Jeep LJ No Drill Safari-Style Bikini Header. Making it work!

Posted on 2020/06/02 by rob

I bought a Besttop “No Drill” safari-style bikini header for my 2006 Jeep Wrangler LJ. The online forums have mixed opinions about ease of installation or re-installation. If I had read that thread first, I might have purchased the drill header and hacked it to work on my Jeep.

Even those who have the top often complain about the install difficulty, and I bought this to be able to put on and off at ease, so I want to be able to put it on and off easily. Online advice includes leaving it in the sun and bending the corners of the header strip for better flex. I even tried heating the strip and corners with a heat gun.

After fighting with it for 30+ minutes, I decided the design was flawed, and attempted to figure out why it was so difficult to get the front strip to stay in the header. There are a range of interconnected reasons:

  • The header strip in the top is too long
  • The header strip is hard to fit into the rounded edges of the header
  • The header strip cannot flex sufficiently to enable it to stay in the header while tightening and tweaking
  • The fabric wants (needs!) to flex at the corners more than the header strip will allow

I found a way to modify the header strip that makes it easy to do the initial strip and tightening, independent of tightening the corners. This was via trial and error. You can do exactly as I say here, or try to customize the hacks for your own needs!

Modify the header strip sewn into the top. I used a pair of tin snips, scissors may not be strong enough. I cut out approximately the 1st and 4th inch on each side according to the images below. The “interior” cut is 3/8″ on either side of the 1/4″ indentation already there to indicate where it should flex. Cut the strip down to, but not into the sewing along the strip, you want to preserve the integrity of the sewing!

  • cuts on each side of header

Installation. I can do this in 8 minutes on average (7-9 minutes). By myself. I have timed it 4 times.

Step 1. Preposition the top over the Jeep LJ. To assist with drops, loosely secure the rear straps (left photo). Drape the front of the top about 1-2 inches beyond the working header, and tie a slip knot securing the center strap to the center windshield footman loop (right photo). This helps catch the header if you drop it so it does not fall into the cab! Not necessary, but a safety time saver.

Step 2. Insert the center portion of the header into the channel. You can ignore the ends and just fold them up and out of the way. This is the game changer in installing — it will go in and stay the first time! And mechanically separates the challenge of getting the corners in. Get back in the cab and tighten the center strap that was slip tied to the footman’s loop. See photo below.

Step 3. Secure the corners. Per the instructions, insert the velcro through the corners at the front of each door frame. Insert the “end header piece” into the channel and secure the velcro, bending the corners per the instructions. When done, you will have a secure corner, and a slight dimple in the top where the fabric buckles a bit (this is more evidence of what the intact header was preventing!).

Step 4. Secure the side channels into the factory door surround (see instructions if you do not have this) and secure the middle and rear straps, but not completely tight yet.

Step 5. Re-tighten the center strap to the footman’s loop a final time. I find this allows a final level of tightness.

Step 6. Fully secure the mid and rear straps on each side. Congrats!

I hope someone finds this helpful. If I were to start over, I would likely have modified the drill-top to work with my Jeep. But this does work, and I find the time taken is not too long given the frequency that I might be taking it on and off.

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SWR measurements of a SOTABeams Band Hopper

Posted on 2020/05/19 by rob

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

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

Freq (MHz)SWR
14.0001.1
14.1051.0
14.3251.3

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

30m SWR

Freq (MHz)SWR
10.0001.0
10.1501.5
10.3002.0

40m SWR

Freq (MHz)SWR
7.0001.1
7.0401.0
7.1501.5
7.2662.0
7.3002.2

80m SWR

Freq (MHz)SWR
3.5001.7
3.5231.5
3.5891.1
3.6451.5
3.6902.0

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

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IKEA couch spring repair

Posted on 2017/11/26 by rob

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 to pull spring. 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 Re-attached springs. At least for 12 hours ...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.  Upholstery clip holding IKEA springAnd 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. Ready to bounce!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!

 

 

 

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Scout’s vigil and the beginning of the aftermath

Posted on 2017/09/19 by rob

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.

****

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.

When it was over, hundreds stayed around, and started yelling, discussing, grieving. Anger was voiced at how we got to this place, anger at GT’s President, anger at a lack of sufficient counseling services. From there it digressed into what I would call generalized anti-establishment anger: rage against buildings, statues, the income of the President, rankings, etc.

I did not think it would get this bad. I found myself unwittingly in the middle of the protesters (at least, I suspect it was the group that started the protests) and I have one observation: as far as I can tell, these were not Georgia Tech students. Or very few at least. When the memorial event was over and people started shouting back and forth, those advocating violence were resoundingly shouted down by other students.

