Tuesday, September 30, 2008

80m QRP AM Transmitter - first contact!

Encouraged by the success of the beacon transmitter, I've built another version that is amplitude modulated using a 600 ohm telephone transformer.

The transmitter is just 2 transistors, (not counting the mic pre-amp and audio power amplifier), here's how it looks:

AM Transmitter.jpg

Whistling into the microphone looks like this on the cro:

AM Waveform.jpg

I'm certainly not getting 100% modulation.

I've just had a contact with Sam, VK2BVS, who reported that with his pre-amp in I'm 10dB over S9, with excellent quality audio "like the BBC".

Next step is to box all this up and make it a bit easier to switch from receive to transmit. (Currently I have to clip a clip lead on to power it and switch a co-ax switch).

The circuit is closely based on the beacon by Alan VK2ZAY. My construction is huge compared to his.

80m AM transmitter.png

For the audio amplifier to drive this I used a Jaycar "Short Circuits 3" #13 High Power 12V amp which seems to do the trick quite nicely.

Monday, September 29, 2008

80m QRP Beacon on the air

After biting off more than I could chew a few times recently, I've successfully built a QRP (low power) beacon for 80m.


It's on air at the moment on 3.686Mhz sending a morse ident with my email address so I'm hoping to get a few signal reports.

I think it's putting out about 250mW.

There are some obvious faults, I can hear chirp, clicks and when it's off carrier from the oscillator leaks out to some extent.

The keyer is an Atmel AVR ATMega816 which is complete overkill in this case.

The circuit is very closely based on Alan VK2ZAY's design except that I didn't have any 2N7000s so I've used a single IRF510 with a bit of bias.

I used perforated board with just a copper spot under each hole and it went together rather well (for me).

beacon board.jpg

I don't speak morse yet, but here's what I'm sending:


Anyhow, please tune in to 3.686Mhz and let me know if you can hear my slow morse.


Hi Peter,

Read about your 80m QRP beacon mentioned on hamnews and had a listen.

It’s peaking about S5 in Canberra. I’m using a TS-480SAT with a 40/80m trapped dipole. Here is some of what I decoded using Ham Radio Deluxe DM780 software:


As you can see I’m missing/badly reading some characters and have interference but the message is coming through, probably be better received by a human than a computer…but I’m no morse code expert…

Had QRM from SSB and another CW signal nearby by managed to filter most of it out.


Ian Sinclair VK1DI

Update 2

I'm taking it off air while.

Sunday, September 28, 2008

Valve technology needed for post nuclear sked

john.jpgThe NSW home brew "trash n treasure" meeting today at Dural was great thanks to the work of John Hale VK2ASU (left) and Stephen Lowing VK2BLQ (below).

Together they presented on the theory and practice of constructing using valve technology.

John handed around common valves including a tiny device and told the story of his first home made valve radio. The theory of how valves work, by using heat to emit electrons and then using charged grids to control their flow in the vacuum chamber is at once, both simple and sophisticated.

stephen.jpgStephen talked about where to pick up common valves even today and showed some of his past projects which are beautifully constructed.

The board he's holding here is a regenerative receiver that is powered by batteries including just 9V for the plate voltage.

It was pointed out the the electromagnetic pulse from a nuclear explosion (or even a devices specifically designed to generate an EMP) will kill most modern technology and if we want to have a chance to participate in the post apocalyptic radio skeds we'd better get on and build some valve equipment.


Luckily, the group that turned up managed to fit into the air-conditioned WIA hut today, but it's great news that the construction of a larger shed on the Dural block is finally going ahead.


I can still remember valve equipment (aside from that big tube at the front of televisions until recently), but my children have no idea about this technology.


It won't be long until all living memory is gone.

Saturday, September 27, 2008

The best hi fi system

tognetti.jpgLast night we were fortunate to have a wonderful experience - we sat in on a bit of a rehearsal of the Australian Chamber Orchestra.

I was able to sit right in the middle with the orchestra very close and all around. The communication between the players and Richard Tognetti, all done with body language and eyes, is fascinating.

The most impressive thing for me was the quality of the sound. I listen to too much music through small computer speakers and headphones, but it's amazing what poor reproduction even good headphones produce compared to the real thing.

There is a richness of tone from a bow being drawn across a string, I think the cello in particular, that doesn't seem to come across in recordings.

I recall hi fi sales blurb that used to claim that certain systems were "just like having a symphony orchestra in your living room", the reply was always to ask if that was really desirable as they'd drink your house dry.

