Rob's Blog

I am not yet a SOTA/POTA activator, though I would like to be (actually, I have one SOTA activation on 2m VHF). However, I do travel with my radio, and have brought my Kx3 on trips, along with a 20m end-fed and/or a load-coil with whip and tail antenna.

I have built and tuned over a half dozen antennas with home-made baluns, mostly dipoles and doublets, also verticals. My antenna at home is a fan dipole with separate 20/40/80 elements all tuned to 1:1 SWR. I wanted a linked dipole that was sufficient for 100W so I could use my home radio (the rig is in a luggable case) or my KX3. I made one for 20/40, but it was too heavy for my telescoping pole for portable use. After spending a lot of time trying to figure out the coax that is just good enough for 100W, the wire good enough, the smallest but most useful toroid, etc. I decided that I was reinventing something and SOTABeams had these details figured out! I likely could not make one for a lot less than what they charge, so I bought the 20/30/40/80 Bandhopper from DX Engineering.

I brought it with me on a trip to Florida a few weeks ago, went to set it up for use, and discovered that that one leg was broken (accidental cut? my packing fault?). Packed it up. The following week I fixed the broken link by tying a knot for a secure link, soldering the ends, and encased it all in heat shrink tubing.

A couple of weeks later, I decided to head to “the land” to measure this antenna. We own a 3 acre plot of land adjacent to a county park with a nice clearing on locally high ground. The nearest house is over 1000 feet away. It is like a private field day lot and ideal for operating, and I keep a tag line in a tree for just this reason. And a picnic table!

Antenna test site. Complete with picnic table! My Jeep is in the distance to keep it sufficiently far from the antenna.

I unlinked all of the links to measure the 20m response, and raised the antenna to a height for a 45 degree inverted V with the 40m ends about 3 feet above the ground. I know from my past antenna builds that distance to the ground matters (more on that later), but this was a good starting point. The 20m elements were 10-12 feet above the ground. Measurements were made with an MFJ-269 SWR meter.

To my surprise, at 20m, the antenna had a 1:1 SWR at about 14.700 MHz. It was similarly too high at 30m (10.432 MHz), and measured 1.1 SWR at 7.150 MHz on 40m. I wondered if the knot I tied at the break had something to do with it. My math said that a frequency this off likely required a lengthening  of each dipole leg of about 6.5″, but the wire associated with the knot was under 3″. I cut away the heat shrink tubing, replaced it with a crimp connector. and repeated. Still resonant on 20m at 14.560 MHz — still too high.

My experience is that ground effects matter with inverted Vs close to the ground. Maybe the SOTABeam was tuned for exactly this scenario, thinking about how a portable operator might operate in real world conditions.

I lowered the height of the inverted V, still 45 degrees or so, so that the 20m ends were inches above the ground. I measured the following results for 20m:

20m SWR

I continued this same process for 30m, 40m and 80m, adjusting height so the leads were within inches above the ground.

30m SWR

40m SWR

80m SWR

I could have tweaked these by adjusting ground height, playing with the lead links (can clip upline or downline for minor lengthening and shortening). But my take-away from this is that the Bandhopper is very well tuned, and tuned for an inverted V at a height with the ends nearly at the ground, and optimized for the low end of each band. This makes sense given the prevalence of CW in SOTA operations, which is at the low end of the band.

Just for fun, I decided to see how well the antenna would work as a quick and dirty vertical. My experience with home-made verticals is that ground height from the balun matters, and radial length matters as well, especially if using few radials (like one!). I tested the vertical at 20m, 30m, and 40m with the “ground half” of the dipole linked to the same length and just coiled in a loose pile a few feet around the base. Optimal SWR in all cases was with the balun at the vertical base just above ground height. The SWR was 1.3-1.4 across the band for 20m, 1.6-1.7 across the band for 30m, and 40m ranged from 1.8 (7.000 MHz) to 1.5 (7.150 MHz) to 1.4 (7.300 MHz).

