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.