Tag Archives: Amateur Television

New 70cm Yagi

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M2 Antenna Systems 432-9WLA Specifications

M2 Antenna Systems 432-9WLA Specifications

We decided to replace our current 70cm yagi with a newer, higher performance one from M2 Antenna Systems. We choose the M2 432-9WLA. The new antenna has a higher gain and a cleaner pattern than our current 70cm yagi. It also has a longer boom.

New Yagi Ready For Installation

New Yagi Ready For Installation

The first step in the project was to assemble the antenna and check its SWR on the ground. The elements on an antenna like this typically vary by small amounts and are usually not arranged from shortest to longest. It is important to carefully measure each element during installation to confirm that each element is installed at the correct location on the boom.

The folks at M2 Antenna Systems made up a custom boom support truss for us. This is important given the potential for ice and snow accumulation that we face here in New England. We also made up a section of LMR-600uF coax to connect the antenna to the feedline and preamp system on our tower.

Driven Element Details

Driven Element Details

The new antenna uses a Folded Dipole style feed point. This system is essentially a T-matching arrangement where the two sides of the driven element are fed 180 degrees out of phase. It is important to set the locations of the shorting blocks carefully to ensure proper operation of the driven element and a resulting low SWR.

Yagi Going Up The Tower

Yagi Going Up The Tower

Matt, KC1XX, and Andrew from XXTowers handled the installation of the new Yagi on our tower. The installation involved climbing our 100 ft tower and the 25 ft mast at the top to remove the old yagi and install the new one. Note the careful rigging of the new antenna and associated feedline. This allows the new antenna to be pulled up the tower without damaging it.

Climbing a mast is not for the faint at heart! An installation like this one is clearly a job for experienced professionals. Andrew makes this task look easy. Our tower camera captured some video (click on the image above to play) of Andrew’s handy work.

Completed Installation

Completed Installation

The new yagi (top antenna in the picture above) is installed on a 5 ft fiberglass mast extension. The extension is used to ensure that the antenna does not “see” a metal mast which would disrupt the antenna’s pattern. The final installed height of our new yagi is a little over 125 ft. Note Andrew’s good work in attaching the feedline to the mast.

432-9WLA Installed SDR - Shack End

432-9WLA Installed SDR – Shack End

With the new yagi installed and hooked up, we made a final check of the end-to-end SWR from the shack. The antenna’s SWR is very good and the 2:1 SWR bandwidth extends from the bottom of the 70cm band to almost 450 Mhz. The new antenna is optimized for weak signal work up through the ATV sub-band and its SWR is below 1.2:1 in this range.

Fred, AB1OC

2016 ARRL Field Day!

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2016 Field Day Site Layout

2016 Field Day Site Layout

I had the privilege of acting as the Field Day Incident Commander for the Nashua Area Radio Club this year. Field Day is the most important operating event for the Nashua Area Radio Club each year. We operated under our club callsign, N1FD and we were 7A here in New Hampshire, USA. We included some new antennas including a Three Element 40m V-Beam, a Satellite Station, and a 70cm Digital ATV Station in our operation this year. You can see some of the details which went into the planning of our 2016 Operation on our Club’s Tech Night Page.

The video above shows highlights from our 2016 Operation. As you can see, we had a lot of fun this year. Our club has 120+ members and we had a large turnout for Field Day. You can see more about our 2016 Field Day operation on our Field Day Page including photos, a score summary, and a recap presentation shared at a recent club meeting. I hope that you enjoy sharing our memories.

73,

– Fred, AB1OC

A New Project – Digital Fast Scan Amateur Television

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Digital ATV CQ Call

Digital Amateur Television (ATV) CQ Call

Skip, K1NKR a local friend and VHF/UHF expert and I began talking about the idea of building a Fast Scan Amateur Television (ATV) System some time ago. Our early research and the antenna equipment which we had in place at our stations led us to plan our ATV project around the 70 cm band. The 70 cm band plan in the United States has allocations for Fast Scan ATV transmissions with a bandwidth of up to 6 MHz. Our research led us to Jim Andrews, KH6HTV’s excellent website where we discovered that it was possible to build a Digital ATV station using reasonably priced commercially available DVB-T format Modulators and Demodulators. Jim’s site has a wealth of great Applications Notes on Digital ATV and it’s a great place to start learning about this technology. A combination of a DVB-T Modulator and Demodulator from Hi-Des was chosen as the heart of our Digital ATV System. We also worked with Jim to secure the needed Wideband Linear Power Amplifiers for the 70 cm band. We began receiving the equipment to build our Digital ATV Stations late last year. We’ve done quite a bit of testing on the air and some custom development work which has resulted in a pair of excellent-performing Digital ATV stations. The picture above shows a Digital ATV “CQ” that I sent to initiate one of our early QSOs.

