Reflection Technology

Evening in Pisa

The Flea – a minimalist CW transceiver

Here’s an amazingly simple 1W morse code transceiver in the tradition
of the Pixie but with much more output power and a narrower bandwidth
receiver (the oscillator crystal forms part of the receive input
filter):br /br /http://ea3fxf.googlepages.com/fleabr /br /The xtal is in the receive path so the bandwidth is quite narrow and will stop broadcast interference. A PCB layout is included. The page is just a summary – have a look at the linked .DOC file for the full article.

The Last Lecture

I’ve just watched “The Last Lecture” by Randy Pausch.

Carnegie Mellon Professor Randy Pausch, who is dying from pancreatic cancer, gave his last lecture at the university Sept. 18, 2007, before a packed McConomy Auditorium. In his moving talk, “Really Achieving Your Childhood Dreams,” Pausch talked about his lessons learned and gave advice to students on how to achieve their own career and personal goals. For more, visit www.cmu.edu/randyslecture.

It’s very hard to know what to say, except “watch it” …

The Robots are coming …

Really great (and real) video of a robot that can reassemble itself when kicked apart.

YouTube – Modular robot reassembles when kicked apart

Great Red Photos from Wired.com

Top 10 Red Photos, Decided by You

Zeitgeist – the Movie (free)

Saw a reference to it on www.slashdot.org (I think) – looked interesting but can’t remember why – will add more comments later
Zeitgeist – The Movie, 2007

TinyP2P – a Peer-to-Peer Client-Server in 15 lines of Python

Here’s a delightfully simple (well concise anyway) peer-to-peer program – it can run as either a client or a server and if wrapped (as the original was) is only 15 lines of Python.

It’s also a very good example of how concise python can be:

Annotated TinyP2P – Annotated version:
   http://www.exonsoft.com/~kochin/TinyP2P/tinyp2p.html

Original Version:

# tinyp2p.py 1.0 (documentation at http://freedom-to-tinker.com/tinyp2p.html)
import sys, os, SimpleXMLRPCServer, xmlrpclib, re, hmac # (C) 2004, E.W. Felten
ar,pw,res = (sys.argv,lambda u:hmac.new(sys.argv[1],u).hexdigest(),re.search)
pxy,xs = (xmlrpclib.ServerProxy,SimpleXMLRPCServer.SimpleXMLRPCServer)
def ls(p=""):return filter(lambda n:(p=="")or res(p,n),os.listdir(os.getcwd()))
if ar[2]!="client": # license: http://creativecommons.org/licenses/by-nc-sa/2.0
myU,prs,srv = ("http://"+ar[3]+":"+ar[4], ar[5:],lambda x:x.serve_forever())
def pr(x=[]): return ([(y in prs) or prs.append(y) for y in x] or 1) and prs
def c(n): return ((lambda f: (f.read(), f.close()))(file(n)))[0]
f=lambda p,n,a:(p==pw(myU))and(((n==0)and pr(a))or((n==1)and [ls(a)])or c(a))
def aug(u): return ((u==myU) and pr()) or pr(pxy(u).f(pw(u),0,pr([myU])))
pr() and [aug(s) for s in aug(pr()[0])]
(lambda sv:sv.register_function(f,"f") or srv(sv))(xs((ar[3],int(ar[4]))))
for url in pxy(ar[3]).f(pw(ar[3]),0,[]):
for fn in filter(lambda n:not n in ls(), (pxy(url).f(pw(url),1,ar[4]))[0]):
(lambda fi:fi.write(pxy(url).f(pw(url),2,fn)) or fi.close())(file(fn,"wc"))

GeekMenu – An advanced PortableApps Launcher

GeekMenu is a rather polished PortableApps Menu variant that looks really nice.

It can automatically mount a Truecrypt drive or (on untrusted computers) NOT mount, or mount read-only. Plus lots of other features.

To quote

“geek.menu is a fork of the PortableApps.com Menu, adding support for
security features, internet searching capabilities, category support,
autorun apps, and much, much more. It can serve as a replacement for
the portableApps menu.”

Download from Sourceforge http://sourceforge.net/project/showfiles.php?group_id=209346

The portableApps system is intended to allow you to take all the programs you usually use with you on a USB flash drive and not rely (or save setting) on the computer you’re using.

Essential Vi Commands

Vi is one of the ordinal editors on Unix, and now Linux machines. It has a minimal interface but can be very fast and is great if you have a slow connection.

The Wikipedia article http://en.wikipedia.org/wiki/Ed_(text_editor)

has a very nice 10 line summary.

This note is primarily so I can remember where to find it again :-)

Making Vacuum Tubes (valves) for radios at home

Here’s movie of someone (F2FO) making valves – the amplifying part of a radio – in a home workshop. It’s ingenious, quite clear and very clever.

The video goes from bits of metal and glass to a working radio. The subtitling is in French but that doesn’t hinder understanding, as the presentation is quite professional.

http://paillard.claude.free.fr

Inspiring …

OLPC (One-Laptop-Per-Child) – Stories from Peru

This is an interesting article showing the effect of introducing a new technology on the lives of school children in Peru.

http://wiki.laptop.org/go/OLPC_Peru/Arahuay

The One-Laptop-Per-Child initiative was started by Nicolas Negroponte from MIT as a way of bringing robust laptops to poor children in poor countries for less than $100 each. More details about OLPC at www.laptop.org

The Beauty of Maths, Indian Clerks and Aversion

The author is a govenor at a girls school in the UK. She has some particularly perceptive comments about mathematics ability or more accurately, maths anxiety and parents …

It starts:

The beauty of maths

A POINT OF VIEW
By Lisa Jardine

The story of an Indian clerk with an extraordinary talent for mathematics should inspire young people to see the beauty that lies in numbers.

