Around a year ago (Spring 2022), I decided to attempt a Full Wave Horizontal Loop for 160 meters–and you would be right in thinking, that’s a lot of wire. I bought 550 feet of 14 gauge stranded THHN from the hardware store. I will say I’m glad I bought this before the escalation of prices and some stores putting it behind lock and key.
The wire I bought was in two spools. I am sure I could have bought 1000′ spool, which I’d eventually use, but that was a larger cost than I felt like spending at the time. I ended up buying a 500′ spool and a small 50′ spool and attaching them with a butt splice (waterproofed and knotted).
Here is the feed point. There is no balun in the PVC, only a connection to the SO-239. I actually had a commercial choke in there but took it out due to a faulty connection. If you look closely at the loops, you will notice a mix 31 torroid I tossed in there.
The cable you see is in fact 75 ohm coax with F-connectors. It is 100 feet of RG-11. I used this to transform the impedance of the feed point to 50 ohms. I intended to modify the RG-11 length for matching but to much surprise and happiness it worked out perfectly with a single 100 foot section used during testing. It runs into 50 ohm RG-400 after the polyphaser.
Check out the analyzer data below to see how well this worked out. While it is true that the RG-11 here is copper clad steel, not solid copper, I did not find the need to buy the much more expensive solid copper 75 ohm coax. Some studies I read showed the skin affect (or lack there of) at 160m was not noticeable at 100 feet. Whether true or not may depend on your setup.
Now let’s look at the data from the antenna analyzer (Rig Expert AA-650 Zoom) at the feed point. Before the RG-11, |Z| was 108.6 ohms at 1912 KHz.
Here is the same data after 100 feet of RG-11. Not too bad in my opinion and only a small touch up tune maybe at the band edges.
And finally, the data from inside the shack after the polyphaser and RG-400.
Some final notes. Clearly each setup will be different. I think I ended up with about 515 feet of wire. My setup varies in height as I used trees as supports over varying ground terrain. The height is around 45 feet at the feed point, but may only be 20 feet above the ground in some locations (my property has many rock outcrops changing the elevation). It’s four sided, but not a square or a rectangle. Maybe closer to a right trapezoid and fed in the corner, not a side. Most importantly, it WORKS and it is substantially quieter than my 270 foot Off Center Fed Dipole (OCFD).
Hope to hear you on 160m! The Top Band SSB net is on 1900 KHz M-F at 2030 EST Winter and 2100 EDT Summer: topics of discussion Monday through Thursday with open round table on Fridays. I also work FT8 on 1840 KHz USB often if you want an FM09 contact!
I decided to post a draft of this page since I keep referencing it on a few nets. Watch for updates as I continue to update and refine the build and this page. Updated 16 July 2023.
This how-to instruction set will build a local lightning detection notification system which will send an email via Python script running on a Raspberry Pi. This of course, could be adapted to run on other hardware platforms easily.
* In 2022 Google stopped allowing “less secure apps” to access email. When they removed allowing the user to decide for themself to enable or disable, it rendered the email for many Raspberry Pi users to non-functioning (this would apply in other builds as well). It appears a work around was found, though I have not tried it. You can read about it here: G-Mail and less secure sign-in technology.
First, set up your Raspberry Pi if you have not already. There are many instruction sets on the Internet including this one: https://www.raspberrypi.com/tutorials/how-to-set-up-raspberry-pi/. Also, any Debian-based Operating System should work fine if you can’t source a Raspberry Pi. In my case I am using the Raspberry Pi 4 Model B Rev 1.2 running Raspbian GNU/Linux 10 (buster). I do plan to move this over to an Ubuntu machine one day to free this Pi up for other experiments.
Check and see if you have Python2 installed by running Python -V at the command prompt. You can use newer versions if you wish, but my code snippets in this example were written for the version noted below.
