Sunday, May 24, 2009

2 Meter Portable Ops

Yesterday Karl VK5FOSS and I VK5FNET, worked through the check list to do a test set up for the 2 meter portable rig. The aim was to get all the kit together for operating in the field. Why would we do that you ask? Well last year I wasn't really quite ready for either of the rallies that we worked at. The ROSA and the Classic Rally of Adelaide. Both time Karl and I worked as radio operators. The main function of the role is to record information on the stage and pass this information as 'messages' to Rally Control.

HAM radio operators work under the banner of WICEN. WICEN is an organisation for emergency radio communications to help in message passing for the emergency organisations like the Country Fire Services, Police, Ambulances, etc. The aim here is for radio operators to work well under pressure to get messages through under tricky conditions. I've been told that despite the technical problems I had at the rallies, I did a good job and should continue working in this field. So once I am confident I have useful portable kit I will join WICEN and do more formal activities with them. Here is a summary from the de-brief of the last rallies.

Anyway, so yesterday we made a list of things we are missing and working to narrow that down. Along with places to find said missing items. Things like; good rope, large non-black tent pegs, tubing for another mast, extra RF patch cables, another dummy load, a good box on wheels that can be pulled or pushed like a sack truck and fix my SWR meter.

So later in the day we put together a couple more patch leads and a 7.5watt dummy load for Karl. I have also spent a fair bit of time working on the SWR meter. I looks good to me, but I think I'll follow up with some of the local HAMs to confirm that its accurate as I had to repair the input connector. Which meant disassembling the whole thing and rebuilding it again, which means it will need re-calibration.

Was planning some more study for the next exam today, but a long list of around the house jobs are yet to be done. You know the ones, mowing, digging, weeding, tidying... Maybe tonight =)
The main reason I need to push to get these exams out of the way is that I really want to work packet at the next rally. This is where my radio/linux/networking/computing interests all meet. There is so much stuff to explore in this space, thankfully it doesn't seem to change very fast, so I will have a chance to catch up =) Then I can start work into the areas of HF and 2 meter packet radio with some of the local guys. Not sure where that will end yet =)


Progress on NE602 based direct conversion receiver

So today I stayed home due to brain pain, it had been building up for the last few days. Also I had difficulty with my balance. To the point that walking involved bumping into everything. Lots of water and pain killers helped a little, breakfast and coffee later helped a little too. However the head ache didn't wear off until late into the afternoon with more sleep. So I spent some of the day sitting down, tidying the shed.

The cool thing about that was I found a couple of little paper bags with parts that I had bought months back and promptly filed for safe keeping in boxes! Anyhow, that list of parts contained an SA602, 3.579MHz crystals, a variable poly-cap, a large breadboard and some zeners.

This was all the missing parts for the NE602 based direct conversion receiver I've been wanting to build. So late this afternoon I sorted out all the other parts, put them in a box and setup on the kitchen table to assemble. My soldering iron and other tools are currently at a friends, so I pretty much had to assemble everything up on the breadboard.

Made dinner, a tasty curry with shallot pancakes. Then assembled it as per the circuit from W1AW. I am not sure where I first found it, google has a few references to it about. There are also a few variations on the NE602 direct conversion receiver, like the MRX-40_Mini_Receiver and another that I like using LC tank circuits for both the RF input filter and the oscillator side.

I fired it up but heard absolutely nothing. Much comparing with the diagram led to adding the vcc and ground rail for the LM386, after which I could hear familiar hash with the speaker held very close to my ear. I dug out the Pixie2 hoping to create some kind of signal. However the oscillator from the Pixie2 did not create the expected signal or inteference on the DC receiver. So this needs looking at another day when I can focus for more than ten minutes at a time. Hopefully this coming weekend wont involve any more headaches.


Fun with radio - part 2

Now that I have built a receiver, as the first stage in a QRSS grabber, how do I calibrate it?

