June 2010

20m contact made on the bicycle mobile station

Well, I can’t call it a “bicycle mobile” contact per se… it was made using the bicycle mobile station however. This afternoon about 1:50PM UTC+10 I made contact with VK100WIA being operated by the South Coast Amateur Radio Club at a frequency of 14.188MHz USB.

The station was being powered by mains, and transmitting 100W (most of it probably rattling the tuner) on a 6′ long CB whip mounted on the back of the bicycle mobile station. The SWR without the tuner was very high, so I’m going to have to look at tuning this in a lot better than it currently is. I registered a S5 Q4 signal with the other station, who was a perfectly clear S8 Q5 copy at my end. I was also hearing New Zealand elsewhere on the band… very stong signal.

I will need to tune the antenna up quite a bit for it to work on 20m… I’m surprised it even worked at all! I tried a few other bands… 10m was dead quiet, couldn’t get any of the FM repeaters, no activity. 6m, I could trigger VK4RBX at Ipswich, but no one about it seems.

This is from my driveway at my home QTH … not in a high location. So a bit of peddling up the hill and I might get quite a distance with my rather limited antennas… but I’m going to see if I can tune the thing in a bit better. My observation of others’ is that one does better when the tuner is an integral part of the antenna, and this is what I’m going to have to do. If the tuner is going to have to do hard work, then let’s get it out into the open and helping the cause.

In the meantime, I’ll have to print a couple of QSL cards… I still need to send one to Mario OS8M from the Christmas evening contact I made on 20m… but it’s only just now that we’ve got a working printer again.

VK4MSL/BM Part 2: Upgrade of bike… upgrade of set… HF here I come

Well… just this afternoon, I made some steps towards getting HF going on the bicycle mobile station.

I’ve had the station going a while now… and with the new workplace being so close to home, I’m often heard on 2m, usually on three repeaters:

  • Bayside VK4RBS: 146.875MHz FM
  • Mt. Cotton VK4RAX: 147.075MHz FM
  • Mt. Glorious VK4RBN 147.000MHz FM

Usually, it’s VK4RBS in the centre of town unless there’s activity on VK4RAX.  VK4RAX as I get closer to home.  I’d listen to the latter all the way, but pagers clobber the receiver on the poor FT-290R II.  Hearing pagers is bad enough … try it through a headset!  Made worse by the fact that the headset is a semi-homebrew design, embedded inside a motorcycle helmet… so I can’t easily take it off.  Once I’m out of the city however, the pagers aren’t an issue.

Range is pretty good… I use a quarter-wave ground-plane antenna on 2m… actually, the antenna itself is the same as on my previous bicycle-mobile station… a tunable whip antenna.  The antenna is intended for mobile use on a car, so to give it a reasonable counterpoise, I cut a 500mm long piece of aluminium angle, and bolted the antenna mount to that.  I found that alone, wasn’t good enough, and since added a 500mm long piece of copper wire that hangs out the back.  That brings the SWR down nicely into the range where the FT-290R II is happy to work with it.

I have been able to open the squelch of the Toowoomba (VK4RDD) repeater, once waiting at lights at West Ashgrove, and another time, underneath the Goodwill Bridge at the Queensland Maritime Museum near South Bank in Brisbane.  I also can work the Ipswich repeater, VK4RAI while walking up the hill along Cooper’s Camp Road at Bardon… about a distance of 80km out to the repeater’s location (near Marburg).

This is using the FT-290RII with the 25W linear option, and the aforementioned antenna.

This afternoon, I figured out how to interface the electret microphone in the headset to the FT-897D.  The wiring standard I use for my headsets is a customised one… using DB15HD connectors (VGA-like).  A female DB15HD exists on the headset side, this is to prevent some goose trying to plug a headset into a VGA card on a computer.  The following is a rough schematic of a typical headset using this wiring scheme.

Typical headset wiring schematic... looking into female DB15HD connector.

There are three pins that are normally unused… On a couple of my interfaces, +5V and 0V are wired up… it was initally thought I’d use these for power rails … one supplied by the headset (one of my planned “headsets” was a former in-car hands-free kit for a Nokia 3310, and so you’d be able to charge the phone this way), the other supplied by the device (many radios supply a 3.3V or 5V rail).

For the FT-897D, the microphone used is normally the dynamic type… that is, uses a balanced (differential) audio feed.  On the FT-290R II, I tie Mic – to 0V, and just use it single-ended, which works fine… but a better way is to actually convert the single-ended microphone signal to differential.  How does one do this?  Well, the answer came out of the TI TLV320AIC3204 datasheet which I’ve been reading quite a bit lately.

TLV320AIC3204 Typical Circuit Configuration, showing microphone wiring (Source & Copyright: Texas Instruments)

Typical electret microphone configuration (Source: Wikipedia)

I noticed something odd about the way they wired up an electret microphone.  Rather than wiring it up as shown on the left… they instead mirror the positive side; feeding through a resistor to 0V, but tapping off via a series capacitor to the CODEC input (see right; click image to enlarge).  Why were they doing this I wondered?  Then I found it.  Inside the electret capsule is a J-FET which amplifies the weak signal from the microphone itself.  By hooking a resistor on both sides, and using two capacitors, they were creating a phase splitter.  I stumbled across that article on Wikipedia, and it was then I knew what they were doing.