$ python -V Python 2.7.16
If you do not have Python, it can be installed with:
rtl_433 is a very powerful tool! It can interpret numerous devices so be sure to check out the link above. Did you realize most cars can be tracked via the tire sensors which is now government mandated in many areas? Well now you do and this tool will also read cars as they drive by on the street! It’s all open and unencrypted. I make this point not to encourage snooping but to make folks aware of a pet peeve of mine which are new cars spewing data without knowledge or consent of most owners. Anyway, back to the lightning sensor discussion…
You will also need the msmtp package if you wish to send email notifications. Another package called mailutils is also helpful along with the mail transport agent. Those can be installed by running:
Which can also be combined as: $ sudo apt-get install msmtp mailutils msmtp-mta
Here is the final setup of the Raspberry Pi with power (white cable), network (orange cable) and RTL-SDR Dongle in one of the USB ports. I also have a small band pass filter on the antenna connection (black cable at bottom with SMA connector). This additional filter isn’t generally needed but since I have a lot of radio activity going on in the area, I figured it couldn’t hurt. It doesn’t have great reviews but I tested it and it was a bit off frequency but not enough to impact my setup. Here is the link: https://www.amazon.com/Interface-Bandpass-Receiver-Dedicated-422-446MHz/dp/B0B1QSBZKR
The good thing about using this particular SDR Dongle is that it should be recognized by the Pi’s Operating System without installing anything additional. You can use the command ‘lsusb’ to be sure. Here you see it on the second output line below (Bus 001 Device 003).
$ lsusb Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub Bus 001 Device 003: ID 0bda:2838 Realtek Semiconductor Corp. RTL2838 DVB-T Bus 001 Device 002: ID 2109:3431 VIA Labs, Inc. Hub Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
If you run rtl_433 with no options, you will start getting a lot of data displayed continuously until you press Ctrl-C in the terminal. Below you will see two different Acurite-6045M devices running (id 85 and id 127). There was no modification to the Acurite devices. This is right out of the box with batteries installed.
Screen capture of rtl_433 running
A couple things of note. Acurite appears to send the data three times. I presume this is their standard to ensure the transmission is received properly. Second, the lightning strike count is a rolling counter which wraps from 255 back to 0. That becomes important in the Python code because you will need to look for a change in the counter, not an absolute number. I also restrict the data collected to only the Acurite protocol needed (thus not filling up my log with tire sensors and many others). The -R option allows that selection. The protocol needed for the Acurite 6045M is “40”, i.e. running as this command only reads the Acurite 6045M and similar sensors and outputs formats (via -F option) json and http (more on that below). The protocol list can be found at https://github.com/merbanan/rtl_433.
/usr/local/bin/rtl_433 -R 40 -F json -F http
Another fun aspect of the rtl_433 package is the ability to format the output as json, csv, http, syslog and a few others. It has an integrated http server which defaults to port 8433 when invoked with rtl_433 -F http. Point your web browser to http://127.0.0.1:8433 or whatever your Raspberry Pi’s IP is (if not local).
Screen capture of http data on port 8433
Now if all you want to do is view the data, you can stop here. The next steps are if you want to set up the Raspberry Pi to notify you via email or text that the lightning count has changed. I was hoping that the “active” tag in the data would be enough, but testing shows it is not. In my tests, the Acurite sensor goes into active mode regularly for unknown reasons. I suspect some is RFI, but I have not done enough testing. Ideally if the RFI field were true, the sensor should not go into active mode, but it’s hard to say what the thinking was in the design of the sensor. Even the author of rtl_433 states there are some transmitted bits in the message that have not been found to correlate to useful data. Check out the acurite.c code for an in-depth analysis.
For email sending, you use msmtp. I have never enjoyed working with msmtp. I find it rather clunky and usually have to fiddle around with it a bit. You must create a config file name msmtprc. For lots more information, try searching for msmtprc configuration. Here’s one example: https://centurio.net/2020/09/21/configure-mail-transport-agent-on-raspbian-with-external-smtp-server/. My example config file is below, redacted of real account login information of course. Make sure you have the /etc/ssl/certs/ca-certificates.crt as well. If you don’t have it properly installed, you might have to research how to get it on your particular system. My hosted email account has port 465 available for sending mail. You will have to modify the settings below based on your email provider.
$ cat /etc/msmtprc defaults auth on tls on tls_starttls off tls_trust_file /etc/ssl/certs/ca-certificates.crt logfile /var/log/msmtp.log aliases /etc/aliases auto_from off # Account details account yourusername host mail.yourserver.com port 465 from yourusername@yourserver.com user yourusername@yourserver.com password S0m3P@$$w0RD # Default Account account default : yourusername
You can try a test email using the following (this is one line, be careful with copy paste):
$ echo "Notification System Test" | mail --debug-level=6 -s "Test" -a "From:Notification System sendinguser@domain.com" recievinguser@domain.com
I find the “-a From” header helps get though some spam filters, especially to a cellular phone text gateway. You should see the following output after sending the mail command and get an email for the specified recipient.
