Ah, it was a good morning in the N2CQR shack! Last week I ran into fellow ham David Cowhig at work. I was regaling him with tales of Herring Aid and Tuna Tin derring-do. Oh the stations I had heard with the receiver! And the stations that I'd worked with the transmitter! Then David asked the question: "Yea, but have you worked anybody with the receiver paired up with the transmitter?" Uh, no. Not yet.
Well this morning I took care of that. 7040 kc. 1115 UTC. W4ELP was calling CQ. He wasn't too strong, and I wasn't sure if we were on the same side of zero beat (that's what happens with direct conversion -- you get all the sigs in two places on the dial) but I took a shot at it. And he heard me!
Here's the icing on the cake: This was his SECOND QSO with my Tuna Tin 2! Ed had been contact #4 when I was running the TT2 with the Drake 2B. After exchanging reports he asked "Bill ARE YOU STILL ON THE TUNA TIN?"
The rig (TX AND RX) is pictured above. Close-up of the receiver appears below. And below that is a picture of Ed, W4ELP, in his Georgia shack. Note the HW-8.
Thanks Ed! Thanks David!
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Opposite "sense" winding and resulting phase shift
My second attempt at building a Herring Aid 5 (the first was 1976) continues.
I thought I had discovered an error in the schematic that (I hoped) explained my failure to get this simple receiver running (scroll down for details). But Dex, ZL2DEX, in New Zealand spotted something that got QST off the hook and put all the blame back on me:
I had failed to check the rotational sense of the windings. The schematic called for 4 turns over the Radio Shack choke. So I just went ahead and wound them. I didn't pay any attention to the direction of the winding. I then hooked it up in accordance with the phasing dots in the diagram. And it didn't work. So I switched the coil connections around. And it worked. Aha! I thought! QST messed up! It wasn't my fault.
Dex brought me back to reality. He noted that I probably wound the coils with the wrong rotational sense. I confirmed this. I rewound the coil following the rotational sense of the choke. I hooked it up following the phasing dots of the schematic. This time the oscillator started right up. So the problem wasn't an incorrect drawing of the phasing dots. Instead it was my failure to remember that phasing is more than just the top or the bottom of a transformer's winding. Rotational sense is also important. That's why "phasing dots" are sometimes referred to as "sense dots."
This doesn't come up very often, because most of the toroidal transformers we make are bifilar or trifilar -- the windings are always in the correct sense because we twist the wires together before putting them on the coil. When we look at those phasing dots, we are focused on getting the proper tops of coils connected to the appropriate bottoms of other windings. We don't pay any attention to the sense of the windings. Thanks to Dex for bringing me back to my senses :-o
Grob's Basic Electronics has this definition for those phasing dots:
| " | Used on transformer windings to identify those leads having the same instantaneous polarity." |
This morning I did a little experiment to confirm all this: I took a toroidal core and wound a little transformer. Using a dual trace scope, I looked at the input and output wave forms. Sure enough, when the windings are in the same rotational sense, there is no phase shift. But when that secondary is wound in the opposite sense, you get a 180 degree phase shift. I know this is very basic, but it was fun to re-learn it and to confirm is.
But I still don't have the little receiver running. I think there are a few problems. That single BJT mixer stage needs a lot of RF (2.5 volts p-p) from the oscillator. Also, I think the 10 uH chokes that I am using are not the same as the chokes used in the original Herring Aid design. So when I build transformers on these chokes, they don't work very well.
But I will keep at it. It has been 38 years... I can wait another week or two.
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htmOur coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmokeOur Book Store: http://astore.amazon.com/contracross-20
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