Archive
Australian TV Tuner Offers 4 RTLSDR Tuners in One Internal Card
Over at RTL-SDR.com is a report of a fascinating development with the DigitalNow Quad DVB-T Receiver, apparently well suited to working as a very powerful multi-SDR solution.
I just wanted to let you guys know that the Digital Now Quad DVB-T Receiver (http://digitalnow.com.au/product_pages/Quad.html) works. It’s a PCI-e card with 4 tuners on it, linked up internally via USB. This has pleased me no-end – I might finally be able to get DAB+ working on my media centre!
I had to add the following line to librtlsdr.c
{ 0×0413, 0×6680, “QuadDVBT” }
I wouldn’t be surprised if this patch makes its way onto the slightly more user-friendly Windows pre-compiled drivers before too long. If you live in Australia, or don’t mind paying for shipping, you could have one for AU $179, with the Australian Dollar roughly at parity to the U.S. version. For $45 per tuner it’s a great looking integrated solution and is much more elegant than a USB hub and a stack of dedicated dongles. Looks like this one has a PAL connector.
Kegerator with Arduino-Based Beer Level Indicators
Andrew of Andrew’s Telephony/IT Blog came up with a fascinating project where he built a 3-tap kegerator out of a 7 cu. ft. GE chest freezer, an Arduino, and a variety of flow rate sensors to display exactly how much beer is left in any keg at a given time. It’s a very in-depth project, and it looks like it’s turned out both awesome and functional.
Go check it out!
Bad Capacitors Strike Again
I’m working on another Bose 901 Series 1 equalizer. It looks to be the same manufacturing run as the first one I wrote up last July, uses the same components, and those components look like they’ve had the same failure mode.
The rather dubious EM-branded capacitors have the same discoloration on the top middle I saw on the other Bose, as well as on the Farnsworth K-262P which had been repaired once before. I’m curious what the physical failure is, as the discoloration would suggest to me overheating, but that seems very unlikely in this circuit and application. Newly manufactured replacements aren’t likely to have this problem as the film technology has improved significantly in the last 40 years.
Hardware Pong Mod Makes Smaller Paddles
While browsing Hack-a-Day, I ran into an awesome hack for the original Pong game. One enterprising hobbyist built his own Pong from scratch following the schematics. It’s a big job but it’s manageable since it’s all discrete logic. I’ve just been re-watching That ’70s Show and in one episode Red and Kelso modify the Pong to make smaller paddles. I was shocked to learn this is both feasible, and even somewhat believable for them to have done in their garage with a screwdriver and a soldering iron.
A neat discovery to add more storage to a laptop.
I acquired a few HP ProBook 4415s laptops which had been scrapped, and decided to rebuild them into working machines. I’ve been needing a new personal/media laptop for a bit, and these are capable little machines with an HDMI output for connecting to my home theatre system.
While cruising eBay for missing trim panels I stumbled across something I’d never seen before – an extremely easy way to add a second hard drive or SSD to any laptop currently fitted with an optical drive: optical drive adapter caddies!
Remove your existing CD drive, drop your new hard drive into this caddy and slide it in where the optical drive used to go. It’s that easy – expanded capacity. Laptop surgery isn’t always for the faint of heart, and this also offers a good way for a road warrior to expand capacity or add a backup drive. Since optical media is really falling by the wayside, unless you watch a lot of disc-based movies on your laptop it’s unlikely you’d miss the optical drive.
I searched around some more, and it looks like these adapters are available for most relatively recent and popular laptop models. I’ll probably buy one for the next time one of my laptop hard drives needs to be upgraded.
Shortwave Radio Reception with the RTL-SDR Dongle
I bought and did a quick setup on my RTLSDR dongle using SDR# a few weeks ago, where I used it to listen to FM radio stations around my area and a few public safety frequencies. That’s all well and good, but I’m much more interested in shortwave listening – when the weather is good, I can pick up a fair number of stations on my Hallicrafters receiver and there’s even more out there that I can’t tune in with that old equipment.
The RTLSDR tunes from around 64MHz up through around 1800MHz, but shortwave frequencies are much lower – only up to around 30MHz. Using an RF mixer, it’s possible to shift the signal into the RTL’s tuning range. Portuguese designer CT1FFU developed a mixing upconverter which adds 106.25MHz to the incoming signals, shifting them up into the correct receiving range and filtering out signals about 50MHz to prevent interference. His version comes as a kit which requires surface-mount soldering, but German retailer Wimo offers mostly-assembled versions of the kit which only need the antenna terminals and power connector soldered.
