[Elecraft] 75ohm Impedance question K3S and Antenna side.

[Fred Jensen]

Ummm ... not quite.  A "perfect" half-wave transmission line will 
reproduce the impedance of the load [which has been alleged to be 35 
ohms but this is an all-band antenna so that may vary some] at the 
source [TX] end.  The real line will come close, its loss will have a 
small effect.  His ATU will see whatever the feedpoint complex impedance 
is, not necessarily 50 ohms.

I'd suggest a good common-mode choke at the feedpoint too which might 
mean a short pigtail of RG-8 ... not sure if there are ferrite toroids 
that will fit the CATV hardline.  Jim, K9YC, has probably the best 
source of data on chokes, ferrites, et al at k9yc.com/Publish.htm

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 3/31/2020 8:52 PM, John K9UWA wrote:
> Cut the hardline to multiples of 1/2 wavelength and the swr will be 1 to 1 on both
> ends. 50 in 50 out. In this case the OP needs around 200 feet. Once your get the
> velocity factor for the 1/2" hardline... that is ballpark 80 to 83%.  for 3.540 mhz is
> 265 feet x .8 = 212 feet.   If you don't have a piece of test gear to get it cut
> correctly then put a 50 ohm dummy load at the far end keep cutting until your
> wattmeter says 1 to 1 swr. 1/2 wave multiples will hit most of the ham bands. A
> little high in the 30m band. Close enough.
> 73
> John k9uwa
>