Sunday, July 2, 2017

Cable and Wire Color Code

Click for enlarged view.
This photo shows one side of a Bell System job aid that displays the pair numbers corresponding to the 25 tip & ring color code combinations. The white tab can be rotated around the perimeter to display the right-most 2 digits of each pair number for a given range of pairs. The back side provides the same information for the succeeding range of 300 pairs.

For more on the color code topic, see this Wikipedia article.

This may take some of you back to the days when large and small copper cables were dominant in the outside plant of telcos.


Friday, April 21, 2017

Bell Ringers on the Map

Below are two map views showing the locations of many Bell Ringers who have participated in the Saturday morning net during the past 8 or so years. Many more have been on the net during its long history.

Click on image to enlarge.
The first image includes the most distant member participants. The colored circles represent the distance in miles from the location of W4BXI, who is near the center of the member geographic distribution. The radius of each circle is:
Red: 100 miles, Yellow: 200 miles, Green: 300 miles, Blue: 400 miles
This view and the next one show that the majority of members are in Alabama or Georgia and most are within the red circle.

Click on image to enlarge.

This second image expands the red circle for a better view of the Alabama and Georgia member locations. 

Tuesday, November 8, 2016

D-STAR Article in WBCCI Amateur Radio Club Bulletin

The club's November 2016 Bulletin contains the article shown below about D-STAR usage and components. The article is co-written by Bell Ringer Hank Montgomery, K4HM.

WBCCI Amateur Radio Club enters the Digital Era

A Few Radio Links

William Hepburn's Radio and TV DX Information Centre

Here are two that were mentioned in a recent club presentation about short wave listening:

Friday, October 7, 2016

SDR Screen Shots of Received Voice Transmissions

During this morning's QSO on 3740 kHz, Jim K4JPM shared his Flex Radio screen via Google Hangout. He had good reception of the lower sideband voice transmissions from W4BXI and W4UOA. The screen shots below show an abnormal property of each signal. Jim activated the peak mode on his receive display to hold the peak value at each frequency over a period of many seconds of voice transmission. The displays show a panadapter view (amplitude vs frequency) on top with a waterfall display (amplitude [brightness] vs frequency and time) below. The light-shaded box on the panadapter indicates the receiver's audio bandwidth setting. Signals outside of this box are not heard in the speakers.

W4BXI signal at K4JPM
Above is the view of W4BXI's signal on Jim's Flex Radio. Click on the image for a full-size view. The notable detail here is the presence of carrier at 3740 kHz (red vertical line). The LSB voice band shows the fairly typical male voice with more energy at the lower audio frequencies.

W4UOA signal at K4JPM
Above is the view of W4UOA's signal on Jim's Flex Radio. Click on the image for a full-size view. Note the presence of energy in the upper sidebands (to the right of the red line).

- John WA5MLF

Sunday, February 14, 2016

160 m Horizontal Loop Analysis

Here are some plots generated from the NEC analysis of a square horizontal loop at 45 ft above fertile ground, consisting of 540 ft of 12-gauge copper wire.

Below are 3-D radiation patterns for selected frequencies. 2-D plots in the horizontal plane or vertical plane can also be produced for any azimuth or elevation angle. These are based on the source (transmitter) being connected at the midpoint of one side of the square loop. The default NEC modeling of a feedline assumes no radiation, so the patterns are unaffected if a feedline is included.
Click on any graphic for a magnified view.

1.8 MHz
3.6 MHz

5.357 MHz

7.2 MHz

10.1 MHz
14.2 MHz

18.1 MHz
21.2 MHz

24.9 MHz
28.5 MHz

Below are plots of SWR and feed point impedance (magnitude in ohms) for 3 different lengths of the loop:  528, 540 and 552 ft. The legend at upper right identifies each case by color of the plotted data curves. Each curve is based on 188 data points. Click on any image for a magnified view.

SWR vs frequency

Impedance at feed point

I've also analyzed the effects on SWR and impedance of including a feedline length with various lengths, but need to validate the results further before posting here. Previous analysis and measurements of an actual 80 m loop indicated that the SWR dips shifted toward higher frequencies as the feedline was shortened.

Friday, December 11, 2015

HF Radio Propagation Modeling

Today's antenna modeling programs, like EZNEC and 4nec2, use the decades-old NEC program code to calculate the electric and magnetic fields produced by an antenna in 3 dimensions. (They also model parameters like impedance to assess the power efficiency of the antenna and transmission line combination.) We normally look at the radiation pattern results for the far field, considered to be greater than 2 wavelengths away from the antenna. NEC-based software is not equipped to model the fields at a great distance. The software does not model what happens to the electromagnetic energy as it propagates over a long distance.

To complete the picture of radio communication between two HF transceivers we need to look at radio propagation tools. Here are two links that list some of the available resources:
Both links make reference to VOACAP, which I became aware of while using 4nec2. I have not yet tried to use it, but I saw that VOACAP has both online and downloadable versions. 4nec2 has a utility for exporting an antenna design in the format required by VOACAP to model the propagation. Common pre-built antenna models can also be used as inputs to VOACAP. For point-to-point propagation modeling the design of the antenna at each end should be known. The first link above has a nice primer on VOACAP and a quick guide with lots of information.

The second link above also lists a program HFWIN32 which is said to contain 32-bit versions of three published propagation modeling tools: ICEPAC, VOACAP and REC533. Some more recent instructions and links are available at this web site.

A newer, freeware program HamCAP is designed to interface with VOACAP to predict HF radio propagation.

Playing with these propagation models may contribute to a better understanding of which antenna types should work best for a given frequency, time of day, geographic locations and solar conditions.