Antenna Tuners (Part 1)
The Physics of What is Involved (Part 2)
If you are like us, you have heard wives’ tales that antenna tuners (eg. MFJ or Comet) are just fooling you and are a waste of time for amateur use. Certainly, they have their limitations. We think that these limitations must be the source of the confusion. By way of commentary, a remote antenna tuner will be much more effective than one fed directly by your transceiver.
These two articles look “under the hood” to see what antenna tuning is when done manually. But a word of warning–these articles are not for the technically faint of heart. You will need a deep knowledge of electronics to get much past the first paragraph.
Radio Receiver Sensitivity
A receiver’s sensitivity specification (measured in microVolts) is a key operational parameter but advantages can be nullified with poor adjacent channel rejection. We found an informative article on the QRZnow.com website on this topic that we want to share.
The Cavity Duplexer
Have you ever wondered what a repeater’s duplexer was all about?
Many amateurs of great vintage do not even know that there is such a thing as a duplexer. A duplexer makes it possible to both receive and transmit on two frequencies, out of the same antenna, at the same time. Repeaters (as we know them) would not be possible without a duplexer.
The above hyperlinked article goes into great detail explaining the nature of a duplexer and includes plans for making a “home-brew” repeater of the reader’s own.
Duplexer Operations and Design
This article describes in very great detail and with excellent examples, various aspects of a duplexer design and implementation.
Measurement of Degradation Caused by EMI
Active EMI in a transceiver’s (or repeater’s) vicinity will raise the noise floor and very effectively shorten its active region. People will “hear” you a long distance away but at the same time be unable to open your squelch.
This paper by the Society of Automotive Engineers (SAE) explains the phenomena very nicely and enumerates a procedure to quantify the effect. You will also get a good education to prep you for your FCC license upgrade exam.
Make Your 12 dB SINAD Measurement with Purchased Software
ComTekk of Taos, New Mexico, is a producer of various electronic equipment and measuring devices. The company has produced and sells what is purported to be software for your PC that will use its sound card together with your RF signal generator to measure your receiver’s ability to pull in weak signals. In fact, it is a distortion analyzer optimized for measurement of a radio receiver’s SINAD reading.
We are not presently in a position to recommend it having not used or heard reports of its use. However, ComTekk does offer a trial version for you to check it out.
Here is a link to its online User Manual.
Here is a link to download its trial version.
