W4WVP

Listeners to the Arlington County Net and subscribers to the w4wvp-members mailing list have heard and seen a lot recently about the MT63 multi-tone digital modulation technique. Why?

Some Arlington Amateur Radio Club (ARC) members took an interest in digital communications at the July 2011 meeting, when Ken, WB4AKK, and I (assisting, with no speaking lines) demonstrated use of FLDIGI software for several modes of digital communication. Interest in the MT63 mode, in particular, ramped up when Kim, KD9XB, announced on the June 5, 2012, Arlington County Net that he had checked into the Fairfax County ARES Net and found them using MT63 to transmit data, such as rosters of check-ins, over the repeater. They use it because the MT63 modulation scheme, using a 2000 Hz audio bandwidth (MT63-2000 or -2k), efficiently uses most of the audio spectrum available on ham VHF/UHF FM voice radios and repeaters to achieve good throughput of text and (with the FLWRAP application) binary data, such as images or word-processor documents. It has some drawbacks, such as long latency (delay from time text is entered until it is decoded), which make it unattractive for keyboard-to-keyboard chats on HF (for that, try PSK31), but it is very good if one has, say, dozens of FEMA, Red Cross, Hospital, or other specially formatted messages to communicate using common ham gear (HTs, mobile VHF/UHF FM transceivers, and laptops running Windows, Mac OS-X, or various GNU/Linux distributions.

Other digital modes are also used on Fairfax County ARES Net, and you may want to try them, simplex or on the W4WVP/R. In any case, please give voice traffic priority on W4WVP/R. For the post-Arlington County Net digital sessions, let’s first strive to communicate among ourselves using MT63-2000.

Software

As noted, FLDIGI software may be used for MT63 on PCs running Windows, Mac OS-X, or GNU/Linux. It is free and open-source. But other software can also do MT63, such as the Digital Master 780 (DM780) program in the Ham Radio Deluxe software suite.

There is also an MT63-2000 app for devices running AndroidOS. [Thanks to KI4DHW and KD9XB for this info. N4ERD has looked for an app for iPhone but found none, so far.]

Software Configuration

When setting up software for MT63 on the Arlington County Net, choose the 2000 Hz bandwidth option and the [2012-08-18 update by KD9XB:] short interleaving option. The extended character set option is probably not needed, but we may learn more about this as we experiment.

Hardware

You may interface your PC to your transceiver acoustically (the air-gap method) or using an interface cable and associated circuitry. The air-gap method is easiest; I recommend you try it first. You may decide you want to invest the effort to construct an interface cable to make operating more convenient.

Some interfacing information is provided in the FLDIGI Manual. One size does not fit all; the interface must be compatible with your transceiver and the connectors of your PC.

For users of the Tigertronics SignaLink USB Interface, Tigertronics provides interfacing information and hardware for many transceivers.

KA8OPJ shared this info on interfacing his Yaesu FT-817ND:

Various radios take different cabling, and sometimes different sets for particular modes. Also, the PTT driver (unless you actually push the button) may take external circuitry. Audio coupling has its advantages!!

Examples

• My old Baycom packet controller (the same model NW3V used to have) took only two 2-conductor mono plugs to an ICOM IC2AT HT: one to the microphone and one to the earphone. Because it used a serial port, I hadn’t used it in several years: There was no serial port on my recent computers.
• My FLDIGI PSK31 to Yaesu FT817ND “DATA” connector (mini-DIN, like the plug from a $3 PS/2 mouse) took a $15 USB-to-serial converter plus a small switching network (two resistors, one diode, and one 2N2222 transistor). However, it does NOT have the microphone and earphone connectors needed for MT63, because they are NOT present on the DATA connector. This is similar to the SignaLink adaptor. My total investment for PSK31 was $15 plus an hour of assembly time, plus a trip to MicroCenter for USB-serial. WB4AKK gave me the min-DIN connector.
• My FLDIGI MT63 to FT817ND connections use a more complex network, similar to the one in the FLDIGI instructions. The microphone, earphone, and PTT lines are all transformer-isolated. The PTT uses the tone from the right stereo channel of the computer rather than the manual switches some of the folks use. Instead of a bipolar transistor like 2N2222, I used a HEXFET. The radio’s earphone connector is mono. The radio’s microphone and PTT connector use the RJ45 microphone connector, but there’s no microphone or earphone line on the DATA connector. (KK4JQR please note.) Parts took a trip to MicroCenter; assembly >3 hours.
• My Yaesu VX3R has a 3-conductor stereo earphone plug on the side: This can be used for listening, by connecting directly to the computer’s microphone plug. The 4-conductor microphone+stereo earphone plug on the top uses the FT817ND network, plus it needs additional circuitry (one resistor + one capacitor) to combine microphone AC (left stereo channel from the computer) and PTT DC (right stereo channel through the transistor).

Again, audio coupling for MT63 took <5 minutes to install FLDIGI, and no additional hardware ….

/Mike KA8OPJ

For users of Yaesu FT-250R HTs, the CT-44 accessory may be useful. The FT-250R user manual provides interfacing information.

Building an HF Stealth Antenna within a Tight Budget
Ken Heitner WB4AKK

Arlington Amateur Radio Club
Operating Mobile HF is Potentially Fun & Useful
The key problem with HF mobile is the antenna.
Various HF whips over the years have come and gone
Most HF mobiles today use the screwdriver antenna. You can build your own??
Maybe the approach used in the Stealth HF antenna is the way to go.

An Example of a Stealth HF Mobile Antenna
Another View of Stealth Antenna – See the Radiating Element

Can We Afford This ? – No. Can We Build This? – Maybe
This is a commercial product, and that means expensive
But if the concept is valid, maybe we can build a simpler and cheaper version
So let us examine how it works

Operating Concepts – 1
The basic antenna concept is a magnetic loop antenna
The 50 ohm coax feeds the antenna via a small loop.
The main loop is tuned to resonance by the high voltage capacitor

Operating Concepts – 2
The Stealth antenna is build on a modified loop concept.
The coax feeds on side of the antenna, in what might remind you of a gamma match
The loop is also tuned by a HV capacitor

Operating Concept – 3
Yet another feedpoint concept is the omega match
This concept is offered in the loop matchboxes made by MFJ
This may be easier to tune for a perfect match

Operating Concept – 4
This approach might be good for those whose radio already has a built in antenna tuner
It just steps up the low antenna impedance with a wide band transformer

General Project Approach
Simplify the antenna geometry so it is easier to build
Build the basic antenna framework first
Consider alternative feedpoint approaches for trial and error testing
Who knows – Maybe one of us will come up with even a better way to do this

Simplified Antenna Geometry- Plan View
Simplified Antenna Geometry – Elevation View

Simplified Antenna Geometry
Makes the antenna buildable from commonly available copper and PVC pipe
Once the basic antenna is built, then we can try different feedpoint concepts and see what we like. Each antenna can be customized for your vehicle roof size

Discussion Time !
Let me hear who would be interested in trying this project out.
Let us leave the details for a separate meeting of those specifically interested.
No rush….We can do this at our own pace
Might be fun for the next VA QSO Party.

A member of REACT visited with me during the Arlington County Fair. He mentioned that many members of REACT have amateur radio licenses. He also noted that REACT has repeaters that use the GMRS frequency allocations. GMRS channels are provided for UHF repeaters. REACT has repeaters set up in Washington, DC area. These require GMRS radios with appropriate setups to operate.