March 2013 Archives

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...

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.

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