macOS Sierra SSH “Permission Denied”

Saturday 2016-11-12

keychain-mac-tutoIf you used DSA keys to log in to your SSH server and have upgraded your client machine to macOS Sierra (or OSX Sierra if you like), you probably ran into this problem:

client$ ssh -p 8123 george@ -i ~/.ssh/id_dsa 
Permission denied (publickey).

The answer to this problem is replacing the DSA key with an RSA key, but how do you do on the server when your only means for connecting is the OSX client machine you just upgraded? Here’s how:

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Designing a Fox-hunt antenna

Sunday 2016-06-19

3d radiation patternMany years ago, I used to do some radio fox hunting with cars. Usually these hunts are at night to make it more exciting, and can be great fun. As I got older I lost interest and moved on to other things. But last year, I decided to have a go at a popular balloon fox hunt on 144MHz. This is quite a large scale and professionally organized fox hunt by Dutch Radio Amateurs. Read the rest of this entry »

Measuring Coax Length and Loss

Sunday 2015-11-01

100-1015 BNC T ConnectorEver wondered how well your 50Ω coaxial cable is working? If you have a reasonably fast oscilloscope, preferably up to 100MHz and a signal generator which can generate short bursts, you can measure not only the length of your cable, but also the return loss at a certain frequency. From that, we can learn the attenuation of the cable.

This blog post describes the classic time domain reflection measurement using the following setup:

Measuring TDR
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How to get your users to install JCE

Friday 2015-09-04

220px-Lorenz-SZ42-2In every Java project where I need to do strong cryptography, I run into these dreaded unreadable stacktraces which send you into the woods. After a long search I usually discover that the Unlimited Strength Java Cryptography Extensions are not installed. To prevent frustration of users of your software, you can simply add a bit of informative logging to help him/her solve it when the solution is known.

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Ashley Madison in perspective

Monday 2015-08-24

lady justiceHowever I disagree with sites like Ashley Madison and the way its owners scam people, last week I have noticed something far more disturbing. As I understand, Ashley Madison was charging people for their profiles to be deleted, and then did not (promptly) delete them. I guess some of it’s “hackers” got caught up in this and decided to attack Ashley Madison for that. Up to this point, merely a quarrel between two parties which may have better been solved by legal procedure.

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Solving the JAXB “unexpected element” problem

Monday 2015-06-08

-1If you are using JAXB in a maven/java project to unmarshal an XML document and you get:

javax.xml.bind.UnmarshalException: unexpected element (uri:”urn:iso:std:somestuff:xsd:somestuff”, local:”Document”). Expected elements are (none)

Or if you are using JAXB to marshal an XML document and you get:

com.sun.istack.internal.SAXException2: unable to marshal type “generated.somestuff.Document” as an element because it is missing an @XmlRootElement annotation

You have probably fallen victim of the fact that JAXB does not do “Simple Binding” by default. If your project is a maven project and you generated classes based on an xsd file, this is how you fix it (without changing the xsd file):

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Better modulation for the Baofeng UV-5RA

Sunday 2015-05-10

baofeng-uv-5ra-plusUndoubtedly the Baofeng UV-5Rx delivers a lot of radio for your buck. However some models in the range have a bad reputation for the transmitted audio sounding soft and muffled.

In 2013, Remco PA3FYM obtained the schematics of the radio and devised a modification where transistor Q17 of the VOX is re-purposed as preamplifier in the microphone audio circuit. It works wonders for your radio. For people needing a bit more visual guidance, below is a walktrough of how I did this to my Baofeng UV-5RA.

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