Ionosonde sweeps the 40 m band

 

 

 

 

 

 

 

While viewing the 40 m band with my SDRplay receiver I saw a strong ionosonde signal sweeping across the band, as shown in the above screenshot. The top part shows the signal on the panadapter view (horizontal axis is frequency, vertical axis is amplitude). The bottom part shows the waterfall display (horizontal axis is frequency, vertical axis is time, progressing downward). Signal amplitude is represented by brightness. The sweep shows here as a diagonal line. Other stations on the band are operating on fixed frequencies.

Data collected by the ionosondes around the world are publicly available. See my blog posting: Graphs of Maximum Usable Frequency from Ionosonde Data for more information. The collection and analysis of data from ionosondes is managed by the GLOBAL IONOSPHERE RADIO OBSERVATORY.

I captured a video of the SDRplay window that includes a sweep, as seen below. There is no sound in this recording. Normally one hears only a short chirp as the sweep passes through the receiver's audio bandwidth. On this view the 2.8 kHz audio bandwidth is the thin vertical column in the center. Other active signals on the band are seen as the up-and-down white vertical spikes.

 

Radio Propagation Issues for the RV Service Net

During several months of observing the Eastern/Central RV Service Net and providing remote station access to W4BXI, the ability of net participants to communicate was analyzed.

The results of our study are presented in this document (PDF), which is focused on the 40 m band propagation during the time frame of the morning net on 7191 kHz. Marginal radio propagation at the current low point in the Solar Cycle makes it difficult for net participants to hear each other.

Our presentation combines observations of signal levels, net participant reports, ionospheric "soundings" and propagation modeling.

John WA5MLF
Dan KC4GO

RV Service Net - 11 April 2019

During the second hour of Thursday's net I captured some audio and screen shots of the activity. The net control station, Sam WA4ICK, was S9+10 to me (in Baton Rouge) and painted a strong image on my FLEX-3000 SDR waterfall/panadapter view as shown below.

Click on image for an expanded view.

Improved propagation noted by several net participants can be attributed to an active region (with sunspots) on the Sun that has rotated back into Earth view and is raising the solar flux. On April 11 the sunspot number was 13.

A sample of the audio recording from around the middle of the second hour illustrates the reception here of signals from WA4ICK and W3TOM. Below is a screen shot of a portion of the audio waveform. You can see how the signal-to-noise (S/N) ratio changes after the hand-off from WA4ICK to W3TOM at about 1/3 of the way from the left.

Click on image for an expanded view.

The first third has a narrow baseline between syllables, indicative of my receive AGC turning down the gain in the presence of the strong signal. The remainder of the waveform has a lower S/N ratio as indicated by the thick baseline. Some fading is evident. The signal improved after the first few seconds. In this later 2/3 of the waveform the AGC opened up to allow more signal, but the noise was also higher. Click here for a 47-second recording that includes the portion represented by the above waveform.

 I have two longer recordings that I can share with interested parties upon request.

73,
John WA5MLF

RV Service Net Reception at WA5MLF

During the last half-hour of yesterday's RV Service Net the signal from W4UOA was solid at Baton Rouge. The distance from my station to W4UOA is 430 miles.

Below is a screen shot captured at 0751 CDT, while W4BXI was transmitting on 7191 kHz  from W4UOA. Another strong signal can be seen below 7188 kHz.

Click to enlarge view.

A little earlier (0728 CDT) I recorded KB0BH checking into the Net and acknowledged by W4BXI. The recording (click here) was made from my Flex-3000 transceiver in Baton Rouge.

73,
John WA5MLF

Audio Recordings from 75 m and 40 m

I made several recordings of received audio on my transceiver in Baton Rouge this morning.
Below are links to the MP3 recordings.






3.740 MHz
The marginal copy on this band is consistent with poor propagation at this time of day for my distance from north Alabama. Sunrise today was at 0649 at my location. Some QSB also experienced.

1. W4BXI at 0818 CDT, talking via N4NR's station, using the RemoteHams Internet interface. At the time, several stations noticed his audio seemed to have room echo or "in the barrel" sound. I think this was his first time to transmit via RemoteHams.
2. N4NR at 0822 CDT, talking via RemoteHams interface through his home station
3. W4BXI at 0823 CDT, talking via N4NR's station, using the RemoteHams interface.
4. N4NR at 0834 CDT, talking via RemoteHams interface through home his station

7.233 MHz
Here are recordings of several stations at the time of our Saturday morning net.

1. WA4PUB and K9JWJ at 0914 CDT
2. N4NR at 0919 CDT talking via RemoteHams interface through his home station
3. KB4XX at 0920 CDT
4. W4BXI at 0920 CDT talking via N4NR's station, using the RemoteHams interface

John WA5MLF

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. 

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:

• Real-Time HF Propagation Prediction
• High Frequency Propagation Models

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.
 

Map of Members on Saturday Net

Here are two views from Google Earth that show the locations of Bell Ringer members who have checked into our Saturday morning net during the past two years, according to records kept by W4BXI. The first view covers a wide area to show all station locations. Four circles show a range in miles from W4BXI's location. The legend at top right gives the radius for each circle.

Click on map for enlarged view.

The second view covers a smaller area to expand the view of the many stations located in Alabama and Georgia. Three circles show the range in miles from W4BXI's location.

Click on map for enlarged view.

These map views may help us to better understand the variation in reception among our members according to their ranges and the radio propagation experienced by frequency band and time of day.

I can easily add and remove stations and generate range circles centered on any point on the map.

W4BXI - Net control on RV Service Net

Click here for an audio recording of W4BXI on the RV Service Net on 7191 kHz, as heard on my transceiver in Baton Rouge. This was at 0645 CDT this morning. John's signal was reading S9.

Saturday Net on 7230 kHz

The signal reports among participants in the Saturday, 26 Dec 2009 net confirmed the continuing lack of propagation at distances of less than about 250 miles. Without a map in front of me that shows the locations of participants, it is hard to visualize the relative distances and directions among stations. Below is a map view showing the participants' locations and a dark shaded area representing the approximate zone of "no copy" (aka donut hole) relative to Birmingham. Click on the image to magnify.

To represent the ability of various stations to hear each other I produced another view with color-coded lines between many (but not all) pairs of stations. Red signifies good copy and blue signifies poor or no copy. In general, stations that are at least 250 miles apart were able to copy each other, although this distance threshold seemed to be growing as time progressed beyond the 0900 CST start of the net. W4BXI reported poor copy of K9JWJ although they are 307 miles apart. I used purple to mark that path.

Hopefully, this picture will improve as sunspot cycle 24 gets going!