VE7XEN's ham radio and electronics blog

Quansheng TG-45UV Protocol Reversing

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On a whim, I recently purchased the apparently new Quansheng TG-45UV to replace the Quansheng TG-UV2 I lost this last summer. A review and/or video might be forthcoming, but in the meantime I spent some time reverse engineering the serial protocol / data structure. If you have one of these radios and want programming software, the Quansheng TG-K4AT UV software works and is what I based my efforts on.

Recording NBFM Scanner with RTLSDR

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Ever want to use your $20 RTLSDR dongle as a simple FM scanner to listen to your local public safety or ham radio repeater traffic? @nottheoilrig on my local hackspace’s mailing list inquired about how to record analog FM off the air to a file. After some fiddling, I found this is quite simple with the rtl_fm tool included in the osmocom rtl-sdr distribution. The dongle and software does quite a good job scanning too, it’s pickup time is very quick even monitoring many channels.

Canon PowerShot S110 repair attempt

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Ever wonder what’s inside your digital camera? Here’s the imager and optics assembly from a Canon PowerShot S110 that I destroyed with mineral-y water and was trying to repair. Click for gigantic. Isn’t that CMOS sensor beautiful?

Programming the ATtiny841 with avrdude

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Working with my good friend Daniel McLaren on a cool interactive art project, I designed a board around the ATtiny841, which is a nifty new entry to the AVR portfolio. Unfortunately when intial power up of the board was successful, I found I was totally unable to write code to the device with avrdude as I normally would; the chip is unsupported in even the latest version. I found a helpful post on AVRFreaks with a code listing for avrdude.conf that was purported to work, but I found it produced verfication errors (and a non-working chip) every time.

After much mucking around and recreating the part in avrdude a dozen times, I got it to work.

eBay AD9850 board performance testing

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Prompted by user Skimask over on the eevblog forums, I undertook some performance testing of an AD9850 module, readily available from eBay (search 'AD9850 DDS') for under $10 shipped. These are advertised as 0-40MHz devices, and appear to include the datasheet-recommended 5-pole output filter and a 125MHz canned oscillator. Measured distortion and spurious performance is excellent, especially for the bargain-basement price.

Project Start: tinyCounter low power HF frequency counter

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I've ordered myself an EA3GCY ILER-20 kit, and being a single-band QRP hand-tuned radio, I want a convenient counter. I'm going to be using this in the field on battery power, so it's got to sip the juice and be small (tiny!) and light. The design should be suitable for any small HF rig (and maybe 6 metres) with an easily accessible point to measure the VFO.

I put together a design and just ordered PCBs. BOM cost is on the order of $25 in single quantities, and a good $5 is the TCXO I selected in the interest of needlessly chasing accuracy. That should give it 10Hz resolution at ~10Hz refresh, with 0.5ppm stability.

The design is based around the VIM-878 LCD module I chose. This is an 8-digit 14-segment (starburst) LCD that seems about the right size for integration into a small rig. Next I picked the TI MSP430F4132 as main processor, thanks to its included LCD driver, cheap development tools (the $5 MSP430 Launchpad) and my relative familiarity with the architecture.

Basic topology will have an input amp driving an 8-bit counter directly, with the carry connected to a counter in the MSP430. The external counter is gated by the processor from a timer; the same edge also captures the carry count in the other timer module; the processor is clocked by the TCXO divided by 2 with a D flip-flop to get it close to the MSP430's maximum clock.

Boards should be here in a few weeks and I can start fooling around. I wonder if anything will work first try...


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It's been a while since I've posted here, and many of the things I pledged to follow up on... haven't been followed up on. I've started several blogs in my life, and never seem to get past the 10 past mark without losing interest and giving up. This one's no exception, but if anyone is following this (or reads it in an archaeological dig 100s of years from now), here's the short version:

  • Stratum-1 NTP server—this one I finished. It's an ATNGW100 (AVR32 processor) single-board computer running OpenWRT with a modified kernel (and fixed ntp package) to enable a GPIO interrupt to trigger PPS input. GPS is a Motorola Oncore UT+. All packed into an aluminum case designed for an ALIX board. Unfortunately I think I've lost my OpenWRT modifications in a source control "accident" and I was having trouble getting a nanokernel working, so it's not as good as I'd like. But it tracks to better than 1µs according to ntp. Good enough for me.
  • Arrow OSJ 146/440 J-pole—this thing is great. It's just mounted on a 6' fence and booms into all the nearby repeaters. I haven't tested it to find its limits, but it works well and looks practically new after being mounted for a year. Great value, no complaints at all.
  • APRS Tracker—I got pretty far with this one. The modem works, the GPS interface code all works, the hardware works. It's a working tracker. But I haven't got around to creating any kind of configuration interface or adding 'nice to have' features like smart beaconing, carrier detection, radio power control or any sleep modes. Needs a new power supply design too. Maybe I'll revisit it in the future, maybe it's another on the never finished pile. If anyone's interested in design files or code, I'll send what I've got if you ask nicely.
  • UHFSDR—works, sort of. I'm not quite sure what the issue is, but the noise floor seems rather high and consequently the sensitivity and signal quality is awful. It does work and I can pick up strong VHF stations easily, but the local airport's ATIS is barely perceptible, while it comes through loud and clear on my IC-2200H's air band receiver. I even built an SDR-widget to see if that would help, but it makes little difference. I can't find anything wrong with the board, everything seems to trace out alright, so I've basically given up on this one. Unless it's something in the transformer DBM, can those things go wrong?
  • Mobile VHF antenna—my last post was about a shoddy mobile VHF antenna. Well, I replaced it with a TRAM 1180 dual band antenna, properly mounted this time on the trunk lip. It feels solidly built and works well, no complaints.

