Unlikely contraptions

[w8cbc]

This train of thought began with the receiver construction thread. That's not an unlikely contraption. Most of what I've put together over the years though, well, I really didn't have a clue what I was doing. I've generally done things my own way. Sometimes they've worked.

Case in point:

Start with a Sansui QR-1500 quad receiver. AM/FM, 25 watts/channel, fairly high-end in its day (1974). It had been Dad's. I wound up with it at age 17.

Well, the FM section was kind of broad and rather insensitive. I tweaked and twiddled and managed to screw up the IF. It took awhile to figure out how to realign it so it would perform as it had before.

I still wanted better selectivity and sensitivity. So, I decided to add another IF stage just before the limiter. The only thing I tried that didn't oscillate was a 2N4401 with a ceramic 10M7 filter (pulled from something, I don't remember what) at its output, Vcc taken from its input through a choke. I then had to realign the IF section again as I'd set its cans somewhere around 11 MC.

I still had problems with instability though. So I wound up wrapping the added stage in aluminum foil and placing it "out of the way".

That receiver as haywired has logged hundreds of stations by tropo, Es, and aurora. Solar flares will move its S meter. It can pull in a weak signal adjacent to a strong one. Mission accomplished. The last time I had it apart (to replace the rear channel outputs) I looked at that foil-wrapped board and wondered how it could even work. I had thoughts of pulling it and redesigning it better, then decided not to.

Then I got interested in SCA. I built a 565-based decoder and yanked the rear headphone jack (I'd mangled it trying to rewire) and put in a mono jack with the demodulated composite. It worked. I discovered that there really wasn't much interesting on those subcarriers that I could pick up. That 565 box is still around in my stuff somewheres. It has a lm386 for its output.

After that, it was SWBC. I haywired together a mixer circuit with a mosfet, crystal oscillator, and a variable cap and a bunch of coils for the preselector. I was forever hunting for LO crystals. I cut some masking tape into thin strips and stuck them to the Sansui's face, calibrated for the various crystals I could scare up.

There were lots of interesting signals. But I decided I also wanted to be able to decipher SSB. So I built (rather more cleanly than the rest, in a metal box) a tunable BFO, 440-470 kc, and force-fed it into the Sansui's AM antenna terminals. Enough leaked through the front end for it to work.

Not long after all that, I bought a Sangean ATS-803A and put the mixer and BFO away in the junk box.

It is amazing in a way that the Sansui still works after all the horrible things I did to it. I like to think what I did there led to bigger and better things. It sure explored a lot of RF spectrum in its time.

Just think of a screwy kid cranking the BBC World Service, happy as anything to be hearing it at 15070 kc at 1 in the morning. Then comes the knock on the door: Turn that f'ing thing DOWN!. http://www.qrz.com/iB_html/non-cgi/emoticons/biggrin.gif

[N0WVA]

Ive never butchered...er...uh modified a piece of equipment to that extent, but it just goes to show that some of us will stop at nothing when it comes to hamming. I would have loved to tune that thing!

[w8cbc]

It was twiddlesome, all right. http://www.qrz.com/iB_html/non-cgi/emoticons/biggrin.gif

I was purely BCL/SWL then, there were no thoughts yet of getting a ticket and transmitting.

I'm sure I'm not the only one who did goofy stuff like this.

Anyone...?

[N0WVA]

Well, I used to use two SW receivers, one to beat against the incoming signal the other was receiving.

I was pretty crazy about radio when I was growing up, I even put together a spark machine out of a auto coil and hooked it up to a long wire hoping someone would hear me zapping away. The only outcome I remember was the strange smell of ozone in my bedroom as the spark jumed across to the antenna terminal.

When I figured out how to build an oscillator, I used to try and tune it to a SSB signal and key it, hoping somebody would hear me and make mention of it. Sadly no one heard my piss weak one transistor oscillator. http://www.qrz.com/iB_html/non-cgi/emoticons/sad.gif

Also, there was the time when I took an old AM FM receiver board, hooked up a 6 volt lantern battery to it somehow , got the Local oscillator to work as a transmitter. I had hooked the output of my tape player in series with the battery and it would modulate the oscillator. I could tune it across the entire FM band and range was about half a mile. I still dont know exactly what I was doing to make it work, but it sure was fun! I cant remember too well what I had done when I was 10.

[ky5u]

When you said "haywired" made me think of all the contraptions I built over the years with heavy duty coat hangers. I call them "clips".

In Pensacola, my 2m/70cm push up pole was held to the house by a "clip" with no screws. I could take it down in 30 seconds yet is stayed up through several tropical storms (take it down for the bigguns). Just yesterday, my wife bought a patio lounger that was missing some hardware on a "no return" sale. A coathanger and a few "clips" later and it was solidly together. Hand a wind chime on the patio? A snip, snip, and a clip.