BARC 2008

Roofing Filters, Transmitted IMD and Receiver Performance.



What's important when it comes to choosing a radio?

Boulder Amateur Radio Club (BARC) Presentation, 2008.

  • A very long presentation  (1 hr. 45 min.)
  • Spoken slowly, for better understanding
  • A good presentation for beginners
  • With lots of examples


In this presentation you will see:

  • Why and how Rob's interest in testing developed.  
  • Why radios with good specs, still performed miserably in contests.
  • Why radios with upward and downward conversion were overloading in contests.
  • What Close-in Dynamic Range is.
  • And why it matters more for CW than for SSB.
  • How "Roofing Filters" help solve this problem.
  • What Transmitter Intermodulation Distortion (IMD) is, and how typical new transceivers are worse in IMD than older transceivers.
  • Comparisons of various popular transceivers.

Highlights of this Presentation

Here are some of the things which Rob covers better in this presentation than in the later ones (mostly because he had more time available to explain and answer questions):


  • Dynamic Range, what it means, and why it is important.
  • FlexRadio Technology, what problems it cures, but what new problems it has. Though serious at first, these are not so serious anymore, except under certain circumstances.  More on this is covered at the end of his 2011 presentation.
  • Hilberling PT-8000 Technology, a brief description of how it is different from other transceivers.
  • AGC Deficiencies, how almost all modern transceivers have significant ACG problems, what is triggering them and how it is negatively affecting receiver performance.


FINALLY, some of the best information in this presentation is not on the slides.  It is delivered in the Questions and Answers session at the end of the presentation.

Download Presentation and Audio File:

Roofing Filters, Transmitted IMD and Receiver Performance
By Rob Sherwood, NC0B
What's important when it comes to choosing a radio?
PDF-Dokument [537.9 KB]

NOTE:  This is the PDF version of Rob's presentation.  

  • After you have downloaded it, save it to your computer
  • Open the saved file with Adobe Acrobat Reader (or similar)
  • Then click "VIEW" at the top, choose "Rotate View", and then "Clockwise".
MP3 Audio for this presentation (BARC 2008)
MP3-Audiodatei [21.9 MB]

NOTE:  This is a very large MP3 Audio file.  It is also very long (1 hr. 45 min.).  After downloading the file, save it to you computer.  That way if you have to close before finishing the session, you won't have to re-download the file later when you are ready to continue listening to it.