Wednesday, September 24, 2008

One tree dies, an antenna will live

tree.jpgToday is tree lopping day. We're getting rid of a pesky liquid amber and a pine tree. Both of these shade the garden.

The huge gum tree is staying but I noticed that the tree men climbed the gum to tie ropes to liquid amber branches to control their fall. I had a bright idea and have asked them to run a line for me over a very high branch in the gum tree. "No worries" they said.

This means I'll have a loop of venetian blind cord going right up that very tall gum tree which I can use to raise up awesome long wire antennas or support one end of an 80 dipole.

These tree lopping guys are both smart and fit, here's a time lapse video with one frame taken every sixty seconds.

The job's done and I can definitely recommend Aura Tree Services they were efficient and professional. Great blokes too.

We have a lot more sky now and I'm back on 80m with good reports.

When I mentioned I'd made a stop motion video they were very interested and I gave them a CD with the high quality video on it.


The loop of venetian cord is in place so I can easily hoist things up 10m or so.

I first tried an end fed long wire but the noise on 80m was bad, so I've put up my old 40/80m trap dipole with one end up in the gum tree and the other end over the house to a tree in the street.

The new antenna is working really well. The extra height has further reduced noise, I've had some PSK31 contacts on 40m (7.040) and am hearing some magnificent signals on 80m.

Monday, September 22, 2008

BaristaReview site build

logo160.pngI'm pleased to report that I've built a real application in Django on Google App Engine.

BaristaReview is a site that I've always wanted, specifically to let me find (and review) coffee shops near where I am.

Although it's loaded with Australian cafes to start with, it's not localised except for it being in English.

The great benefit to me of Google App Engine is the low cost of entry and ultimate ability to scale right up to whatever success we might achieve without having to supply any hardware ourselves.

It's been a fascinating little project with lots to learn about:

  • Google App Engine

  • Google Maps and geocoding

  • Django 1.0

  • Serving images from a database

  • memcache(d) for caching images

  • integrating blogger into a sub-domain

There's still lots to do, not to mention the iPhone version people keep asking for, please let me know if you see bugs or unexpected behaviour.

Google App Engine is a little new and I do run into a few issues deploying sometimes, but generally the site seems to perform pretty well.

Please look up your favourite cafes and if they aren't there, go ahead and add them!

Saturday, September 20, 2008

Trying to build transmitter for 20m

A personal objective for a long time has been to have a radio contact with a home made transmitter. After many false starts I've focussed on a transmitter for 20m.

The oscillator now works nicely. Early attempts, it turned out, were running on totally the wrong frequency, that's now fixed (with a different circuit) and the waveform looks nice and puts about 1V peak to peak into 50 ohms which I think is 2.5mW.


The next step is to raise this level up to a few watts so that I can be heard at least by VK2BVS who lives near by.

In a burst of foolish enthusiasm, I added a gain stage followed by a class C driver and an IRF510 final, rather messy but the box will be good for the next iteration.


Alas the final oscillates magnificently, presumably my construction is far too spread out. I'm not deterred by this and will have another go this time using a design from Drew Diamond rather than random circuit snippets found on the internet.

I feel I'm making real progress, despite no outright success, my debugging skills are improving with experience.

Wednesday, September 17, 2008

Fence troubles

treeFence.jpgLast week's demolition of the back yard went so smoothly (if a little behind schedule) that I was starting to think that I had the knack of dealing with trades people.

With the demolition, the fencing and the (still to come) tree lopping, I went through the local papers and chose three companies to get quotes from. The winner was on a combination of the price, clarity of the quote and how much I liked the person (Geoff) who came out.

I won't name them, yet, but the fencing company that won the fierce contest to replace the old wire fence with a new colourbond fence has different people doing the quoting to the people who do the work.

Today the worker guy Bill came out and balked at the amount of work required to clear the brush along the fence line.


The quote said it would take 1.5 hours, he feels it's at least a day's work and I'd have to agree. Some of the brush, as you can see above, is really quite substantial trees.

My first inclination was to simply cancel and engage one of the other quotes, but the materials have already been delivered and I fear this could get messy.

Anyhow, the worker guy has now left and the company is coming out to have another look... more breaking news as it comes to hand.


Today, Friday, I decided to keep ringing "Pete's Local Fencing" of Collaroy until I got some kind of commitment that something was going to happen. After four calls, I'm told that Greg will pop by either Saturday or Monday to take a look, and that the job has been given to Matt to do.

Update 2

It's Tuesday. Greg didn't turn up. I left a message on Monday but they didn't ring back. Called again and Greg is in the yard for about an hour and will call me.. (I doubt it).

