QRM on 60 m

Here is a screen shot of waterfall display during KE4ID's turn on 60 m. Some Spanish speakers were operating 2 kHz above -- at 5405.5 kHz at 0734 CST.

80 m Loop Feedline Analysis

Recently I used NEC antenna modeling software to analyze the effects of different feedline lengths on SWR for an 80 m horizontal loop at 40 ft height above the "medium hills and forest terrain" ground model. The goal was to see the effects of various feedline lengths that either conformed with or departed from the lengths recommended by W8JI in his article Choosing the Correct Balun in table  3.

I collected the model's data output in increments of 0.2 MHz from 3 MHz to 29 MHz. (The modeling software permits a maximum of 256 data points.) The data were collected for the following lengths of 450-ohm feedline:  384, 400, 418, 467, 512 ft.

The graph below presents the calculated SWR at nine selected frequencies. All feedline cases show a high SWR peak in the 60 m band.  (Click on the image for a larger view.)

 All lengths have similar SWR values at the lower frequencies, and more variation at the higher frequencies. The recommended lengths of 384 and 512 ft (multiples of 127.9 ft) seem to have a bit less variation in SWR at the high frequencies, although 418 ft behaves pretty well. 400 and 467 ft look less favorable.  In the real world, experimentation will lead to an optimal or an acceptable feedline length.  Naturally, it is best to avoid combinations that give very high SWR in a frequency range of interest, since the high SWR will require the antenna tuner to compensate more and the overall antenna efficiency is reduced.

Below are the full calculated SWR plots from the modeling program for each of the feedline lengths. No other antenna parameters were changed. (Click on each image for a larger view. These are reduced-resolution copies, but should suffice for overall impressions.) I found that shorter feedlines, especially 128 and 256 ft (not presented here), gave smoother curves, but I don't have an explanation.  The plots start at 3 MHz, for nicer scaling on the frequency axis, but the antenna is designed for about 3.5 MHz, so the SWR is high at 3 MHz. 

384 ft feedline

400 ft feedline

418 ft feedline

467 ft feedline

512 ft feedline

The program's output numeric data files provide SWR, reflection coefficient, resistance, reactance impedance and phase for every frequency.  Radiation pattern data are also available and can be displayed graphically. For this analysis, the radiation patterns are all identical, since the model's transmission line element is specialized, compared with the wire elements, and does not contribute to the radiation pattern. If the radiation effects of a feedline must be considered in a model, then it must be included in the model as a pair of parallel wires.  For more information on this topic, see part 4 of the QST article series "A Beginner's Guide to Modeling with NEC" by L. B. Cebik.

75 m spectral view at 0738 CDT

Here's a view of 75 m showing low signal levels for this time of day.

Java updates -- suppress sponsor offers

Those who use Java on a regular basis know that when a version update is published, its installer offers to include some third-party programs that are selected by default to install. Yesterday I learned from the Security Now netcast that the Java control panel includes an option, in the advanced tab, to suppress the offering of third-party programs. The screen shot below shows the location of this option.

 
I tested it on a PC this morning and confirmed that it works.

-John

Understanding Linux

The website How-To Geek published this article about 10 popular distributions of Linux. Of the ones listed, I have used, to various degrees, Ubuntu, Mint, Slackware and Puppy. I'm using one as I write this, but the web is (thankfully) agnostic.

The above article contains several links to other articles that can provide a better understanding of what all the Linux choices and piece-parts are about. If you are curious, I suggest browsing the following articles in this order:

What Is A Linux Distro
A brief discussion of the concept of a Linux distribution

8 Pieces of Software That Make Up Linux Systems
This one covers in more detail the components of a distribution.

Linux Desktop Environments
This one covers various desktop environments that may be part of a distribution or may be pulled into a Linux installation. A Linux user may choose from among several distributions that are identical except for the desktop environment. Those who wish to use or try Linux on older hardware are often advised in web articles or postings to consider the light-weight desktop environments Xfce or LXDE. Some Linux veterans have actually set up their installations to enable switching between two different desktop environments. Most users probably try out several distributions, running from a live CD (slow) or a USB flash drive before choosing one or more to install in some permanent fashion.

The web site Distro Watch is my favorite for finding and exploring different distributions. You can browse the main page or use the search filters to find candidate distributions for certain needs. You'll also note that the site catalogs BSD and Solaris, in addition to Linux. For those who are curious, this article explains the difference between BSD and Linux. The use of BSD as the base of Mac OS X is mentioned.

John

WiFi Tips & Tools

Episode 76 of the Know How show on TWIT.TV covered some good tips and tools for setting up and maintaining your 2.4 GHz WiFi system. (They promised to cover the 5 GHz band on a future show. I'll search for that after completing this post.) There's a brief summary in the show notes -- scroll down the page to the topics: WiFi Tools, AP/Router Setup, and Antennas.  I recommend downloading and viewing one of the video copies of the show. Jump ahead in your video player to 18:51 where the WiFi topic coverage starts. It runs about 13 minutes total.