I commented in Bills blog, SolderSmoke News, about the how the two pixie 2's David Rowe and I built were not on the same frequency despite being the same circuit. They are about 2KHz apart, which we put down to the tolerances in the components.

My HF rig has a 'digial readout' that measures down to 1KHz increments. QRSS uses a 'band' of 100Hz wide. Thats right, a tenth of what my smallest increment on the HF rig. So how to I measure that?

I'm looking to build a frequency counter or meter. Are there homebrew designs out there?

kim vk5fnet

Fun with radio - part 1

Yesterday I spent an afternoon working with David Rowe building a Pixie 2;

The Pixie 2 a tiny direct conversion radio intended for training new HAMs in under standing radio and building electronics. The initial build was a little bit troublesome as the oscillator wasn't. This makes it quite hard to build the rest of the radio, as it can be built in stages; the oscillator, the PA/detector, the audio amplifier.

Well the afternoon turned out to be quite productive and with a working radio picking up Davids Pixie transmitting from a foot away on the work bench. It puts out a whopping 200milliWatts and the output waveform on the oscilloscope was very sinusoidal.

David has a full amateur radio license and is a very cluey electronics engineer. I have my foundation license, so while I'm not worried about building a transmitter yet, I am quite interested in software defined radio(SDR) and QRSS. Which is what this project/journey is all about.

Whats next? Well as I now have a DC radio with audio output, SDR being the end goal, the next thing to build is the audio interface to the laptop so I can get the Linux QRSS client running...

kim vk5fnet

Band Pass Filters

Last night I built up an input band pass filter. The point of this little beastie is filter out the RF from above and below the band or radio frequency that you want to receive on.

I found a page on the band pass filters.

So the original Pixie 2 circuit - a direct conversion receiver I'd like to use for QRSS - has a low pass filter. Firstly, the reason the BPF project was started, is to remove all the spurious noise from other bands. Mainly the huge signal from the commercial AM broadcasters around 1.8MHz. Secondly, I want to make pretty sure that I'm not spraying harmonics across higher bands.

Some testing with the original LPF from the crystal oscillator shows a nice sine wave like signal with some noise on the peak of the upper cycle. However the Chebyshev BFP has lots of harmonics and looks like its attenuating a lot. I need to get some advice on reading the output of my CRO. Also a spectrum analyzer would be a very hand tool. But I'm not real happy with the output of the Chebyshev, it actually looks worse than the input side from the oscillator.

It seems, on advice from VK5TR / VK5JST, that many of the generic toroids from Altronics, DSE & Jaycar, may not have a suitable Q factor. Jim suggested the FT68-41 toroid cores. The suggested core is the T94-6. Will have to find a source of toroids specifically for the purpose. Not found any local suppliers, but will keep looking.

BPF == band pass filter
LPF == low pass filter
HPF == high pass filter
CRO == cathode ray oscilloscope
harmonics == multiples of the frequency that you are generating


More on toroids

Been searching for info about the toroids from Altronics. Setting up a band pass filter for the QRSS receiver.

The L4534 seems to be the same dimensions as the T130-2.

OD = 1.30 / 33.0 mm +/- 0.02 in
ID = .780 in / 19.8 mm +/- 0.02 in
Ht = .437 in / 11.1 mm +/- 0.025 in

Also I've found a useful site on the standard sizes.

The T130-2 has a AL of 11 +/-5%. So then to calculate the inductance like so; uH=(AL*Turns2)/1000

The L4517 does not match up to any of the standard sizes. Its just a bit bigger than the T50-2. So I'll use that as a model and obviously subtract some turns ...

I have three of the L4517's would with 36 turns of 0.5mm enabled wire for an inductance of 12uH. Now to pick out the capacitors for the BPF. Then find the smallest way to build it all up on copper clad board for the Pixie2 in the Haighs tin.

kim vk5fnet

Fun with toroids

The aim here is to find an inexpensive source of toroids for kits for QRSS receivers. Jaycar and Altronics have a reasonable number of shops around the place and also do Internet and mail order, so folks should be able to get the parts easily enough.