Monday, September 15, 2008

Cleared the back yard

Previous owners of our house felt compelled to fill the back yard with stuff. We've now cleared it and are on our way to a nice garden.

Here's before:

And after:

A few trees to go and then it's time for a veggie patch.

If you're in Sydney and looking for a company to do demolition, I can personally recommend C.J.E. Excavation & Demolition - very professional, polite and efficient.

Lost another hard disk - we love Time Machine

disk.jpgWe seem to lose a laptop hard drive about every twelve months and yesterday my daughter lost the drive in her MacBook.

There was music, documents, bookmarks, settings and of course a few vital assignments in progress.

A few years ago this would have been a devastating event but the good news is that Apple's Time Machine backup system is so simple to use that she actually does back up. She had done a backup the morning of the loss.

The drive was out of warranty so I trotted off and bought a replacement, re-installed Leopard and restored from the external Time Machine backup.

The process was smooth and easy. Great stuff.


I tried to get over the air Time Machine backup to work but kept getting an error saying it was "unable to mount" the server. It turned out that my problem was that I'd already mounted the server (in order to set it as the backup volume in TM). Unmounting it before starting the backup appears to be doing the trick.

The first backup looks like taking 5 hours for me.

Update 2

We now have wireless TM backups working from two laptops to a drive connected to an Airport Extreme. It's obviously not as fast as a local drive and I'm not sure what happens if you put the computer to sleep with that disk mounted, but it's certainly convenient.

Sunday, September 14, 2008

Current Dr Who series is excellent

Picture 1.pngI remember being really scared by the Daleks as a young child, and I've always had a soft spot for Dr Who.

This current series started out looking a bit like the high production value was out of balance with the plots but the last three weeks, here in Australia, with the two part "Silence in the library" and "Forest of the dead", and last week "Midnight" were really great.

7:30 Sunday nights ABC1.

Friday, September 12, 2008

Backyard sun path stop motion

I'm trying to figure out the best part of the garden to put the vegetable patch so today I recorded a full day of stop motion video using a little Nikon point n shoot.

It's not looking too good unless we do some serious tree downsizing. Of course it will be better in summer.

As you can see the removal of the swimming pool is pretty much complete, just some topsoil to come.

This stop motion feature of the Nikon coolpix is excellent. The camera ran from about 6:30am until after 5pm without going flat. None of my other cameras seem to have this ability.

Incidentally, I searched for something to turn a series of still pictures into a movie and couldn't find much. It turns out that good old QuickTime Player has this feature built in:
Picture 1.png

You just open any image in a folder containing the series, choose how many frames per second you want:
Picture 2.png

And you have a movie.

QuickTime Player is such a strange application, it does lots of useful things that make it more than a player.

VK2BVSs Awesome antenna

vk2bvs.jpgI've been pretty active on 14MHz again lately, mostly PSK31 where I chat with VK2ATC, VK2VFV, VK2PN, and if he gets back on, VK2ZAY. It's an amazing mode where, this morning I chatted with UA0QGG in Russia on just 5W.

Was tuning around and heard very very strong signal from VK2BVS who is quite near by. Today I dropped over to inspect his impressive antenna array. He's on all HF bands from 160M up and uses two collections of inverted V antennas connected together.

I don't think I'd get away with such a structure, err flagpole, here but it's something to aspire to.

Thanks Sam for your hospitality.

Wednesday, September 10, 2008

Reclaiming the back yard - removing the pool

When we moved in, we really didn't want a pool, but it came with the house.

I've maintained it for more then ten years, mostly cleaning leaves, adding chlorine, fixing pumps and supplying electricity.

It was the electricity that finally tipped me over the edge. As part of a daughter's school project we went around and measured the power consumption of things around the house. The pool pump, which runs between 5 and 8 hours a day uses 1,600W.

The other funny thing about this house is that aside from the pool, which really chops up the back yard, there's a two-car garage - in the back yard.


We decided to get rid of both monstrosities in one go. I'm working from home to the sound of jack hammers, but already I'm excited about the prospect of a larger back yard space and more sunlight.


This should be over in a few days, a new fence goes up next week. Later we'll add a small garden shed to take all the implements which are currently stored in a tent:


When the subsiding has settled, we have grand plans for a small vegetable garden. I've been listening to the excellent digitdownunder podcast for tips and ideas.

I'm thinking of one of those built-up style beds where you don't have to grovel on the ground to work on it.

Tony sent me some information on seeds, small fruit trees and a compost bin he recommends. So much to learn.

I am a bit worried about the lack of sun, you can see the shadows from the large trees here:

I plan to do a full day stop motion to see where the problems are soon.