Originally Posted by bob85
if you used odd multiple electrical 1/4waves of 75ohm coax terminated with 50ohm pure resistance input impedance seen looking into each line becomes
Zin = Zo^2
the characteristic impedance of the line (75ohm) squared, divided by (50ohm X=0) load
if the loads are not 50ohm X=0 the phase relationship between current and voltage along the 75ohm lines shifts and all bets are off.
Good morning Bob. I use this test formula that I've used for years, and it is base on the feed point impedance for a single installed radiator. Of course both antennas should be the same of very similar for this to prove out and work right the way I understand it.
I don't know if it's good or not, and I don't know the source. Could be my old antenna Mentor buddy gave it to me when we were building co-phase harnesses years ago.
Z = SQR (load impedance ohm x transformer line impedance)
Example of 37 ohm 102" antennas using RG6, 75 ohm, or RG71U, 93 ohm.
37x75=2775 SQR = 52.7 ohms results at the TX
end of harness. So, if using a 50 ohm feed line in system, then further transformation can occur, and the following is supposed to calculate the new impedance value using the results from the first calculation.
52.7x50=2635 SQR = 51.3 ohms.
Then we trimmed the pig tail ends of our harness to the lowest SWR and I figured, if everything was good, maybe the Z value for the TX
end of the match should be close to 51.3 ohms.
I never questioned the idea, and I really don't understand all the nuances of this business. So, if you find this in error or totally off base...then let me know.
Do you see anything wrong with the images I posted above? Is that pretty much what I should be seeing with such a setup?