I've also obtained some new equipment and toys:

  • HP 8657A 0.1-1040MHz generator—bought on eBay "for parts or not working" for a steal. Turned out to work well, I went through the alignment procedure in the service manual and it appears to work perfectly. It was useful for determining that the UHFSDR was indeed not working for shit.
  • Rigol DS2072 70MHz DSO—bought this guy new as a Christmas present to myself. I'm spoiled. Now to figure out how to hack it to the DS2202, which has identical hardware inside...

So there's the state of affairs. You're up to date. I'm going to see about maybe posting more often, I've got another pile of related projects in the pipline now. Hang on for announcements of those, long before it's clear if they'll be completed.


Workman WEP2000 - killed!

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A couple posts ago I mentioned the WEP2000 I'd purchased to give mobile VHF a try, contrary to my original plan to just use it for APRS. For a while, I was reasonably happy with it; it was a pain to tune, but I was getting good signal reports and receive was good enough for my purposes. In the past week or two though I'd noticed that while it was working, the receive power was much lower than it should have been, so I went to check the tuning on the through-the-glass box on the rear window. What I found was unpleasant - the tuning slug's plastic threads had melted and it was completely seized and askew. No wonder the receive wasn't working very well - and transmit neither.

I guess I only have myself to blame - I had it hooked up to a 65W radio and it was only rated for 25W (though RadioWorld, who I bought it from, claims it's good for 50W - I think not!). Most of my channels had the radio turned down to its 25W setting though - certainly any that I was making my infrequent QSOs on, anyway; I'm not a wordy or outgoing one. So while the ultimate blame may lie with me, I still can't recommend this as a robust antenna. I'd expect that a lengthy QSO even with a 25W radio would roast this poor matching/coupling box.

Verdict: don't buy unless you're running true QRP, in which case it's decent value for money, being very cheap.

Antennas Ordered & Future Projects

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Shortly after getting my ham license I started fooling around with antennas. Built myself a very shoddy 2m ground plane 1/4 wave just to get an antenna outside for use with my HT, as the whips can't get anywhere from inside. Then I decided to upgrade to a proper antenna - a coaxial dipole design by W6NBC published in the July 2009 QST. This worked fantastically well for a couple of months, then a solder joint broke between the antenna connector and the radiator element. I've repaired it, waterproofed it better and it just doesn't work anymore - I'm scared to transmit into it as the receive signal is so bad. I've taken it apart several times and reflowed the problematic solder joint to no avail - it seems something inside the lamp-tube coax has gone wrong. Given how much grief this design has given me I decided to just pay for a commercial design that will work properly. I considered building myself one of the popular copper pipe J-poles, but without equipment to properly tune it, and with the price of copper it's as expensive as buying one and not nearly as foolproof. I want something a little more substantial than the ladder-line J-pole design.

After a look around at some of the inexpensive designs, I thought I'd stick with the J-pole design and go for an Arrow OSJ 146/440 dual-band J-pole. Based on the reviews this seems to be a well-built, well-performing antenna that should be small enough not to be obtrusive. The only other serious options at a similar price were poorly-constructed ground planes. Anything else decent was about double the price. So I'll give a try, it was only $40 after all. I just have to remember to take care to waterproof the coax connection...

Since I was making an order with a fairly substantial shipping cost, I figured I'd also pick up something else that I want for an upcoming project - a cheap, small, easy to hide VHF antenna that doesn't need great performance. I'm working on a from-scratch APRS tracker design (and making good progress!), and would like my own install to be somewhat 'stealth'. I've selected a small through-the-glass design by Workman, the WEP2000. This antenna probably sucks, but with the 25W radio I plan to use, and just for APRS tracking, it should do the job and fit the criteria of being simple to install and hide-able enough to be less-than-obvious. Perhaps I will swap it for a simple HT antenna used internally to the car later, and use this one for a real radio. We'll see how it performs... it can't be worse than the HT+whip I'm current using while mobile! This little guy was only $25, including a whack of coax pre-attached.

I've also begun construction on the UHFSDR by WB6DHW, which is a 1.75MHz - 700MHz RX/TX SDR based around the Si570. I'll need to add some filtering and a poweramp for serious use, but it should be fun to play with even on its own. Stay tuned for more on that project, as well as my APRS tracker once I get far enough to begin real testing on that.