recycled steerable dipole

I rescued an old teevee antenna from Karl before he escaped the state. (he has gone to vk7 land).
it had a number of 'large' elements on it for VHF and lots of small elements on it for UHF. =D

I striped all the elements off the boom and started looking at useful arrangements using the longest ones. did some numbers and worked out that i could use the largest and third largest elements and reuse the 'egg' insulators for a reflector element, then wrap an inductor around the 'egg'.... =)

Did the measurements, rough numbers for the coil, should be good for the middle of 10 meters. \o/
Put it together, then spent the rest of the afternoon cutting firewood. consequently I ache all over! =/

So after the pot-belly stove is fired up and the dinner is on the boil, I test the antenna to see where in the 10 meter band it works ok.

So it fails as a dipole for 10 meters. Rather badly actually the SWR > 5:1 across the whole band =(
Not to be discouraged I tested it on 15 meters. Bingo! The SWR < 1.5:1 across most the band. \o/

So lesson for today, is my modeling/measuring concept is right out. However the consequence is that if I tinker with the coil I should be able to find a tap point suitable for 10 meters. A job for next weekend though.

I










I've added some images of the process and what the final center and loading coil looks like.
It is not particularly self supporting, as the final elements are much longer than the original teevee antenna.

73,

Kim VK5FNET

80 meter DC Rx step 1 - Diode ring mixer

Decided to take a break from the QRSS Rx. Its doing _something_ but I don't know if its on frequency or if the bandpass filter is obliterating the incoming RF or if my antenna is really crap.

So I hunted around for another project to keep myself busy with in the mean time. Picked up a copy of Practical Wireless, February 2010. George Dobbs G3RJV, has a receiver first built in 1968 that he re-explores. An 80 meter DC Rx.

Thought it might be a simpler project to work my way through. Also if it pans out, would be good to take it along to the AHARS Show and Tell night.

We just had the AHARS Members Buy and Sell night, a week ago and I purchased a handful of T37's and T50's. This will help move along a bunch of projects I have been wanting to do for ages =)

So here is the first step, the diode ring mixer in the middle of the copper clad board...

I think I will put the band pass filter on one side and the oscillator on the other and shield them both. Then add the audio board on another copper clad board. Perhaps build it up in a Haighs tin...?

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

One 8 step sequencer running on the bench

I spent a bit too much time googling for synth music and sequencers over the last few days. I had a lot of fun just reading about folks projects and how they built up various kits or designed from scratch different arrangements. I have not really spent much time working with 4000 series or 7400 series ICs in the last ten years. Well not since first year Uni to be honest. That was a long time ago and my memory for truth tables is long forgotten.

So, I almost cheated but finding the friendliest schematic I could find and trying to build that up. You know how it goes, adapting part of this circuit as a stage one of your project. Well I had a few problems. My 4017 wasn't behaving at all! I spent several hours on the bench trying to figure out why I couldn't get the thing to behave. The first problem was that I missed a ground connection on pin 12, eventually running a bypass cap to the reset pin before it settled down and started to do the right thing. But the first LED wasn't behaving itself at all ...

Some further testing revealed that the LED in the first position was a flashing LED! So its now in its own draw, in the component cabinet. The 555 was a whole lot easier to work with and was pretty much doing what it was supposed to from assembly. The potentiometer has a dead spot right at the fast end of oscillator, so may need to swap the wires on the pads, or get a new 1megaohm 'pot'.

I will say that after having the 'friendly' schematic, I did change most the resistor values, add a few extra capacitors and lay it up differently on the plug-in breadboard. Its not a new circuit, but I learned a lot, mainly how to trouble shoot this little thing.

So what have I achieved here? More motivation to tinker in the shed/shack on the plug-in breadboard and play around with the circuit. Getting things working build up the motivation to do more. I have a tall ladder before me. I'm aiming to make the rungs nice a close together. Easier to climb that way ;)

Anyhow, happy homebrewing to all!

72,

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

mashup ideas: solar powered radio

From the maker blog a while back they ran a series of posts on joule theif.

Bill on the SolderSmoke blog ran a couple of articles on mechanically keyed transmitters, like the ET phone home rig, also a rew ideas around clock powered keying.

So my brain was buzzing away recently and it wasn't until I spotted the solar powered garden lights, that ceased to work a couple of months ago, that I thought about re-using them. The little solar cells only put out 0.8-1.1 volts. Three in series put out around 3.2 volts in full sun light. I need to go back and see what kind of current they can sink though...

To power something like an arduino keyed tx or a DC receiver with NE612, I would need a solid and regulated 5 volts.

It wasn't until this morning, on the irc channel of our local homebrewers, that I thought about mashing up the joule theif and the 80 meter DC receiver to make a solar powered radio =) It would make it limited to day light hours, but its certainly workable. Still have some other things to work on first, but certainly the next project on the list =)

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.

Kim VK5FNET

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

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

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 =)

Kim VK5FNET