Tuesday, November 30, 2010

Photography, brilliant project case and a fire breathing dragon

The last ARNSW Home Brew group meeting at Dural for the year and quite an entertaining one at that. Stephen VK2BLQ stole the show with the brilliant idea of using old CD drive housings to build home brew equipment in.


Aluminium angle stock makes the ends perfectly. He's nicely built a CW transceiver. I'm kicking myself for throwing some of these out even in the last few weeks.


John Hale gave an excellent talk on photographing projects or really any device of small size. Here he shows the use of a seamless background and a telephoto to avoid distortion.


I'm pretty happy with my Ricoh for close up work like this. (Detail from Stephen's rig).


I rambled about wire dipoles, pulleys and cleats but the most surprising talk was about the building and operation of a fire-breathing dragon head.


Thanks as always to the organisers and the WIA.

Monday, November 29, 2010

wsprnet.org is down

Sadly, it looks like wsprnet.org is down and has been for an hour or more at the time of writing.

I notice that it has been struggling a bit lately, in particular since the WSPR story made the front page of QST.

Hopefully it isn't too serious. I certainly miss it.

Update

It's back up.

Saturday, November 27, 2010

WSPR analysis with gnuplot

Just posting this for my own reference really. I find that spreadsheets don't really cope with lots of data to plot so gnuplot is the way to go, but it's a little hard to figure out.

I want to plot Ross VK1UN's reception of my WSPR signal using the data on the site. Here's the output I want (pretty much).

WSPR.png

To get this, I go to the wsprnet.org site, run a report of my transmissions and vk1un's receptions of me. Then I copy the table data from the web browser and paste it into a text file called "wspr.txt", then I run this python script to clean it up ready for gnuplot.


import csv

INFILE = "wspr.txt"
OUTFILE = "data.txt"

infile = csv.reader(open(INFILE, "r"),
delimiter = "\t")
outfile = csv.writer(open(OUTFILE, "w"))
for row in infile:
timestamp = row[0].strip()
call = row[1].strip()
sn = row[3].strip()
receiver = row[7].strip()
#print("'%s': '%s'" % (timestamp, sn))
outrow = (timestamp, sn)
outfile.writerow(outrow)


Then I run the following gnuplot commands to draw the graph above.


set terminal png size 405, 320
set title "40m WSPR VK2TPM - VK1UN"
set output "WSPR.png"
set xlabel "DATE"
set ylabel "S/N"
set xdata time
set timefmt "%Y-%m-%d %H:%M"
set xtics format "%d"
set datafile separator ","
plot "data.txt" using 1:2 title 'S/N' with points


One thing that eludes me is how to get the date xlabel to change once a day. Any tips most welcome.

By the way the plot shows two days on the half wave dipole followed by one day on the half size G5RV. Not much between them. (Well, not enough data to tell).

Here's VK6ZRY's reception reports:

WSPR.png

Friday, November 26, 2010

Electronic technical books will win quickly

I've been lying in the hammock reading my ARRL Handbook and noticed the CD Rom in the back. It turns out they give you a complete copy of the book in PDF format.

Dragged it over to iTunes and found that it is very readable on the iPad. One problem, dear ARRL publishers, is that the files are simply called 01.pdf, 02.pdf and so on, with no metadata. Happily, iTunes can edit the metadata quite easily (although it seems to feel that it's editing music files).

front.jpg

Reading such a big heavy book on the iPad is much nicer than trying to hold the big heavy book up, plus you get search (well, within each chapter).

PDF is OK but the text can be a little small, it would be great to have an ePub version. Quite frankly, I never want the physical book again. It won't be long before most technical book buyers feel the same way I think.

Wednesday, November 24, 2010

Google search results with page preview

I just got this Google preview display next to my search results.


(click to enlarge).

It pops up quickly as you roll over the result line. Not all sites have previews but lots do.

Sunday, November 21, 2010

CZH-05B 500mW FM transmitter

I like to listen to the VK2WI Sunday broadcast. It's part of my weekly routine. This week I was able to listen to it lying in a hammock thanks to a new arrival, a small FM transmitter purchased on eBay.

Front.jpg

It's synthesised for frequency stability. At 500mW it saturates the house but doesn't go much past the neighbours. On the back there is a BNC connector and it comes with a little antenna. No doubt an external antenna would extend the range.

Internally, construction is of a very high standard:

Internal.jpg

It came with an over the top switched giant power supply. There is some hum evident in the signal but no doubt that could be improved with a regulated supply.

Over the years I've built many little FM transmitters but they always drift to some extent. It's nice to have something stable like this.

I think there could be a market for a radio station that broadcasts selected podcasts, my latest discovery is The Changelog. Now I can just make my own.

Saturday, November 20, 2010

Sony Reader PRS-350 review

101335.jpegSony kindly sent me a loan PRS-350 for review this week.

The PRS-350 is a small e-ink book reader, less than the size of a novel (5"), but with a "paper white" touch screen. The display is 800 x 600 pixels and capable of reasonable grey scale display and of course works nicely in daylight. It has 2GB of built in storage.

The review unit I received was pretty grotty from previous users but cleaned up well with a damp cloth. I guess that's the drawback of any touch screen - including the iPad.

Around the rim, the device has slide power switch to wake it up, a stylus top right, one of the various micro-USB connectors (the same as the HTC phone I use which is handy but not the standard one used on many devices, and a reset hole.

On the front there are buttons for previous and next page, home, text size and options. I'd be inclined to make the next and previous page more prominent as they'll be used hundreds of times more than the others.

