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20m End Fed Half Wave (EFHW) Build

Ham Radio

by admin on August 17, 2021 2 Comments

I recently acquired an intertest in Slow Scan TV (SSTV) and one of the most popular frequencies for SSTV exchanges is 14.230 MHz. My 270 foot Off-Center Fed Multiband has a Standing Wave Ratio (SWR) of 3:1 on 14.230 MHz before tuning so I was looking for better efficiency. Here is a great presentation on the end-fed by K1RF if you are interested in learning a lot more.

Here’s my list of parts:

Plastic Project Box
Magnet Wire (Enameled #14 AWG or similar)
Torroid Cores (I used three Mix 43 Mouser #:623-5943003801)
100 pF Capacitor (Mouser #:75-HVCC203Y6P101MEAX)
Wire for Antenna (I used #14 AWG)
N or SO-239 Connector
Miscellaneous nuts and bolts
Cord/Rope to hang the box and antenna end
Zip ties
Electrical tape
Solder and solder gun
Drill and drill bits
Cable (I used 100 feet of LMR 400)
Ground connection (I used the MFJ-270 capable of 400 watts). Remember the coax shield is a counterpoise.

Here is a little more explanation of what I was trying to do… I wanted a very specific single band antenna tuned to 14.230 in the 20m band, preferably end-fed for the location I wanted. Most EFHW antennas I found online for purchase were rated at 100 watts (some up to 300w) peak envelope power and are okay for my 100w radio if I were in single side band mode which has a lower duty-cycle. Digital is different. The duty cycle is much more intense lending itself to a max PEP of maybe 30w on the 100w pre-made antennas found on DX Engineering (I reached out to the manufacturer Par EndFedz to confirm their design max before attempting the build). My hope is that my three core design should do the trick for whatever power I want to run in the future on 20m. By the way, these are what I had left over from a previous similar project so I found a good use for them here.

A transformer is needed for this type of antenna to match the high-impedance feed point down to something that is suited for the cable and radio (aka 50 ohms). With an EFHW, a 49:1 is needed for this. I used the 49:1 transformer design found on Ham Radio Archives – Jason Jardina which is an excellent resource and explanation of the transformer.

49:1 Transformer. Original credit to K1TA via W5JJW linked above

There really wasn’t much to the winding of the cores, but of note, I did have to use electrical tape because the enameled wire I used got nicked really easily on the first try. Cores are zip-tied together as well as to the box itself via a couple holes I drilled in the back (later sealed). Also, I fiddled with the windings a bit to make sure I got the results I wanted. I tried to use a plastic bolt to hold in the cores but that did not work so the zip ties were my second choice. I am unsure of the heat generated so I may need to check this from time to time. I am hoping with the large box and three cores, heat will be less of an issue.

The transformer is installed upside down compared to the earlier drawing

The hook in the center is for hanging, the other hook is for stress relief of the connector. This early version had a wingnut for the antenna connection, but I ended up changing that out for a third eye-bolt.

Okay so here’s where I goofed with what I wanted. I thought I had 14 AWG stranded wire for the antenna. Turns out I had solid. But I was really excited to get this on the air, so I used it anyway. Definitely not going to tolerate flexing as much in the trees but it still radiates and when it comes time to replace it, I’d have to buy new wire anyway. So just kept it moving…

The image is at an odd angle, so I assure you, that LMR400 is not a sharp kink! I have a piece of automotive fuel hose over the LMR400 with a pipe clamp holding the paracord in place. Paracord is also what I am using to hang the box with. There are small weep holes in the bottom as well.

The insulator is a rubber automotive strap!

Since trees move, there is always strain on the antenna wire. Sometimes I loosen antenna ropes if there is predicted high winds. I also have one antenna (80m EFHW) with springs inserted in the rope section. I was looking for a good insulator at the local hardware store when I found a cheap automotive rubber strap. Insulator and flexible, perfect! I probably would have preferred something with even more give considering I have solid wire, but again, that’s fine for now. The nice thing about wire antennas is that a broken wire is an easy fix.

The paracord hanging is my pull strap to lower to ground level to trim antenna to resonance. I started with a significantly longer antenna than I needed (tuned at about 9 MHz at start) and then gently cut the wire in small increments to get it to almost exactly 14.230 MHz. The pull down string made this fast and easy. I raised it to full height every few cuts to see exactly what the readings would be raised.