Finding those adapters was a bit challenging – I have a helical antenna which terminates in that alligator clip, feeding into a coax break-out, with an SMA-Coax converter. On the other end is an SMA gender-changer and an SMA to MCX adapter. Ultimately I ordered them from eBay and they work as intended. The USB port provides the +5V power supply for the converter’s operation but otherwise isn’t connected.
Reception is acceptable. With the aid of the SDR software, I can see where signals are more readily, but issues with my antenna setup and local interference are keeping it from performing as well as the Hallicrafters. I can identify human voices on more stations, but it seems there are fewer I can actually listen to with this equipment. I’ll probably try building a tuned loop antenna similar to this one, and see what I can do with better noise rejection and directionality. I might also add a low noise amplifier after whichever better antenna I end up using.
If anyone has a favorite, easy-to-build loop antenna for 10-160M I’d love to hear about it.
Build Log and Review: Mable Audio VT-86PP Kit Hi-Fi Amp Project [Chinese Gear]
About a year ago, someone left a comment that really looked like spam on one of my pages advertising a web store selling tube audio gear and parts for guitar and audio amplifiers. Against everything I’ve ever learned about behaving on the Internet, and my better judgement, I ended up actually buying a kit from that vendor Mable Audio located in Shenzhen China. They have several kits available with a few options: 6V6 or EL84 for output, 6SL7 or 12AX7 for the input stage and also a beefier EL34/12AX7 amplifier for about double the price. They have a ton of components and guitar amplifier parts and kits as well.
I selected the 6V6/6SL7 kit because I like the larger tubes, and had a set of 1937-issue 6V6G tubes that look more interesting than the small GT-style tubes it came with.
The kit arrived as a box of miscellaneous parts and the chassis. There was no particular documentation included, but the schematic was sent to me via e-mail. Also, the silver decorative plate (in the center of the photo) is no longer included in these kits despite being pictured, as I was told after I purchased. Not the end of the world, though. The kit included a large power transformer, two output transformers (23% Ultralinear), two huge 470uF 450V filter capacitors, all the needed tubes, signal capacitors, connectors, controls, high quality ceramic sockets and lengths of 600V-rated wire to assemble it all with.
The amplifier itself has decent schematics, on paper anyway, although the output impedance is inaccurate on the datasheet: the datasheet, schematic, and transformer color code documents all specify multiple taps but the provided hardware only supports an 8-ohm speaker. This is acceptable, though, as most home theatre speakers are 8 ohm anyway.
INPUT IMPEDANCE : 100K ohm(RCA)
OUTPUT IMPEDANCE:4ohm – 16 ohm8 Ohm
OUTPUT POWER: 12w x2/(ultralinear)class AB P-P
DAMPING FACTOR : >3
FREQUENCY RESPONCE: 20Hz-20KHz(REF.OUPUT)
TOTAL GAIN: 28dB
INPUT SENSITIVITY: 300mV-600mV
S/N: >89dB (HUM NOISE <3mV
CHANNEL BALANCE: <1dB 20Hz-20KHz (MAX.VOLUME)
CHANNEL SERPRATION:>65dB 20Hz-20KHz
TUBE COMPLEMENT: 6P6P(6V6) X4
6N9P(6SL7)X2
POWER REQUIREMENT: AC220V OR 110V OR 240V + -5% 50~60Hz
Assembly wasn’t terrible, but the build quality of the chassis was marginal at best. The top surface of the chassis bolts to the chassis pan itself to hide mounting rails and dividers, and the holes on the top panel didn’t perfectly line up with the socket locations on the bottom panel. This meant that after mounting the sockets to the bottom where they belong the top cover wouldn’t slide over them because it was interfering by about 1mm on one of the sockets. It took significant pressure to force it on and made a very loud snapping noise when it did so, but the socket and cover were all intact. It’s definitely not coming off again, though. Additionally, the cover over the transformers is supposed to mount using several screws at the corners, but only two screw holes lined up.
The sockets are ceramic and the sockets gold-plated, and the transformers look appropriately sized, though, so it’s on to building past mounting up the parts. This project was a long time in the making, as I mounted the sockets and chassis up on July 12th 2011 and then did no further work until March 2012. I worked my way through the schematic, roughly right to left. This amplifier is a power supply, and two identical amplifier channels. I’d highlight on the schematic as I completed both mirror halves, and this made it easy to keep track of where I was going.
Some photos showing filling in the components:
After assembly, I had a few left-over parts:
A really weird assortment of leftover parts at that. I declined to connect the headphone output (on advice that it was probably not safe for any headphones that I might actually like due to the connection – not unique to this amp, many other circuits have similar issues) which accounts for 2 of those resistors, but there’s still 13 more + a small capacitor that weren’t called for anywhere. And there are two extra panel-mount RCA input jacks. And a ton of extra wire. But for all the extra they did include, there were 4 resistor types (8 resistors total) that were not included, so it was a trip down to Vetco Electronics in Bellevue to pick up replacements. The replacements are the Red- and Tan- bodied resistors. Not quite sure what to make of that.
