Saturday, January 31, 2009

Crystal locked 80m direct conversion receiver

To go with my recently constructed 80m double side band transmitter, I've just completed a crystal locked direct conversion receiver.

DC receiver.jpg

The circuit is based on the Neophyte receiver from QST except that I used a crystal oscillator configuration in place of the LC controlled one.

It's an NE602 connected to the antenna via a single tuned stage, with balanced audio feeding an LM386 audio amplifier.

As you can see, it's very simple. I spend more money on boxes than on all the components.

I purchased a bunch of common crystals at 3.5795Mhz and have put one in the receiver and another in the DSB transmitter. I zero beat the residual carrier to match their frequency.

As Peter Parker commented on an earlier post, I am able to hear DSB on a DC receiver. He said that frequency stability was more important that with SSB reception so I went for a crystal locked receiver.

The next thing I need is a nice way to switch RF and power between transmitter and receiver - currently this process is rather cumbersome and takes too long.

I'll see if I can find someone for a fully home brew contact with me.

Update: First fully home brew contact

To make it a bit more practical to switch between receive and transmit I've constructed a switch box that switches both RF and DC between two sides.

The whole set up looks like this, the switch box is on the left:


While I did have to ring up VK2BVS to get him to tune to my crystal locked frequency, it was a great pleasure to have a conversation using a home built transmitter and receiver.

As the receiver was zero beat to my carrier and Sam had tuned to my carrier he sounded excellent right away.

The direct conversion receiver sounds very pleasant, as this one is crystal locked the only adjustment is a 1K pot on the antenna as RF gain - this works just fine as a volume control too.

It's a very happy day here at VK2TPM.

Friday, January 30, 2009

Amazing transmitter that uses an ATMega16 sampling audio in real time and instructing an AD9851 DDS to FM

The arrival of the WIA's "Amateur Radio" magazine is always a pleasure but as a home brew enthusiast I find myself flipping through looking for circuits (often from the fabulous Drew Diamond).

This month an article really caught my eye...


While I'm up to speed with the use of microprocessors I don't welcome seeing projects in many magazines that are just a Pic or Atmel chip with a bit of I/O and nothing else. What's more annoying is that the interesting part - the bit that shows how it works - the source code, isn't printed; so the article is not very useful on it's own.

Promoted strangely on the cover of AR as "A transceiver for an interesting and exciting band", Dale Hughes, VK1DSH presents his design for a 10m FM transceiver where the transmitter's microphone audio is sampled at 14kHz using the on-chip analog to digital converter. The chip converts the audio samples into the data stream needed to tell the AD9851 DDS chip to frequency modulate at the output frequency.

Bill wrote to me "Basically, during transmit the code enters a tight loop which does an auto-trigger ADC conversion then uses the previously converted value to adjust the current DDS frequency, so the output is always one sample behind. This happens at about 14k Hz and each DDS value is sent via SPI to the DDS chip which then updates its operating frequency. It's quite simple really and I was very pleased with the result."

It never dawned on me that these little chips had the grunt for real time audio sampling or that the DDS chip could be FMd like this.

The receiver is elegant too, based on a MC3357 FM receiver chip with the local oscillator also coming from the DDS.

Dale's email address wasn't easy to find so I wrote to the credited reviewer, Bill Maxwell, VK7MX who put me in touch. Dale quickly sent through the assembly source and also a slide show he presented at Gippstech last year about DSP with AVRs.

In that slide show Dale describes both FM generation and AM demodulation (the latter sampled at 7kHz), he mentions that SSB is not possible with the AVR. Mind you he's running the chip at 16Mhz and I'm sure I've seen some overclocking experiments.

Thanks Dale!

Wednesday, January 28, 2009

Back to my mac works

backtomymac.pngFor some reason it hasn't worked in the past. Presumably the combination of strict routers at either end and some problems with the implementation.

There's a bunch of things that can go wrong, but now the messages are much more useful.

Currently I'm running 10.5.6 and taking my Air to a workplace each day. I enabled "Back to my mac" on each end and was pleased to see my home machine - a Mini, show up and be amenable to screen and file sharing while at work.

Very handy.

At home we have an Airport Extreme which is able to do the right port forwarding. In the office whatever they have won't do it, which is fine.

Sunday, January 25, 2009

1000Km contact on home brew 80m DSB rig

rig.jpgWell, I'm absolutely stoked! I've just had a 30 minute contact with Peter, VK3EPW, who's in Melbourne.

Both of us running home brew transmitters. (He's running a home brew receiver too, but I'm not quite at that point).