Using my AA-650 antenna analyzer, I obtained the following readings which was better than I had hoped:

14.230 MHz has impedance of 47.8! RL is very low at 22 dB as well.

With those results, I have also been using this antenna for FT4 and FT8. I can hear the difference in those modes when I switch the antennas. I definitely hear more audible frequencies in the mix.

And here is the final setup!

Interestingly enough, the day after I finished this project, the ARRL sent out an advertisement with a kit for a multiband EFHW with a rated power of 250 watts (ARRL EFHW Kit). Might be a good place to start experimenting for some folks!

Index: 18

Streaming Audio Using Darkice

by admin on February 6, 2021 0 Comments

It is easy to use a Raspberry Pi to stream audio to your own webserver (running on the RPi) or using a global site such as Broadcastify. Though I used a RPi to build this, it is not unique to the RPi and can run on a variety of systems (I have used the same setup on my Ubuntu laptop).

Here’s what you will need:

Raspberry Pi (any will work but I use a RPi4 with 4GB RAM)
USB Audio Dongle
Speaker to Line Audio Converter (build or buy)
Scanner (or other radio output device)
Assorted audio connectors and cables
An Internet connection of course

Assumptions:

You have a working knowledge of installing the Raspberry Pi Operating System and can access it on your network or directly from a console setup
Your scanner or radio receiving device works and has an antenna and can receive the frequency or range you wish to broadcast
You are able to open a port for port forwarding on your Internet router to the port running Icecast (if you want to open the server to the world)

First, get your Raspberry Pi set up however you like with the Raspberry Pi Operating System according to the instructions found here (or using your own method). The instructions here should work for pretty much any modern Debian-based Linux distribution.

Now for the hardware setup. Your scanner or radio’s audio needs to be taken down from speaker level to line level. They do make converters you can buy such as these on Google. But you can also build one. I used this design found here with two 3.5mm jacks for the connections:

Speaker to Line Level Converter from https://www.epanorama.net/circuits/speaker_to_line.html

One note on this, it assumes your scanner is mono so no reason to use a stereo 3.5mm plug. Here’s my built version on the above diagram:

Speaker to Line Converter (using Mono to Stereo Connectors)

On an older version I had a commercial converter shows in this picture:

Now let’s put it all together with the USB Audio device inserted into the RPi and the microphone jack running through the speaker to line converter to the speaker out jack of the scanner. By the way, this setup is in my laundry room because it is opposite the ham antenna side. There will still be some de-sensing on transmit especially with these older scanners. There is an external discone antenna it is connected to (see BC760XLT Scanner Repair for the background story).

Now we move on to the software side of things. Boot up your RPi and once you have the system up and running how you like it, install Darkice via the command:

sudo apt-get install darkice

You will need to create/modify the Darkice configuration file. The default location is in /etc but you can specify an alternate location when you run the darkice command to start your streaming.

There is a great darkice.cfg example at the following link which is the one I used as my starting point on the Raspberry Pi:

https://wiki.radioreference.com/index.php/Live_Audio/Ubuntu_Darkice

You will need to sign up for a Broadcastify feed provider account and get the “mountpoint” and “password” from your account page and input it in the configuration file. Also note you may have to change the configuration slightly depending on your hardware. I had to change the “device” setting to “hw:2,0” and “sampleRate” to “44100” based on my configuration. You can view your hardware location via the “aplay -l” command. NOTE! When I rebooted headless (no monitor) the HDMI connection changed the hardware ports, so be aware this might happen.

Similar to the issue described on the page linked above, Darkice does not reliably restart on reboot. I’ve tried various configurations, running it as root, etc. and nothing has proven effective. If I find a solution I will post it.

Darkice should be run as a normal user, not root. The reason for the comment here is that when you run it as a normal user it will tell you try running as root, that is not needed.

If all is well, run darkice from the command prompt and your feed will show active over at Broadcastify! As I said before, you might have to fiddle around with the sample rate or other settings to get it just right for your configuration. For reference, here is how I start my Darkice instance:

nohup darkice -c /home/pi/darkice.cfg &

The “nohup” signifies No Hangup which leaves the process running after I log out. The “-c” specifies the configuration file and the “&” means run as a daemon/background process. Since I run headless, I ssh into my RPi and start darkice this way from my remote terminal.