I elected to replace the LED power indicator with an NE-2A neon bulb instead, so it would be the same color as the glow of the tube heaters.
There is a minor issue with this one, though. There is an anti-arcing capacitor across the switch. I placed the NE-2A between the switched side of the switch and the AC neutral (it runs directly from AC mains through a 150K 1/4W resistor). With the switch turned off, the capacitor allows AC leakage of a few mA to pass to the cold side of the switch. The current leakage is less than the excitation current of the transformer, so the transformer appears “open” to the low signal as it’s entirely eaten because it’s not strong enough to set up a magnetic field. This causes the current through the 150K resistor and neon….so the bulb lights up when the power is off, now. With the power on, the capacitor is out of the circuit and the transformer is an extremely low impedance, so all the current goes through the transformer primary and none into the 150K resistor and the NE-2A bulb. The result? The power switch indicator is backwards. The light comes on when the device is turned off, and goes out when you turn it on. I intend to fix this at some point, but am not entirely sure what the best approach might be. The volume control itself is abysmally low quality, probably the only part in the kit I actually think is just plain “bad”. The return spring is weak and the switch touchy and it binds up easily.
There was also another issue: I wired the volume control backwards. “Right” is lower, now, instead of “Left” as is the convention. I evaluated fixing this problem, but while poking around one of the volume control’s pins started coming out of its molding and I didn’t want to risk destroying the control, so that’s a problem that won’t be fixed in this iteration.
I did a quick visual for obvious shorts and powered it up the first time with the 6P6P (Chinese 6V6GT) tubes which were included, as I didn’t want to risk my classic tubes. If there’s going to be a problem it’d be on first power up, for any amplifier from anywhere. The transformers all made a great *THUNK * noise when they energized for the first time, but quickly de-energized again. I poked around some more and found I’d missed a solder connection on the bridge rectifier. I soldered it back on and tried again and everything was fine! First power-up successful, with no re-work needed.
Then again on the test bench with the 6V6G tubes:
Still good! And for some post-production glamour shots:
Now, I’ve moved the amplifier onto my desk and will use it for personal stereo when not using the Surround Sound receiver.
In conclusion: Mable Audio is a reputable supplier. Their product sounds great, and was of acceptable build quality for an entry-level amplifier. The chassis and platform itself will be a great starting point for more modification projects in the future. I rate this kit as a 3.5/5 due to the mechanical issues with the chassis fit and the power switch, but the electronics quality and circuit design seem to be solid. I would recommend this kit to anyone who wants to build an inexpensive tube amp from parts – but, given the complete lack of instructions or documentation beyond a schematic and some color code diagrams, make sure you go slowly and check your work and are somewhat familiar with how to read electrical schematics.
- Pro: Inexpensive for what it is.
- Pro: Good quality components, for the most part.
- Pro: Attractive styling.
- Pro: Fairly straightforward build.
- Con: Terrible quality power switch. Just terrible.
- Con: Mechanical fit on mine wasn’t the best.
- Con: Only 99% of the parts in my kit were the right ones.
For $175 + shipping from China, it’s not a bad deal. Similar kits from more well-known sources, or U.S./European makers, run at least double the price. Once assembled, it’s very attractive and has a lot of potential for future upgrades. This was a fun and rewarding project and a nice change of pace from vintage gear while still keeping the tube connection.
What’s been your most difficult challenge at work, and how did you overcome it? [Crazy Boat Connections]
I was swapping war stories with another technology professional the other day and we got to talking about our “best problem” scenarios. I happen to have an interesting story from my days as IT Manager of the Las Vegas Casino Lines, and how I solved a vexing issue with our shipboard Internet connection that had been around for a year and was costing the company money every time the ship sailed.
The Las Vegas Casino Lines were, as the name implies, a gaming establishment that operated out past the International Boundary out of Port Canaveral, FL. They went out of business a few years ago (spurring my move to Seattle), but while they were in business had a fairly sophisticated network on- and off-shore to allow tracking systems, cash- and game-management systems, security, navigation and communications to all continue without interruption even when the ship was out at sea.
This WWAN connection was provided by a Verizon Wireless air card and an external antenna. The only trouble was, every time the ship was out, it would randomly lose connection. Without a connection, patrons couldn’t withdraw cash from the onboard ATM, charge gaming credits to their credit cards, or do anything really. If you had money, you could keep playing, but if not you got to enjoy a 4-hour smoke-filled boat ride.