So I’ve done the same thing here… Rather than a single-ended design, I have interfaced the electret microphone to the radio using the phase-splitter technique.  The schematic I use (with DB15HD pinouts) is below:

FT-897D Headset interface

I’m yet to take the whole shebang for a ride… I have a 6′ long CB (27MHz) whip that, last time I tried, tuned up nicely on 10m and 6m… might work somewhat down on 20m. I have had a VK2 station come roaring in at S7 when listening on 80m via this antenna on the back of my fold-up bicycle, but unsurprisingly it’s pretty deaf there… I plan to get a second antenna mount and suitable spring (so the antenna doesn’t get snapped by a low branch), make up a new bracket, and mount that some time in the coming weeks… then we shall see what the bands are like around Brisbane.

Getting back into Gentoo

Well, after a long hiatus that must have seemed like an eternity for some, I’m starting to dust off my old MIPS boxes and getting things back up and running again.

I’ve shifted positions, and now work at West End as a subcontractor for Jacques Electronics, and so instead of my journey starting from The Gap at 4:30AM to arrive at Laidley at 7:30AM, I jump on the bike and pedal 1.5 hours to West End. The work involves some embedded Linux development on Freescale i.MX27… and for some of my work, I’ve been using a cross-compiled Gentoo environment as a NFS-root, and on the device’s NAND flash.

This means I have a lot more time to do things. Amongst other things, this includes getting Gentoo stagebuilds back on track. One blocker to this progress has been issues compiling gcc 4.4. In short, I get an ICE (internal compiler error) whenever I try, and others have reported the same thing on their systems too. I couldn’t get around it using the compiler on the machines I have available, and my desktop computer was down with dead HDDs, so I couldn’t use that to cross-compile anything either. So the project was stuck at that point.

Fast forward to now… I had some money streaming in from the last project at Laidley. As far as I knew at the time, all that was wrong with my desktop was dead HDDs (it had 4 SCSI HDDs on an Adaptec controller). SATA had improved a great deal since I moved the machine to SCSI (at the time I was fed up with IDE drives dying), so I decided time to move to that. I also decided to upgrade my netbook computer, and my laptop. So about $350 got spent on 3 new HDDs (1 3.5″ 1TB SATA, 1 2.5″ 500GB SATA and 1 2.5″ 250GB IDE) and one PCI SATA controller (Silicon Image SiI3114-based).

The Yeeloong has an odd quirk with the new 500GB HDD I put in it, but luckily, easy enough to work around — in short the PROM doesn’t see the HDD, so I boot grub2-yeeloong off a USB flash drive, and that loads the kernel. Once the kernel is loaded, the system runs fine off the internal HDD, so it’s a minor inconvenience… and could be seen like an “ignition” key required to start the computer.

My other laptop, a P4M 2GHz took to its new HDD no problems, expanding the disk from 40GB to 250GB, the biggest I could get. My desktop however, it turned out there was more dramas to be had. The motherboard (an ASUS CUV4X-D) appears to have developed other faults, and now the machine is unworkable. Scratching around, I managed to scrounge an old Duron 900MHz CPU and motherboard, with 512MB DDR RAM… so into the case that went, along with the new PCI SATA controller and the HDD. Had all sorts of fun and games getting Windows 2000 to install onto the HDD, getting the machine to boot from the HDD, and other issues.

The booting issue was solved when I used the RAID utilities (from a Win2k install on an IDE HDD) to update the firmware. I put together a Windows 2000 Pro CD with SP4 and the RAID drivers and since then, the machine has been happily dual-booting Gentoo and Windows 2000. I also had FreeBSD on there too, but I’ve taken that off for now, might put it back later. The only issue I have is with the video card (which was from the now dead desktop), a HIS Radeon 9200SE. It works fine in 2D only, no 3D acceleration on Linux, and no acceleration at all on Win2K… I did have acceleration going there, so not sure what happened… but 2D is enough for what I do anyway.

As I type this I have successfully built a toolchain for mipsel-unknown-linux-gnu. I have a mips-unknown-linux-gnu toolchain being built, and currently I am cross-compiling (canadian-cross) a version of gcc-4.4.4 for mipsel-unknown-linux-gnu which I intend to install on my Yeeloong to get me past this blocker. I’ll do the same for mips-unknown-linux-gnu once that is done.

With new o32 stages on their way, I can then take another look at n32, and possibly n64 in the more distant future. None of the SGI machines boot properly at present, although 3 out of the 4 turn on, so that’s a start. The fourth (my Octane) I’ll have to have a closer look at, but last time I tried turning it on several months ago, it was dead as a door nail.

I don’t see myself getting on IRC anytime soon… I’m not about when most people are available to talk to me, and for non-realtime discussion, email is a more efficient medium, so I might as well stick to that. At least I have some systems back online however, and some development work will resume once I figure out what the present status is. And next financial year, I think a new desktop computer is in order. 😉