N0A - Nixa, MO Field Day

N0SAP - Sap provided the following photos from the Field Day operations of the Nixa Amateur Radio Club. Click on any photo for a larger view.

Click here to view a local TV news video about the event.

Ham Radio Audio and Resources

During a discussion of online receivers this morning Bruce K4CMC told us about the blog Ham Radio Audio and Resources. If you scroll down there to the section labeled 5) Online Receiver's you'll find a list with many links. (The blog author misuses apostrophes.)

Included among them is the Lebanon, Tennessee Receiver provided by Trish Ray, K4ZE that we were remembering from an earlier QSO.

Thanks, Bruce!

Thanks to Phil KB4XX for sending an updated link the K4ZE receiver. See S-Meter Website Receivers for another listing of receivers. I suspect that these also appear in the blog listed above.

WA4PTZ Loop Analysis

Using the sketch Tim provided of his loop antenna, I entered the measurements into the 4nec2 program and got the far field patterns shown below. These are calculated with a 50-ohm generator at the feed point -- no feed line included. I expect that the field patterns would be similar with the feed line included.









160 m horizontal gain. Major lobes approximately north-south.










160 m vertical pattern. Mostly straight up, as expected.











75 m horizontal pattern. 4 lobes











75 m vertical pattern. 2 lobes; angle of radiation moving away from vertical.










40 m horizontal pattern. More lobes appearing.











40 m vertical pattern. Lobes continue to move toward lower angle.











20 m horizontal pattern. Lobes increasing rapidly and some nulls are deep.










Here's the 3D color coded version of the 20 m pattern.









20 m vertical pattern. Radiation angles continue to progress lower.











I have not looked at the patterns yet for higher bands. Below are SWR and impedance plots, without feed line included.

Creating a Horizontal Loop Antenna

Tim WA4PTZ wrote a nice paper to inspire other amateurs to discover the excellence of this simple antenna. Thanks, Tim!

W4BXI System Audio

W4BXI has gradually built a versatile interconnection of components that enable him to hear audio from two transceivers and to interface two-way audio between a transceiver and his contacts using Skype for VoIP calls via the Internet. Of course, he also incorporates the 20th century phone patch as another option.

As John's system has grown some issues have emerged about how to best interface various components while avoiding ground loops, feedback and level mismatch. Recent email exchanges with W4UOA and WA5MLF led to their developing some system diagrams to aid in discussion and identification of configuration choices. Below is a diagram from W4UOA that gives a complete picture of the capabilities assembled by W4BXI. (Click on it to enlarge.)

This shows that John can access various audio streams at the mixer as well as participate in a Skype VoIP conference via the Bridge Computer. Carl has included a list of control operator procedures describing how the main components are used. In testing today John determined that he can also initiate a Skype conference on the Rig Computer and connect those participants to his FT-1000 transceiver.

In order to focus more closely on the two-way audio paths, WA5MLF prepared the diagram shown below that does not include all components and audio mixer connections. (Click on it to enlarge.)
The audio mixer is shown with its separate left and right channel inputs from the FT-1000 and outputs to a headset. A new input to the headset's right earphone is the Skype caller's talk path (dashed line in the drawing). Phone patch #4 is used to combine the talk and listen (transceiver transmit and receive) audio while avoiding the creation of a feedback path. Phone patch #2 is used primarily for ground loop isolation, and can be replaced by a single transformer.

Comments and suggestions are welcome.

Smith Chart

Why do we need it? This is answered very well by David J. Jefferies in his article where he says:

"The SMITH chart is a graphical calculator that allows the relatively complicated mathematical calculations, which use complex algebra and numbers, to be replaced with geometrical constructs, and it allows us to see at a glance what the effects of altering the transmission line (feed) geometry will be. If used regularly, it gives the practitioner a really good feel for the behaviour of transmission lines and the wide range of impedance that a transmitter may see for situations of moderately high mismatch (VSWR)."

Many articles about the Smith chart seem to focus first on proving its mathematical validity. It is not necessary to have a rigorous understanding of its mathematical basis to get useful results from it as a tool.

A nice approach to understanding the format and applications of a Smith chart, without getting bogged down in math, is provided in the December 2007 QST, page 48. This is the first of a 3-part series that totals only 6 pages.

Another good introduction is the Smith Chart Tutorial suggested by John W4BXI. This one makes nice use of colors to illustrate the construction of the chart and includes several good simple applications. Don't be put off by the first two pages.

An impressive collection of Smith chart resources was suggested by Phil KB4XX. It includes a list of 20 tutorial articles, including the one referenced in the previous paragraph.

Several web sites provide downloadable copies of the Smith chart that you can print locally for use in working your own transmission line and matching problems. Several are included at the collection link above. My favorite sources are:

• Impedance Smith chart at Print Free Graph Paper. Once there, select Smith Chart Graph Paper on the first pull-down menu.
• Admittance Smith chart
• Combined chart (impedance and admittance scales -- color print is a must!)

Loop Antennas

This morning on 3968 we discussed loop antennas briefly. Phil referenced The Loop Skywire article from QST November 1985. Tim is pleased with the results from his loop antenna and emphasized that it need not be a full wavelength to be usable on 160 m. Larry commented about a recent club presentation about a member's 500+ ft loop antenna fed with high-quality coax and using a remote antenna tuner. The Loop Skywire article seems to emphasize keeping cost low.

N4KC published a detailed article on his loop antenna and its performance relative to other antennas installed at his location.

Another loop design that I found interesting was featured in the March 2008 QST, page 56. The author describes a 187-ft loop of #26 AWG black insulated Copperweld wire. It terminates directly on an SGC SG-237 antenna tuner mounted just below the window sill where the antenna wires enter his antenna-restricted apartment.