Anyhow, some time back I picked up all the 15.2X8.53X5.94 toroid cores, L4517 the local Aztronics. They sell from the Altronics catalog. So these cores are not standard sizes or models that are used in HAM radio, so far that I can make out. They are pretty close to a T50-2, as they are supposed to be iron core, but are a bit larger diameter. Using 0.5mm/24bs enameled copper wire, WW4016, from Jaycar, I've spread the turns out over at least 80% of the toroid, values as follows;
  • 10 turns gives 0.001mH

  • 20 turns gives 0.003mH

  • 25 turns gives 0.005mH

  • 36 turns gives 0.012mH - for 3.5MHz BPF

I could probably squeeze on another 5 turns, but 10-36 turns covers the inductance that I need right now. Perhaps other gauges of wire will yield other usable values. These toroids as they are setup are intended for low pass filters or band pass filters. The Pixie 2 needs just one in its current configuration. I intend to build up a better filter as there is lots of AM broadcast signal there when down on the flat in Adelaide.

kim vk5fnet

dreams of arduinos

Its one of those local public holidays today. Cup day or something. The kind that make you sleep in, warm enough to organise firewood and mow the back lawn. Well whats left of the lawn from the water bans and hot summer, but then theres the go inside time. Cool down with a chilled beverage and surf the 'net time.

I've been following the SolderSmoke blog and podcast, Bill mentioned that he put in a submission to Hack A Day about QRSS. Hack A Day is one of those sites that just gets the juices in the brain a pumping and thinking about building various things.

The first thing I found this morning was pluggable modules on an arduino shield, like lego blocks to enable fast prototyping of hardware and software.

The second was a two servo, four legged robot powered by four AA batteries and an Arduino.

The third was a tiny parallel supercomputer; the non-von1-supercomputer. There was another project a while back implementing a basic stamp supercomputer.

From a link somewhere I found one of the things that I keep crossing paths with, a home made Arduino board project. I found one today that set my mind racing off down the path of pluggable modules; the cheapduino.

So while not specifically parallel, but pluggable architectures of embedded systems. It could simplify the design of the individual board if a backplane had all the power, clock and a MPI interface for each CPU.

Perhaps a single USB connected backplane with a serial interface for each pluggable daughter board, in a simple frame that lets each daughter board have an edge connected I/O space. Something like the cards in a QBUS VAX. Smaller obviously, about five centimeters or two inches a side.

On that you could build a service per CPU, say, temperature logging, writing to a SD card, inrfa red comms., two wheeled robot platform built with servos, xigbee Tx/Rx, bluetooth...

I'm sure that there are loads of other ideas in this space. Its all about context and filling a need, its just strange some days where ones mind wanders... parallel pluggable embedded systems, which I'm sure one call call a mini-frame. Hmmmm ... theres an LCA talk in that I'm sure.


Saturday, May 23, 2009

Podcasts I've been listening to recently

Recently I've been listening to a couple of podcasts about HAM radio, homebrew, computers and Linux.

I have been hanging out for the next podcast from Bill N2CQR. Bill posts usually once a fortnight and keeps an interesting blog called SolderSmoke. Homebrew amateur radio, some travel log, some amateur astronomy and other related geeky things.

A couple of weeks back I found Linux in the HAM Shack, which is self explanatory really. Russ K5TUX and Richard KB5JBV, aim to walk you through all the popular things you's likely do with computers in HAM radio. Assume radio experience, but not Linux experience.

I have at least a hour bus trip to work and then another hour home again, so these podcasts help fill the voids in my head with useful radio thoughts =)


Friday, May 22, 2009

SolderSmoke the book has arrived

My copy of the SolderSmoke book has arrived. Much reading ahead.