When you first plug it in to your computer, two storage devices are mounted, one with applications that download the software installer (a good idea - rather than directly installing an old version of the software),

Screen shot 2010-11-20 at 7.59.47 PM.png

another with a mysterious directory with "database", "Digital Editions" and some pdfs with the user manual and instructions on how to get content.

Screen shot 2010-11-20 at 8.00.22 PM.png

Unfortunately you don't seem to be able to simply drag content to the reader so software needs to be installed.

Screen shot 2010-11-20 at 8.00.07 PM.png

The installer wants to reboot the machine, I'm on a Mac here, and that always worries me as it indicates it's going to install something that runs in the background. Sure enough, after reboot, even when not plugged in there is a program running called "Reader Library Launcher". There is no uninstaller.

The "Reader Library" software shows your library on the computer, a status display of any transfers, your local disk and an ebook store:

Screen shot 2010-11-20 at 8.08.14 PM.png

Clicking one of those links simply opens your web browser at their store, so it's not an immersive experience like Kindle or iTunes. The instructions on the Borders store for "Reader Users" are a bit scary:

Screen shot 2010-11-20 at 9.34.02 PM.png

I mostly purchase books from O'Reilly in ePub format and for some reason you can't just drag them in to the application, you need to "Import" them.

For me, ePub has emerged as the winning book format, with its ability to reflow the text around graphics and the open nature of the file format (a zipped xml file) it's what I look for in a book reader.

The Sony PRS-350 does a good job with my test epub file, dithering the colour images down and showing the text styles nicely. The touch screen means that links work the way you expect without having to move through a page link by link.

It's great having search but the keyboard is a little cramped and the slow updating of the e-ink display makes this kind of user interaction a little clunky.

Summary

The device is good, it handles even large ePub books well and does a good job with fonts and images. The software is not so good, the integration with stores is poor and even books you own can't be just dragged to the window or the device.

The touch screen, even on a matt display works well and I can see why an iPad owner would want one for times when they want to read in daylight.

RRP is AU$229 which seems fair but not quite in "impulse purchase" range.

Wednesday, November 17, 2010

G5RV compared with dipole using WSPR

It's hard to measure one antenna against another on HF due to the huge variations in conditions even minute by minute.

Recently I bought a half size G5RV multi-band (compromise) antenna and while it's incredibly convenient my feeling is that while reception is as good, people just don't hear me as well.

To test this, I used WSPR on 40m to record the S/N that people hear me with running 1W.

This graph plots 1 nightly cycle of transmission on the G5RV followed by two on the old 40m wire dipole.

wspr chart.png

Higher up the chart is better and there are outliers, but the average of reception seems markedly better on the simple dipole on average.

More samples need to be taken and my analysis needs to be better thought through.

Saturday, November 13, 2010

QSL Cards arrived - a blast from the past

I've never played the QSL card game, where you send a card off to people you talk to on Amateur radio to confirm the contact. Recently an envelope arrived stuffed with QSL cards people had sent me in recent years.

UA0lqf.jpg

Back:

Scan 1.jpg

Thanks Dmitry, UA0LQI (I think) in the Russian Far East. I remember when I was a kid listening to short wave I sent off to Radio Moscow and received a lovely QSL card back from them - my parents were appalled and thought I'd be tagged as a Communist for life!

Scan 3.jpg

Thanks Pierre F5GPE in Grenoble, France.

ve3hmk.jpg

A charming design from VE3HMK.

These contacts are all from a period when I was pretty active on 20m PSK31.

Thanks to the VK2QSL Bureau, greatly appreciated.

Sunday, November 07, 2010

Half size G5RV arrived

A half size commercial G5RV just arrived from ebay seller capitalstoresaustralia. It seems well constructed, certainly better wire than the zip cord I normally use.

R0013133.jpg

It hangs pretty well in the space I have between the tree and the house where my 40m dipole went. On the MiniVNA you can see the SWR plot:

g5rv.png

SWR seems good on 40m and 20m and fair on 10m. I can't see how you'd use it on 15m.

Perfect day for hanging antennas:

antenna weather.png

Happily it's south of me, however there is tons of static crashes so it's a bit hard to evaluate the antenna at the moment. I'm running WSPR on 20m and so far reception is excellent.

I paid AU$61.21 all up which seems a bit much for some bits of wire but overall I'm happy with what I got.

Update

Well, that didn't last long. It's very windy here tonight and the antenna is down. It broke at the junction between one wire leg and the central connector. To be fair, it's pretty interesting weather here at the moment:

Saturday, November 06, 2010

Tet-Emtron wire dipole centre pieces

I picked up a few of these excellent plastic wire dipole centre pieces from Tet-Emtron at the last Gosford field day and I'm now starting to figure out a good way to use them.

IMAG0020.jpg

Wing nuts are the answer.

IMAG0021.jpg

I've been using perspex sampler squares but these are really well thought out and constructed. I've now cut and tuned wire dipoles for 40m, 30m, and 20m and with my pulley and cleat system it's pretty quick to change them over.

Best time for an HF contact using WSPR Data

I'm hoping to have a contact with old friend VK3ZZC and to figure out the best time to suggest a sked I look to the WSPR data between my station and Ross VK1UN/1 (who's actually located in Melbourne at the moment).

I grabbed the historical data of Ross receiving me from the WSPR spot database and plotted it in local time.

Sydney to Melbourne spots.png

Although Ross spots me all through the 24 hours, the best times are 5am and 7 to 8pm.

It would be nice if it was a little easier to grab the data for this kind of plot, but it's a very useful resource.