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Re: LF: Dummy-Load on LW

To: [email protected]
Subject: Re: LF: Dummy-Load on LW
From: "Hans-Joachim Brandt" <[email protected]>
Date: 11 Nov 2003 23:45 GMT
Reply-to: [email protected]
Sender: <[email protected]>
Dear all,

around 1959, when I joined Rohde&Schwarz in Munich, 60 ohms has been the standard cable impedance in Germany for all broadcast and television transmitters in the fifties and for other commercial RF equipment. Cage and other transmitting antennas were also designed for 60 ohms. I have also built my first amateur radio dummy load for 60 ohms. I do not know exactly the reason for 60 ohms, somebody has told me that this impedance has been a compromise between 50 ohms and 75 ohms, (perhaps following the idea that 75 ohms allows the production of cables with minimum losses whilst 50 ohms would allow to send higher power through a coaxial cable). On the other hand 75 ohms has been used and is still in use for video equipment in TV transmitters and studio equipment; higher video voltages needed for TV modulator stages have often been terminated with 150 ohms to save power, generating double the voltage with the same current.
But in the sixties a change to 50 ohms impedance for RF equipment became 
standard also in Germany, there was a need to match to the international market 
standards.

Concerning receiving antennas, the first VHF FM and TV antennas in the early 
fifties in Germany were folded dipoles with a 300 ohms symmetrical cable feed. 
But soon the folded dipole with reflector (and some directors) became popular, 
using 240 ohms symmetrical cable for about two decades (thus confirming Wolf's 
[DL4YHF] contribution), TV distribution systems in houses used 60 ohms with a 
4:1 balun to connect the antennas (for the TV receivers with 240 ohms 
symmetrical input another 1:4 balun was needed to connect them to the 60 ohms 
house system). Later on TV receivers and TV receiving antennas were changed to 
75 Ohms coaxial, CATV systems used 75 ohms from the beginning, the CATV start 
in Germany has been rather late, about 1984.

By the way, a lot of russian Surplus HF equipment which became available in Germany after the breakdown of the iron curtain, even automatic antenna tuners, were designed for 75 ohms impedance. 73 Ha-Jo, DJ1ZB
"Walter Blanchard" <[email protected]> schrieb:
DK8ND's email raises an interesting point. Can any of our German friends tell 
me why an impedance of 60 ohms was popular in Germany for some time but not 
anywhere else?

Walter G3JKV.




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