Digital ATV Transceiver

Digital ATV Transceiver

Here’s a picture of Skip receiving my “CQ” at his end. The picture quality produced by the equipment that we’re using and the DVB-T format is phenomenal. The Hi-Des Modulator which we are using has a large number of parameters that can be set to determine the format and bandwidth of the signals we generate. After some experimentation, we have settled on using QPSK modulation and a 6 MHz signal bandwidth. This combination delivers excellent picture quality with more than adequate motion performance. We see very few if any picture artifacts using our current format. We’ve also done some experimentation with QPSK and a 4 MHz signal bandwidth. I plan to share more on signal formats in a future article on our blog.

Digital ATV System User Interface

Digital ATV System User Interface

We are both using HD Digital Camcorders as our primary video signal sources and 1080p monitors to display our received signals. I opted to include an HDMI Video Switch from Gefen in my setup which also allows me to send video and graphics from a variety of different sources including my PC over the air. The monitor in the picture above on the right is a touchscreen display that I use to control my ATV Transceiver system.

AB1OC Digital ATV Transceiver

AB1OC Digital ATV Transceiver

Early on, I decided to build a Transceiver-like setup. I wanted to create a unit that was simple to use just like the HF Transceivers that are available today. Some of the key capabilities that I wanted to create include:

  • Real-time selection and switching between multiple HD video sources
  • Transmission of PC sourced Video and Graphics over the air
  • Preview and cueing of the next video transmission while receiving
  • Simultaneous display of both receive and pending transmit video
  • Built-in Transmit/Receive (T/R) switching with termination and protection of the Tx power stage
  • Sequencing of T/R stages including my tower-mounted pre-amplifier system
  • Power and SWR monitoring with an automatic trip on high SWR
  • An internal low-noise RF preamplifier to provide additional receive signal gain if needed
  • Touchscreen graphical interface for configuration and operating the station
  • Recording of both sides of on-air video QSOs to an attached PC

To achieve these goals, I decided to build a Raspberry Pi 2-based Linux controller for my ATV Transceiver and to package all of the ATV components and video switching/conversion gear needed in a small rack mount enclosure. Many of the components in the system communicate with each other over an Ethernet LAN and the transceiver is networked to computers and other devices via an external Ethernet connection. More on the details of the Transceiver design to come in a future article.

Skip and I recently produced a short video to demonstrate how Fast Scan Digital ATV works and to show the quality that these systems are capable of producing. Our project is still a work in progress and I expect that we will continue to learn as we perform more tests and continue the development of our systems. I plan to post additional articles here to share the details of our designs and learnings from our on-air testing as we proceed.

– Fred, AB1OC

First Tower Part 8 – VHF/UHF Antenna System Design

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M2 2M Beam

M2 Antenna Systems 2m Yagi

We have an interest in weak signal work on the 2m and 70cm bands. We currently have a vertical ground plane antenna installed at about 50 ft for accessing our local repeaters on these bands but the surrounding tree cover and lack of gain have prevented us from pursuing our interest in VHF/UHF contesting, Grid Square collecting, etc. on these bands. We designed our tower to accommodate long-boom Yagi’s on 2m and 70cm for these purposes and we have decided to install them as part of our project. I spoke with Jason at M2 Antenna Systems this evening and after some discussion about our goals and the tower and station equipment we have, we decided upon the following antennas and related equipment for VHF/UHF weak system work:

Both of these antennas have good gain and F/B ratios and very good patterns. Initially, we will drive the system with our Icom IC-9100 Transceiver. This rig provides 100W on 2M and 75W on 70cm barefoot. This should be enough power to have some fun on these bands initially. We plan to add an amplifier on 2m and 70cm in the future so we selected antennas capable of handing 1KW+ of power. We are also having M2 Antenna Systems put together a custom pre-amp and high-power switching system to mount at the top of the tower which will accommodate our planned power levels in the future. Both antennas feature rugged construction to help them withstand the winters that we have here in New Hampshire, USA.

M2 70cm Beam

M2 Antenna Systems 70cm Yagi

It is important to pay careful attention to the feedline losses at these frequencies. This is especially important for us as we need 200’+ of coax feedline to get from our shack to the top of the tower/mast where the antennas are located. To ensure good performance, we set a target for the total losses in the feedlines to be no more than 1.5 dB. To meet this goal, we settled on the following configuration:

Using these components, both feedlines will have about 1.2 dB of loss end to end. We will place both beams on the 15′ mast above our upper SteppIR DB36 Yagi. We plan to place the 70cm Yagi at the top of the mast and the 2m Yagi between the DB36 and the 70cm Yagi in the middle of the mast. This configuration should minimize any interactions between the three antennas.

You can read more about our tower project via the articles which follow:

– Fred, AB1OC