007: Return loss bridge for HF and VHF (3.5-144MHz)

 出来上がったら先ずDUTポートをオープンにしてスペアナをノーマライズし、40dB以上のリターンロスを持つ50Ω終端器(HP908A、HP8491A (40dB)ATTなど)をDUTポートに装着して損失量を確認する。SWRブリッジの良し悪しは一つにはこの時のロスの大きさで決まるが、3.5MHzから50MHzまでは35dB以上あったから十分に高精度である。144MHzでも30dBまでのリターンロス(SWR1.06)なら測れるからブリッジのバランスは相当良いレベルにある。ミニサーキットの方結の方向性実測データと比べるとやや落ちるが、それでも十分実用域にあると言える。なおトップバンドの1.9MHzを測る場合は、ソータバランの巻き数を1~2t増やす必要がある。製作は2011年。

Directional coupler for HF-VHF and UHF had it, but I came to want the return-loss bridge which can be used easily on HF and 50MHz. To suppress ill-balance of resistance almost often to balance a bridge, first, desired. Resistor of 50 Ω (1%) was sorted out with the fluke which JA0BZC possesses and 49.956 Ω, 49.957 Ω and 49.953 Ω were chosen. A mutual error is less than 0.01 %, and an error with 50 Ω is less than 0.1 %. And the sota balun put in a detector port used something of a bifilar transformer of 6 turns on FB801.

If making is finished, the DUT port is made open and the spectrum analyzer should be normalized, and then it's loaded on termination resistor like HP908A with more than 40 dB of return-loss and the actual loss amount of the bridge is confirmed. The good or bad in a SWR bridge is decided with the value of this loss. Because there was more than 35 dB of loss from 3.5MHz to 50MHz, it's highly precise sufficiently. As you can measure return-loss to 30dB (SWR1.06) even on 144MHz, the balance in a bridge seemed to be quite good. It's inferior little compared with directivity of directional coupler of a mini circuit co., but it can be said still that it's in an enough practical area. It's necessary to increase the wire turns of a sota balun by 1-2t when 1.9MHz of top band is measured. Making was in 2011.




<<PREV _____ NEXT>>