I’ve been playing with the op-amp circuits some more. While the Radio Shack 741 chip more or less worked as advertised, and I was able to amplify audio out of my iPhone (although slightly distorted, for whatever reason), the NE5532 op-amp that came with my SW-40 kit was not playing along at all. I looked at the spec sheets and checked and re-checked my breadboard connections but I only got complete rubbish from the output of that chip (using the same circuit as with the 741, for either 20 dB gain or unity gain). This chip seemed to “sort of” work while in the kit board and connected to the soldered-in supporting cast of resistors and capacitors. But it honestly didn’t sound nearly as good as the 741 did, and the amplification was minimal (and came with bad AC hum it picked up from my supply).
So, I concluded that this chip may be “fried”. And I ordered some more through Mouser. If it turns out that somehow the chip is fine, it won’t hurt to have a few spares, since I’m fully capable of destroying them later on, especially through wear and tear of possible field use (or static carpets someplace).
I decided to move on to the good ‘ole NE602 mixer and LO portion, a configuration I’m much more familiar with. There’s also the IF crystal filter, which I will put on to the VNA and grab a snapshot of it’s s-parameters (just as I did with my Bitx-20 last year). I plan to model the crystals and plot with Puff again, as I think this is a good exercise for me going forward with other rig designs. This time I’d also like to try and use some pre-packaged filter analysis software courtesy of ARRL. I have the disks and I might as well give them a try too.
My goal is to finish this project by the end of June. There may still be some packaging issues dribbling into July but those shouldn’t be too awful. The SW20 was a robust little kit and I’m expecting this one to fly well right off the bat too.
In other news, there was a nice little opening on 6m for part of the ARRL contest that was going on this weekend. Sunday night I got in on some rare 6m CW contacts up and down the New England coast and into Nova Scotia. I also snagged a station down in Bermuda and a few close-in grids near Roanoke. It was fun to see the band come alive. I heard some frustrated commentary from some saying that the band had openings but nobody was on, and they were getting tired of just sitting there calling CQ! I guess even pressing the pre-programmed “CQ” button on the modern rigs gets tiresome after awhile.
Some minor news in the shack involved making up some jumper cables for the bench. I now have a high current Astron 12V supply at the ready along with two analog multimeters (one just a voltmeter) and one digital multimeter. This is the nicest bench I’ve ever had, by far. Working on projects is much more efficient and fun now.
Coming up, I plan on doing some camping, and, hopefully, some operating from my old SW-20 kit rig. I’d bring the Bitx-20 but with compromised antennas (and probably shaky propagation at night) I just don’t think this is the right time. Ideally I’d run the SW-40, but, well, it’s still on the bench!