I just stumbled across this forum in doing some research for setting up my own station. These forums seem great already.
Back in the mid-late '90s I had a show for almost 2 yrs on an American FM pirate station that got shut down after basically openly flaunting the law for all of that time, broadcasting 2 and eventually up to 7 nights (and partial days) per week. Basically not at all trying to hide, letting the community know what we were doing etc. They broadcast out of an urban house (3 stories tall) with an antenna mounted on the roof, I think it was 1 watt (I was not much involved on the technical end) and I'd guess a 1/2 wave antenna, and this managed a good 2-3 mile radius of coverage, especially good in cars, which in our city means a potential audience of hundreds of thousands of people.
I'm very interested now that I see built transmitters are cheaper etc. in doing my own broadcasting. It looks like things are so much cheaper and more portable and even pre-assembled now that it isn't even funny... a one-person station with a modicum of tech know-how seems feasable these days.
My idea is that I could run a transmitter with a 1/4 wave antenna (collapsable/portable) as a fully portable, self-contained thing. I'd like to "hit it and quit it" - get up high in different locations that are the tallest in the immediate neighborhood, do maybe 30 min, 15 min or 45 min of programming that I threw previously to an mp3 player, and scoot.
I figure the odds of getting caught are much slimmer operating in this fashion, especially varying locations. I have my eyes on certain parking garages and abandoned buildings and public transit structures that a person could hang out at and transmit from (silently in effect as the programming is pre-set) for less than an hour without drawing much attention.
The transmitter I want to buy says it operates best at 12V 2AH DC. I see that there are various 12V batteries and power packs out there, including rechargables. (Incidentally I'm looking to get a 1W low power/ 20W high power setting transmitter. Even if I get 2-3 miles radius coverage I'd be pretty happy with that - that's a LOT of potential listeners. I've already been online to select as empty an FM frequency as we have in these parts.)
Q #1: What's a good portable 12V DC power source. one that will not fry the transmitter by throwing out more than 2AH (I see there are 12V 2AH acid batteries...)? And what's a good method for connecting a 12V 2AH acid battery with F1 connectors if this is in fact a sane thing to do. How about those boat emergency power packs - at 12V DC will they fry the transmitter?
Q #2: I'm reading that a LPF is a must. Is this something I can buy more or less set to plug in and go, or do I have to do some soddering etc? What do I need to look for in LPF technical specifications?
Q #3: Setting aside for a moment my sanity for wanting to do this at all, is what I'm proposing feasable from a technical standpoint? Can a person run a station from a rooftop essentially out of a 20-30 lb backpack and an mp3 player..?
Thanks in advance, I'm going to keep an eye on this thread and these forums. EXCELLENT WORK, FRIENDS!
A #1. Depending on the operational time frame the 12v 2AH acid batteries would work good for those situations where shore power is unavailable. You can also attach a solar panel and voltage/current regulator to charge up those batteries during the day. The CZH 7C is a very good choice to start with. It is a small 12VDC stereo FM transmitter capable of two power modes, 1.5 watts and 7 watts. It draws little current even at 7 watts, runs quiet and has one hell of a deep rich clean sound.
A #2. A low pass filter is a vital part of the transmission system. No matter if the transmitter itself has a low pass filter, ALWAYS install an external low pass filter between the transmitter and antenna coax. The 7 pole variety is best and you want a filter that can handle at least twice the total power output of the transmitter. Low pass filters can be purchased assembled and they just simply plug in between the TX and antenna coax.
A #3. Yes. I have seen suitcase setups complete with transmitter, portable CD players, small mixer, battery supply and antenna all mounted up in the suitcase. The ultimate "on the go" system, not to mention a pretty damned good cover.
Peace!
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I'm seeing most 12V batteries have F1 outputs... does anyone have a good idea/ a schematic or so forth (ideally just a commercially available product...) for rigging that to the power supply port of the sort in a CZH 7C or similar transmitter? I called Radio Shack about this without obviously mentioning my full intent and the guy there thought it might require at least a couple of items to step from the F1 to something that can be plugged right in. I've done a lot of search engine work on this and although finding the right cell is easy enough finding a way to hook it to the transmitter has been a problem. I really just don't want to overload the thing and kill it. (There are for example a lot of 12V batteries with higher AH ratings; 3 seems common - is that something I need to really avoid? I've been assuming so.)
On the LPF - will any one work (I see a very wide variety of styles, prices and specs on eBay for example), do I need to worry about the wattage of the transmitter, do I need different ones for different wattage settings?
I have a *basic* understanding of the tech going on and I'm willing to put the time in to learn more. Thanks again, I have made this site a Favorite and will be sharing experiences should there be interesting results...
