What is a dB, dBm, dBu, dBc, (Tutorial Videos from W2AEW on Youtube)

If the concept of decibels (dB) is confusing, this Youtube video from W2AEW has a very clear explanation with a demonstration using a spectrum analyzer:

• What is a dB, dBm, dBu, dBc, etc. on a Spectrum Analyzer?

https://www.youtube.com/watch?v=1mulRI-EZ80#aid=P-LGfIJuuH8

Remember: dB is a ratio of Power levels, so when you need to do a ratio of Voltages, the formula is different.  He doesn't mention that until late in the video.  However, he gives a much clearer explanation of why the formula is different (20 x Log10() vs 10 x Log10()) by doing the
math to demonstrate where the difference comes from.

(Remember P=I x E or P = (V^{^2})/R ?)

There is a table at the beginning of the video of the few things you should memorize both for your amateur radio test and for general use later:

• 3 dB represents a ratio that is a doubling.  Of the two things being compared, one has twice as much power as the reference.
• -3 dB represents a ratio that is a half.
• 10 dB is 10 times greater.
• 20 dB is 100 times greater.

Note: W2AEW has posted a whole bunch of good video tutorials on electronics and radio.

https://www.youtube.com/user/w2aew

A couple that might be relevant to prepping for your General Class amateur radio exam:

• Back to Basics: Voltage and Current in Capacitors and Inductors
• Basics of RF Mixers in Radio Receivers / Mixer Tutorial / Frequency Conversion

I've also found his oscilloscope and spectrum analyzer tutorials to be very useful.  He's very good at explaining and documenting things.  Compared to a normal text presentation, the demonstrations / experiments really drive the concepts home and show that it's possible to try these things for yourself.

Enjoy.

 

Exploring the Wireless World with Software Defined Radio

From the rtl-sdr.com blog: links to a 12 minute video, and a longer  40 minute version, by Balint Seeber showing some of what is available in the VHF and UHF bands using a computer and a software defined radio receiver.

While the videos are from a company that produce high-end SDRs, most of what is shown can be done with a $20 RTL SDR USB stick and freely available software.

http://www.rtl-sdr.com/exploring-wireless-world-usrp-b200/




If you are interested in playing with one of these, make sure you get one
that has the R820T tuner chip which can receive from 24 - 1766 MHz.  These
will do FM, AM, Broadcast (wide) FM, LSB, USB.  You will need some
adapters to hook it up to a better antenna.

Good sources are: NooElec and Adafruit:   NooElec also sells through Amazon.
Adafruit is a great source for all sorts of do-it-yourself electronics.

http://www.nooelec.com/store/software-defined-radio/sdr-receivers.html
http://www.adafruit.com/products/1497

If you are looking to save a few bucks, you can get these from china direct
sites like Deal Extreme, but it will take a few weeks to get to you.



Links:

• rtl-sdr.com - a blog site that aggregates a number of interesting SDR related posts from around the web.
• Balint Seeber's Youtube Channel Includes a GNU Radio / SDR tutorial series
• Ettus Research's Youtube Channel - maker of the USDR, where Balint works.
  

Using an Oscilloscope to Check Your (Transmitted) Signal

N2NOV had posted that Tektronix now has a Youtube channel with videos on how to properly use an Oscilloscope.  Many years ago, Tektronix published a good free PDF, The XYZ's of Oscilloscopes. It was
good but a little dry compared to a video presentation.

Well equipped radio operators have a special type of dedicated oscilloscope called a service monitor which allows viewing your transmitted signal, by tapping the radio frequency (RF) from the transmission line. Recently I came across a Youtube video that showed how to build a very simple RF sampling circuit that would allow using a common oscilloscope to monitor the RF output of your transmitter (transceiver).  While this won't do everything that a dedicated service monitor would do, it's a pretty cool way to check your signal if you only have an oscilloscope.  The RF sampler circuit described should be less than $10 in parts.

Personally I find this sort of thing to be very cool.  Even if I had an unlimited budget for buying equipment. I don't have the room to store it in NYC.

• How to Use an Oscilloscope
• Tektronix Youtube Channel
• How to monitor your Ham Radio Transmitter using an Oscilloscope

Note: This will only be useful for monitoring AM and SSB transmissions. I hope to come across something not too difficult to build that would be useful for looking at the output of an FM transmitter like the type most commonly used on VHF and UHF.

Good Tutorial on TCP/IP Diagnostics using Traceroute

MTK, just sent me this today.  It's a presentation and paper by Richard A. Steenbergen, from 2009 that covers the finer points of diagnosing TCP/IP networking problems with Traceroute.  It looks like it was originally presented as a tutorial at NANOG.  Why am I posting this?  If you tried to google "traceroute tutorial" you'd get tons of fairly lame overviews that show some traceroute output and attempt to explain it. 

To quote one of the intro slides:

Few people are actually skilled at interpreting traceroute.  Most ISP NOCs and even most mid-level engineering staff are not able to correctly interpret a complex traceroute.  This Leads to a significant number of misdiagnosed issues, false reports, etc, which flood the NOCs of networks world-wide.  The false report rate is so high that it is almost impossible to
report a real traceroute-based issue through all the noise.

There is a lot of nitty gritty practical details in here. Even if you rarely use traceroute, you'll learn a lot from this. This is one of those rare, good presentations and papers to file away so you can refer back to it and hopefully use to enlighten others.

• Presentation: A Practical Guide to (Correctly) Troubleshooting with Traceroute
• The Paper: Traceroute, PDF, 20 pp
• NANOG listing for the tutorial, includes a link to a .WMV video 

Hope This Helps.