Most of the newer books on radio electronics list a 50ohm load as the standard and correct type of cable to use for a line. However I know the basic dipole antenna is around 72ohms impedence correct? So wouldn't it be more sane to use a 75ohm feed line and tune the transmitter to this impedence?
Here's the thing... I could use 50ohm coax no prob, but hey with people tossing out CATV coax at 75ohm in the trash I wonder if it could be used just as easily for short runs and low powered HF transmitters. It should be very cost effective as long as the transmitter can handle or be tuned to the impedence correct?
I used every last bit of my RG8 for my FM VHF transmitter. I am still interested in building a SW transmitter and getting on 6925 but the issue is lack of money and tons of 75ohm cable laying around. I am talking over 100 feet of cable I got from a friend that is either going to get trashed or used. So couldn't I build a TX to use a 75ohm load instead of the usual 50ohm load and not have major issues?
In fact looking in old ARRL ham books from the 60s it seems that 75ohm coax was common to use back then for HF. So why does everyone today think that 50ohm have to be the standard? Why would CATV cable be a bad idea, or maybe I am onto something? Maybe I don't know what I am talking about but a dipole is closer to 75ohms impedence then 52ohms, so tell me why this shouldn't work just fine with a correctly tuned TX?
Just a random idea. I know CATV closed circuit television cable is being tossed to the trash left and right so why not use it for radio feed line?
Yes, a dipole over perfect ground is 72 ohms. A dipole over imperfect ground will be anything but. Average ground will give it close to a 50 ohm match, as will bringing the dipole legs in together in a horizontal "V" shape will also lower the impedance.
If you aren't using a balun or choke of some sort, don't worry because your line is radiating as much as your antenna anyway
Here's a tip - if you have a perfect 1:1 match at your antenna (use a SWR meter right at the antenna - no longer than 10cm patch cable) and you use a transmission line length of 1/2 wavelength (or multiple of), the transmission line will simply reflect that impedance. You could use 93 ohm computer cable and still get 1:1 SWR under those circumstances
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