Saturday, October 30, 2010

Dual-band "fan dipole" for 40 and 30m

I've been having great success with 40m WSPR with my 1W going right around the world (at certain times of the day) but much of the WSPR activity is on 30m.

Today I ran a second wire dipole cut for 30m below the main dipole suspended with strings cut for 30m and connected to the same coax.


It worked out pretty well and I'm keen to see how it goes over night. That plot is from a MiniVNA which makes it very easy to get everything adjusted.

There's a half G5RV on it's way and I'm looking forward to getting more bands but it's unlikely that I'll see the exceptionally low SWR I get with my simple wire dipoles.

Looks like it's working nicely:

Screen shot 2010-10-30 at 5.37.36 PM.png

As the "grey zone" approaches it gets better:

Screen shot 2010-10-30 at 6.59.06 PM.png

A nice balance of hearing and being heard. I'm running 1W here and have just been spotted by W1BW 16,209Km away. (The earth's circumference is 40,000Km, so I'm on the way to the other side).

Screen shot 2010-10-31 at 6.19.07 PM.png

I'm using a new centre connection with screws so I can switch wires more easily.


Sunday, October 24, 2010

Visit boat supplier for wire dipole supplies

A new wire dipole for 40m has gone up at chez marxy.

As it's suspended by the wire itself I decided not to use a balun in order to avoid the weight. The coax to wire joins are attached to a perspex sample square the local perspex supplier appears to happily give away. It's soldered and the whole lot is smeared with silicone bathroom sealant.

The wire is held at the ends with 3mm braided cord from the boating supply shop. They sell 100m for $30 and I find cord made for yachts survives the weather better than venetian blind cord.

At each end I have a pulley mounted on the house and tree.

Finally, for ease of fix and release, I've mounted cleats suitable for 3mm cord.

All this makes it very quick and easy to raise and lower the dipole.

This (no balun) wire dipole seems to be working extremely well, at least according to my wspr spots. I called back on 40m after the VK2WI broadcast  this morning and they clearly heard me better than I could hear them. Despite the lack of balun I'm not getting RF in the shack.

I notice that the resonant dip is very sharp but I got it resonant at 7.1Mhz without too much trouble.

All the bits and pieces from a boat supply shop are tested on ships at sea and seem far superior to the stuff I get at the local hardware store. The tension on an antenna is much less than what a sail causes and the ability to survive salt air means that it will last in my yard.

Monday, October 18, 2010

HF Radio lives, and is fast, at least for the military

Thanks Nigel for pointing this out. They say the've made HF communications so easy to use that no specialist knowledge is required. No mention of antennas though.

Sunday, October 17, 2010

Higher quality aerial imagery at

This was mentioned on the VK2WI Sunday broadcast. They have aerial imagery that is higher quality than what you get on and it's updated every few months by the look of it.

Here's a sample near Circular Quay.

Screen shot 2010-10-17 at 11.07.57 AM.png

If you go to it's worth trying different dates as the quality varies and sometimes exposure is out.

Saturday, October 16, 2010

Shelves in the shack, thanks SolderSmoke

On a walk this morning I listened to a brand new SolderSmoke podcast, back after taking a break while Bill's family moved back to the US.

My workbench was such a mess that it's been hard to get in there and melt solder. Basically, I need to dispose of some junk or add some shelves.

shack before 016.jpg

I took the easy option and put in some nice new shelves.

shack after 015.jpg

It's really not cramped, it's cosy.

We've had big wind here in Sydney and one leg of my 40m wire dipole has fallen off so my next priority is to fix that.

It was great to hear the podcast again, and Bill, I think your audio on the old laptop running Ubuntu is the best its ever been. I wish you'd put out a podcast every day.

Thursday, October 14, 2010

Ubuntu desktop 10.10 no ntp by default?

I've been running my WSPR station on a new Ubuntu Desktop 10.10 install on an MSI laptop and for mysterious reasons hadn't been spotting anyone or being spotted. I could see strong traces though.

Happily, this is now fixed quite markedly:


My thanks go out to Nick, VK2DX who wrote to point out that my clock was off.

It turns out that this Ubuntu install does not include the NTP daemon.

I think this may cause problems for other software as well.

Sunday, October 10, 2010

Is Pygame faster than PIL? How about pyglet?

In my work I draw a lot of polygons on PNG images.


