just fine, as follows: 10m 28.0 - 1.6, 28.8 - 1.5 15m 21.0 - 1.0 21.4 - 1.5 20m 14.0 - 1.4 14.3 - 1.2 40m 7.070 - 1.0, swr bandwidth (< 2:1) 150 kHz 80m 3.520 - 1.0, swr bandwidth 70 kHz 160m 1.830 - 1.0 Feedline loss measures right on the predicted value, as well as I can tell with my ham-level instrumentation. I don't think I was just lucky, but maybe I was. Comments? 73, Pete N4ZR Check out the World HF Contest Station Database at www.pvrc.org ```
 Current Thread [Towertalk] Newbie Question, Troy Thoele [Towertalk] Newbie Question, ac7nj@bentonrea.com [Towertalk] Newbie Question, Red [Towertalk] Newbie Question, Pete Smith [Towertalk] Newbie Question, Troy Flowers [Towertalk] Newbie Question, Pete Smith <= [Towertalk] Newbie Question, Bill Hider (N3RR) Fw: [Towertalk] Newbie Question, NN7K@reno.rmci.net Fw: [Towertalk] Newbie Question, Tom Rauch Fw: [Towertalk] Newbie Question, NN7K@reno.rmci.net Fw: [Towertalk] Newbie Question, Tom Rauch Fw: [Towertalk] Newbie Question, Chris BONDE [Towertalk] Newbie Question, n4kg@juno.com [Towertalk] HF antennas, David [Towertalk] HF antennas, Frank W8HO Fw: [Towertalk] Newbie Question, EUGENE SMAR