Amateur Television on a Budget
Amateur television was one of those things that always intrigued me - maybe it's the childhood fantasy of being on TV, or the thought of owning your own "TV station". Whatever the original interest, there is something special about sending pictures to other people - just ask the millions of people who swap their photos over the Internet every day.
ATV represents the ultimate in "picture swapping" - live, broadcast quality (depending on the camera, etc) moving pictures. But with that comes the perception that ATV is expensive and only for the well off ham. Nothing could be further than the truth, as I have discovered. Yes, you can spend tens of thoudands of dollars on an ATV studio, cameras, transmitters and the like, but like most facets of amateur radio, you don't have to.
What got me started in ATV was the discovery that I had enough equipment sitting in the shack to receive not one, but 3 bands of amateur television - namely 70cm AM, 23cm FMTV and 13cm FMTV. Of this gear, only one item, a Pace satellite TV receiver which cost all of $10 at a hamfest, was bought specifically with ATV in mind!
So what does a $10 ATV receive setup consist of? Well, the first (and arguably most important part) is a TV set, or a VCR/monitor setup which is what I have. My monitor was surplus from work, and I saved it from the scrap heap. It also doubles as a second TV when I want to watch the telly in the shack! The VCR is a spare VCR I had lying around, but if you're not that lucky, you can look around for a secondhand VCR which won't play tapes. The tuner section usually will still work. This TV or TV/VCR setup is the most important past of an ATV station, and also, by itself, is capable of receiving ATV transmissions in the top part of the 70cm band (in Australia, the upper ATV channel is at 444.250 MHz - or around "channel 16" UHF). For an antenna, the existing domestic UHF TV antenna will suffice for strong signals, but a dedicated antenna should be considered.
While AM (or more correctly, VSB) modulation, the same as used for broadcast TV, is used on 70cm, FM is favoured on the higher bands. Here in Melbourne, the 23cm input to the ATV repeater uses FM, and I'm not aware of any AM TV activity on 23cm or higher, all the hams I know use FM. Normal TVs don't receive FMTV well, so some form of converter is needed. While the ideal solution is to build a dedicated FMTV receiver, which will cost only around $100 and several hours of one's time, it's a fortunate coincidence that many satellite TV systems used a LNB at the dish, followed by a receiver which had a tuneable IF that covered at least 900-1400 MHz, sometimes as wide as 750 - 1750 MHz. 23cm ATV at 1250 or 1283 MHz falls right in the middle of the satellite receiver IF passband, and analogue satellite TV in its basic form is FM! These old satellite receivers can be bought for $10 at hamfests, and with the addition of a preamp, will receive 23cm FMTV transmissions. Because FMTV uses less deviation than satellite TV, reception won't be quite as good as that obtained by a purpose built receiver, but some satellite receivers can be modified to improve their performance. Satellite receivers also have DC power supplied on their input connector, which can be useful for powering masthead preamps or converters for other bands (but if you directly connect an antenna, be careful!). As for an antenna, a loop Yagi is quite popular on 23cm.
Once one has the capability to receive 23cm FMTV, adding other bands is quite easy, as all that is needed is an appropriate converter. If you're lucky and have a Pace satellite receiver, or another FM receiver capable of going down to 750 MHz, 13cm reception can literally cost nothing, or very little! Some old Conifer MMDS TV converters were designed to convert 2200 MHz to the 500-600 MHz portion of the UHF band, and have a 1657 MHz local oscillator. The same converters will also convert 2414 MHz to 757 MHz and 2438 MHz to 781 MHz without modification. What's more, they work well off the satellite receiver's DC power - truly plug and play! :-) As the converters come with their own grid reflector (mine has an 18 dBi antenna), nothing more is needed for 13cm. Unfortunately, the newer converters that were used for Galaxy pay TV and the like use a 1951 MHz local oscillator and aren't as easy to use for FM ATV (you would need either an FM demodulator for 460-480 MHz or upconvert to a satellite receiver IF). However, if anyone nearby uses AM TV, the Galaxy converters will put these transmissions in the lower part of the UHF band. Now your ATV receive setup covers 3 bands for very little expense - the most expensive parts are the 23cm antenna (homebrew) and interconnecting cables.
It's possible to go further. I'm looking for an old Ku band LNB, which can be modified to receive 10 GHz ATV, in conjunction with a satellite or other 23cm receiver. These things are appearing at hamfests these days for very reasonable (around the $10 mark) prices. I already have dishes for this band, but surplus dishes should be obtainable, or a dish can be home brewed (I have heard that mild steel woks often have a near paraboloid shape).
That takes care of the receiver. As for the transmitter, the easiest way to go here is build a kit. For VK amateurs, Mini Kits in Adelaide have a range of VHF/UHF/microwave kits, including ATV transmitters and receivers for most bands from 70cm to 10 GHz at reasonable prices. Setting up an ATV transmitter does cost a bit more, in the order of a few hundred dollars, mainly because of the cost of obtaining a reasonable amount of power on the microwave bands. But it's still well within the reach of most amateurs, provided one is prepared to spend a bit of time and effort constructing the equipment (ahh, the smell of burning flux! :) ).
Finally, there's the matter of signal sources, namely cameras, VCRs and other video devices. There's a number of old cameras around. I have an old home porta pack, which consists of a colour video camera and a VCR. It requires a lot of light to operate, but still works. The VCR also works, so I can make videos while away from the transmitter and play material recorded previously to air. I would prefer a more modern CCD camera, as these work better in low (i.e. indoor) lighting, have better picture quality and are more compact. There is also a kit around for a PC driven character generator, which would be useful for displaying callsigns and other information. It's also possible to construct relatively inexpensive character generators for portable use. I also have an old Apple ][ computer, which has a PAL video output. This may be useful for IDs and other information.
ATV in this shack is still in its early days, but I hope I've dispelled the myth that it has to be expensive (of course, it can be!), and is within the reach of most amateurs, with a little effort. SWLs are in an even better position. Most capital cities and some regional cities have an ATV repeater, and many of these can be received with an ordinary TV set. For those in Melbourne, look at the extreme bottom end of the UHF TV band for any signals (actual frequency is 444.250 MHz). You may be able to receive the VK3RTV repeater if someone is on air. I'd suggest trying at 8PM on a Wednesday evening, when APC News is being broadcast (i.e. when there is a known signal). Sydney viewers can try between 7PM and 8PM on a Sunday evening, when the local ATV club starts a broadcast, followed by the VK2 Division of the WIA. Sydneysiders should tune around UHF channel 35 to view the ATV repeater.