Topband: 0-Degree Hybrids - resistor tolerance

K9AY k9ay at
Tue Nov 29 13:26:29 PST 2011


The short answer -- You'll rarely experience any problems if the resistor 
value is not optimum.

The most important function of the resistor is to limit the loss to 6 dB and 
limit the maximum VSWR if one of the two split ports is open- or 
short-circuit. For this task, precision is not an issue.

The other function is to achieve optimum balance and isolation between the 
two split ports. With all ports terminated in their characteristic 
impedances, you'll get perhaps 50 dB isolation with a 5% tolerance resistor 
(assuming proper winding technique). In an RX antenna splitter, high 
isolation is most important if two radios are sharing the same antenna, 
e.g., SO2R on 160 and 80.

73, Gary

> Gents,
> Assuming 75-ohm inputs, what's the tolerance
> of the 150-ohm "balancing" resistor used on a
> 0-degree hybrid combiner such as the one shown
> in ON4UN's LBDXing book, Fifth edition,
> page 7-23, figure 7-24?
> Thanks,
> Charlie, N0TT

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