The following are low power AM and FM transmitter kits which I have assembled and/or read about in my course of study. Hopefully this can help some of you decide wether it is really worth it to build a transmitter from a kit verses purchasing a pre-assembled transmitter. I will include pictures soon!
Ramsey tends to somewhat over-rate this kit, but if you build it carefully and do not mind doing some excessive tweaking, this transmitter can be a great asset to your Part 15 FM Station here in the US, as well as an asset to lower powered stations in foreign countries. It is an FM Stereo Transmitter based off of the BA1404 IC which provides a pretty good stereo quality signal anywhere within a 30 to 300ft range depending upon the type and location of the antenna you choose to use. In foreign countries where regulations permit, you could probably cover about a mile with this transmitter provided you have a good location and an excellent antenna such as a 5/8 wave broadcast antenna. The kit is easy to assemble even for a beginner and would make a wonderful first kit. The price is just under $50. The kit may be useful as a sound feed inside of a church auditorium to assist those who are hard at hearing, or even a nighborhood radio station covering one to two blocks. Beyond that, it isn't much good unless you modify it from its original design. There are several websites online which go into great detail on how to do this. As far as kits are concerned, Ramsey does a great job at printing detailed and easy-to-follow instructions and the quality is good as well.. The frequency tends to drift a bit, but this problem is easily overcome by allowing your transmitter to "warm up" for an hour or two before use. The output power is about 10 milliwatts which is enough to cover a few blocks with a Part 15 antenna, as well as break the rules if you use an external antenna of greater than 1/4 wave. Don't tell me I didn't warn you!
The Ramsey FM-25A is a PLL Synthesized FM Stereo Transmitter which has a few features that make it a much better choice than the FM-10C. The signal is jumper settable and remains rock solid with no frequency drift. The stereo quality is also considerably better than that of the FM-10C. Range is about the same if the kit is built in "low power" mode. The kit does offer an alternate means of construction which puts it in "high power" mode giving it approximately 250mw of power for range of up to a quarter mile. This could serve as a "talking billboard" for your church for passers by to tune into, as well as a neighborhood, camp, or small village radio station for the immediate area. A good antenna is a must in order to achieve this type of range. The price is a bit steep at just under $150. For this kind of money you should really look into purchasing a pre-built transmitter!
The Ramsey AM-1 is a "FCC part 15 compliant" 100mw transmitter that covers selectable portions of the AM broadcast band. The audio quality has much to be desired, however , the range can be as much as 1/4 mile (maybe more depending upon antenna, location, and conditions according to the manual). In practice, the most range I have ever heard of anyone getting with this transmitter is about 500 feet. If you use one of these as a neighborhood or small village radio station, you will also need to devote some time and money into building a decent antenna. Elevation is also an important thing. You will get MUCH more range from the attic, steeple, or second floor than the first floor! It would make a perfect "talking billboard" for your church or Christian camp. It is very simple to construct and would make an outstanding first kit. The price is not bad either, less than $50. Be sure to select a clear frequency away from surrounding stations as the frequency tends to be a little drifty at times. When you assemble this kit, be sure to select a frequency above 1500khz because range is better in the upper portion of the AM broadcast band. Without an elaborately designed antenna and good groud connection, you may not get more than a 100ft range. Antenna, elevation, and location are everything!
This is Ramsey's PLL Synthesized version of the above kit and it is also jumper settable for rock solid frequency stability and no frequency drift. The kit is a good deal more difficult to construct than any of the above kits and should only be taken on by an experienced kit builder. The circuit requires measured voltage readings to operate properly and precision winding of RF chokes wherein leaving out one turn could mess up the output power big time! Range is up to 1/4 mile or more depending upon antenna, location, and conditions. This kit is also jumper settable to 1 watt of power where regulations allow, which may be enough power to cover an entire small town or village. The kit is about $100. It is tough to build but may be worth it if you know what you are doing. Assemble this SLOWLY! For the price, you should consider purchasing the more reliable and easier to assemble SSTRAN AMT3000 from www.sstran.com.
