Wednesday, January 17, 2007

Testing filters

I arrived home late last night after the local radio club meeting and found that the band-pass filters had come in the mail. Hooray! It was too late to mess with them much, but I did dig them out of the box just to make sure they had all arrived safely. Each one was there: the big box with the switch for all the contest bands, and the three individual filters for 30m, 17m, and 12m.
As I was looking them over, Sandy said, "They look nice. How do you know they work?"
Good question! I own an Elecraft Wideband Noise Generator (one of Elecraft's
Mini Modules) which puts out a nice signal across all bands. All I needed to do was hook a radio up to the filters, supply a signal from the noise generator, and see if the filters kept that signal to only the band selected. Below is a shot of the test setup:

Connecting the big filter box was easy and it worked flawlessly. I could switch bands on the radio and then use the big switch on the front of the unit to select the corresponding band, hearing a strong signal only when the proper pass-band was selected.
Next, I tried the individual filters. The 30m filter worked fine. I could tune to 40m and 20m and hear little more than a slight hiss (down from the S8 signal on 30m). The other two filters, however, didn't perform as well. The 17m filter let through nearly all of the signal to the radio listening on 15m and above. Similarly, the 12m filter didn't seem as effective as the 10m filter in the big box. Perhaps I did something wrong, or perhaps my experiment is faulty. Or, perhaps the filters don't work. I don't know. Either way, I'll call Industrial Communication Engineers, Ltd. in the morning to get some help. Right now, though, it seems like the 17m and 12m filters are going back to Indiana, and not going to Montserrat.
In other news, I had a good day at work today, figuring out some stuff that had been vexing me. That's the good news. The bad news is I'm too exhausted to work on the log processing software tonight (something I had hoped to do). Tomorrow is my BSO concert and this weekend I've got a VE session and contest on Saturday. There is not a lot of time to get things done! The countdown continues.
Just 11 days to go...


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