Sure, this receiver is not "state of the art." But that's the whole point. I wanted to finish the receiver project that I couldn't finish back in 1976.
I tried to stick as close as possible to the original design and parts. NORCAL came up with an updated schematic in 1998 with parts that are more readily available. But Designer Jay Rusgrove was shooting for something that could be built with all the parts coming from Radio Shack. I think that is probably one of the factors that attracted me to the project way back when. That's why Jay went with varactor tuning (no hard-to-get variable caps!). And that's why he used coils that were wound on Radio Shack 10uH RF chokes (no need for hard-to-find toroidal cores). In this sense there is some common ground between the BITX rigs and the Herring Aid 5.
I stuck with the RF-choke as a coil idea for the VFO, but went with the NORCAL-prescribed toroids for the front end and mixer coils. (I may go back and try to use chokes in these circuits, but I'm not sure my junk-box will yield the kind of RF chokes that Jay used).
I wish I had known a few things when I was building this back in 1976: More knowledge about how to wind the coils would have been a big help. I wish I had realized that I could use a SW receiver to get the oscillator on the right frequency. I guess this was in the days before Ugly and Manhattan building techniques, but it would have been nice to know that there was no need to actually etch a board for this project (I did!).
The coils really are a bit tricky. Jay didn't use any trimmer caps, so I guess you had to just hope that the front end coil and cap resonated somewhere near 40 meters. As for tuning the oscillator, Jay recommended scrunching and un-scrunching the turns on the RF choke. Yikes! Give me some trimmer caps!
I also found that you have to watch the level of the RF going from the oscillator to the mixer. Too much, and the receiver is deaf. Too little, same result. You need to experiment a bit with the number of turns on the pick-up coil from the oscillator.
The warnings about the pitfalls of that single BJT mixer were right on the mark: Lots of AM SW breakthrough. But I kind of like the background music. Strong RFI from local FM broadcast stations was another story (WMZQ is a country music station!). I reached into my junkbox and found a low-pass filter from a Heathkit DX-60. I just put that between the antenna and the receiver and the country music was GONE!
I really love this little receiver. I have it playing 40 meter CW as I type. It sounds great. I feel the urge to built a Tuna Tin 2 and put both of them on 40.
In the original Tuna Tin 2 article, Doug DeMaw notes that Jay Rusgrove was thinking of doing a companion receiver and says that he was thinking of calling it the "Clam Can 5" ! There were jokes about receivers for hams with "tin ears" and about there being "something fishy" about these rigs.
Thanks to Doug DeMaw and Jay Rusgrove and QST for bringing us these little circuits.
In response to popular demand, "SolderSmoke -- Global Adventures in Wireless Electronics" is now available as an e-book for Amazon's Kindle.
Here's the site:
For the print version:
For shipping from a printer in the U.S. (probably better for N. American buyers) Click here: SolderSmoke USA Version
For shipping from a printer in the UK, Spain, or the USA (probably better for UK and other European buyers)
Click here: SolderSmoke EU Version
The two versions are identical, except for a minor difference in the paper used. That's why the prices are a bit different.
Bill's OTHER Book (Warning: Not About Radio)
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W4HBK's QRSS Grabber: The Amazing Pensacola Snapper (Live!)