Radio Communications Laboratory RC2545T
Not a kit! This powerful FM transmitter comes fully assembled and ready to go. It uses VCO tuning and comes preset to a frequency of 95mhz. If that frequency is not vacant in your area, than I do NOT recommend this transmitter. Although you "can" change the frequency by adjusting the trimmer capacitor closest to the AUDIO jack, I do NOT recommend doing so as any major adjustment WILL BLOW THE FINAL TRANSISTOR on this circuit. If 95mhz is clear in your area, this unit works GREAT and has a typical range of 1 to 2 miles using just a simple twin-telescopic ariel or 1/4 wave groundplane antenna, perfect for a small town or village Christian radio station. The transmitter puts out around 500mw of power, which may exceed FCC power limits in the Unted States when hooked to a good antenna, so be warned! For the price of around $20, it is truely unbeatable except for the fact that the product is from India and the shipping on it is another $25. This being one of the only drawbacks!
Radio Communications Laboratory RC2547T
A true little jewel and a MUST HAVE for any serious short range FM station. It is a PLL Synthesized version of the above and has rock-solid frequency ability. It is tunable in 1mhz steps throughout the entire FM Band. Possible frequencies are 87.9, 88.9, 89.9, 90.9, 91.9. 92.9, 93.9, 94.9, 95.9, 96.9, 97.9, 98.9, 99.9, 100.9, 101.9, 102.9, 103.9, 104.9, 105.9, 106.9, and 107.9mhz. Power is settable between 2mw and just over 600mw by a switch that turns the final amplifier stage on and off. Range is around 2 miles with a 1/4 or 1/2 wavelength groundplane antenna, making a perfectly awesome short range station which will cover small towns or villages. Truely better than any Ramsey kit for the money! Costs only about $50, and like before, it comes from India so you pay $25 shipping and handling. You might as well have them throw in a RC2545T while you're at it and save on the postage! Can and will exceed FCC power limits when used with a good antenna, so be warned!
Wild Planet Radio DJ
There have been numerous posts on online forums regarding this inexpensive kids' toy which is no longer in production. In my opinion it is one of the most poorly designed AM transmitters ever. Careful modifications of this unit can extend the range a little bit farther than it was intended to transmit out of the box. I myself have attempted to modify one of these toys in accordance with online postings, only to be somewhat dissappointed. Yes, you can get more power out of this rig by adjusting the antenna tuning capacitor and by replacing the antenna with a better one. Adjusting the antenna trimmer capacitor will about quadruple the power of this "kit", however, condisering that the original factory power setting is only about 1.3 miliwatts, the final power will still be less than 7 milliwatts. At this power level, the maximum range will be about 100 yards with a decent antenna system, whoopee! While this is somewhat impressive for a toy intended to entertain 6 year olds, it is by no means a good transmitter for your neighborhood or talking billboard. It is not even adequate for use as a system to assist the hard at hearing in your church auditorium because it only runs off of batteries. If you try to hook up a wal-wart power adapter to the unit, it will fry the CMOS chips inside, thus destroying the unit! I even tried a 5v regulated power supply (the unit is rated 6v maximum) and it still destroyed the unit. Not a good investment! Also, the operating frequency is set to 1610khz and cannot be changed without replacing the crystal in the main oscillator. If you feel that you must "experiment" with this rig, check your local thrift stores. I have found them working for $7 at such places. You may want to desolder the CMOS chips and solder chip sockets into the board. This way you can just replace the chips when you end up destroying the thing!
Vectronics VEC-1290K AM Broadcast Transmitter
Of all the kits I have assembled so far, this is by far one of the best of the transmitters for range, stability, and audio quality. This transmitter absolutely runs circles around the Ramsey AM-1 and AM-25 transmitters. The kit is available from http://www.vectronics.com/ and costs $29.95. The frequency ranges are jumper settable and the carrier frequency is produced digitally. The trimmer caps help set the actual frequency of operation as well as antenna matching. Most kits in this price rangs do not have a way to match the transmitter to the antenna internaly. This one does!! Range is typically from 50 feet to 1/4 mile dependent upon antenna and grounding system used. The kit specifies that the antenna supplied (a 6-foot piece of wire) is perfectly matched to the set and use of any other antenna will result in an impossible match. This statement is in fact totally FALSE. It has been proven in operation that this transmitter will support up to a 12 foot antenna (10 foot maximum for "part 15" operation) which includes most short antenna systems mentioned elsewhere online.
