The Op asked a simple question: "... would I notice any serious
difference in the aerial matching etc, between the use of 50 ohm and 75
ohm coax at HF"
I gave him a factual answer: if he has an antenna providing a close
match to 50 Ohms, any length of 75 Ohm line between 0.15 wavelength and
0.35 wavelength long (or corresponding odd multiples) will result in a
SWR(50) greater than 2:1 at the radio. That covers one third of all
possible line lengths - hardly an isolated "worst case".
Of course, those lengths are readily easy to avoid on a monoband
antenna; not so easy on a 5-band 20m thru 10m beam with a single feedline!
73,
Steve G3TXQ
On 19/02/2013 19:16, Jim Brown wrote:
On 2/19/2013 10:54 AM, Steve Hunt wrote:
The SWR on the 75 Ohm line will be 1.5:1, but if the line is a
quarter-wave or odd multiple long, the 50 Ohm load impedance is
transformed to 75*1.5 or 112.5 Ohms - that's an SWR(50) of 2.25:1.
In fact any line length between 0.15 wavelength and 0.35 wavelength
will transform the load impedance to produce an SWR(50) greater than
2:1.
My, my -- some of us do work pretty hard to find worst case scenarios.
73, Jim K9YC
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|