Every spring at this time I like to summarize the standard viewpoint held by KDX Worldround Radio regarding Part 15 AM radio transmitters.
Most persons contemplating to build a low power AM station begin to wonder which transmitter will give the most range. But two other questions should come first:
1.) What is the available budget?
2.) How much engineering experience do you have?
The trick to getting the most on a small budget is to build your own transmitter from sstran.com, the AMT3000 or AMT5000.
But without the skill to solder and build a kit part by part, a larger budget is required to obtain a ready-built transmitter from several suppliers in this category. In essence, one is paying for his own lack of skill; that is, paying someone else for having built and marketed a complete package.
For those having the choice of going either way the question of range depends of such factors as RF output efficiency of the transmitter and antenna design with good radial ground system.
The AMT5000 operates in the Class E mode achieving 98% output efficiency (manual p.26), well above the norm of other transmitter designs which more typically achieve perhaps 50% output efficiency.
Arguments abound regarding output efficiencies of the costly prebuilt transmitters, but their output efficiencies are only claimed but undisclosed, resulting thus far in mere sports-like "challenges" regarding range.
Even the least costly AMT3000 from sstran.com, designed for in-home use, can be upgraded to a serious contender in the range category by following the free instructions for improving the output/antenna system.
Here at KDX Worldround Radio we operate an AMT3000 with our own self-built loading coil/antenna, and an AMT5000 according to the manual instructions, and our only concern regarding range of either transmitter is to pull back so as not to trigger an "inspection" for excess field strength.
What's in your wallet?
For those with both limited budgets and engineering skills, there's always the Talking House, or, if you can find one, ChezRadio's Talking Sign. They do a reasonable job at a budget price (often new for $50 or less).
And if you can find a Talking House ATU, then your signal using that particular transmitter will improve strength-wise, getting close to the big boys (i.e., ProCaster & Rangemaster).
If you really want to get on the air, you can always find a way.
In my opening post I shared some thoughts on choosing a low power AM transmitter to enter the field of legal broadcasting.
Thanks to Artisan for adding a valuable tip on getting ready-made transmitters on a small budget, which I had not thought of.
Part of the opening discussion focussed on transmitter output, the signal reaching into the surrounding neighborhood from the antenna.
Also of serious concern is the transmitter input, which can become as complicated as building a kit with the added complexity of needing to design the audio connections yourself. It can amount to much more than simple audio patch cables.
For example, if your transmitter is located outdoors away from buildings and obstructions, the audio source will be located indoors, perhaps 60-feet away.
If fed by wire the audio can remain "unbalanced" up to 25-feet or so, but after that the wires will begin to pick-up hum and lose the higher musical notes. If you are unfamiliar with the terms "balanced and unbalanced" you need engineering help.
Fortunately this website, part15(dot)us, has many experienced radio engineers who freely share their knowledge.
For my transmitter inputs I'm stepping beyond wires to send audio from point-to-point: I'm experimenting with studio-transmitter-links (STL) which utilize a wireless method of transporting the signal throught the air. I've used Part 15 FM for this, and am beginning a project using the 900 MHz band, for which I'll need engineering advice.
Radio experimenters used to build their own transmitters, kits like the Knight phonon oscillator, and one and two transistor AM broadcaster circuits from electronics magazines, even FM transmitters could be built.
One really simple one to try now is getting a crystal oscillator can and connecting an audio transformer to give it modulation, it only takes a couple of parts to assemble.
Maybe this site could come out with a reference design with easy to get parts, so that experimenters could get started on the air right away, while they figure out what kit or commercial transmitter to use, a form of valuable experience.