Twisted Waves Across the Venice Lagoon

I don't really understand the physics behind this, but it seems to be important. And the video is a lot of fun. There is much Italian brio and bella figura in this. They even got Princess Elettra Marconi involved. And the video features audio from Marconi himself.
Hypertuning! Radio Vorticity! Helicoidal Parabolic Antennas! Gondolas! Segnale Ricevuto! Bravi!

http://physicsworld.com/cws/article/news/48869

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Mars in Opposition

Jupiter and Venus are getting all the media attention because they happen to appear close in the sky, but Mars is the real object to see this month. It is in opposition (see diagram). This happens every two years. Last time we were out in the Sabine Hills north of Rome (sniff, sniff).

I cleaned the 6 inch mirror on my Dobsonian telescope a while back, and when I put the whole thing back together, something wasn't quite right. I was getting dim and blurry views. So yesterday I went into telescope maintenance mode and, as the Brits would say, got it all sorted.

I was out looking at Mars last night. The view is not nearly as spectacular as the image above, but it is very nice. But I can't see much of the northern polar cap -- it is, after all, summer time in the Martian Northern Hemisphere.


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Ralph Baer, Electronic Wizard

Here is a another nice video, this one about Ralph Baer, one of the pioneers of video games. At age 90 Ralph is still creating things at his workbench.

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Amazing R/C Airplane Video From Germany

Wow, this is real techno-art. Take seven minutes, put it on full screen, crank up the audio and sit back to enjoy a unique aerial view of a beautiful part of Germany. Thanks to Bill, N5AB, for alerting us to this.

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JBOT Thoughts

Posted today to the BITX-20 Group:

Good to see so many JBOTs under construction. I recently built two of them. Farhan has asked me to share with the group my experiences using -43 core toroids. Ironically, TV cores are a bit harder to find here, so I had to go with the fancier toroids!

In my first amp (used in a 17 meter DSB rig) I used the smaller FT-37-43 cores in all three transformers. T1 and T2 were wound and placed in the same way that Farhan did with the TV cores. For T3 I used superglue to stack 4 of the cores 2x2, then wrapped them with a bit of electrical tape. I wound T3 so the input wires were on one side and the output on the other. (On this amp, I had started out using some large binocular cores from the junk box, but I had a tough time getting the amp stable with these cores, possibly because using them resulted in longer lead lengths. So I went back to the smaller FT-37-43 cores).

In the second amp (used in a 17 meter SINGLE Sideband rig) I used FT-50-43 cores for T1 and T2. The bigger gores were a little easier to work with. I glued them vertically to the copper clad board. For T3, I again went with 4 FT-37-43 cores. (I tried using 4 FT-50-43 cores for T-3, but I found that output was low, so I went back to the smaller cores for T3). Note that on the second amp, I put some insulation between the heatsinks and the copper clad board (gorilla tape) -- I was worried about possible short to ground if the anodized layer on the heatsinks got breached.

In building my amps, I used the photo on Farhan's Phonestack page as my guide.

As is always the case with amps that I build, I found that a certain amount of "taming of the beast" had to take place before I got the devices stable. This is certainly the result of the kind of homebrew devices into which they are being inserted! Following advice from Doug DeMaw, I made liberal use of ferrite beads. I put one on the lead carrying 12 volts to the amp board. I put another on the lead from the 12 volt line to the final's RF choke. And I put one on the line carrying the .6 volt bias to the secondary center tap of T2.

I put a bit of shielding (copper-clad board) between the low pass filter and T3.

These steps allowed these amps to work nicely with my contraptions.

As long as we are talking about JBOTS, I have a question for the group:

On my second amp, I noticed that the output was a bit lower than it should have been -- only about 1.5 watts. I did a lot of troubleshooting, then I finally checked the bias currents in the first two stages. I found that BOTH were running at about 50 ma.

I looked at Farhan's JBOT notes and found that the second stage is supposed to be running at 100 ma. I found that the base bias voltage on the second stage was 1.13 volts, while the first stage had 1.9 volts on the base. That didn't seem right.

I then turned to the bias.exe program that comes with EMRFD. I plugged in the values from the JBOT schematic and, sure enough, the predicted collector bias current was 50 ma, not the 100ma the design was looking for.

Using that program, I made some changes to the base resistor in the second stage. I found that with 150 ohms instead of 100 ohms, the collector bias current goes up to the desired 100 ohms. This also seemed to bring power output up to the desired range of 3-4 watts (output should be a bit lower at 18 MHz, right?)

More info (and pictures) on my JBOT adventures can be found here:
http://soldersmoke.blogspot.com/search/label/JBOT

GOOD LUCK WITH YOUR JBOTS!

73 Bill N2CQR
http://soldersmoke.blogspot.com

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

Australia's Largest Hamfest

Hi Bill,

Just wanted to pass some pics of the Central Coast ARC Hamfest in New South Wales at Wyong approx 100km north of Sydney and about 80-90km south of my QTH. As you can see there was a reasonable amount of people there and some boot sales as well.


The first thing that I found in the boot sale area was a copy of SSDRA (1977 vintage) almost as old as I am. I found it in one of those boxes under a table with other books on top. I immediately gave the book to the guy selling it and asked how much, and to my surprise he said $5 Aust. I couldn't get my money out quick enough and put it my bag that I had for collecting all those small parts. See attached pic of said book. I saw a brand new copy of EMRFD at the WIA stand for $85.
On my way around the boot sales I also saw this Hallicrafters radio and I thought of you and took a photo of it the only thing was I have no idea what model it is?

I also picked up a couple of small variable caps with the nice ceramic fronts on them and only $1 each. I also picked up some hard drawn stranded copper wire 2.5mm dia & 200m long for only $170 which isn't too bad a price here in Oz.

The biggest part of the day was catching up with all the guys I know from the area where I am now and others I haven't seen since I went last time in 2008, so it was a great outing and will have to start reading another book and start looking at maybe making a HB 30m APRS Txer for when I go I my next trip.

73,

Adam

VK2YK & VK6GA

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CircuitLab Online Simulator

I gave the new CircuitLabs online circuit simulator a test drive this morning. It worked very well, even on my clunky old computer. I think this online system will open up circuit simulation for people who haven't used a simulator before. And it looks like a great tool for collaboration. Give it a spin!

https://www.circuitlab.com/

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