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The least cost way to just try out Amateur Television - ATV - with a neighborhood ham, ham club demo, public service events and R/C transmitting live action color video a half mile or more line of sight, is to buy a Videolynx 434 50 mW transmitter module for $99 and connect it to your camcorder or any camera with a video output, 9V alkaline battery and 70cm antenna - receive it with the TV set to analog cable channel 59. If you want sound and able to select any of the 4 standard 70cm ATV frequencies, then the Videolynx Z70A at $149 is for you. For higher power and greater DX add a linear amp - see the transmitting section below. |
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See pages 9-11 to 9-13 in the ARRL Operating Manual 10th edition. Also see the ARRL Handbook for Radio Communications Image Communications chapter. |
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![]() Balloon ATV See the earth live from 80,000 ft like this view with a VM-70X transmitter module in a high altitude balloon. |
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![]() Any TV with a cable TV tuner can receive ATV directly on the 70cm ham band. |
![]() TX70-5s 4W+ 70cm Transmitter 4 channels with sound. TX ATV to a local repeater, EOC, or direct to local hams. Package your own using the Videolynx VM-70X. |
![]() 440-5S Arrow Antenna 5 element, end mounted, 25" boom and 50 Ohms. Great for home or portable. |
Receiving ATV It is best to select a TV that does not go to blue screen or automatic shut off when there is a snowy picture or no signal present. You dont want the TV to shut off while monitoring a local ATV repeater, searching for DX or aligning your beam. Some TV's require reprogramming the active channel memory so that you can use cable channels 57-60 or channel 3 or 8 if using a downconverter for the 900 or 1200 MHz bands. The easiest is to connect the TV to your Cable TV service if analog, then push the channel program button in the CATV mode. This should set the TV up to select most all channels even when no signal is present when no ham is on the air at that instant. New TV's will contain an analog NTSC cable channel tuner in addition to digital channels per FCC Rule 15.118(b) to accommodate all cable TV systems, but it is a good idea to keep your old analog only TV's for ATV work rather than trash them when you buy a new digital TV. A net can greatly benefit getting ATVers by video to show and tell rather than trying to describe something by voice only - "Pictures are worth a thousand words." With ATV you can have full duplex audio - while one transmits and talks on the ATV sound subcarrier, everyone else can watch and listen on their cable ready TV set (cable ch 58, 59, 60) or TV with our downconverter, and at the same time talk back on a two meter FM voice frequency (better interaction and eliminates the long winded). How about setting ATV up at your ham club and transmitting the meeting live or by tape later to those members who cannot attend. The possibilities are endless - see our ATV application notes web pages.
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Transmitting ATV Analog ATV on the 70cm band is the most popular for ATV since any standard TV can be used to receive directly on analog cable channels 57-60, simple analog transmitters are least cost, and the lower the frequency, the farther the DX with all else equal. Very few multimode UHF transmitters and transceivers support the broad band ATV mode. Most all ATVers use transmitters specifically made for video. Sending analog video is easy by plugging in your camcorder, video camera, digital camera, VCR, or any device with Video outputs that can output on an A/V cable and be normally seen in a video monitor, VCR or TV sets A/V inputs. Most camera mic's are amplified and output line audio which can be plugged into the ATV transmitters line audio input. FM ATV occupies 3 times the bandwidth of analog and can be found in the 33cm bands and above in areas where the particular bands are less used by other modes - consult your local band plan. FM has a 12dB advantage to the snow free signal level vs. analog, but requires a separate FM receiver. Analog AM weak signals can be seen better. Digital ATV is being experimented with, is much more complex and with a variety of modes. 2 or 6 MHz QPSK DVB-T has emerged as the preferred DATV mode. US TV's do not receive DVB-T but this mode is used in Europe and much of the rest of the world. Some inexpensive set top boxes found on the internet will receive DVB-T but may not tune the ham band without a downconverter or not do the narrower 2 MHz bandwidth mode in the 70cm band. However, prices are coming down, see Hi-Des HV-100EH modulator and HV-110 receiver made for the ham market. With DTV, the picture is either P5 or not there - Cliff Effect. The cliff effect receive level is shown on the graph above right. DVB-T 6 MHz QPSK has the best cliff effect signal sensitivity and seems to be the most practical for DX and general ham use. Other bandwidths and digital modulation modes would fall in-between -100 dBm and -80 dBm. See KH6HTV's appnotes and products for DVB-T. Nano Stations are being used with IP cameras direct and on Ham 2 and 5 gHz Mesh networks - see AREDN. The few seconds delay or latency with these digital systems to do their encoding and decoding do take some getting used to when talking back on two meters or crossband duplex. See our Video Latency Test web page. TX70-5s >4W, 4 standard channel 70cm ATV Transmitter. |
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Over the years we have gone back and forth between having available a transceiver or a transmitter that would pair up with a downconverter. The demand has always been about 50-50. So now, since 2008 new TV's have analog cable tuners built in, we went back to stand alone transmitters. Also, you may not need a transceiver, downconverter or TV to use at the transmit location at a public service event. Some areas may only operate through a crossband repeater and very little simplex. Separate units also offer a lower entry cost to 70cm ATV since a cable ready TV can be used to receive on the 70cm ham band.
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70cm Antennas For portable Emcomm, public service work or if antenna size is limited for what ever reason, we suggest the Arrow Antenna 5 element 440-5S beam as shown at right that gives 8 dBd on a 25 inch boom. The 10 element 10L-70cm gives 11 dBd on a 62 inch boom. Either beam will give you more than 20 miles even running 4 Watts with the TX70-5s or Videolynx VM-70X transmitter module snow free line of sight ATV which is great for portable or just hitting the local ATV repeater. Also see Homebrew Antennas. Note that even with home made ground planes at each end running 4 Watts the snow free DX is over 2 miles. Low loss coax cable and properly made connectors are also important. It does not make sense to invest in a high power transmitter and/or high gain antenna, only to lose a lot of power heating up lossy coax. For runs over 20ft, we suggest the 4/10 inch diameter coax - ie: Times LMR-400, Andrews CNT-400 - or larger with N plugs. N plugs have a gasket that will keep water from getting inside the shield and ruining the coax. If you don't want to put on your own plugs, places like RF Parts, Cable X-Perts, and others can supply various lengths with connectors ready to go. |
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