Chaney Electronics AM Broadcaster
A great introductory AM transmitter and an exceptional value. Priced at just $8 from Chaney Electronics, this 2-stage AM transmitter is both easy to assemble and a good preformer. The transmitter is designed to operate off of a 9v battery, however, provides much better range when used with a 12V regulated poser supply and a good ground. The unit is small enough to fit within a piece of average sized PVC pipe, making it ideal for housing at the same site as the antenna per "Part 15" optimum performance quoe. Also small enough to be mounted at the antenna site in a small weatherproof box. The only downside to this transmitter is the fact that they use a cheap trimmer capacitor for tuning, and it is near impossivble to get it on frequency. You may want to order a more heavy-duty trimmer from Mouser or Digikey at the same time you order this kt. Otherwise it is very impressive for its cost and simplicity of construction and may potentially be a good candidate for use in a low-cost neighborhood AM station. It truly has all the makings of an effective and yet very simple transmitter. Who says a transmitter must be complex in order to be good?? The guy who I bought mine from originally was selling them on Ebay and I uncanningly ended up paying $29.99 for mine. It wasn't until much later that I found them for $8 plus s&h from the manufacturer! The guy on Ebay did however mention that a few buyers claimed to get 1 mile of coverage from their kit. I do not know how true this statement is however!!
Li'L 7 AM Transmitter
A tube transmitter "kit" available on Phil's Old Radios website. This transmitter is easy to assemble and is a great introduction to tube-type broadcaster circuits. I built mine in a few evenings and it only costed me about $30 to assemble. It transmits across the room pretty decently but it needs quite a bit of audio input in order to modulate the signal fully. When hooked to a stereo amplifier on high volume, it works quite nicely. You will also want a good ground connection and a good antenna with this small transmitter. With the proper antenna and ground connection, this little transmitter puts out quite an impressive signal making it great for use in church auditoriums to aid the hard at hearing., and with a decent antenna would probably make a good neighborhood AM station! Find complete instructions on how to assemble one of these yourself at http://www.antiqueradio.org/transmitter.htm
Velleman P 1771 FM Oscillator Transmitter Kit
You may have seen one of these before, in fact, if you are at all familiar with FM transmitter kits, you probably have seen this one as it is available on the http://www.jameco.com/ website as well as from smaller and lesser-known dealers such as http://www.allelectronics.com/ . The kit sells for about $12 at either site and I must say that it is not too bad. For those of us who do not need the stereo capability of the Ramsey FM-10a or FM-25, this is the answer. The one I built easily covers 200 ft when powered by a 12V regulated power supply and fed into a 1/4 wave dipole antenna via 50 ohm coax cable.. I have heard that it can put out anywhere from 20 to 100 miliwatts depending on what kind of a power supply you use. One guy online said that he hooked his up to a 15 volt bench power supply and got his to go 1/8 mile with a 1/2 wave groundplane. From what I have observed from mine, I must say that this would most likely work depending upon the antenna and location of the transmitter. Be careful if you try this because you might burn the thing up! This kit comes highly recommended as an ideal first kit for ease of construction. If nothing else, buy one for a newbie to practice their soldering. They will probably find the finished product to be quite awesome and may even become hooked on radio themselves. Highly recommended for training would-be missionary radio people in RF electronics basics! With this kit, be sure to also purchase either an RCA pcb connector or F-type RF connector for easy hookup of your antenna cable.
QKits Kit #171 250mw FM Linear Amplifier Kit
This kit is available from http://www.qkits.com/, another kit producer which is similar to Ramsey as far as products are concerned. For just 14.99, you can buy this kit and assemble an FM linear amplifier capable of boosting the power of your FM-10a or FM-25 kit up to 250mw. Into a decent antenna, it should give you at least 1/2 mile of solid coverage. I tried hooking this up to my FM Stereo Generator, but the generator did not put out enough RF to drive the amplifier, only enough to "switch it on". Your transmitter must be able to put out at least 7mw of power (but no more than 10mw) or this amplifier will do you little to no good. The FM-10a is a perfect match for this amplifier, as is the Velleman FM Transmitter mentioned. For further information on how to get more power out of your FM-10a transmitter kit and for plans to build a smaller and simpler (cheaper) amplifier than this, see the following website: http://www.mycal.net/old/projects/mpr/fm10faq.htm . Beware that any of these modifications could void your right to use your FM transmitter in the US or Canada due to FCC power limits.
The most simple AM transmitter ever!
