just finished a colpits oscillator for the DC Rx

Spent a couple of enjoyable hours here on the workbench building up a colpits oscillator, which is very similar to the one recently build by Bill, N2CQR, see over at the SolderSmoke blog.

You can see the frequency counter, 10.13805 MHz. I spent some time mucking around with the variable capacitor in series with the crystal. At best all the options I had would move the rock up or down by 100Hz. Although later when I mounted the variable capacitor in parallel with the impedance matching transformer, I noticed that it would pull it a total of 4Khz. Not sure if this is the right way to tune it, but it seems to work for now. So set it up for 10.140MHz, assembled the LO board into the little case. Hooked the audio and power up to the peecee and fired up QRSS-VD.

So much noise! I turned off everything that I didn't absolutely need and went around rearranging cables. So now the capture is cleaner. However there don't appear to be any QRSS signals in the air ...

Will do more tinkering later and check the clipboard. May need to do a lot more work on the dipole.

Kim VK5FNET

QRSS receiver up and running

Well its taken a good long while, but I've finished off the QRSS receiver and have a grabber running. I'm not picking up any obvious signals. I have not checked the clipboard, but thought I'd tinker around anyway.

Seems to be something weird going on with the oscillator, I can't get the frequency counter to pick anything up under 66MHz, which is way out of the ball park. I noticed that when I bump the crystal or hold my finger on the crystal the capture changes significantly.

So may need to move the oscillator off the main board and box it up and put a high impedance buffer on it to be able to check the frequency with the external counter.

more work on the DC Rx

Spent several hours in the shack over the weekend. Heres the results;






Now need to add power, a 5V rail and the audio out.

More work on QRSS DC Rx and a photo

Its been a slow week, been home crook most of it. Done a few odd jobs around the house and have been meaning to post this image for a few days. Made a saw horse for working with longer lengths of timber. Getting the paint striping out of the way, so we can repaint the study. Along with lots of reading.

Have added some more components to the QRSS DC Rx. Took this photo before adding the front end capacitors. Spent some time working out a replacement for the T37-6 transformer. Came to the conclusion that I couldn't do it with the materials that I have. Terry has come to the rescue however, he has just received a parcel of various toroids, transistors, etc. Terry has offered to send me one, so I am expecting one in the mail any day now =) This has been along time coming. Really looking forward to getting this rig on the air!

Ooops, just realised that I've not yet put on the feedback resistors... More work to go =)

72,

Kim VK5FNET

Making a band pass filter, or I hate toroids

I have made some progress on the NE602 direct conversion receiver. I have layed up most the components onto a copper clad board and I now need to add the band pass filter and the front end interface to connect up to an antenna.

I hit a similar problem with the Pixie2 I made previously. I don't have access to any of the named toroids that you find in the HAM radio journals and books. You know, names like T37-6. So I'm doing the numbers to try to lash up a air-space coil instead.

I'm reproducing the 30m QRSS Receiver as built by Hans Summers, G0UPL. Its a hardware defined radio that outouts audio to a peecee to decode.

I have a handful of plastic coil formers that appear to be 1/4" x 1". They have a fiber board on the bottom with five terminals to connect you inductor elements to and your pcb.

So using the calculator at kitsandparts I worked out that following table;

Turns	Inductance
2	0.01uF
5	0.07uF
35	3.67uF

So I've spent half the day crunching the numbers to work out how to get an air-spaced to get the numbers to match the above... The numbers just don't work =/ I'm sure I'll find something and maybe I'll just have to put a bunch of cash aside and make an order to the US.

72,

Kim VK5FNET

new 10m dipole

Replaced the dipole this morning. Cut to length some pvc coated speaker cable that had once been an end fed long wire. Its light and grey so not so easy to see as the red 30amp power cable I was using before. Also ran coax straight up to the center of the dipole and will run a similar arangement to the QRSS Rx of Hans Summers, G0UPL. Now onto modifying the receiver =).

72's

Kim - VK5FNET

QRSS receiver crystal for 10 meters

The 28.188MHz crystal arrived today from Nick, VK1AA. Have been hanging out for it to arrive and would really like to get a receiver up and running.

This weekend looks like being a scorcher, about 38c, so a bit of indoors building will be in order. Which also leads one to think about oscillator stability. With night time temperatures of 15c to day time temperatures of 35+c degrees there is plent of room for drift.

Thoughts on work to do;

• An antenna for 10 meters; vertical or dipole?


• If heading down the di-pole route, balanced or OCFD?


• Maybe a balun?


• A transmission line should be straight forward, I have some spare clean RG-213.


• How about a tuner, then how do I measure if its really working?


• If a vertical, what about a copper cactus or a just a 5/8 vertical?


• Should I make the local oscillator in a separate box?


• If so I could drive the Kenwood to TX test ... wonder what specs are required to drive its VFO port?


• Then modify the 'sudden tunner' style DC receiver. Based on an NE602 and LM386.


• Hook up to peecee with 96KHz sound card.


• Grab with glfer or baudline.


• Announce its ready...


• Later develop something more focused around web based delivery.


• Find a design for a non-computer 'controlled beacon'. A condition of the Foundation Licence.


• Perhaps a beacon controller as simple as a pair of NE555's and a 4017. The first NE555 at a 30 second on/30 second off interval, driving the clock line of the 4017. The first output pin of the 4017 could then drive the second NE555 with a 3 second on/3second off interval. Effectively sending a '5' every ten minutes in QRSS 3 second dots. The '5' being from the call sign of VK5. My call sign being VK5FNET. But thats a job for another time, but would be nice to know what folks think...

So, thoughts on work to be this weekend;

• Get any antenna up


• Get a length of RG-213 terminated with PL259 connectors


• Blow the dust of my 4:1 balun I made some time back and check the connectors out


• Modify the 80m DC RX to run on 10m


• Patch up some audio cable for the DCRx to peecee sound card


• Work out how to capture images or do screen dumps from glfer


• Announce it...

Doesn't sound like much on 'paper', but on top of the domestic chores should be a busy weekend.

72's

Kim - VK5FNET

10 meters

On the Knights QRSS mail list theres been talk of activating more HF bands. Specifically 10 and 15 meters. There issues with activating 40 meters as there are access issues for non advance licences in the US and band plan issues across Europe. Not 100% sure how 40 meters is carved up elsewhere, but in Australia, Foundation, Standard and Advance all have access from 7.000-7.300MHz.

There have been a couple of contests on 10 meters with some success. This has lead to conversations on list to start putting SDR receivers and QRSS transmitters on 10 meters. The 100Hz QRSS band is 28.188,000 - 28.188,100 MHz. Folks have used other portions of the 10 meter band, around 28.322MHz if I remember rightly. Which seems to be around the QRP and QRO un-manned beacons.

Nick, VK1AA who is shipping the G80, G40, G2030, and G5 Genesis radios, has put up an offer to send out a batch of crystals on 28.188 MHz to folks free. So long as they get a MEPT or receiver up on the air for QRSS. I shot off an email straight away and am still patiently waiting for it in the mail.

I have started mods to the W1AW NE602/LM386 direct conversion receiver I build up for 80 meters. Needs rework on the band pass filter and local oscillator. Should be fun!

72's

Kim

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; www.kenneke.com/~jon/pixie/

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

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.


Kim VK5FNET