QST - September 2010 - (Page 47)
these parameters on a graph showing them versus frequency. These two parameters are usually plotted together on the same graph, and because they have distinctly different plots it is easy to tell them apart. Whenever a graph is encountered with plots recognized to be return loss or insertion loss, but the designations on the Y-axis are something else, such as “Negative Response,” or “Negative S11 or S21,” or “Negative Transmission,” or “Negative Return,” the editor should remove the negative signs and the confusing designations and replace them with “Insertion Loss” and “Return Loss” as appropriate. Since a passive filter
is being discussed, the reader is interested in learning the insertion loss or return loss in the least confusing manner. The designations of “Negative Transmission” and “Negative Return” do not meet this requirement. Good examples of graphs correctly depicting plots of return loss and insertion loss may be seen in the pages of the following ARRL Handbooks: 1) 2007, Figures 12.67 (reproduced here as Figure 1) and 12.68 on page 12.38, and Figure 12.74 on page 12.40; 2) 2008 and 2009, Figure 12.77 on page 12.35; and 3) 2010, Figure 11.98 on page 11.48
Figure 2 — This graph is reproduced from Figure 11.98 in the 2010 ARRL Handbook. It shows the insertion loss response for the low-pass and high-pass portions of an 80 meter diplexer ﬁlter. Also shown is the return loss of the ﬁlter.
(reproduced here as Figure 2). I originally prepared Figures 12.67 and 12.68, and they appeared in my February 1999 QST article, “Second-HarmonicOptimized Low-Pass Filters.” For these plots, the parameters of Insertion Loss and Return Loss were specified as positive values. In the current version of Jim Tonne’s ELSIE computer program, however, these same parameters are specified as “Negative Transmission (dB)” and Negative Return (dB).” The word “Gain” following “Return” is not included but is implied, so that “Negative Return Gain” equals “Return Loss.” This manner of specifying Return Loss on a plot is awkward, and not recommended. With references to the authoritative articles of Dr Bird and Dr Shuch, provided in this letter, I hope that any further references to “negative return loss” and “negative insertion loss” will no longer appear in Amateur Radio publications or other technical literature. If any readers of the ARRL Handbook, QST, QEX or other ARRL publications discover such errors, I encourage those readers to bring them to the attention of the responsible editors, to help prevent these errors from being repeated. I believe it is important that our common electronics literature not be polluted with incorrect terminology. Your cooperation and assistance will be appreciated. — 73, Ed Wetherhold, W3NQN, ARRL Technical Advisor, 1426 Catlyn Pl, Annapolis, MD 21401; firstname.lastname@example.org
Technical Correspondence items have not been tested by QST or the ARRL unless otherwise stated. Although we can’t guarantee that a given idea will work for your situation, we make every effort to screen out harmful information. Materials for this column may be sent to ARRL, 225 Main St, Newington, CT 06111; or via e-mail to email@example.com. Please include your name, call sign, complete mailing address, daytime telephone number and e-mail address on all correspondence. Whether praising or criticizing a work, please send the author(s) a copy of your comments. The publishers of QST assume no responsibility for statements made herein by correspondents.
NN4ZZ TILTPLATE FOR TILTOVER TOWERS
The TiltPlate from NN4ZZ is an accessory for tiltover towers designed to allow Yagi antenna booms to swivel out of the way so the tower and antenna can be lowered all the way to ground level. The TiltPlate comes in two models, one for antennas up to 15 square feet and one for larger antennas up to 25 square feet. Hardware is stainless steel. Prices start at $750. To order or for more information visit nn4zz. com/tiltplate. htm.
In the “Hands-On Radio: Experiment #89 — Overvoltage Protection” [Jun 2010, pp 55-56], the reference to The 2010 ARRL Handbook in the third column on page 55 should be to section 7.16.8 on page 7.57. Art, VE2AHH, found that D1, the voltage protective device specified in “Compact Voltage Protector and Fuse Assembly for 100 W Transceivers” [Apr 2010, pp 30-32], was on backorder at Mouser. Art found that a 625-1.5KE15A-E3 is a substitute that is in stock and the same as that specified except that it is a lead free part. With that change, all parts are available from Mouser.
September 2010 47
Table of Contents for the Digital Edition of QST - September 2010
QST - September 2010
It Seems to Us: Disaster Drills: The Last Word?
This Just In
Guide to ARRL Member Services
Up Front in QST
A Solar Powered Repeater for Emergency Communications
A Portable Antenna Mast and Support for Your RV
One Ham’s DC Power Connector Preference
Attic Antenna Experiments
The Doctor is IN
Getting on the Air
Hints & Kinks
The Flight of PBH-8
Ham Radio Manufacturing: An Inside Look
JOTA 2010 is October 16-17
2009-2010 School Club Roundup Results
ARES®: 75 and Counting
2010 Simulated Emergency Test
This Month in Contesting
2010 ARRL DX Phone Contest Results
2008 ARRL International DX Contest (Phone) Scores
The World Above 50 MHz
Amateur Radio World
At the Foundation
Convention and Hamfest Calendar
ARRL VEC Volunteer Examiner Honor Roll
Field Organization Reports
75, 50 and 25 Years Ago
Index of Advertisers
QST - September 2010