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|Return Loss Bridge
of the tasks that I wanted to perform on the newly designed 2N2/20 was to
characterize the input impedance of the receive strip, and the output impedance
of the transmit strip. This Return Loss Bridge was built for that purpose.
The design comes directly out of "Experimental Methods in RF Design" by Wes
Hayward, W7ZOI et. al., figure 7.41 on page 7.23. It works exactly as described.
Here is the schematic of the bridge. The resistors used are 51 Ohm, 1/4 watt carbon film units. 49.9 Ohm metal film resistors probably would have been a better choice, but those were not in the parts bins, and I was in a hurry!
This project again used Manhattan-style construction. The 3 side panels with BNC connectors were built first. They were then solderd to the bottom panel. Once all of the other parts were soldered in place, the unit could be tested.
With testing complete, the remaining top panel could be soldered into place, along with adding some simple labels. To close the remaining side, a cover was fabricated from tin plated hobby steel sheet, and also tack soldered into place.
A detail picture of the tin plated steel cover. Just the corners were soldered so that it could be removed easily if internal repairs were needed.
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