[NJARC] Interesting question from the AWA Reflector

[John Ruccolo]

Hi Folks,

Any ideas?

Regards,

John -- Kilo Charlie Two Uniform Alpha Kilo


From: va3awa <VA3AWA at sympatico.ca>
Subject: [AWA] Anyone have the answer for my UK friend?
To: antiquewirelessassociation at yahoogroups.com
Date: Saturday, October 11, 2008, 8:58 AM

Can somebody explain to me why if a diople impedance is 75 ohms in free 
space. 
And eary manufactures like KW and Vangaurd, Pye etc and also Marconi 
with their lab test equipment all used 75 ohms as the standard. 
When and Why did later manufactures (Japanise) settle for 50 Ohms as 
stadard. It is impossible to match 75 ohms to 50 ohms without using a 
matching device. 
I have been running some simulated test on the computer for various 
wire antennas and without exception all were heigher than 50 Ohms. 
Mostly between 65 and 80 ohms. 
Which of course means than 75 ohm coax should be used and not 50 ohm, 
leaving the ATU to match the 75 ohm to the TX output of 50 ohms. 

(I believe that Walt's 30 metre antenna uses 75 ohms ?). 

Was it because they can not design Transistor transmitter to hadle 75 
ohms, maybe because of collector secondary breakdown ? 

There must be a reason, any ideas ?