Saturday, July 26, 2014

New transceiver for the shack - with valves!

Great day at Dural today. Particularly impressed with the home brew moving coil compass built for a model boat. I didn't mean to but ended up walking away with a beautiful Yaesu FT-101E for $200.


Had a contact with Stephen, VK2BLQ, who reports that I sound normal so that's all good. Plate and Load knobs are new to me but fun to learn about.

For my younger readers, this is what a valve looks like:



The compass was fascinating, it uses a spinning coil with an amplifier in the centre. Power is fed in through the ball bearings and the output is sent by an LED light.


We turned it on and compared with a compass in a smartphone.


A wonderful device, but I think technology may have moved on.

Tuesday, July 22, 2014

Appearance on RN's Download this Show

A busy week, media wise. I was on RN's Download this Show:


Also wrote an opinion piece about how the BitTorrent technology can be used for good as well as evil, published by the ABC.

Saturday, July 19, 2014

What's cheaper than a Raspberry Pi and runs linux well?

I'm interested in playing with some of the new virtualisation technologies, such as docker. For this stuff my usual go to toy, the Raspberry Pi doesn't quite cut it. This morning I spotted a Dell Optiplex PC, Core 2 Duo 2.5GHz, 2G Ram, 250GB disk for $35 on eBay with no bids.


Ending an auction at 7:15am on Sunday morning may not be the best way to sell technology.

So far I've installed the 64bit version of Ubuntu Server 14.04 and following the instructions from the excellent Ubuntu documentation created a virtual machine in which I've installed another copy of the Ubuntu Server.

This works magically, the qemu environment can be set up to share the virtual console via VNC and from my desktop machine I answer the install prompts as if sitting at an actual machine. Here's how it looks:


Now I can safely try all sorts of crazy things in this virtual server and just delete anything I'm not happy with.

Here's the giant new server (with a Raspberry Pi next to it for scale):


There are bargains out there, but I should say that this was a crazy price. You can pick up similar systems for under $200 pretty easily though.

Sunday, June 29, 2014

Balun day at Amateur Radio NSW

Today was "balun day" which began with breakfast followed by a terrific talk from Mark, VK2XOF, about the theory and practice of building current baluns. The biggest mystery for me is what core to use.


After the theory, and lunch, we all received out balun kits from TET-Emtron. I went for the TB-11K 1:1 kit rated at 1kW peak. We then built our kits under the guidance of folks who had built them before.


Finally there was a spectrum analyser and antenna analyser on hand to measure the baluns. Some home constructed baluns were found to have high reflected power which was very interesting to see.


The method for assessing a balanced to unbalanced balun's operation is to attach a 50 ohm load on to the antenna terminals, feed it from an antenna analyser and connect one and then the other of the antenna terminals to the ground of the input and see if the impedance changes very much - if all is working well it should not change.

My sincere thanks to the ARNSW committee and all who clearly worked hard to make this day a great success. Thanks also to TET-Emtron for producing the fantastic kits and for their support.

Saturday, June 28, 2014

Windy in Sydney this afternoon


Up here on the 28th floor it was pretty windy today. The doppler wind radar looked pretty interesting. RNDSUP seems like a fun technology.

Friday, June 20, 2014

ABC Download This Show appearance - Chromecast, Upworthy, Unicode

We're videoing radio again this week. Here we are in the Radio National studio talking about technology.




Exciting news for people who like watching radio programs on video - Download This Show is now available on ABC iview. (Search for it or look in the iview channel).

Monday, June 16, 2014

DDS VFO purchase

I recently purchased an old crystal controlled Codan lunchbox radio and want to put it on 40 and 80m so I've found a rather nice DDS VFO on ebay for AU$45. This one has two PIC CPUs on the board, a nice backlit display and comes with a tuning knob but no info on wiring it up.

The same unit is in other ebay auctions and one of them has this "schematic" which will be a help, if it's correct.


My board came with some cables with sockets to match the connectors on the board and the rotary encoder. Here's other info, for future reference. (It all seems a little mysterious to me but hopefully will be clear when I play around with it).

Note that the wiring of the rotary encoder in the sketch above (from an eBay ad) is shown from the rear of the encoder. I wired it up in reverse and it works but the tuning goes clockwise for up in frequency.

My thanks to Stephen VK2BLQ for access to his workshop, here's my VFO all boxed up.


One criticism of these boards is the lack of mounting holes. I've stuffed the box with cloth to press it against the front and that works fine but is not ideal.

I've now added a 9V three terminal regulator so that the unit can run from my 12V bench supply.

All up this is a terrific VFO, pushing while turning the knob changes the digit that will be adjusted so it's quick to get around. Thanks to commenter Yiannis, the documentation and software source has been traced to Ham Radio India.

The objective of this device for me was to use it as a VFO for my Codan 6924 radio. There's a handy page outlining how to do this. This weekend I ran a cable to an empty crystal spot.


This makes the old radio look very fancy.


As I tune around I notice carriers sweeping by at some frequency ranges but not others. I took the DDS over to VK2BLQ's lab and it seems that for many frequency ranges the output drops dramatically. I'm not sure what's going on here but my guess is that it's designed to cover only certain bands and not others.