Peter gave me pretty good reports, I'm around S8 to him, sometimes fading to S7 when I'm hard to read and sometimes peaking at S9 where I'm easy to hear. There's a fair bit of static from storms around tonight for both of us but we had a fine contact and my simple transmitter apparently sounds very good. "Sounded like a bought radio".

One question that came up for both of us, and I'll have to research the answer is: can a direct conversion receiver receive a double sideband transmission?

Feeling very positive about home brew radio tonight, but now it's time to go sleepy ni nis and dream of the next project.

NSW Home brew meeting at dural

We gathered at the WIA Dural site today for a show and tell and a talk on recovering components from PCBs.

The construction of the new shed is progressing well.


Contrary to my first guess, that isn't the roof on top of the slab, it's the walls.

There was the usual bits and pieces of interesting junk to pick through.


John has built a brilliant 3 transistor high gain audio amplifier that can drive headphones from small signals such as those from a direct conversion mixer.


Kevin showed a helical antenna he built for a Telstra wireless broadband setup on the edge of coverage.


John also showed a loop antenna for 40 and 80m built in a hula hoop.


The main presentation by Mark went through all the normally expensive or hard to obtain components that can be found for free in discarded circuit boards.


Mark had lots of practical tips of getting components off boards with plumbers soldering irons, gas jets, and heat guns. It's not a subtle art.


Alan, VK2ZAY has a nice writeup too.

8 Pole IF from VK3EPW

I've been publishing design and construction notes from Peter, VK3EPW and he's sent more information on his 8MHz IF. Rather than creating a separate post it's been integrated into the original article here.

Check it out! Peter's construction and dedication to shielding is something to behold.

Thanks for sharing Peter.

Saturday, January 24, 2009

Home brew 80m DSB first contact

homeBrew.jpgI finally debugged my rebuilt 80m DSB transmitter based on the design in Drew Diamond's first radio projects book.

The first version suffered from RF instability due to my poor wiring.

I've probably gone a bit overboard with nice metal boxes for the three parts: exciter, power amplifier, and 4Mhz low pass filter stages but it's paid off.


Very kindly Sam VK2BVS came on to the frequency and we had a good chat. At first he reported that I was distorted but in the end came to the conclusion that it was just that I'm about 50Hz lower than the 3670 crystal is labelled.

Later he said the audio was fine and the carrier very low (we've very close).

Anyhow, for me, this is a great achievement. I guess the next logical step is to build a receiver for the same frequency and a better arrangement for switching between transmit and receive - it currently involves plugging and switching.

Friday, January 23, 2009

Broke his neck erecting aerial

No, not me thank goodness. I enjoy looking at the 100 year old photo archive and today searched for "ham radio" and stumbled upon this excellent photo and thread of info.


It seems that poor Lester Picker fell 55 feet while erecting an aerial for the radio shown at his bedside. Poor chap.

Monday, January 19, 2009

Motels with "free wireless broadband"?

Sounded too good to be true, and yes it was. We stayed at the Sandcastles apartments at Coffs Harbour which advertised "free wireless broadband".


As we checked in I noted two WRT-54g routers on the reception desk. It turned out that the "freeness" only amounted to half an hour of use, after that you had to buy tokens in inconvenient combinations of hours and expiry times.

chair.jpgThey are running Chillispot and I certainly experienced some outages where I couldn't get an IP address from the DHCP server. I rang reception and she had just one possible action which was to restart the router. That didn't help. I wasn't too fussed and after a few hours it started working again.

I really wish I could tether my iPhone and just use that for internet while on the road.

The other amusing thing about Sandcastles was these amazing deck chairs that rather reminded me of the furniture at the milk bar in a Clockwork Orange.

Sunday, January 18, 2009

The Mid North Coast Radio Expo 2009

Just attended the Mid North Coast Radio Expo and had a fine time.

front door.jpg

Chatted to lots of people, had a good look at the exhibits, bought a few bits and pieces. Here's a photo tour for those that couldn't make it to Coffs Harbour this year.

Here's the nice lady who takes your $5.

Welcome desk.jpg

Lots of displays around the walls and down the centre of the hall.


Lee Andrews had an excellent range available. I bought a co-ax switch.


Bushcom had HF whips on display.


A great display of home brew equipment.



Not sure who was on this desk.



Valves for sale.


VK4ICE imports some nice portable whips, I bought a pluggable 80m-6m whip for $119.


Very nice chaps.


The SES folks were very friendly and showed me the HF AM radios that are still in use by some.


Some tempting second hand gear at good prices.


A terrific display of Elecraft gear.


Including the tempting KX1.


VK2TOM had some rubidium frequency standards for sale.



