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Monday, 17 April 2017

Thinking of sharing your raspberry pi image, Save time by shrinking the image first (also some security tips)



Considering sharing a Raspberry Pi Image, or using one?

When you think you have a great Raspberry pi image and you want to share it to the world for testing and comments, there is nothing more frustrating that an oversized image which takes ages to download and even longer to install on the SD card.

First lets get rid of the packages we don't need and take up the most room from a default raspberry pi image

sudo apt-get remove --purge libreoffice-*
sudo apt-get remove --purge wolfram-engine


Now we need to make a copy of your SD card (image)

Credit to Andrew Oakley: http://www.aoakley.com/articles/2015-10-09-resizing-sd-images.php

Making the Image


Let's start by making an image. Pop your SD card in your PC's card reader. Most likely the file manager will open a window or two. Close these windows if so.
Now find out where the card is mounted. Go to a terminal session and type:
df -h
You'll see something like:
/dev/sde1                   56M   20M   37M  36% /media/aoakley/boot1
/dev/sde2                  7.2G  3.8G  3.0G  56% /media/aoakley/ec2aa3d2-eee7-454e-8260-d145df5ddcba
The important thing is that you now know that your SD card is on /dev/sde . It has two partitions, /dev/sde1 and /dev/sde2.
Your system might mount the card somewhere else, such as /dev/sdg or even /dev/sdb. Make a note of where your card is mounted and use this wherever I use /dev/sde , /dev/sde1 or /dev/sde2.
Let's unmount this but leave the card in the card reader. This will let us take an image.
sudo umount /dev/sde1 /dev/sde2
Obviously if yours is on /dev/sdb or /dev/sdg or whatever, you'll need to type that in appropriately. It is highly unlikely that your SD card is on /dev/sda unless you're mad enough to do this entirely on a Raspberry Pi. Typically /dev/sda will be your hard disk or SSD, so don't mess with that.
sudo might ask for a password. Check that you really, really haven't typed /dev/sda unless you really, really know what you're doing, then enter your password.
I use dcfldd for making card images, which is a replacement for the old dd disk duplication program. dcfldd has a number of improvements, most notably a progress meter so you can see it working, and be confident that it hasn't crashed.
Install dcfldd if you haven't already got it (it won't hurt to try to install it again):
sudo apt-get update && sudo apt-get install dcfldd
Now take the image. Again, change /dev/sde to wherever your SD card is mounted.
sudo dcfldd if=/dev/sde of=imagename.img
You can change imagename to whatever you like - I use YYYYMMDD dates and names, so 20151009-tutorial.img for example.
The image will start to be taken, together with a nice progress counter (which you don't get with old-style dd ). When it finishes there may be a pause before you get the command line prompt back - give it a minute or two to flush the cache.
Once finished, you should force a synchronise of any outstanding input or output (there shouldn't be any, but just to be sure), then the card will be safe to remove.
sudo sync
You may now safely remove the card.
Next, let's change the ownership of the .img file. The image file will be owned by root (because we used sudo). It's probably a wise move to change the ownership to your user. For example, my username is james but you'll need to change this to your username:
sudo chown james.james imagename.img
We use james twice because we are changing both the ownership and the group.
Okay, you've got an image file; you have backed up your SD card. But it's probably quite a big file - as big as the SD card itself. Let's start making it smaller.


Using a simple script

next we need to copy a script and make it executable on our system.

Credit to Andrew Oakley here: https://github.com/aoakley 
as it is his script we will be using.

copy or download the script from this link: https://github.com/aoakley/cotswoldjam/tree/master/raspbian-shrink

create a new file in your home folder (on your linux box)

vi shrink.sh
escape a (insert)
edit paste
escape : w q (escape save file and quit)
chmod 7777 shrink.sh (modify file to be executable)

Now test the file runs ok type: sudo ./shrink.sh
should get the following output:









To run the script simply type: sudo ./shrink.sh image.img smallimage.img











Once it finishes running (minute or so) we get the following output





















as you can see we now have  a new image which is .2GB smaller, results will vary, the above was just run on the standard Jessie image (without removing the office and other packages)




Security warning!!!!


A word about distributing images on the Internet.
Remember if you have used the image with any personal information (e-mail, web browsing, etc.) then all of this history will be in the image file. you e-mail account, any saved user names and passwords, this is quite scary.

Similarly, if you download a shared image be aware this could contain programs which collect and share your data. any old script could be running in the back ground and sharing all sorts of personal information back to the  distributor.

One very quick fix is to ensure the public and private SSH keys are changed so that no one can get access to your Raspberry Pi computer remotely.

  1. Become root, or append ‘sudo’ on the front of all the following commands.
  2. Delete old ssh host keys: rm /etc/ssh/ssh_host_*
  3. Reconfigure OpenSSH Server: dpkg-reconfigure openssh-server
  4. Update all ssh client(s) ~/.ssh/known_hosts files otherwise you’ll get the REMOTE HOST KEY HAS CHANGED error message.

Online / Web based Kiwi SDR WSPR monitoring stations at your disposal

The new KIWI SDR allows users to share their station on-line and allow us to log in and tune around.