Then the drums and banner appeared out of nowhere, and the F-the-Police chants started. I’d estimate it was no more than 50 people. When the drums started, Tech students’ notable apathy for protest (or a desire to go back and study) was true to form. Students left at an increasing rate, many to the student center and the counselors therein. A lot of students just wanted to be left alone and grieve.

I walked to my car. I got home 20 minutes later when the GT Emergency Alert was sent out.

This is the worst thing to happen to my campus in a generation. Torching a car? WTF is wrong with you people?

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RFID-activated High-Current Power Supply Switch

Posted on 2017/04/30 by rob

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.

 

 

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Backslash line continuation in code comments

Posted on 2016/07/18 by rob

I spent several hours this weekend tracking down a bug that highlights something I never knew about GCC (and the Arduino IDE, which uses GCC). At first I was inclined to blame the limited Arduino IDE, but that in itself based on GCC. So I replicated the behavior using command line GCC on a the code below, on both Linux and a Mac.

Compile and run the following code in GCC:


#include <stdio.h>

int main()
{
printf(“Hello Line 1\n”) ; // this is a comment
printf(“Hallo Line 2\n”) ; // comment with back \
printf(“Hullo Line 3\n”) ; // This line will not print – try it!
printf(“Hillo Line 4\n”) ; // last line
}

Line 3 does not print!

As a long time UNIX user, I get what is going on — the backslash forces a line continuation — so line 3 is effectively considered part of the comment on line 2!

But why does GCC parse this way? C/C++ already doesn’t care about line breaks and continuations, since all parsing has well defined delineations.  In fact, // is an “exception” that doesn’t require a matching terminating delineation — it is the line feed.  But the norm is that it is only used for one-line comments.  Except I guess those one-line comments can be continued on the next line …

I came across this issue while editing/debugging a font set and display library for an Arduino display project. I am posting this in case someone else ever tries to google the answer.

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Arduino Class Sunday July 24 2016

Posted on 2016/06/11 by rob

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:

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

  • 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

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.

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Tontec 480×320 touchscreen display with Raspberry Pi

Posted on 2016/05/27 by rob

Last December, I purchased a Tontec 480×320 touchscreen display for use with a Raspberry Pi.  Complete with case (amazon link).  I bought it along with a Raspberry Pi Model B in order to play with software-defined radio (SDR), motivated by the FreqShow example at Adafruit.  In fact, I wanted to get this example working.

But the display sold by Adafruit is not the display I bought, and I found a lot of online questions trying to get the Tontec display working with Raspberry Pi.  X windows applications worked, but the pygame library returned errors, and I tracked it down to the ability of the distribution I had installed to work with the graphics (not X windows) mode.

After several hours and lots of installs and reinstalls, the following two steps worked to get the Tontec display working.  Note that this was as of December 2015, and maybe jessie has changed by now.

Now the instructions of the example at Adafruit work.  I tried taking a short-cut and installing rtl-sdr from a package using apt-get — it did not work quite right.  The instructions on adafruit (download and compile from github) worked.

Tip: I don’t like the Pi automatically booting into X windows.  It is annoying.  You can disable it with sudo systemctl disable lightdm.service.  If you want to manually get X windows started, you can always run /etc/init.d/lightdm (start | stop) to do so.

 

 

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Serial communication with a Kenwood TS-570D

Posted on 2016/03/31 by rob

I am setting up an amateur radio station at my local maker space, Decatur Makers.  Our transceiver is a Kenwood TS-570D.

I have spent a lot of time debugging how to get serial communications working between the Kenwood and a computer. Here is what I have learned. I have duplicated these results with two different computers (a Mac and a Linux box).

  • The Kenwood connector is male.  Odd but true.  You need a straight through female-female DB9 cable to connect to a typical 9 pin serial port.   Some gender adapters and female-female cables are configured as null modem cables, so be sure.
  • No handshaking or hardware/software flow control; BUT
  • The RTS (request to send) pin must be set high on the computer for the Kenwood to respond.  It will still receive commands if the RTS is not set, but not send responses.
  • The maximum baud rate that works is 4800 (8-N-1 or 8-N-2). Nothing faster worked.  Online forums confirm similar results.

