[TowerTalk] Fwd: RG-149: 50 ohm/70 ohm - does it matter?

[Dan Schaaf]

1:2 or 2:1 ???

SWR with 50 ohm load and 75 ohm feeder the SWR is likely to be 75/50 = 1.5:1 
AT RESONANCE point of the antenna. Once you deviate from the resonant point, 
it is no longer a 50 ohm resistive load. It will be resistive +/- reactive. 
And the resistive part will not likely be 50 ohms.

Now, you can use a tuner in the shack to BS the amp into thinking there is 
50 ohms out there. Or you can put a remote auto tuner at the antenna and be 
sure of a good, matched load.



Best Regards
Dan Schaaf
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60 Meters www.60metersonline.net
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-----Original Message----- 
From: Hans Hammarquist
Sent: Friday, December 13, 2013 3:03 PM
To: towertalk at contesting.com
Subject: [TowerTalk] Fwd: RG-149: 50 ohm/70 ohm - does it matter?

If you have a true 50 ohm load and a 75 ohm feeder you may end up with an 
SWR of 1:2, which many SS amps can't handle. That's the worst condition.


I am using 75 ohms myself and rarely run into problems. (That's what the 
tuners are for.) An "old" tube amp with a pi-filter can tolerate an SWR of 
1:2 without problems.


If you have any problems, just call in the North Seeking Plast Owl". :) I do 
that all the time.


Hans - N2JFS



-----Original Message-----
From: kr2q <kr2q at optimum.net>
To: towertalk <towertalk at contesting.com>
Cc: towertalk <towertalk at contesting.com>
Sent: Fri, Dec 13, 2013 7:52 am
Subject: [TowerTalk] RG-149: 50 ohm/70 ohm - does it matter?


Hi....

I work in hospital administration.  My ugrad degree is in Biology and my 
masters
degree is in healthcare administration.  In other words, I'm no engineer.

However, I took a look at Mikes home page and it seems like he has a 
"simple"
antenna setup (ie, no stacks = no phasing concerns).

So what's the diff if it's 50/52/70/75 ohm feedline?  The mismatch (if not 
50)
will be "nothing" and therefore the extra loss will be "nothing." 
Transmission
line is always transmission line.  As long as the line itself is not 
"lossy,"
does it matter?

Looking for sage advice for those with degrees or prowess in this area.

de Doug KR2Q
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