Friday, March 30, 2012

Cofetel Updates Mexican AM List

Mexico's Federal Telecommunications Commission "Cofetel" has published the Mexican AM station list in .PDF form again, posted March 22, 2012. This is a rare event that seems to happen only every 6-18 months. The data is up-to-date as of February 29 (yes this is a leap year).

Get it at the Cofetel site.

No official Mexican AM database in downloadable form, like the FCC database, is evident. It would be nice to have this in readable format in order to incorporate it into a program, like my Radio Data MW program. If someone knows of a link to an official Mexican governmental source, please let me know.

The supposed "official" Mexican governmental link to the AM station list (again in .PDF form) continues to return 503 Service Temporarily Unavailable, and has done so for at least a couple of years. This, I'm sure, was simply a copy of the Federal Telecommunications Commission .PDF. Perhaps we should start recognizing Cofetel as the official source from now on.

Viva Mexico!

Friday, March 2, 2012

Loop Calculator One

Loop Calculator One is a program which will display detailed information about coils, including accurate inductance for short and long coils of many types. It is especially tailored for inductance calculations of polygonal-shaped mediumwave receiving loops.


To download, see the link at the top of the right sidebar under LATEST PROGRAMS. The sidebar at the top right will have the most current link in case the program is updated. The link will change in the case of an update, so I would avoid copying and pasting it into a forum or other web page. Come to the main page of this blog instead.

Click image to enlarge.


Being a mediumwave DXer and wanting to construct my own passive loop devices, I was unhappy with virtually all the web-based coil calculators found on the internet. They used either inaccurate formulas, or formulas that weren't even designed for large but very short polygonal coils like our passive loop, or they didn't correct for internal inductance, self-inductance, mutual inductance, or self-capacitance. The few stand-alone programs out there didn't satisfy either. I set out quite some time ago to accumulate information, formulas, and data to start writing the inductance calculator program. The going was slow. Investigating the history and ferreting out the accurate information took much more time than I thought.

The result was and is Loop Calculator One. Four main formulas (plus two extras) are presented. Two formulas build on the fact that a polygonal loop inductance can be calculated by figuring its equivalent circular size using area and perimeter equivalents, with modification, then calculating the inductance from that as if it was a circular loop. H. Nagaoka's old inductance formula and Wheeler's 1982 Continuous formula, both for circular coils, are used in this way to arrive at surprisingly accurate results. More surprising, I discovered that Nagaoka's old turn of the twentieth century formula using Lundin's formulation of Nagaoka's non-magnetic uniformity coefficiant holds amazing accuracy across a wide range of loop form factors. An excellent treatise on calculating the modified equivalent circular loop radius of a polygonal form can be found at electronbunker.

The remaining four formulas are by F. W. Grover of the NBS (National Bureau of Standards). In 1929, Grover offered two remarkable formulas for solenoid and flat spiral polygonal loops in his paper, "The Calculation of the Inductance of Single-Layer Coils and Spirals Wound with Wire of Large Cross Section", Proceedings of the Institute of Radio Engineers. His two simplified versions for polygonal loops appear in the book "Inductance Calculations: Working Formulas and Tables", (Van Nostrand, 1946 and Dover, 1962 and 2004). Loop Calulator One also presents these four formulas.

All formula results are corrected for self-inductance, mutual inductance, internal inductance at frequency of operation (which is user-definable), and self-capacitance (by check box). Much additional information is displayed about the loop or coil, including calculated tuning range from a user-defined variable capacitor, the coil's form factor, Nagaoka's constant, and more.

Wire gauge can be input directly in American Wire Gauge format, or as a user-specified diameter. R. G. Medhurst's calculated self-capacitance estimate is displayed and can be user-entered to see how it effects the tuning range of the loop.

As a side bonus, a separate formula box can calculate the actual self-capacitance of the loop using the low and high capacitor values and the actual discovered low and high tuning range by using a receiver.

Small circular "radio" (long) coils can be calculated. The Nagaoka and Wheeler formulas are used in these calculations.


Install is simple. Download the .zip file and unzip. Click on the LoopCalculatorOne.exe file to run. This program makes no registry changes and saves no data to your hard drive. It has been developed and tested in Windows 7. It should work fine in Windows Vista and XP environments, and Windows 8. It is written in the old standby Visual Basic 6.

Included in the .zip is a readme.txt file. Be sure to have a look. Also included is an American Wire Gauge chart showing wire diameters.

I hope you enjoy this program and find it useful.