Now we move on to the Python code. Let me be clear here! This code will work but it is a quick approach. You can tailor it anyway you want and certainly clean it up to be more efficient. I am still working on the code to add other features and multiple sensors, etc. What that means is this is an earlier version that ran for many months. It does work, just not as clean and neat as it could be. Remember, be careful with copy and paste.
import json
import sys
import datetime
import subprocess
k = 0
start = 0
strike_count_old = 0
outputfile = open(r"/home/pi/lightning.txt", "a")
try:
for line in iter(sys.stdin.readline, b''):
k = k + 1
if k > 9:
signal_string = json.loads(line)
if signal_string["model"] == "Acurite-6045M":
#print signal_string
strike_count_new = signal_string["strike_count"]
if strike_count_new != strike_count_old:
distance = signal_string["storm_dist"]
text = "{} - LIGHTNING STRIKE {} mi away. Historical count is now {}.".format(datetime.datetime.now().strftime("%m/%d/%Y %H:%M:%S"), distance, strike_count_new)
if start > 0:
outputfile.write(text)
outputfile.write("\n")
outputfile.flush()
subprocess.call(['echo "{}" | mail -s "LIGHTNING STRIKE" -a "From:Notification System <sendinguser@domain.com>" receipient@domain.com'.format(text)], shell=True)
else:
start = 1
strike_count_old = strike_count_new
else:
#text = "No strike at time but data is {}.\n".format(signal_string)
#outputfile.write(text)
#outputfile.flush()
pass
except KeyboardInterrupt:
sys.stdout.flush()
outputfile.close()
pass
I’ve left some of the testing lines in there as well which are commented out plus I skip over the first number of lines read to make sure the input gets settled. (I will explain more on the code at a later time). This code reads the json format the rtl_433 will output from “-F json”. I saved this in a file called lightning.py in /home/pi. You will pipe the output from rtl_433 via the -F json command. In my example, I am also running the http server so I can view live data in a web browser. This code will send an email for every strike with the calculated distance (presumed in miles) along with the current rolling strike counter. With this snippet, it only looks for a device named “Acurite-6045M”. It would need more specificity if used with multiple sensors (what I am experimenting with now).
#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
/usr/local/bin/rtl_433 -R 40 -F json -F http | /usr/bin/python /home/pi/lightning.py
exit 0
One final comment about the code. This will send ALL detected lightning strikes to email. Depending on your area, this could be a lot! I will eventually modify the code to compile the data, but again, this is proof of concept at this point. Besides adding diversity of sensors, my other planned addition is a commanded visual cue when lightning in the area.
This is a quick post about making a “slim jim” 2 meter antenna out of DX Engineering‘s 450 ohm ladder line. I based my build off of KE4NU’s write-up found here: https://www.hamuniverse.com/ke4nu450slimjim.html. I will note my specific findings and measurements below.
I did make this for a trip I was going on right away so I did not take pictures during the build as I normally would have.
Design watermarked by N4UJW and found at the link above from KE4NU.
Here’s what you will need:
450 Ohm ladder line (actually window line)
Solder / Iron
Wire cutters / stripper
Coax and/or connector
Tape measure
Antenna Analyzer (if available)
My design was exactly 58 inches, with the two ends soldiered together making a full loop.
Now let’s look at the notch. I cut one inch exactly from 19-20 inches from the bottom of the antenna where the two conductors were soldered together (not the feed point).
For the feed point, as you would expect, it should need some adjustment on the exact spot to solder. The center connector goes to the long side of the slim jim. I had a cut piece of coax already available, so I just used that. My feed point worked best at 55-3/4 inches from the top, or rather, 2-1/4 inches from the bottom junction of the conductors.
After everything was tested with the antenna analyzer and soldered in place, it was wrapped with electrical tape. If this were to be outside in the weather, I’d recommend sealing it. Also, I added a bunch of turns with the coax through a mix 31 torroid from Mouser.
I used this in my hotel room hanging from the curtain rod and it still maintained a good SWR. Just remember these antennas are sensitive to nearby objects.
