Tag Archives: Homebrew

Education and Training, Featured, General, Newsletter, Station Equipment, Youth Activities

Kit build for February 2019: Morse Tutor Keyer

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Morse Tutor Keyer Kit by K1EL

Kit build for 2019

The change of seasons brings us again to the darkest months, a good time to concentrate on indoor activities  like station updates and kit building. This February 12th the club will hold its annual kit build during Tech Night. The kit selected this year is the Morse Tutor Keyer Kit by K1EL. You can have a quick look at the manual for this kit here.

Club buy of kits

As part of its STEM initiative, NARS has purchased a number of these kits in bulk and has been using them in student kit builds in local area schools. Buying directly from the club means getting a discount on the kit, and directly supporting this educational outreach.

BUY THE KIT HERE: MTB-KIT order page

What to bring to kit build night

The kit will supply the board and parts necessary to complete the project. You’ll need to bring appropriate tools including:

  • Soldering iron and solder
  • Small needle-nose pliers
  • Small diagonal/flush cutters for trimming component leads
  • Small flat blade and Phillips head screwdrivers
  • Your reading glasses (a note to myself, if no one else!)
  • A printout of the manual for the kit (or a copy downloaded to your tablet)
  • Recommended: Multimeter
  • Optional: a small magnifying glass

Don’t forget to bring batteries! The unit requires 3 AAA cells.

The spirit of kit build night

NARS has many new members since the last kit build. Those of us who have experience with kit building should lend a hand to those new to the adventure. Take a moment and help mentor your fellow club members, especially our youngest recruits, so they walk away with a working kit and the sense of accomplishment that goes with it.

Remember: Watch for the link on the website for ordering your kit.

Antennas, Featured, General, Homebrewing, Newsletter

Homebrew ADS-B antenna for airplane tracking

Flight Tracking

December will bring Thomas Kavanaugh, KC1ELF, for a presentation on Plane Tracking with ADS-B. This is something you can do in your own shack for very little cost if you’re willing to do a little work. Mr. Kavanaugh will provide us with a great overview in December’s General Meeting, and I’ll follow that up with a Tech Night RTL-SDR Workshop where we’ll make, among other things, a software defined radio to receive ADS-B signals.

In this article I’m going to show you how to make an antenna for ADS-B using just a little coax with a BNC connector, a bottle cap, a little wire, and a hot glue gun.

Designing an antenna for 1090 MHz

ADS-B is transmitted on 1090 MHz. For most of us, that frequency range is outside our experience. Fear not. Everything you know about making a dipole still works for this. The frequency is 1080 MHz so the length of each side of the dipole should be 234/1080 = 0.217 feet, or 2.6 inches. Not very big!

An antenna that small needs to have something solid to hold it to the coax. Below is my solution. I cut two wires to a little more than 2-1/2 inches in length. Then I took a plastic bottle cap and drilled holes for coax through the top and the two wires on the side. Figure 1 below shows this partially assembled.

Figure 1. Coax to dipole wire connections.

I began with a short coax jumper fitted with two male BNC connectors. I just cut one of the connectors off and fed the bare end through the top of the bottle cap. Then I soldered the short wires to the center conductor and braid of the coax. It was a tight fit in there, and the braid of this coax really didn’t like to be soldered, but the final connection was good enough to proceed.

Finally, we want to fix all these connection into something solid. For that I used a hot glue gun to partially fill the bottle cap. This is shown in Figure 2 below.

Figure 2. Connections potted with hot glue

Installing the antenna

ADS-B transmissions are vertically polarized so it is important to hang the dipole with the elements in a vertical orientation. Here’s an earlier prototype of mine hanging in my attic. Just a single brass hook (and a zip tie) was all it took to get the antenna installed. See Figure 3.

Figure 3. Installing the antenna for vertical polarization.

Looking Ahead

I’ll be doing an article on building a Raspberry Pi computer capable of doing flight tracking later this month. It will need an antenna like this to work, though, so here’s your chance to do your homework early!

Antennas, Featured, General, Homebrewing, Newsletter, Station Equipment

Add SDR Capabilities to Your Radio [part 2]

In my last post, I discussed how to add an SDR to your station using the built-in capabilities of your radio. If your radio doesn’t have this fancy antenna switching and selection feature, you can still integrate an SDR pan adapter into your shack using the handy MFJ-1708B or MFJ-1708B-SDRS devices.

SDR Capabilities
Antenna sharing device from MFJ

These devices can be used to allow your SDR to share the same antenna as your transceiver while protecting it from transmitted signals. It does this in one of two ways (or a combination).

  1. Key down input. Transceivers have a line that is used to trigger external amplifiers called key down or key out line. Usually, this line goes to ground when the transmitter is transmitting. (You should read your radio’s manual to verify this.) If you connect this device to this radio output then it will disconnect the SDR while you transmit.
  2. The device also has an RF sensing circuit that will disconnect the SDR from the antenna if it detects the transceiver transmitting.

Because these units use relays you might want to have a slight delay before reconnecting the SDR to the antenna after a transmission. That delay time can be selected by turning the “DELAY” control near the left edge.

The unit is simple to configure: connect power (12v) and your radio key out signal to “CTRL”,  then connect your transceiver, SDR, and antenna connections to the proper ports. Finally, adjust the delay control until it works for your style of operating. That’s it!

Here’s Pascal, VA2PV, with a quick overview of an earlier version of these devices.

Click the video above to see Pascal describe these devices

Note that Pascal is reviewing one of the earlier models of this device. MFJ made some improvements to these units almost immediately after they began shipping. Be sure to get the one with a “B” after the numbers to ensure you get the new-and-improved model.

MFJ actually makes two versions of the new model: one with a regular SO-239 connector for the SDR, and one with an SMA connector for the SDR. The SMA version is shown below.

SDR Capabilities
SMA version of the unit

Amazon has some nice patch cables for very little money to complete the project.

SDR Capbilities
SMA patch cables

Note: If you do have an external amplifier be sure to put the MFJ unit between your transceiver and the amplifier!

I’ll post a few more notes on SDRs and uses for them in your shack over the next month or so. Please plan to join us for the December 11th Tech Night SDR workshop where we’ll help you get your computer and SDR talking.

Radio Amateurs Developing Skills Worldwide