Thursday, June 1, 2017

HF Radio Propagation Modeling

Below is a series of cropped screen shots I collected at 0830 CDT today from the VOACAP map feature of the KE9NS PowerSDR software that I am currently using. My station location is marked with the red star. The predicted signal level scale ranges from blue (strongest) to green to yellow to orange to gray (weakest). Only the 30 m plot has gray contour lines. The 60 m plot has vertical lines that mark two of the defined frequency channels.



















During earlier discussion of this topic, Tom KQ5S told us about the VOACAP propagation modeling presented on the K6TU web site. The link I provided here gives an overview of what's needed to run the model program on the web site.

A little web searching today about "do-it-yourself" VOACAP usage brought the following article from 2004:

Two other search results raised my awareness of the VOACAP dependence on sunspot data and how it is defined and published:
My searching today reminded me that the VOACAP capability is also a plug-in built into the 4nec2 antenna modeling software that I use. I've seen it in one of the program menus, but have not digested the documentation enough to use it.

John WA5MLF

Monday, April 24, 2017

Saturday, April 22, 2017

160 m Dipole - Old and New

Here is a series of plots that compare the radiation patterns of two versions of multi-band dipole antennas at KB0BH:
  • Old dipole: 240 ft end-to-end, 35 ft high, 450-ohm balanced line feed
  • New dipole: 230 ft end-to-end, 60 ft high, 450-ohm balanced line feed
Modeling for the old dipole includes the fact that 20 ft on each end hangs down vertically.
The graphics below include horizontally polarized pattern in the horizontal plane and vertically polarized pattern in the vertical plane. Three frequencies were analyzed (1.9, 3.7, 7.2 MHz). The frequencies are identified near the upper left corner of each plot.

In all cases the antenna structure is oriented from left to right on the plots. 

Each plot shows the patterns for both antenna cases, for comparison. The color legend is shown at the lower left corner of each plot. Numerical markers for maximum gain and beam width are for the new dipole. Click on any image for a full size view.















The software can provide additional types of radiation patterns.

Monday, March 13, 2017

Map of QSO participants

I updated a pair of Google Earth map views to show the locations of participants in our morning round table QSOs on 75 m. These are extensions of the earlier maps I made a few years ago of participants in the Saturday Bell Ringers Net. Click on either graphic below for a full-size view. The place marker dot, not the call sign label, represents the location of each station.



The view above shows frequent and infrequent participants. Four range circles, centered on W4BXI, are labeled with each radius in miles.



This second view is zoomed in to better display the stations within 100 miles of W4BXI.


Monday, March 6, 2017

Baluns -- Under the Hood

Below are views of 3 baluns that I own, with their covers removed to see the internals. The first photo shows 2 LDG baluns that are rated for 200 W. The one on the left is a 1:1 current or choke-type balun. The one on the right is a 4:1 balun that appears to be a voltage-type balun.  For some in-depth discussion of balun types, see this article by W7EL.

LDG baluns



1:1 Current Balun
4:1 Voltage Balun

Above are schematics of the two LDG baluns, using graphics from the W7EL article.

The next 4 photos show the internals of a DX Engineering balun DXE-BAL050-H10-AT that is rated for 5 kW CW and 10 kW SSB.






-  John

Comparing 3 Feed Line Lengths

I added another 3 ft of 450-ohm ladder line to my antenna feed line, bringing the total length of ladder line to about 99 ft. Using data measured by my antenna analyzer, I compared the current data with what I collected with the previous lengths of 91 and 96 ft.  Below are graphs that compare the SWR and impedance (magnitude) for the 80 m and 40 m bands.


SWR 80 m
SWR 40 m










|Z| 80 m










|Z| 40 m












Click on any graph to view it full size. These graphs show the effects of lengthening the ladder line feed while keeping the antenna length constant at 102 ft end-to-end.






Sunday, March 5, 2017

Bringing Gamma Back -- Alzheimer's Research

A December 2016 NPR Radiolab podcast reported on research using mice that discovered the beneficial effects of blue light flashing at the brain's gamma wave frequency, reversing Alzheimer's effects, at least temporarily. The audio program runs for almost 25 minutes and has a few promotional announcements (commercials).

Below the web page graphic are some recommended links for additional information.
This video link is a nice summary of the research with excellent computer animations.

YouTube provided this related link. It shows an 83-year old man who claims to have recovered from severe Alzheimer's symptoms with a certain daily medication combined with a few supplements and dietary elements associated with populations that do not develop Alzheimer's disease.

John