Towertalk
[Top] [All Lists]

## [TowerTalk] Re: Force12

 To: [TowerTalk] Re: Force12 Mike"
 ```Hey Tom, See my comments below: ----- Original Message ----- From: To: ; Sent: Thursday, October 11, 2001 8:56 AM Subject: Re: [TowerTalk] Re: Force12 > On Thu, 11 Oct 2001 "Mike" writes: > > BIG SNIP > > > > > Yes, of course, but switch over to a 50 ohm reference and then > > mover your 50 ohm VSWR meter along the length of the line. > > At 1/4 wavelength from the 35 ohm load, the 50 ohm VSWR will > > be 160/50 = 3.2:1. Move another 1/4 wavelength (total 1/2 > > wavelength) from the load and the 50 ohm VSWR will be 50/35 = > > 1:43:1 VSWR. > > > > HUH? Where did you get 160 Ohms? > > The formula for a 1/4 WL transmissionline transformer is > > Zin X Zout = Zo^2 (Zo squared) > > Zout = Zo^2 / Zin = 50^2 / 35 = 2500 / 35 = 71.4 ohms > at 1/4 WL from the 35 ohm load for a 50 ohm cable. > > SWR = 71.4 / 50 = 1.43, same as at the load, ignoring losses. > > OH wait, I see, you are assuming a 75 ohm coax. > > Then the IMPEDANCE 1/4 WL from the 35 ohm load is > 160 ohms but the SWR = 160 /75 = 2.13, same as at > the load (75 / 35 = 2.14). > > SWR is a function of the LOAD impedance AND the LINE > impedance. You can't just arbitrarily change the reference > impedance unless you also change the line impedance. > > IF you placed a 50 ohm line after 1/4 WL of 75 ohm line > with a 35 ohm load, THEN the SWR in the 50 ohm line > would be 160 / 50 = 3.2 as you stated, but the SWR in > the 75 ohm line is still only 2.14 > > IF you place a 50 ohm line after 1WL of 75 ohm coax > the SWR = 50 / 35 = 1.4 in the 50 ohm line and is still > 2.14 in the 75 ohm line. > > Using a REFERENCE impedance that is different from > the LINE impedance is MEANINGLESS. Not if I am using the 75 ohm coax as a transformer in a 50 ohm system. All my meters are calibrated against Zo = 50 ohms, yet I have a pile of 75 ohm coax behind my garage. When I used that 75 ohm coax to feed my tribander, I still used the 50 ohm VSWR meter in the shack to determine that match to my equipment. In that case, the length of the line made a big difference (it was cut for a integer multiple of lambda/2). That was my point. 73 de Mike, W4EF.......... > > Tom N4KG > > > ________________________________________________________________ > GET INTERNET ACCESS FROM JUNO! > Juno offers FREE or PREMIUM Internet access for less! > Join Juno today! For your FREE software, visit: > http://dl.www.juno.com/get/web/. List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems, Trylon Titan towers, coax, hardline and more. Also check out our self supporting towers up to 100 feet for under \$1500!! http://www.anwireless.com ----- FAQ on WWW: http://www.contesting.com/FAQ/towertalk Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com ```
 Current Thread [TowerTalk] Re: Force12, (continued) [TowerTalk] Re: Force12, Wes Attaway [TowerTalk] Re: Force12,