Propagation Maps for 7 MHz

Using the VOACAP online program, I collected color-coded maps representing the predicted signal power (dB relative to 1 watt) centered on a designated transmitter site.  In the program this map is obtained from the SDBW button at the lower right corner of the main page.

I used the grid square location for W4UOA as the transmitter site and specified SSB mode, 500 W power and antenna at 33 ft (one of the limited menu selections).

The results are shown below for 1200, 1300 and 1400 UTC, encompassing the period of the RV Service net.  Below is the standard output from the program, for 1200 UTC -- covering the entire world. On the right side is a scale showing the relationship of color to the predicted received dBw signal level.

Since our area of interest for the RV Net is just the USA, I made a cropped version of each map. The results are below this one.

Click on image above for a full size view.

1200 UTC

Above is the cropped copy of the 1200 UTC map. The predicted low signal level within a few hundred miles of W4UOA is clearly seen and is consistent with the observed signal levels during the early part of the first hour of the Net.

1300 UTC

Above is the cropped version of the 1300 UTC map. The low signal (skip zone or doughnut hole) area is shrinking in size at the beginning of the second hour of the Net.

1400 UTC

Here is the 1400 UTC map, showing that good signal levels are now predicted closer to the W4UOA transmitter. This represents the end of the Net's second hour.

On a typical Thursday morning I am not able to copy W4UOA at 1300 UTC, but usually around 1330 UTC the signal comes up to a solid Q5 level. The distance from my station to W4UOA is 430 miles.

Many interesting reports and graphics are available from VOACAP, and I'm still getting acquainted with them. An excellent user guide for the online program is available at this web site. Another option for use is to download and install the program on your own computer. I may try that.

73,
John WA5MLF

AM broadcast received audio -- local and remote

Audio quality testing this morning involved reception of WWL-AM (870 kHz) on my Flex-3000 transceiver. I recorded audio samples from two places:

1. Flex-3000 speaker output
2. RCForb client program output

Below is a drawing that shows the arrangement of radio and computer software, and the software components that are involved in the two audio paths that I used for recording. I also showed the Ethernet connection to the Internet that provides the path to remote users. The testing reported here used only the data path internal to the PC and the external audio cable.

Click above to enlarge.

Here are audio recordings (about 18 seconds each) for the two audio paths. Click on each to hear the audio recording.

1. Flex-3000 speaker output via audio cable
2. RCForb client program output

Screen shots of the audio spectrum of each recording are shown below. Click on either for an expanded view.

Flex-3000 speaker output via audio cable

RCForb client program output

The RCForb graph shows high frequency content above 5000 Hz that may be due to the wide bandwidth of the Virtual Audio Channel and other data paths internal to the PC. It was not noticeable to me when listening via speakers.

John WA5MLF
 

Graphs of Maximum Usable Frequency from Ionosonde Data

In support of a forthcoming article on 40 m propagation during the daily East Coast RV Service Net, data has been collected for two ionosonde sites: one at Eglin AFB in Florida and one at Wallops Island in Virginia. The locations of ionosondes around the world can be seen at this web page. 

Thanks to Dan KC4GO for collecting data on

• critical frequency (foF2)
• MD = MUF(3000) / foF2
• Maximum Usable Frequency (MUF) 

from both sites, spanning 16 months. Data are available in plain text format from the Digital Ionogram Data Base.

The Eglin ionosonde provided 96 data sets for each day, and the Wallops Island ionosonde provided even more. Data were collected for propagation distances of 300 and 500 miles, which were chosen to represent some common distances among regular RV Net participants. The longest distance among regular participants appears to be about 1200 miles.  A review of past ionogram data shows that the MUF at 900 miles or beyond is typically about 7 MHz at the start of the 2-hour net. Shorter distances are likely to have poor to marginal propagation that improves gradually during the Net time frame.

Eglin Graphs

Below are some graphs developed from the Eglin ionosonde data. Click on any graph for a full size view.

The above graph shows the variation of MUF(300) [MUF at 300 miles] over the past 5 months, using data from 1200 UTC each day.

The above graph shows the MUF(300) at 1300 UTC on each of the dates.

 The above graph shows the MUF(500) at 1200 UTC on each of the dates.

 The above graph shows the MUF(500) at 1300 UTC on each of the dates.

 The above graph presents the variation of MUF(500) values during the 2-hour time frame of the RV Service Net.  The data points are taken from the same calendar period as the previous four graphs: 9/1/2019 thru 1/15/2019. The bottom curve shows the minimum value of MUF(500) for each time-of-day point among the 137 days.  The middle curve shows the average or mean value (across the 137 days) of MUF(500) for each time-of-day point. The top curve shows the maximum value of MUF(500) for each time-of-day point among the 137 days.

I plan to produce the same type of graph for MUF(300) [MUF at 300 miles].


Wallops Island Graphs

The above graph shows the MUF(300) at 1200 UTC on each of the dates.

The above graph shows the MUF(300) at 1300 UTC on each of the dates.

The above graph shows the MUF(500) at 1200 UTC on each of the dates.

 
The above graph shows the MUF(500) at 1300 UTC on each of the dates.



John WA5MLF