And not a bad one either. With a bare minimum of parts you can build this transmitter or you can order the "kit" from http://www.scitoys.com/
for under $10. This transmitter will transmit either across the room or across the street, depending upon antenna and ground. Great for science projects or church auditorium broadcasting. Covers small college dorm buildings with a good antenna and ground. The frequency is set stably at 1000khz and stays on frequency all of the time because it uses a TTL crystal oscillator. Also makes a perfect marker generator for calibrating your AM equipment. Harmonics can be picked up at 2mhz, and so on. Not suitable for long range communications, yet can be quite useful. Not really a toy unless you are a radio geek like me!
Knight Kit AM Broadcaster
A kit from the yesteryears that is still popular even today. Allied Electronics went out of business back in the 1970's, so today's builders of this kit must do so from the original schematics. The circuit uses a 12AX7 tube for an audio preamplifier, as well as 2 50C5 tubes for the oscillator and the modulator. It rivals even the best kits available on today's market such as the fabled SSTRAN AMT3000 and the Ramsey AM-25. Schematics and parts list are available online at http://www.smecc.org/knight_kit_home_broadcasters_-_allied_electronics.htm . I am currently working on building one of my own and will post more info and pictures once I am finished with mine. General consensus amoungst builders of this kit is that with a good ground connection and a 10' antenna, this transmitter can be heard about 500 feet away in all directions. With a base loaded antenna, the range can be about 1/2 mile. Great for Part 15 AM use here in the US, or even commercial use in foreign countries using a bit longer antenna (quite a bit longer). Can't wait to get mine up and working!!!
RF Signal generators can make truly awesome AM Broadcaster circuits if modulated by an external audio source or modified to do so properly. Some operate fine as AM Braodcasters in stand-alone mode. Most are modifiable by adding a simple audio transformer to the audio input. http://oak.cats.ohiou.edu/~postr/bapix/Heath_SG.htm goes into great detail on how to modify such devices for use as high-quality AM transmitters. Also, it mentions that by shorting a 510 ohm resistor in the final stage, you can increase your output by about ten fold! I have tried this on both my old EICO RF Signal Generator, as well as my Knight Kit signal generator and the results were quite pleasing! Note that you want the old TUBE TYPE signal generators for this kind of project as the solid state ones are harder to modify. Get one today on Ebay. You can probably "bag one" for about $20 if you shop carefully and bid at the last possible second! Remember, you will probably have to beat some old-timer to the punch in order to get the best possible deal on one of these!!
PLL FM Stereo Transmitter Board 200 mw
Available from http://www.vhf-transmitter.com/ for just $65, this pre-assembled FM Stereo PLL-type transmitter is perfect for at home or Part 15 FM broadcasting usage. Average range with a simple wire antenna is about 150 meters, but is much better with a decent antenna such as a dipole or groundplane. If properly installed, there should be no reason why this setup could not cover a distance well over 1/4 mile. For Part 15 FM Broadcasting, you will want to keep the antenna short and simple or it WILL EXCEED FCC POWER LIMITS! When compared to the Ramsey FM-25, it is a better deal as far as performance, power, and price! The best part is you don't have to assemble it!!
Talking House AM Transmitter
If you don't feel like putting a kit together and you still want to take advantage of every last inch of range that the FCC will allow, then look no farther. Originally designed to sell real estate, this transmitter can do much more than just sell houses. The Talking House AM Transmitter puts out the full legal 100mw of power for part 15 AM stations and can be rigged with the included 10ft indoor wire antenna for about a 500' transmitting radius, or an external antenna can be connected to the external antenna port. If properly matched to an outdoor antenna (see whip and mast setup) the range can easily top 1/2 mile! The latest model has an input in back for live broadcasts and can be hooked right to your studio mixer. Frequency is entered digitally with no frequency drift whatsoever. Audio quality is pretty good too. Although it does not perform quite as well as a Hamilton Rangemaster or a properly tuned SSTRAN AMT-3000, the Talking House Transmitter has it where it counts, and these have been used as the main brain of many a neighborhood or church radio station! Be sure and get the latest version, the black "5 Minute" version, as this is the only version to include a "live broadcast" jack in the back of the unit for a live input. If you get one of the older ones, such as the small gray units, you will have to take them apart to modify them for live broadcast, which can be quite a headache especially when matching the audio input for a good clean sound. Trust me, I have tried to modify one of the older units and succeeded after many hours of research, only to have a less desirable unit than one of the new black "5 minute" units! These sell new from Talking House for about $400.00, but it is not uncommon to get these on Ebay for about $50 to $100 new or used. This is how I got both of mine. Try Ebay first to save the most money!
Will post other reviews when I have more time. For now, God Bless!