The WIA was there, but the only book on display was the 2009 Callbook, so I bought one of those.


An extensive display of vintage radios.


The pedal from a pedal powered radio.


Just to show my wife, there really are other people with call signs embroidered into hats.


Foxhunt gear.


This sniffer from VK3YNG looks very nice.



Outside a very solid portable tower was on display.


I met and had a great chat with George VK4FGHT.


vkhat.jpgAll up, a wonderful day.

Thanks to everyone who organised this and put in so much effort to make it all happen on the day.

The weather was great despite being too hot and then too wet in the days leading up to the big event.

Ham radio is a wonderful hobby and I enjoy meeting other enthusiasts very much.

Finally here's me in my new hat that has the family most amused.

See you next year.

Friday, January 16, 2009

Visiting Coffs Harbour for the Mid North Coast Radio Expo

It is once again my great pleasure to combine a family get-together with the annual Mid North Coast Radio Expo. Today we drove seven hours from Sydney to get to Coffs Harbour.


Accommodation is pretty basic.


Just kidding, we're a couple of doors up the road.

Walking on the beach today was humid but very nice.


Yeah yeah, the iPhone camera isn't too good but at least I have it with me at all times.

We'll have a look around on Saturday, catch up with friends and family, and prepare for Sunday's entertainment.

What's new in iWork 09

IMG_0138.JPGAt first glance the new iWork for 2009 looks very similar to the past version, but there are a few features and some polish that makes it a worthwhile update.

My favourite is the full screen view. Command-Option-U and the whole distracting desktop goes black and all you see is your document, along with the word count and page number. It's a great way to really focus on the task at hand.

When you move the mouse to the top of the screen the menu bar appears.

As a long time fan of outliners as a way to structure a document, and re-organise, it's great to see a superb implementation in Pages.

I'm not a big Keynote user, but there's no doubt it's the best presentation software by a long stretch. The iPhone remote control is genius. I notice that one of the fancy new transitions is not available on my Intel Mac Mini.

Numbers has much more functionality than I've ever used so for me it looks the same.

Overall the programs seem a little snappier and certainly the use of animation transitions is done well without becoming gimmicky.

Apple doesn't harp much on what's new in iWork so I guess there's still a lot of people coming to this suite for the first time.

Export seems to have moved from the File menu to the Share menu. There seems to be a bit of overlap between these two menus, I would have thought that Share might be a part of File.

One slight wrinkle in the purchase process, I downloaded the trial and used it a bit before ordering via the online store. When the box arrived I looked for the serial number that the trial said I'd find in the install book.

It turns out that you just install from the disk that comes in the box, there's no serial number so the story's a little confusing there.

Anyhow, I'm over Microsoft Office. It was virtually mandatory for so many years. iWork opens Office documents without issue and these days I tend to distribute my writing as PDFs so all bases are covered.

Monday, January 12, 2009

Built an 80m DSB transmitter - VK3XU's "simplex sidebander"

Spurred on by the success and what I've learned from my battle with the Bitx20 I sat down and constructed a transmitter from scratch.


It's the "simplex sidebander" from Drew Diamond's "Radio projects for the amateur" first book. Dave, VK3ASE kindly gave me a couple of crystals for 3.670MHz when I visited recently. As you can guess I skipped the crystal filter and made it a double sideband exciter.


The circuit has a 741 Op amp as a mic pre-amp, an NE612 as both the oscillator and mixer, followed by a 2N2222 buffer. That big three terminal thing is a vastly overrated 7806 voltage regulator.

Two more RF stages, comprising a 2N3053 and an IRF510 are on the second board. Finally there's the output low pass filter. I'm waiting for some more Amidon T50-2s to arrive so I can add the other filter stages.

It looks ok on the CRO (me saying "haaalow") and sounds reasonable on the local radio.


When there's no audio, carrier is well supressed. When speaking, I get a nice 6W out by the looks.


My construction is pretty sloppy, leads too long etc, but hey - it's 80m so pretty forgiving thankfully.

I've learned an important lesson: when a toroid is required don't just grab a random loop from the junk box, try to get something of the same material! The Amidon toroid numbers, such as FT50-2, mean FT = Ferrite, 50 is the size, 2 is the material. So, substituting an FT43-2 worked fine. is a good place for specifications and winding calculators.


With the help of Mike, VK2MJW, I've determined that my on-air audio is very distorted. I put this down to the RF power stages being unstable.

Interestingly the transmitter behaves quite well on a dummy load, but when connected to a real antenna tends to go into oscillation.

On it's own the exciter board sounds good. I've mounted the exciter in a nice shielded box and am currently re-building the driver and PA stages with more compact construction.