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Wednesday, 4 September 2013

Where does it lead? A bridge to nowhere!


Following my initial attempts at making a Return Loss Bridge (RLB) last time:

I've taken some advice; the most common suggestion was that my construction was too slap dash! Could do better and must try harder - reminds me of my school reports!

Here's a remade version of the RLB in quite high-res:

Now this is much neater, however, the basic problem is going to be (so I'm being told) that the wires and the box create a feedline - my construction makes that feedline a load of pants....

Now, I then tried to make an alternative RLB using more normal type of construction techniques:

And that has a slightly worse directivity reading to the one in the box!

So, then I followed another suggestion and constructed an RLB using SMD resistors and this one looks like this:

The observant amongst you will see that the resistors are in fact 52R3 (thats 52 point 3 ohms); these were left over from the power meter project back here:

This newly made RLB when boxed measures at 26.3 dB directivity - so this is an improvement and much closer to my target value of 30 dB.

I then decided to rummage further and I found some 100R SMD resistors, and made a third (forth?) RLB using 2 100R resistors in parallel for each 50R theoretical component:

Now this version of the RLB measures as 23dB directivity - so just the same as the first one! Bah - I'll stick with the version containing the 52R3 components for now....

New ham cat's not been helping much:

Fun, egh?

1 comment:

  1. suggest reference article on QEX by W7ZOI about AD8307 power meter, which mentioned that: insert band pass filter to the test circuits to eliminate EMI things, witch improve it dramatically. worthy to try!