Western Washington Amateur Television Society: WWATS holds nets every Wednesday and Saturday night at 8 pm local time. The WW7ATS repeater uses Analog NTSC video that is compatible with older televisions. The video repeater is located on Cougar Mountain and has an input of 434 MHz (horizontal polarization) with output at 1253.25 MHz (vertical polarization). Rather than using the audio component of the NTSC signal, the club uses a traditional FM repeater for audio (W7WWI; 147.08 MHz; +0.6 MHz offset; PL tone 110.9 Hz; EchoLink enabled). This allows the ATV-curious to participate in the nets, and see the video from their YouTube live stream.
NTSC primer: NTSC signals have a 6 MHz bandwidth using vestigial sideband (VSB) modulation. This means the lobes are lopsided, starting at -1.25 MHz from carrier frequency on the lower side, while ending +4.5 MHz away from it on the upper end. The luminance (black and white) is AM modulated, the chroma (color) uses QAM, and the audio portion, using 0.5 MHz on the upper-end uses FM.
Transmit video to the repeater: You will need a NTSC modulator with a carrier frequency of 434.0 MHz. At this carrier frequency, the signal occupies 432.75 to 438.75 MHz. WW7ATS doesn't use NTSC's audio, so you are not required to transmit the audio subcarrier centered at 438.50 MHz. To test your modulator, you can tune an old analog NTSC television set to Cable TV Channel 59. This is part of the 70 cm band, and anyone in the US with an amateur Technician class license can transmit video in this band. Remember your antenna must be horizontally polarized. Because the modulators usually put out very low power, you will almost certainly need to use a linear amplifier to reach the repeater.
Receive video from repeater: The output NTSC carrier is 1253.25 MHz, which occupies the 1252.0-1258.0 MHz ATV channel. Technically, it's just 1252-1257.5 MHz because the audio subcarrier is not used. You will want an antenna optimized for 24 cm frequencies. An old NTSC TV cannot receive signals at these frequencies, so you will need to use a downconverter to move it to a more usable range. See description of my equipment below to find out more.
- Comet SBB-123 1200 MHZ Band High-Gain Mobile Antenna with N male connector
- Comet MG-4N Mobile Magnetic Antenna Mount for use with N male antennas
- KH6HTV Model 23-7 23 cm Down-Converter: I had mine built using an N connector for input and an F connector for output, and selected a LO frequency of 1066 MHz. That means the 1252-1258 MHz signal from WW7ATS gets shifted -1066 MHz to 186-192 MHz which lines up NTSC Over-the-Air TV Channel 9.
- Tyler TTV707-13 13.3" Portable Battery Powered TV: Unfortunately, Amazon is showing this TV is currently unavailable, but it has come in very handy since it can tune old-style NTSC cable and over-the-air channels without reverting to blue-screen on low-power signals. The seller told me they are working to produce more in the future.
- HLLY TVX-50M Transmitter: eBay listing says this is 500 mW RF output, but I think it's really 50 mW based the picture of the circuit board. It can transmit NTSC video and audio on frequencies between 76-780 MHz in steps of 0.1 MHz, so it meets my needs for 434.0 MHz for the ATV experiments. There is no PTT input, so you have to manually flip the power switch when you are ready to transmit. Here is a copy of the manual. I did find references that said HLLY's FM radio transmitters have out of band spurious emissions, but do not know if this applies to their TV transmitters. It is difficult to find analog NTSC modulators, so I was happy to finally find a source. They also make a 2 Watt model (not tested), and a 100 Watt model (but the 100W model does not handle amateur TV frequencies).
- KH6HTV Model 70-9B Linear Amplifier: depending upon how far you live from the repeater, this model may be overkill. There is a less expensive, less power 70-7B model that may work for you instead. I used the "Low" power setting for my test.
- 20 dB annteuator: needed to place this inline between the HLLY and Amp to keep transmitting picture stable
- CrazyFire HD-SDI Camera: may also be overkill for your application. Any camera that can output a NTSC composite video signal can be feed into the HLLY. I got this camera specifically because it has two outputs that can be used simultaneously--a composite SDI and HD-SDI signal that I can feed into a HD-SDI HDMI converter allowing me to see what I'm transmitting on a separate, modern computer monitor.
- Tram 1185 Dual-Band Magnet Antenna: probably need to go back and measure SWR on this between 432.75-438.25.
- West Mountain Radio RIGrunner 4700U: overkill for this task but I like to use Powerpole connectors on all my equipment to make cable management easier. This unit also has a display to let me know how many amps are being drawn and a USB connector.
- Bioenno Power BLF-1240A 40Ah LiFePO4 Battery: overkill, but this is what I use for backup power at my home station, so I just borrowed it for my trip near Cougar Mountain. It has built-in Powerpole connectors making it super easy to move around.
- All the equipment used 12 VDC, so I used a bunch of West Mountain Radio Powerpole to DC plug connectors (2.1 mm: 2.5 mm)
I have also been participating in the net using a Grandstream, but I hope to have the ability to receive and transmit RF from my home in Marysville one of these days.
So how did my field testing go? When I transmitted, I couldn't see the return feed from the repeater. My two mobile antennas may have been too close together, or maybe I need to put some additional filtering in place, but the people on the net said they did get video from me, but that the lighting was really bad. It was dark outside, I was in my car, and tried to add some supplemental lighting, but it didn't seem to gel well with the camera.
- 433 MHz Bandpass Filter: The hope is, if the HLLY TV transmitter is producing spurious emissions, this will help to significantly reduce it.
- Mini-Circuits SHP-1000+ High Pass Filter 1000-3000 MHz: If I put this inline with my receive antenna before the amp during mobile operation, maybe it will let me receive my video from the repeater while I'm transmitting.
- MFJ-8704 434 MHz ATV video transmitter: This may be a good, ham-focused, alternative to the HLLY transmitter. I thought this had been discontinued, but they are apparently still available for order. I received mine but it looks different from the picture on the MFJ website. Mine does not have the 9 Volt battery header and the video input has a male RCA jack instead of female. I haven't tested it yet (waiting on some adapters). Here is a copy of the MFJ-8704 manual.
- Directive Systems 24cm Loop Yagi: I ordered the largest one (DSE2455LY) since I am so far away from the repeater. Hopefully I'll be able to see something with it.
- M2 Antenna 432-6WL: Supposed to be the "ultimate ATV antenna". Let's find out if I can transmit with this thing.