---In BITX20@..., <marktbaldridge@...> wrote :
Okay. That is helpful information.
A couple questions:?
1: Can I assume that I will for the most part tune the inductors together? To make the correct bandpass, they must all be the same value, right?
[john]? More or less. Please note that the 82 pF. caps in the original schematic are wrong. Most people get by with about 33-39 pF. Those and 4-5 uH. seems to tune 20m well. Note that the tuning for the middle transformer is a bit different than for the outer ones. This is normal for a LC filter.
2: Can I attach a 50 ohm spectrum analyzer as I showed in the link? Or will the impedance mismatch cause the filter to not function properly?
[john]? If it does, a simple 4:1 transformer. or even an inline resistor at each end, will probably straighten it out. Experiment. I assume you are disconnecting the BPF temporarily from the circuit anyway. Include an attenuator to control your input signal. Tune for the LEAST coherent signal level.
What I did was build a new BPF based on the one in the BITX20A. It works very well and is a bit easier to adjust. You can also build a new one if you have 3 or 4 FM IF transformers handy. YRMV. Hi.
