Topband: Hybrid Coupler

[NR1DX]

Earl

I have not built the specific 90 degree hybrid in ON4UN's book but I have
built several splitters and phase shift networks using discreet components
with excellent results. 

The thing to remember is that are very high currents involved. As I recall
If you are running full legal power the currents can be on the order of 6.5
amps while voltages are less than 500 Volts. This is true as long as the
SWR's are not very high, High VSWR can lead very quickly to higher voltages. 
Depending on what the values involved are, I typically use 2 or 3 of the old 
style large brown transmitting mica caps (to handle the current) and a small
air variable in parallel to tweak in the final value of the C. These are the 
square mud brown jobs about 1.25" x 1.25" typically rated at 5KV.  I usually 
prowl the hamfests looking for them and over the years built up a stock pile
in the junk box. The smaller 5kv disc caps will not handle the current and
self distruct rather spectacularly. Air variables of very modest size and 
spacing also work well. 

For those who are interested (email me direct) I have rather simple design
info for designing phase shift networks for any given phase shift, line 
impedance and frequency. These can be designed for positive and negative phase 
shifts and take the form of simple PI or T networks. Be patient I will have to 
dig the info out of my archives.

Dave 
NR1DX


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