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