The LED display isn't popping out at you because of the flash picture, but the variac box works as intended. It's reading 100V and 00.0 Amps while the yellow (Horrible Freight) voltmeter reads 102. Which is correct? Is either correct? The digital voltmeter I trust the most isn't pictured, but it was close to midway between the HF meter and the . It turns out that if I tweak the big variac dial until the box's display stops flickering 99 to 100 and back, the trusted DVM says just about 101.
Pretty much all of those are "close enough" for what I expect to be doing with it, which is primarily to reduce the line voltage to some of my older radios and things that haven't been on in a while in order to reduce the risk of something failing because it hasn't been on.
This variac is rated for 5A, which is enough to power anything I've got and maybe a couple of them at the same time. Some collectors of vintage, vacuum tube gear (popularly called boatanchors) run all their equipment on a variac or fixed transformers to reduce the house line voltage a bit. Over the years, the typical house voltage has gone up from more like 110 up to closer to 120, which I suppose was done by power companies to ensure that after the usual voltage drops folks at the end of a branch didn't get too little voltage. The boatanchor collectors say that the higher line voltage stresses the parts too much.
Unlike this project, the antenna is fairly underwhelming and needs a little emphasis. It delivers a bit weaker signal than my vertical when the radio preamp is on (on for the loop, off for the vertical) on the one band I was most concerned about. On the other band, it's much worse than the vertical. On the positive side, though, it delivers some of the claimed ability to null signals off the back.
Off topic, but if I were legally carrying a firearm and wanted to defeat the technology in the link below, would some sort of faraday cage work?ReplyDelete
Although they use non-radar terms in the description, I'm going to assume they're just using weird analogies. Radar works on reflecting back signals from a transmitter.Delete
The wave reflected back is going to vary with the shape and surface geometry of the object. Let's say you have a pocket pistol and you make a Faraday cage for it out of something like aluminum foil. You'll change the details of the reflection, but you don't make the metallic reflection go away. If you're carrying a polymer pistol, you'll increase the amount of reflection. If the aluminum was really form fitting, it would take on the shape of all the features on the surface and would be really recognizable.
So let's say you had something like a Sneaky Pete holster - a rectangular box that completely hides the shape of what you're carrying. If you completely lined it with metal, it could be a good Faraday cage. It would still reflect, but the reflection now looks like a rectangular box and not "gun-shaped".
They could decide that they search any big reflection or they could decide they only go after people when the radar box says, "Gun detected".
That said, there's so much wrong with both the company's website and the Wired article that it's pretty disgusting. Too much emphasis on "concealed weapons", and the Vegas guy's "I have a concealed carry permit myself. But,..." When the big But shows up, you know it's a sham. More targeting the innocent and not doing anything about the bad guys.
Yup....tubes can shrug off an enormous amount of abuse.ReplyDelete
How does the noise level compare between the two antennas? Loops have a reputation for being "quieter", but perhaps that's only valid on higher frequencies.
It's actually pretty comparable - when the rig's preamp is on. It probably simply needs a bit more gain.Delete
This is a "compact" antenna, right?Delete
In all my years of playing with antennas, "compact" antennas have never worked as well as full-size ones. They can can get damn close, but due to the laws of Physics, they'll always be a bit behind...
It’s not really electrically short. My loop is 22’ around, which is just a little short of a quarter wave on 10.1. Gary’s original design was between 1/8 and 1/4 wave on 1.8 MHz; I scaled that to 7 MHz. 1/4 wave on 40m is 33’, so I’m between 1/8 and 1/4, just like Gary’s. Heck, my vertical is close to 1/8 wave on 80 (physically) and it works better.Delete
Oh....duh! For some reason I had it stuck in the brain this was some kind of small, low-noise 160M antenna.Delete
When I lived in my apartment and had the run of the nice, flat roof, I experimented with various loops and random wires, all fed by my SGC. Got some pretty good results with a bottom apex fed "squished delta loop" that was about 70' across the top, which was about 25' above the roof of a two-story commercial building.
Sharp looking project.ReplyDelete
And the digital display in combination with the large dial of the variac looks oddly pleasing.
Picture the big panels used in the 1930s movie Frankenstein. Huge wheels and dials that adjust the high voltage to bring the monster to life. The variac kinda has that vibe to it. The digital meter brings Frankenstein into the digital age.Delete
1" thick slate back panels with BIG knife switches, BIG meters, and BIG knobs to turn.Delete
Oh, and don't forget to add a couple of spark gaps "just because"....
Way back (over 50 years ago) working on large scale computers with vacuum tubes on method we used to test our "live" circuits was to vary the voltages to possibly induce failure. Failing circuits were pulled and sent to the repair lab where the common fix was to put in a fresh vacuum tube. The theory was that in a large (60,000 vacuum tubes) integrated electronic device that if the tubes were allowed to fail it was possible that so many of them would fail at the same time that the system wouldn't even be able to power up and thus it would be impossible to find which individual circuits were failing. So this proactive "marginal testing" method was developed.ReplyDelete
Ah-h ... first-pass success. Sounds like fun. And I bet you didn't need to first run it through a Design Review Committee and get permission from Procurement.ReplyDelete