Go to the follow web page http://sdr.hu/ pick a location / SDR you want to use

On most of the stations you will have the control panel in the bottom left side of the screen, this will allow you to change band and mode, some of the HF stations have a box for extension, the last optin in there is WSPR and you can open a web based WSPR monitor. This could be useful to see if you are spotted at all?






Select WSPR option and the box below will also open on the screen.







Firstly select the band you wish to monitor.
Note if you choose to upload, the owners details are used. On some systems its quite slow to get the data decoded (3 minutes plus) but as you can see we do get some results.




If you visit the WSPR net web site you can search for the websdr call sign (in our case KH6ILT)



As you can see the spots have been uploaded and you can see good graphical representation linking each spot back to its location.










This is by far the simplest way we have found to pop up a WSPR monitoring station thanks to some dedicated SDR owners and to Kiwi for the software (and hardware of course) support.


Friday, 14 April 2017

Wendover woods, looking at a SOTA site


As it was good Friday, I decided to take the Children on a bit of an adventure and head over to Wendover woods near High Wycombe / Chilterns / Amersham.

This is a national Trust site, has good facilities including on site lots of parking for about £4, reasonable toilet, and a cafe.

The Children are kept entertained by a large play park, several trails, which they can take part in building camps and searching for the infamous Gruffalo 



This stone is placed t mark the summit of the hill.


Leo and Oscar with their ice creams ...


Bob M6FLT with his home made 2/70 yagi and the Arrow antenna (CQ sats)


Bob M6FLT using the HF in the mobile, much needed coffee break and warm up


Thomas, Leo and Oscar found the Gruffalo after a good long walk 


James M0JFP listening to the ISS talking to a school in France....see below:




James M0JFP Arrow antenna and baofeng handie working So-50




The arrow antenna taking a break....


Tuesday, 11 April 2017

Phoenix DMR repeater network now available via the DV4-mini and other dongles.

At long last you can now use your dv4-mini, sharkrf and DV mega etc to access the (local for us) Phoenix repeaters / talk groups. This should give DMR a little bit of a kick start and hopefully allow a bit more activity on the local repeaters and allow more interaction from abroad.

DV4Mini

In the DV4mini control panel software, click on the “Expert Settings” tab and under “Choose nearest DMR Master:” select Phoenix-C.






From the DVControl tab you can then select “DV4mini Settings” DMR+, and from the TS2 Reflector list select “4404” for access to TG840.

SharkRF OpenSpot

Log into the web interface and select the “Connectors” tab. Select DMR+. From the Server list, select “Phoenix-C”. 


DVMega

Currently only connection to our network via the MMDVMHost application is possible. When setting up the MMDVMHost software you will need to edit the MMDVM.ini file to point to our Master server. Under the section “[DMR Network]” set the following settings.
[DMR Network]
Enable=1
Address=109.69.105.88
Port=55555
Jitter=300
# Local=3350
Password=PASSWORD
# Options=
RSSI=0
Slot1=0
Slot2=1
Debug=0
If you would like the DVmega to automatically connect to reflector 4404 for use on TG840 remove the “#” before “Options=” and change the line to say.
Options=StartRef=4404;RelinkTime=60;UserLink=1
StartRef = Initial Reflector
RelinkTime = If you change reflector this is the timeout before it switches back to 4404
UserLink = Whether reflectors can be changed via private calls from a radio.
You will need to use the 24112016 version (latest as of 28th Nov 2016) for the Options to work. A windows 32bit version of the MMDVMHost.exe can be found HERE. It should replace the current windows version you are using (rename existing or backup).

for updates and latest information refer to : http://www.dmr-uk.net/index.php/hotspots/


Monday, 10 April 2017

Summits on the Air talk by Michael G0POT


Online club talk on SOTA activation

presented by Michael G0POT



On Friday 7th April, Michael G0POT, kindly did an on-line presentation, sharing his experiences and expertise in SOTA activation, operation and tops tips on keeping safe whilst having fun.

The main SOTA web page is located at: http://sotawatch.org/
You can register there and update your activations and chaser points.


Please click on the link below to watch the presentation




If you have any questions or need any information please get in contact with us info@chertseyrc.uk or twitter @chertseyrc. We would love to hear from you and share how you get on.

Michael did a great write up to go with the above video

Take a look at Michael's other web pages and videos below













AMSAT UK kindly shares our FM and SSB operating guide links


https://amsat-uk.org/2017/03/30/beginners-guides-to-satellite-operating/

and a nice update to the main beginners page too:
https://amsat-uk.org/beginners/

New domain name / branding for the club


Friday, 7 April 2017

Satellite QSL cards for M0JFP









Monday, 3 April 2017

New May #Vbuildathon **Homebrew Satellite Antenna and Diplexer**

We are hosting our second virtual build a thon in May, this time we will be exploring Satellites and how to get on them and use them.

Firstly, how about building a simple and cheap dual band yagi antenna and diplexer which you can use with your existing hand held or more expensive radio.

We will be using WebEx again, so you will need access to a laptop / PC or tablet (phone) Internet connection and a webcam if you want to be seen, a headset may also be useful.

Please register your interest by e-mailing us: chertseyradioclub@hotmail.com

The course is FREE of charge and we will look to source the parts for the project and resell them at cost price, once we have an idea of how many are joining in.

We are looking forward to hearing from you soon

Best 73 James / M0JFP / WO2I
Chertsey Radio Club MX0MXo