Currently I use Python Image Library (PIL) for all my drawing and I'm pretty happy with the performance. Intriguingly, I read here that "Pygame is three or four times faster than PIL" and that got me interested.

I guess it makes sense that a library designed for games would be better optimised than alternatives. I created this simple test to render a random polygon and measure the speed.

import time
import random
import os
from PIL import Image, ImageDraw
import pygame

def PolygonPILTester(polygon):
width = 256
height = 256
img ="RGBA", (width, height), (255, 255, 255, 0)) # rgba
draw = ImageDraw.Draw(img)
draw.polygon(polygon, fill="blue")
f = open("pil.png", "wb"), "PNG")

def PolygonPyGameTester(polygon):
width = 256
height = 256
os.environ['SDL_VIDEODRIVER'] = 'dummy'
pygame.display.set_mode((1,1), 0, 32)
surf = pygame.Surface((256, 256), pygame.SRCALPHA)
pygame.draw.polygon(surf, pygame.Color("blue"), polygon), 'pygame.png')

if __name__ == "__main__":
polygon = []
for i in range(100):
polygon.append((random.randint(1,255), random.randint(1,255)))

start = time.time()
end = time.time()
print("PIL took %s seconds" % (end - start))

start = time.time()
end = time.time()
print("pygame took %s seconds" % (end - start))

Here's pygame's version:


Interestingly in this test, PIL is twice as fast as pygame, here's a typical result:

PIL took 0.015594959259 seconds

pygame took 0.0300869941711 seconds

My guess is that as the author of the gheat code found the reverse that pygame is better at image compositing which is used more for games than for just drawing polygons.

There's another python image library out there, pyglet, but so far I haven't figured out how to do a simple drawing on a new image and save to a PNG file without it wanting an X server. I get "pyglet.window.NoSuchDisplayException: Cannot connect to ""." Any pointers would be appreciated..

Friday, October 08, 2010

Mac Ports geodjango libgeotiff breakage

At some point in the last few weeks I did a Mac Ports update and gdal, which I use in Django broke.

Here's the exception (which gets silently captured and turned into HAS_GDAL = False):

>>> from django.contrib.gis.gdal.driver import Driver
Traceback (most recent call last):
File "", line 1, in
File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/django/contrib/gis/gdal/", line 5, in
from django.contrib.gis.gdal.prototypes import ds as capi
File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/django/contrib/gis/gdal/prototypes/", line 8, in
from django.contrib.gis.gdal.libgdal import lgdal
File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/django/contrib/gis/gdal/", line 37, in
lgdal = CDLL(lib_path)
File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/ctypes/", line 353, in __init__
self._handle = _dlopen(self._name, mode)
OSError: dlopen(/opt/local/lib/libgdal.dylib, 6): Library not loaded: /opt/local/lib/libgeotiff.1.2.5.dylib
Referenced from: /opt/local/lib/libgdal.dylib
Reason: image not found

So something is linked to s version 1 of libgeotiff and it's been upgraded to 2. Here's what I have installed:

sh-3.2# ls /opt/local/lib/libgeotiff*

My workaround for the moment is:

ln -s /opt/local/lib/libgeotiff.dylib /opt/local/lib/libgeotiff.1.2.5.dylib

which seems to work but is obviously risky.

This post is really just a note to myself.

Tuesday, October 05, 2010

Django documentation in epub format

I'm getting used to referring to technical documentation on the iPad and so I'm on the hunt for epub versions of things.

Daily my development is with Django and it was great to find that the documentation, which is built with Sphinx, can easily generate very nice epub output like this:

django epub.PNG

Here's how to generate your own:

pip install -U sphinx
svn co djangosvn
cd djangosvn/docs
make epub
Django.pngThe output is in _build/Django.epub which you then drag to iTunes to install on an iPad.

The only thing missing is a cover image.

For your convenience, I've stuck a copy here.

Update: built Python 2.7 doc as epub

After that success I had a shot at building the Python documentation. The sphinx that comes with the python source is old and doesn't include the epub builder so I used a separate sphinx. All seemed to go well:

epub build.png

Here's the command line:

sphinx-build -b epub -d build/doctrees . build/epub
python.pngFor your convenience I've put a copy here: Python 2.7 epub documentation. (That's a shortened url by the way).

The output looks excellent on an iPad, it's 3,943 pages at normal font size and the iPad does groan a little but it is quite usable. epub is much much better than pdf for reading on tablets.