BREAK BREAK BREAK… Okay you are done if all you wanted is a Broadcastify feed. But some have asked how you would host streaming audio on your own. the following section describes the additional steps which will be needed to do this.

If you want to run your own server you can install Icecast2. Darkice will feed to Icecast. Install Icecast using apt:

sudo apt-get install icecast2

Icecast will install in /etc/icecast2 and run the auto configure program for you. Be sure to remember your passwords as you will need the source password in the darkice.cfg file. The port you choose to run on (default 8000) is the one you will point your browser to on the RPi IP address. You can always edit the icecast.xml configuration file found in the installed directory mentioned above. Another good install document can be found here. Once you have finished the configuration, run:

sudo systemctl start icecast2

You can always replace “start” with “restart” or “stop”. You can also enable it to always run on reboot with “enable” (or do the opposite with “disable”). Once running you can point your browser to http://yourRPiaddress:port where that is the RPi’s IP and port number you chose in the setup. If you are local, you could use http://127.0.0.1:8000, for example. You should see this:

If that page came up, great news you are almost there. The next step is to feed Darkice into Icecast. You do that by adding an Icecast section to the darkice.cfg file using the password you set up in the Icecast installation for sources. If your darkice.cfg has an “[icecast2-1]” section already you can edit it, otherwise add the following, tailored for your installation:

[icecast2-1]
bitrateMode = abr # average bit rate
format = vorbis # format of the stream: ogg vorbis
bitrate = 96 # bitrate of the stream sent to the server
server = 127.0.0.1
port = 8000 # port of the IceCast2 server, usually 8000
password = SOURCEPWD # source password to the IceCast2 server
mountPoint = KC4RCR # mount point of this stream on the IceCast2 server
name = DarkIce
description = KC4RCR Scanner Traffic
url = http://www.kc4rcr.com
genre = Mostly 2 meter ham repeaters around the VA area
public = no # advertise this stream?

Now restart the service using sudo systemctl restart icecast2 if applicable and go back to your web browser and reload the Icecast page. You should see something similar to the following:

You can also login via your admin password (username admin) and see the stream stats and listener info. It is just one mount point here so that’s all that is displayed. Icecast supports a variety of configurations if you are interested. Visit icecast.org for more information.

Index: 18

AM Broadcast Rejection Filter Testing

Ham Radio

by admin on February 5, 2021 0 Comments

I have a 270 foot off-center fed dipole which works pretty well for my 160m and other band needs (with an external tuner). My HF rig is a Yaesu FT-450D which appears to have a great front end to suppress unwanted signals. Occasionally I like to look at the spectrum in Gqrx with my RTL-SDR dongle. But take a look at the image below!

The RTL-SDR does very little to clear this up, but given the reasonable price and utility of the device, it is not unexpected.

I have the RTL2832U model SDR which works on HF

I have a number of very strong AM broadcast stations nearby so I thought I would give a couple filters a go at it. First, I tested with a cheap RTL-SDR brand “Broadcast AM Reject Filter” which attenuates below 2.6MHz.

Now let’s take a look at the Gqrx spectrum waterfall

That’s a great amount of cleanup! Now I know my FT-450D does a better job than the SDR dongle, but I figured I would check out a legitimate filter which can be used with a transmitter. I found the M-402x by Morgan Systems which attenuates below 1.8MHz and can tolerate 200 watts of power (they have another version if you don’t use 160m). I ordered this from KF7P Metalwerks which came quickly and excellently packaged.

Now let’s take a look at this filter in the Gqrx spectrum waterfall like we did with the other. Obviously my attenuation is a little bit less because I wanted to use 160m which is close to the AM broadcast band. Also, these pictures were taken at night when the signal was hitting me the hardest (in the day it looked even better).

I am very happy with the results and the M-402x is now installed with the FT-450D and I am currently listening to a great signal on 1.900MHz!

Index: 5

Category Archives

20m End Fed Half Wave (EFHW) Build

Streaming Audio Using Darkice

AM Broadcast Rejection Filter Testing