I have been thinking recently about the way in which stories we are told when we are young shape our adult lives.

I am reading with great enjoyment a new novel entitled The Indian Clerk, by David Leavitt, based on the life of the early twentieth-century Indian mathematician Srinivasa Ramanujan …

The complete article is at
http://news.bbc.co.uk/2/hi/uk_news/magazine/7144874.stm

Halfway down the above article, there’s an audio version (her as broadcast) – Click on the Listen button (there’s a 20 second prelude to advertise a Christmas show and then Lisa is introduced …)

Somehow the audio version seems easier to remember, not sure why …

Reality & Philip K. Dick, Timothy Leary …

“Reality is that which, when you stop believing in it, doesn’t go away”
– Philip K. Dick

There’s also an interesting discussion of some of his work and that of Timothy Leary in the delightfully entitled article “To Narc on One’s Self: The Head Cases of Timothy Leary and Philip K. Dick” at http://3quarksdaily.blogs.com/3quarksdaily/2006/08/discussed_timot.html

Economic Theory, Black Swans and Sandpiles

I enjoy (but often don’t completely understand) John Mauldin’s Weekly newsletter

This week’s one is entitled “Black Swans and Endogenous Uncertainty”, with sections Ubiquity, Complexity Theory and Sandpiles …

Read the complete article at:

http://www.investorsinsight.com/thoughts_va.aspx?EditionID=625

“Because Of You” By David Sides

David reminds me of Pete Pascoe – a very talented pianist I saw one Sunday afternoon in a free art gallery concert.

HUNGARIAN CHICKEN SCRATCHINGS

This is a real seminar ad – and if you keep reading, it makes sense.
Too good to let disappear …

===========================================================

Mathematics Seminar

“HUNGARIAN CHICKEN SCRATCHINGS
A NEW WEAPON IN THE WAR ON ERROR”

Professor Mike Steel

Director, Biomathematics Research Centre
University of Canterbury

12.00 pm Thursday, 11 August 2005 – ScB3.31

ABSTRACT
Professor Steel is completing a series of three papers with Hungarian collaborator Laszlo Szekely, dealing with information loss in phylogenetics. It will deal with issues related to Maximum Likelihood estimation and admissibility. This will be the first occasion that this material has been presented.

MacGyver Tip: Smooth a scratched DVD with Pledge

MacGyver Tip: Smooth a scratched DVD with Pledge

Using Toothpaste sounds good but can be risky – try this instead 

A Simplified Map of London « strange maps

Off-Centre-Fed (OCF) Antennas

I’ve now decided to use a ZS6BKW antenna as it fits better in an inverted V configuration in my garden but for Multi-band use without tuning, the off-centre fed antenna has a lot going for it (and lots of happy users), so I thought I’d put up some of the useful links I’ve found.

These links describe very clearly how it works (in summary – it’s better NOT to feed at the low impedance point like a dipole as when you double the frequency the same point is now a VERY high impedance – it’s better to accept a little mismatch and get lots of bands instead.

For more detailed explanations (with pictures :-) ) see:

* Good OCF Introduction
http://www.radioelectronicschool.net/files/downloads/ocfdipole.pdf

* Clear explanation but shows the difference using a 20% feedpoint can make -it includes 10MHz)
http://www.w8ji.com/windom_off_center_fed.htm

* A more extensive article with various shortened versions
http://www.stroobandt.com/cl-ocfd/windom/index.html

or without the frame:
http://www.stroobandt.com/cl-ocfd/windom/windom.html

OCF Antennas are sold commercially from
  http://hamcall.net/7bandocf.html

and the user reviews on EHam.net do seem very positive:
  http://www.eham.net/reviews/detail/5838

These are still full length antennas (e.g. 40m/130ft if you want 80M without using an ATU) but without the anti-resonance that makes a 80M dipole hard to feed on 40M (for example), and having the feedpoint at 20% or 33% can sometimes be more convenient.

Cheers
Giovanni – ZL2BOI

ZS6BKW – an Optimised G5RV multi-band wire antenna

I’ve been playing with aerials again (can’t be studying ALL the time) and as I usually do have come around to putting up as much wire as I can and feeding it with 300 ohm ribbon.

I tried the G5RV (in the days before I had an antenna analyser) and didn’t like it much – can’t quite remember why but (from memory) it wasn’t that easy to tune. This corresponds to what I’ve found on the net – the G5RV was never intended as an all-band antenna, however by making it just a bit shorter you can match it easily on lots of bands.

It was derived by Brian Austin ZS6BKW (now G0GSF) and will match most of the HF band excluding 10 & 21MHz.

Have a look at these two articles from Sprat (the journal of the GQRP Club – http://www.gqrp.com):

Martin G3UKV trying it out (with Antenna Analyser results):
ZS6BKW Antenna Revisited (from Sprat #129)

A more extensive article by its designer G0GSF/ZS6BKW, on the rational behind the antenna design:
ZS6BKW revisits his G5RV variant and describes its evolution

Sometime I’ll publish my measurements, but for now, these should give you something to work with …
Giovanni – ZL2BOI