The ship’s antenna for the WWAN connection is circled in red above. The perspective makes the antenna appear a lot bigger, but it really was only a six-foot fiberglass antenna mounted on the railing. The antenna is on the right side of the ship (facing forward) near the bow on the middle deck. I rode along with the ship for a few days while monitoring the connection signal and started to work out a pattern of when the signal dropped off: only when the ship faced certain directions, and more on the return leg of the journey than on the outbound leg.
I had a hunch: the signal is clearly dropping when we face certain directions. What are we connecting to? I visited the FCC’s web site and pulled the listing of fixed cellular transmitters along the Space Coast from our route, and eliminated towers that didn’t belong to Verizon; then plotted the tower locations on the map along with our ship’s turn area and boundary markers. Then, I rode along again and took a GPS track of our ship’s position, which I annotated with comments about signal connectivity.
As it turns out, we lost connectivity when we were on the margins between cell towers, and when we were facing the wrong direction. With the ship traveling north, the antenna was attempting to transmit through the (grounded metal) superstructure of the ship itself to reach the tower. Combined with the fact that microwaves don’t travel as well through salty humid air over the ocean as on land, and it’s a perfect recipe for signal loss. The shipfitters had installed the antenna in a poor location for our application. It was an easy fix, after that: one of the crew helped me run new coax to relocate the antenna to the top of the ship’s tower.
The signal was completely lost at this point – I’d overlooked a small issue. Adding 250 feet of additional coax cabling had introduced a lot more cable loss into the system, so now we needed an amplifier to get the signal out of the ship. Finally, though, the amplifier was installed and the system worked perfectly. Patrons could now charge gambling expenses to their credit cards while out in the middle of the ocean, and everyone was happy.
Unboxing my Sharp PC-4501 classic Personal Computer
It’s 1987 and I’ve been needing a new laptop. After a careful process of comparison shopping I settled on my Sharp PC-4501 from Montgomery Ward. Let’s open it up and take a look!
For only $699.99, it’s a state of the art machine. A 7.16MHz processor, 640KB of RAM, and mine comes with an optional second 3.5″ floppy disk drive! Now I can work on a program and save its data at the same time. It was designed to be especially easy to use.
Good thing they provide unpacking instructions inside the box.
It comes with an instruction manual and the operating system disk.
I’ll make sure to return the warranty card.
Power up…time to go through the BIOS setup!
One thing I don’t like so much is the screen is front-lit with ambient lighting, and is glossy. Makes it a challenge to see what’s being displayed sometimes.
We’ll try out a productivity application.
Looks productive!
I can’t wait to begin editing documents and spreadsheets from my own home. It’ll be so much easier than my old typewriter!
Free Mapping and Tracking for Android [My Tracks]
Beautiful weather has finally arrived in the Pacific Northwest and I’ve been taking advantage of it as often as I have time. One thing about living where it’s grey and rainy for so much of the year, it really almost forces me to go outside and be active when it’s nice out. I’ve been riding my bike around, and wanted an easy way to keep track of my stats like speed, distance, which trails I was riding and altitude. Turns out there’s a free and easy way that integrates well with Android: Google My Tracks
My Tracks uses your phone’s GPS to record your position and plots it on a map, where you can upload it to Google Maps or export your track as an industry-standard KML file for analysis in another application.
You get a print out of your statistics at the end, and can optionally insert markers with interval statistics on a custom schedule. The app has been around for a few years but has become much easier to use lately. My last ride was 12.9 miles long at an average moving speed of 7.5 miles per hour:
Total distance: 20.78 km (12.9 mi)
Total time: 2:56:35
Moving time: 1:43:56
Average speed: 7.06 km/h (4.4 mi/h)
Average moving speed: 11.99 km/h (7.5 mi/h)
Max speed: 34.62 km/h (21.5 mi/h)
Average pace: 8.50 min/km (13.7 min/mi)
Average moving pace: 5.00 min/km (8.1 min/mi)
Min pace: 1.73 min/km (2.8 min/mi)
Max elevation: 179 m (589 ft)
Min elevation: 93 m (304 ft)
Elevation gain: 984 m (3228 ft)
Max grade: 12 %
Min grade: -17 %
Recorded: 5/26/2012 12:21 PM
The application also integrates with a Polar brand heart rate monitor over Bluetooth to record heart rate statistics along with the other information. I don’t have that option yet, but plan to add it fairly soon. This is a great free app that everyone should know about. It’s not just useful for mapping a trail, either – you could use it to mark where you left your car, see where you’ve been in an amusement park, or record the location of interesting landmarks you see while wandering around the city. Check it out!
My Tracks
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