When I do all the above, I can successfully open a terminal window and send CAT control commands to the radio.  If  you have never done this, these commands are the basis of amateur radio – computer communication for control.  Examples:

  • Send FA; The radio will return FA00007123456; — where the long number is the radio frequency in Hz.
  • Send FA00007121321; and the front panel of the radio will switch to 7.12132 MHz (radio does not display last digit, but it is stored)
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KX3 as a (good enough) antenna analyzer

Posted on 2016/02/08 by rob

So I am working on a DIY antenna analyzer/impedance meter.  But I need to validate my design against a known antenna analyzer.  I do not own one.

But I do — my Elecraft KX3 can calculate SWR.  If you know the menus, you can bypass the tuner, press/hold the TUNE button, and read the SWR. The Android app KX3 Companion does this to plot a simple 5 point SWR calculation (the author, Andrea Salvatore IU4APC, writes a lot of great Android amateur radio apps – see her KX3 companion page).

The KX3 has a mode where just about any button you can press or menu option you can change can be controlled via over its serial/USB interface.  So why not write an app?  So I did.  It took a lot of trial and error — reading the SWR from the display was tricky, as was the ordering of some of the command and picking an appropriate settling time.

Use of this Python script requires that the PySerial, ArgParse, and MatPlotLib Python modules are installed. Assuming you change the path to the serial device, I expect it will work on any platform (I developed it on OSX).  The final version is run from the command line but fully featured, and incorporates built-in band lists for the non-WARC bands plus 30m, and outputs a text list as well as graphical plots, with the ability to suppress either.

This program was updated by John Ogrem (WX0M, r2bqdnx@gmail.com), in November 2021. His edits reflect the addition of an “SW” command making it easier to read SWR from the KX3. The revised version is available here ->  kx3swr.py.   My original version is available at -> kx3swr-v1.py.

Disclaimer: this is freely distributed software, untested on your hardware, that will control your radio’s transmitter.  Use at your own risk!

Here is the command line help.

usage: kx3swr.py [-h] [-noplot] [-notext] [-waittime WAITTIME] b [b ...] positional arguments:
b band [band band ...] (choose 10 20 30 40 80 160) optional arguments:
-h, --help show this help message and exit
-noplot do not generate plots
-notext do not generate output text
-waittime WAITTIME change default settling time in seconds after each
measurement (default is 2.5 sec)

Here is the text output of a 20m sweep of my B&W AP-10 (whip with load coil and counterpoise) and the resulting plot.

$ ./kx3swr.py 20
running sweep for 20mband 20m
14.0 1.7
14.025 1.5
14.05 1.4
14.075 1.3
14.1 1.2
14.125 1.2
14.15 1.1
14.175 1.1
14.2 1.2
14.25 1.3
14.3 1.6
14.35 2.0 20m SWR plot creation

swr20m

The SWR can only be read to one decimal place, since it is extracted from the display of the KX3 itself.

Future plans include another command line option to sweep a start and end frequency with a specified increment.  I have never used ArgParse before, but it makes command line parsing and documenting really easy. Now that I know how the serial stuff works, I’d like to put this on a microcontroller system to take into the field with me.

I have learned a few things by having this.  For example, I operate QRP from a condo with a whip and load coil on my balcony.  I usually set the coil lead by listening to the volume, and there are usually two adjacent windings that sound about the same.  From this analysis and running some sweeps, I learned that one winding of the coil changes the resonant frequency by almost 400 kHz, and that moving the lead a 1/4 turn can shift the resonant frequency by 100 kHz.  So picking the right tap by ear alone might only get me within +/- 400 kHz of my desired resonant frequency. I also learned the importance of counterpoise length and positioning.  The above is the best case after some playing with the counterpoise and lead tap location. The KX3 has a great tuner, but a more efficient antenna is a more efficient antenna, especially for transmitting QRP!

Theory of operation: For those who are curious, the general logic of the program is as follows:

  • saves your frequency and operating mode
  • puts the antenna tuner into bypass
  • for each band
    • switches to that band and the initial frequency in the list for that band
    • sweeps a range of frequencies, and for each frequency
      • measures SWR by the TEST button, turns off transmitter 2.5sec later
      • extracts SWR from the display reading
  • restore original frequency and operating mode
  • return tuner to auto-tune
  • print output
  • plot output

This program required a lot more effort than the finished code might suggest.  There was a lot of trial and error using the KX3 Utility in command mode and sending commands, figuring out how the KX3 responded.  Sometimes order and timing matter.  Something theoretically straightforward like reading the SWR from the display turned out to be surprisingly odd. The KX3 Programmer’s Reference was a critical reference for all of this, and many thanks to Elecraft for publishing such a document.

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