[Heathkit] IG-4505

[David C. Hallam]

Ok, I have to replace the mickey mouse arrangement Heathkit used to 
terminate the line in a new line..

David
Kw4DH

On 7/1/2014 5:06 PM, k2cby wrote:
> The RG-58 50-Ohm coax leading from the IG-4505 is a transmission line. You
> want to terminate any transmission line in its characteristic impedance. As
> an oscilloscope calibrator, you will be connecting the IG-4505 to the input
> of the scope's vertical amplifier, which has a characteristic impedance of
> (typically) 10 Meg. with a parallel capacitance of 10 pF or so. If you don't
> include a 51 (or so) Ohm shunt resistor at the far end of the coax, the
> transmission line is going to see what amounts to an open circuit. This
> means that the voltage at the end of the line is going to depend on the
> frequency and the length of the line. This is the last thing you want in a
> scope calibrator! If, on the other hand, the transmission line is terminated
> in its characteristic impedance, the length of the line becomes irrelevant,
> and the voltage at the end of the line will equal the source voltage,
> regardless of frequency (and regardless of the length of the coax). The only
> reason to leave the coax unterminated would be if you were to connect it to
> a low-impedance load - ideally 50 Ohms. If, for example, the load impedance
> were 200 Ohms, you would want to shunt it with 66.6 Ohms at the load end so
> the coax transmission line would "see" a 50-Ohm load.
>
>   
>
> Miles B. Anderson, K2CBY
> 16 Round Pond Lane
> Sag Harbor, NY 11963
> Tel.: (631) 725-4400
>
> Fax.: (631) 725-2223
> e-mail: k2cby at optonline.net
>
>   
>
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