Thursday, March 31, 2011

Experimental AMPS mini-basestation

This is really neat. Mark Atherton has put together a very basic, working, replica of a base station for analog cellular phones. I've blogged about something similar for GSM phones in the past. This analog system is pretty fascinating for me.

We really have the parts to put together something basically similar for ham radio. The audio could be exactly the same as it is now. Add in a control channel and people could call you even if you have the volume turned all the way down. There have been in-channel methods for quite a long time of course. Signalling systems such as CTCSS, DCS, DTMF have been constructed in the past, and barely used. As of yet, noone has constructed an out-of-channel signalling method. The capability is there for APRS I believe. Some APRS capable radios can advertise a frequency you are monitoring in your report. I think one or two may even allow you to QSY to an advertised frequency.

It'd be pretty cool if you could send out an APRS call, have the other parties' radio QSY to your freq if they answer it, test the path, maybe QSY to a mutually accessible repeater if necessary, etc. I have no delusions that this would be constructed or used though. Previous in-channel signalling methods have been around for decades and remain fairly unused, except to access a repeater. Other neat technologies have falling by the wayside, like Kenwood's DCS-based ID tech.

You know what they say, a rolling stone gathers no moss.

Friday, March 25, 2011

A new challenger has appeared: BJ-UV55

Found this on Alibaba the other day. It is a Baojie BJ-UV55 dual band mobile. Emailed the seller and it's not out yet but they expect it to release in May. It seems that Wouxun's as yet unreleased KG-UV920R is spurring other Chinese manufacturers to make their own mobile radios.

The specs are fairly typical. 136-174mhz and 400-470mhz. 45W VHF, 35W UHF.

What I don't know:

  • If the front panel can be remotely mounted.
  • If it has crossband repeat
  • Price
I doubt this company is going to go through the FCC certification process either so your mileage may vary. I just like to keep track of these things.

I guess it's also listed under the model number TC-UV55 and a different company. Not too unusual in China.

Saturday, March 12, 2011

HTPC Capacitors

Ahh, the dreaded bulging capacitor problem. This is a Geforce 5200FX graphics card from my HTPC. Granted, it's pretty old. I built this machine back in 2006 which makes it pretty ancient for computer technology. A couple nights ago I sat down to watch a recording only to have it crash a few seconds into the video. I did a little troubleshooting today to find that the machine gets to POST only when I take the video card out. (Of course, once I do it gives me the error codes for no video card.) I found these caps when examining the card. 4 electrolytic capacitors 6.3v 1000uf all were bulging. The single 16v cap looked perfectly fine. I ordered a new card, but I think I may add some electrolytics to my next Mouser order to see if I can't revive this one too.

I've been playing something of a handyman this past year anyways.

Thursday, March 10, 2011

Another ARM single board computer (SBC)

This is the i.MX53 Quick Start Board:

Full specifications

This should be a pretty neat SBC. It costs $149 and includes a Freescale 1ghz Cortex-A8 ARM processor, 1GB ram, 4GB microsd card with Linux, 5v power supply with worldwide adapters. Expansion boards include a $49 HDMI output and a $199 4.3 800x600 LCD screen. (Which seems a mite overpriced to me given the glut of under-$50 7" photo frames.)

I've also covered the Chumby Hacker Board here. It's $89, and also includes a Freescale ARM processor but only at 454MHZ, 64MB ram and a 512MB microsd card with Linux. On the other hand, while a lot of the processing specs are lower, the Cumby Hacker Board includes several GPIO connections and is even compatible with Ardunio shields. Could be handy for more low level interfacing than this board.

I have yet to find anyone using these boards in a Ham Radio capacity yet. Rig control, Digital modes, Micro Repeater controller, SDR, D-Star adapter (with dongle), Codec2.. There are a lot of possibilities.

Link to the full information on the i.MX53 Quick Start Board on the Freescale website.
Here's the blog post on the Freescale website that I learned about this board.

Sunday, March 6, 2011

Electronic Project Lab

This is one of my favorite "toy"s from my childhood. This was actually my second one, the first was the venerable 200 in one Electronic Project Lab. Radioshack used to carry these things before they decided to become a cellphone kiosk. I'm actually looking to acquire a used 200 in one again, that was always my favorite but mine got really ratty and destroyed many years ago. :(

The radio club is unofficially thinking about finding some of these for a basic electronics class. I'm thinking, why not build a kit of our own? You could probably buy enough components to build 20 of these for $20. The asking price was never really for the hardware. The instruction books with all the projects are really what is valuable. Unfortunately, those aren't freely available. It'd be great to find a community driven project to make a series of circuits to fill this role. It's hard to find freely available circuits that use the same parts.

I loved the spring based hookups that these kits used. Breadboards are good for testing circuits out, but these are very neat in that all your components are fixed in place and you can pretty quickly run wires from one to another. It's nice for car rides also, no risk of losing tiny components as the car is moving. The spring idea is probably covered under some sort of patent though. So any community made clone would probably have to do something different. It'd be great if some place offered a strip of breadboard like material where each hole could be wired up separately underneath. Or, what else could you do?

Circuits could include:
A basic circuit
operation of resistors, resistors in series, parallel, variable
operation of capacitors, showing they store energy, use as time delay, pass AC but block DC, etc.
operation of transistors, as switches, as amplifiers, darlington pair
operation of diodes, rectify AC, etc
operation of transformers, upconvert/downconvert voltage. etc
operation of relays
operation of inductors (???) never covered in the kits I had
voltage dividers
Simple logic circuits (and, nand, or, not, xor, flip flop, latch, etc)

Not only have purely theory based circuits but also edutainment ones such as sirens, "police light"s, timer games etc. Code practice oscillator, crystal radio, AM radio, FM? Radio would be very nice, especially for a radio club! You could wire two kits up to send Morse Code back and forth to each other... neat demonstration for a field day setup.

Anyone wire one up to use as a QRP CW transmitter? I was once playing with my 200in1 kit and accidentally affected our TV. I was maybe 11 and built the metal detector circuit which involved a radio signal. Well, I was somewhat randomly changing parts around and ended up making something that I could sweep around and all of a sudden our TV looked like it was scrambled. It was on ch 6 or 8. So I tuned the TV around the channels and then tuned my circuit with the variable cap and I was able to knock out any channel up to 13. I wrote down my changes, or so I thought.. next time I tried to build that circuit it never worked again. Probably for the best though. :)

Inexpensive digital multimeters can be had for less than $5 shipped on ebay. That can be useful for teaching the skill of using one with such a kit.

These kits are probably the reason I got into electronics and they have also nurtured my love of science (although Mr Wizard had a huge role there too!). I intend on passing on something like this to my kids one day. It'd be incredible if others could do the same as well.