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

[kr2q at optimum.net]

Interesting comments.

Contributor A says the SWR will be 2:1 while Dan says 1.5:1.

I agree with Dan.

Contributor B says, "What if the impedance at the antenna is only 33 ohms....
and you have a quarter wavelength of 75 coax."  Then...Oh horrors.

Well, don't look now, but if the feedpoint is 33 and the coax is 50, I calculate that to be the
same VSWR as if the feedpoint were 50 and the coax were 75.  No?  Nobody worries about 
the former, do they?

How likely is it to get your coax to be in odd multiples of quarter lambda?  I am guessing, "Not too likely."  
And if it is, well, just add some more coax (if you care about SWR).  Would that not work?

>From what I can find, a mismatch (SWR) is not much of a factor in getting your signal to the antenna.
See http://www.skyworksinc.com/uploads/documents/vswrreturn.pdf

I don't know if this is accurate or not (I'm no engineer), but I have found this in several
places after doing a Google on SWR and LOSS.  There is even a calculator out there, that
seems to come up with the same results.  http://www.csgnetwork.com/vswrlosscalc.html

So from what I see 50 to 75 (or 33 to 50) is 1.5:1 with a loss of 0.177 db.  Really?  Really!

>From what the others have said, it might be possible for the 50:75 "mismatch" to matter to you.

Personally, I really like the replies from guys who actually use 75 ohm coax and have seen "no issue."

I asked for expert input and I do thank those that responded.

Back to running my hospital.  :-)

de Doug KR2Q