I ran out of time and did not measure the 15m response of the 40m dipole, but based on my experience with other 40m dipoles I would expect it to be quite usable with an SWR of less than 1.5.

In summary, I am impressed with many aspects of the design of this antenna. The winders are well thought out, and the materials used are as minimal as possible but good enough for the job. If I was doing SOTA activations, I would likely not deal with the added length of 80m and just buy a 20/30/40 or 20/40/60. That may be coming soon!

SYOTA.

Rob Butera KM4MK

About a year ago we purchased and assembled an IKEA sectional sofa for our living space.   A few months later, we notice one of the springs under one of the cushions had sprung loose. And another. By nearly a year later, they all had (except one).

IKEA offers a ten year warranty. But that requires a receipt. People keep furniture receipts? And I would have to return that one section of the sofa.  So I figured I would fix it myself.

C-clamp, shim, zip tie. Voila. Reassembled. Easier said than done — it requires a clamp with enough spread to grab the spring near the end, and enough travel of the screw to pull it back into the plastic clips. Wear safety glasses and gloves in case things go pop. Reassembly looked like below (this is actually a photo from later in this post, but you get the point).  The zip-tie is to stop the C-clamp from popping out the open side of the zig zag.

Or so I thought.  The next morning, all the springs had popped their plastic clips again.  What was going on? Take a look at this photo of the springs (below), taken shortly after reassembly. The reattached springs are on the left. The springs that did not pop are on the right.  What do you notice? They are not the same size springs. The springs on the left half are slightly shorter when untensioned, and if you look at the zig-zags, the ones on the left have a smaller curvature, and there is one more serpentine zig (or zag?) if you count the length on the left vs the right. All the other sections of my sofa have the springs on the right. In short, whether intentionally (they ran out?) or by accident, IKEA used a different and slightly shorter spring on the left, it over tensioned, enough to eventually bend the plastic clips along the front of the couch (where people land when they sit down) so that they no longer would hold the spring in place when faced with even a small amount of vertical movement. You can see on the left (if you expand the picture) how the plastic clips are over-stretched compared to the clips on the right.

The fix.  Upholstery clips. A bag of 25 purchased online.  And 1″ #6 pan-head screws. I removed the original plastic clips (twisted with pliers, cut with knife). I cut a 3/4″ piece of wood to shorten the stretch distance (see pic above) to what seemed right for the spring, anchored to the frame with wood screws.  Setting the height to match the springs on the other side was also important (and also for how the cushion sat on it). Tension with the C-clamp, align the clips, screw.  It is important for the screw angle to be perpendicular to the clip or pointing slightly into the bend.  If it points slightly away from the bend, it may not pull the clip tight (pulling the metal against itself) — ask me how I know!

The finished product – left half has replaced springs. Note I did not replace the spring on the edge. That one did not spring loose, though the plastic clip was still bent. It would have required removing the piece of wood the leg is attached to in order to use the C-clamp. Since it did not spring loose, I left it along and also used 3 zip ties to attach it to the adjacent spring in case it did spring loose.

I re-assembled the sectional sofa and plopped down on the couch a few times for good measure.  It is holding!

Note: A friend asked if I’d share this FB post more widely.  I refuse to make it global on FB, as it would then invite the inevitable cesspool of comments if it was shared widely.  But feel free to link to this.   It was my experience tonight (Sept 18, 2017) at the vigil for Scout Schultz, on the Georgia Tech campus.

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I was there tonight. I thought it was a subtle but appropriate event, and it gave students space to grieve. Kudos to the Student Affairs and the PRIDE students for what was organized. The administration, or at least the public faces students know (Deans, President, Provost) were notably absent. I saw a few of my colleagues (including a School Chair and Vice-Provost), and I’m proud of you for showing up. None were recognized, nor was it appropriate to do so — this was by and for students.

More details forthcoming.

