Mini-circuits hybrid as a cheap RLB with DSA815-TG VSWR option?

[Rory]

First day out of the box, and learning how to use the Rigol DSA815-TG, trying a few things.   
 
While playing with a Mini-Circuits 3dB hybrid splitter, the kind used to connect two receivers to one antenna, checking loss and port-to-port isolation, it occurred to me (when I terminated the common input with 50 ohms and got over 35dB isolation between the two ports) that a hybrid can be used as a return loss bridge, just like the Rigol VB1020. 

So, I got the chance to try the VSWR option before it runs out of time and before the VB1020 I ordered last week (on 2-3 week back order from Tequipment) arrives. To see how accurate it could be, I tried paralleling a couple of 50 ohm terminators on a BNC tee, and the VSWR software reported 2.09:1 VSWR. A 75 ohm load reported 1.59:1 VSWR.  Hooked it up to an 8 element 8-30MHz log periodic antenna and it looked pretty close to the VSWR curves in the manual.

I took a random piece of RG-58 coax about 17" long and connected it to the tee in parallel with 50 ohms and looked at the 1/4 and half-wave resonant points by shorting the far end, the frequency response was pretty close to what it physically measured to be. Got return loss measurements of greater than 45dB at the parallel resonant points.

A $50 hybrid works almost as well as a $500 return loss bridge. What do you think of that?

[nctnico]

Mini-circuits also has directional couplers which are very affordable.

[Neganur]

Couple of reflection bridge projects:

A Baluns and Beads Reflection Bridge, 50 KHz to 1.5 GHz
Three-Bead-Balun Reflection Bridge, 250 KHz to 1.5 GHz
Active Bridge 10 kHz (outstanding up to 30 MHz)  good to ca 300 MHz

edit: URLs corrected

[olsenn]

Couple of reflection bridge projects:

I'm of the belief that test equipment should be purchased (from a reputable seller) and never built, unless you already have a professional equivalent to test/calibrate it against.

[Neganur]

uh, your spectrum analyzer does the calibration / normalization...
what are you using that instrument for again?