Repeater Systems:    ATV      |       Digital Voice       |       EchoLink & IRLP       |       Repeater Rules

In mid-2015, MDARC converted the downlink transmitter of its ATV system to be fully digital. We are now able to transmit four channels of content in the same bandwidth that the old analog transmitter required. This also means that a digital receiver is needed to receive the MDARC ATV signal. Analog reception is no longer operational. Our uplink receiver can now handle both analog and digital, however. So if you are transmitting into our system in analog, your existing analog equipment will still work.

Check into the following nets on W6CX 147.06 MHz + 100 PL repeater:

    * Tech Net on Tuesdays @ 18:00 hours local

    * ATV Net on Thursday @ 20:00 hours local

    * Bathrobe Net on Sundays @ 09:00 hours local

Online Streams

http://w6cxatv.mdarc.org

https://batc.org.uk/live/w6cxatv

System Outputs:

1244.50 MHz DVB-S

System Inputs:

The repeater's receiver provides multiple inputs for you to transmit into; four digital and one analog:

Digital TV Inputs:     1292.50 MHz DVB-S

                                   1273.00 MHz DVB-S/DVB-S2

                                       915.00 MHz DVB-S

                                      430.00 MHz DVB-S

Analog TV Inputs:    1270.00 MHz FM (PL ???)

Receive Equipment

So what do you need to receive MDARC's DATV signals? Here's a short list:

• High gain antenna tunable to 1240 MHz . Vertical polarity.
  Most ATV-ers recommend a yagi pointed at Mt. Diablo's North Peak.

• RG-6 or better coax

• DC blocking adapter

• Digital TV "free to air" satellite receiver: DVB-S2 with HDMI or Composite out

Some Examples:

https://www.amazon.com/GT-MEDIA-Satellite-Receiver-auto-roll/dp/B08HMXK42N

• HDMI or Composite video monitor or TV

• HDMI or Composite cable, depending on the interface between the DVB receiver and your monitor.

You may also need one or more adapters to convert from the antenna connector (usually an N-type) to the F-connector on the RG-6 coax.

Transmit Equipment

If you are planning to buy or build an ATV transmission system, MDARC recommends going digital. You will need:

• Color camera.

• Line level audio.

• One of the following modulators:

• 1270 MHz FM transmitter (email wb6asu@icloud.com for details). (Difficulty: Easy)

• Raspberry Pi 3+ with "Acampo PC" board - This is a variant of the BATC Portsdown (email wb6asu@icloud.com for details). (Difficulty: Easy)*

• DATV Express board with all needed hardware (see their web page for details, www.datv-express.com). (Difficulty: Medium)

  • Note: These boards are no longer being made, you may be able to find them 2nd hand

• Harmonic MV-50 Encoder w/ Harmonic PSM-3600 Satellite Modulator. (Difficulty: Hard)

• Any MPEG-2 Satellite encoder with a DVB-S/S2 modulator that outputs on L-Band (Difficulty: Hard)

• Raspberry Pi 3+ with a LimeSDR running BATC Portsdown (Difficulty: Hard)

• a 1200mhz amplifier designed for ATV/DATV. This needs to be very flat/linear. For most cases you do not need a lot of power, 3-10w is enough. Some examples:

  • Downeast Microwave 1200 Amp. 50mw to 3W  (LNA series)

Note: Downeast Microwave used to make high-power amplifiers, Q5 Signal now does that. You can find older 2318PATV 18w around.

• Q5 Signal 1200 amplifier (high power 25w+)

• LMR400 or better coax.

• 1290 MHz high gain yagi antenna. Vertical polarity.

• Various other cables to connect it all together.

Transmit Modulation specs

• DVB-S

• QPSK 3/4

• Symbol rate 2.222 MB/s

*A word about the Portsdown system

The portsdown system was developed by the BATC out of the UK. It's designed around a PCB connected to a Rasberry Pi with an external PLL. The PI takes video from a USB-based capture device or a Lotitech C920 webcam and modulates the signal from the PLL to generate a RF signal in the specific band requested using DVB-S.  The original design has multiple bands, most are not available in the US, and uses PAL not NTSC. 

Since the initial design of the Portsdown a lot of the hams in Europe have moved over to doing DATV on QO-100. Development on NTSC/US-based features has fallen behind. 

Due to this the MDARC community runs a older version of the Portsdown software code. If you have one of these modulators DO NOT CONNECT IT TO THE INTERNET.

To help with this, Fred WB6ASU re-designed the board to be only 23cm/1200mhz to ensure we have a working board. There are a limited number of them; and it requires surface mount soldering to make. 

More Information:

• Ham TV

• Wikipedia

MDARC Digital ATV Repeater Block Diagram