Notes: 2N3904 transistors were replaced by ones with a much lower VCE voltage. The 220uF decoupling capacitor is critical to avoid odd slow powerup oscillations (likely due to relay inductance).

Schematic at EasyEDA

PDF schematic

The enclosure is a Hughes SatTV box I bought at a thrift store for #1, tossed the board, and saved the power supply for a future project.

What this does: allows an RFID reader to switch the power on a 12V power supply that sources about 20A.  An automotive relay is used to switch the output of the power supply. They keypad activates the relay, and the relay uses a latch configuration to keep the relay on after they keypad output goes low again.

This would be a very simple circuit if not for the fact that the keypad has a power-on glitch (output is activated for about a second), and the power supply whose output is switched is also used to power the keypad! The solution is to have two transistors in series switch the relay switch — one transistor is controlled by the keypad, the other by a 555 timer circuit that does not go high until about 7 seconds after power is turned on.

Finally, the switched output is also tied to a 12V automotive indicator lamp, to remind users that the power supply is on.  The entire system is turned off by just turning off the power supply.

This is a reference post for the Intro Arduino class I am teaching at Decatur Makers on July 24, 2016, from 6pm-9pm.   See the Decatur Makers website for cost and registration info.

Getting Started with the Arduino!

Low-cost user-friendly microcontrollers have made it possible for anyone to quickly create small electronic projects.  Many DIY projects use microcontrollers.  This getting-started session will introduce users to the Arduino system and provide hands on activities with a low cost kit of electronic components, as well as your own Arduino (open hardware clone) to take home.  

What we will (try to) cover:

• Installing the Arduino IDE on your computer
• Basic concepts of the Arduino – what it does, and how it interacts with other devices
• Hands on tutorials
  • blink an LED
  • read a pushbutton switch
  • write to an LCD display

Code for class (the LCD display uses the stock code from the LCD display demo)

• demo_blinkcount
• demo_button_led
• demo_button_led_serial

• LCD display will use the standard arduino.cc tutorial code above. CONNECT RW TO GROUND.  This is not stated, though shown in the diagram.
• IF TIME — analog reading, using stock arduino.cc tutorial (AnalogInOutSerial) and we will modify to demonstrate plot monitor

What you need to bring — a laptop computer.  Windows, Mac, or Linux. Macs sometimes have problems with the drivers (see below).

What you will receive! — an Arduino Uno (clone), breadboard, ~20 jumper wires, ~10 assorted colored LEDs, assorted resistors (10 each of 220/1K/10K/100K Ohm), potentiometer, ~5 pushbuttons with caps, 16×2 LCD display

BEFORE the class

These Arduinos use the CH340 USB serial driver.  You need to install that driver on your computer.  Follow these instructions from Instructables.Com.

If you have not done this, please arrive at the class 45 minutes early.  Based on past experiences, it works fine for most, but there are always a handful of Windows and Mac computers where the installation requires some kicking of the tires.

Reference Material

http://www.arduino.cc is an excellent reference.  It contains an online reference guide to the language and programming environment, and explains each of the example sketchs (programs) built into the programming environment.

All the components in the kit provided are standard components used in many electronic projects.

Adafruit (http://www.adafruit.com) and Sparkfun (http://www.sparkfun.com)  are two common online companies to buy components and kits for microcontroller-based projects (such as LCD displays).  These companies also often have tutorials on their website for each of these components.  eBay is another place to buy many of these components — asian manufacturers often sell and ship direct for much less money than US or European manufacturers, with the tradeoff of a longer shipping time and unknown documentation.

Fixing Driver Issues

Some OSX users had trouble.  Seemed to be fixed by

• Info on this blog post
• Downloading these drivers (original manufacturer?)
• Signed driver — try this next
• Here are locally downloaded links of these drivers: Windows Mac Linux

Additional Code

Here is my sketch for a CW  (morse code) beacon/message sender.  (ZIP file) You can change the #defines for your desired words per minute and the outgoing text, and the program will loop and key the message at the interval specified in the code.