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

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 Pacific

  •  ATV Net on Thursday @ 20:00 hours Pacific

  •  Bathrobe Net on Sundays @ 09:00 hours Pacific

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 

                                       Note: a PL tone is required to access the analog input, however it's not generally used and documentation is missing. 

                                      It will be updated as soon as we're able to verify it.

Receive Equipment

So what do you need to receive MDARC's DATV signals? Here's the minimum required items:

• High gain antenna tunable to 1240 MHz . Vertical polarity.
  Most ATV-ers recommend a yagi pointed at Mt. Diablo's North Peak. If you have a clear line of slight, a vertical 23cm omni may work as well.

• RG-6 or better coax, LMR-400 or 1/2" hard line recommended. Do not use RG8,RG8x, RG213.

• F-connector DC blocking adapter

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

While our signal is DVB-S, MDARC recommends DVB-S2 receivers in preparation for future upgrades.

Club Member Will Roberts ka3vdt has some used, pre-programmed receivers available at http://laser66.com/ham/

GT Media V7 or V8 (Amazon)

• HDMI or Composite video monitor or TV

• HDMI or Composite cable, depending on the interface between the DVB-S2 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 or DVB-S2 receiver.

Transmit Equipment

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

• Color camera (Composite or a Logitech C920 if using ports down)

• Line level audio. (Mixer/Volume control is recommended)

• One of the following modulators configurations (Listed from Easy to Hard to setup):

• 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, DVB-S Only.(email wb6asu@icloud.com for details). (Difficulty: Easy)*

• Raspberry Pi 4 with a Lime SDR/Pluto SDR running BATC Portsdown 4. DVB-S/S2 (Difficulty: Medium)*

• 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/MV-100 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)

• 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 mimic amp 50mw to 3W  (LNA series) 

Depending on your setup, This may be enough to get in, MMICAMP2 and MMICAMP4, are good choices.If not, add the amplifier from below.

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 k/s

• MPEG-2 480i (SD)

      DVB-S2:

• QPSK 5/6

• Symbol rate 1.000 k/s

• MPEG-2 or H264

Note: Portsdown H264 uses PAL by default, and does not work. 

** You can use a single 1200mhz antenna, however a transmit/receive relay is required, and generally is not recommended. Two antennas allows for full-duplex video/validation of signal into the repeater. Example relays are microwave-rated SMA relay from Teledyne or Ducommun/DB Products. 

These are available on Ebay - You will want a 12v version. 24v will not switch on 12v. Most of these relays are rated for 25-30w @ 1.2ghz.

*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 Raspberry Pi with an external PLL. The pi takes video from a USB-based capture device or a Logitech 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, including the use of the Portsdown encoder board. Most UK users now use a Lime or Puto SDR. (Pluto is preferred)

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. 

If you want assistance, please reach out on the MDARC DATV Groups.io group

More Information:

• Ham TV

• Wikipedia

MDARC Digital ATV Repeater Block Diagram
Note: This diagram is from 2015, when the system was built. Some items have changed over time