Update: Now see this discussion of using multiple access points. 

Several WiFi tools are mentioned in the Know How show, to help with evaluating the coverage within your home or business. After viewing the show back in January I added the free WiFi Analyzer to my Android phone. I also like another program inSSIDer that is not mentioned in the show. I've used it with good results on my Windows laptop and my Android phone. The current version 4 for Windows and Mac is available here for $19.99, but the free version that I installed a while back is still available elsewhere. The Android version costs $9.99.

John

Microphone specs & equalization

Since obtaining my Flex-3000 transceiver months ago I've been using the supplied FHM-1 hand microphone.  Early reports from my ham friends said that my voice sounded muffled compared with how I sounded using the old desk microphone with my Heathkit SB-104A. Below is a copy of the microphone specs graph from FlexRadio.  A switch on the microphone has two positions for what they call "tone settings":

• Setting 1 has a flat frequency response of 60 Hz to 16 kHz.
• Setting 2 rolls off some of the low end frequencies (-6 dB at 300 Hz) and provides 3 dB of boost at 2 kHz for "optimum articulation needed for DX / communication quality audio".

On-air reports indicated no appreciable difference between these two settings.

I explored the transmit audio equalization settings in the Flex-3000 to compensate for the microphone's apparent poor high frequency response.  I tried several configurations to boost the treble, up to the available maximum of +15 dB. Although I thought I had all the right boxes checked and buttons clicked, the audio reports were still unsatisfactory. I began to test some quick and dirty arrangements to use either my Andrea NC-61 headset or my original dynamic desk microphone in place of the FHM-1 microphone. These efforts indicated a need for better impedance matching and better shielding to prevent hum. My most recent inclination was to build a microphone preamp circuit in a metal box to accomplish impedance matching, gain, and powering (for the Andrea's electret element). The Flex-3000 front panel jack has 5 V DC available along with PTT, ground, and a balanced microphone input. A rear panel line audio level input is also available.

While reviewing the transmit audio equalization settings early this week I observed the audio closely on the audio spectrum display of the PowerSDR program and listened to myself on the SB-104A. The saved audio profile that I created months ago was not doing what the equalizer curve said it should. I created a new profile from scratch and found that it really did improve the audio spectrum appearance and sound. On air tests the next day confirmed this.  Below is a screen shot of the equalizer settings I am now using.

Note that the audio is boosted 15 dB at the 2 kHz and 4 kHz bands of the equalizer, and is cut below 500 Hz. The little Enabled check box can toggle this equalization with one mouse click. I found that this box was unchecked on the profile I had previously created and saved. I don't know if I lost track of that box during multiple changes followed by multiple saves or if I toggled it off for working digital modes. For the latter, I am now using saved profiles that set frequencies, bandwidth, equalization and audio paths (virtual audio cables) to ensure correct operation while making it easy to return to voice modes.

Thanks to all for their helpful signal reports!

John

80 m Loop Feedpoint SWR

As an aid to recent discussions of whether to use 300-ohm or 450-ohm balanced line to feed a loop antenna for 80 m, I ran an updated antenna model for a square loop, 68 ft per side at 40 ft above average ground, 12-ga copper wire.

Below is a superimposed version of the plot of SWR for a series of 44 frequencies (that I keep in a file for frequent use) to cover the ham band frequencies. The dots on the plot are the discrete frequencies where model calculations are done. The pink plot shows the SWR results for a 300-ohm source connected to one corner of the loop. The blue plot represents a 450-ohm source. Click on the plot to expand the view.

The combined plot shows that the 300-ohm source gives slightly lower SWR on the lower bands (80 and 40 m) while the 450-ohm source gives slightly better SWR on the high bands. (60 m is, of course, the odd-ball.) The differences in SWR are not too significant and either case should be manageable by a decent antenna tuner.

Additional analysis can include a selected length of feedline from the loop to the source (transmitter). The impedance seen at the transmitter end will likely be transformed to a value different from what is seen at the loop's feed point. We know that odd multiples of 1/4 wavelength will transform impedance from low to high or vice versa, while even multiples will present an unchanged impedance at the transmitter. Other lengths will present some other impedance. With some care in feedline length selection we will (hopefully) avoid extreme values of impedance at the transmitter end.

Google+ Notifications

Google+ users may not be aware of the settings that allow you to select which notifications you receive for various postings or other activities. I became aware of this when I first started using Google+ and noticed I was getting many email notifications. I customized my settings to reduce this email traffic. Below are two screen shots showing where to find the settings.

First get the menu by hovering your mouse pointer over Home under the colorful Google+ at the upper left corner. Click on Settings near the bottom of that menu.










A new window opens with lots of settings to manipulate. Scroll down to the area shown in the screen shot below where you see Notifications.

Each category under Notifications will expand when you click on it. There you can choose which notifications to receive and which communication path they should use.








The topic of Notifications is also covered in this Google posting.  Be sure to browse the other settings for other things you may like to customize.

- John