So, first time posting, though I've lurked around the schematics a bit etc. ( I like building electronics...), so Hi All!
Anyways, I have a sudden urge to start a radio station in a particular city in the Heartland, and have been wondering about what power transmitter with what sort of antenna to get good range...
I have unfettered access to a ~150ft building, and would like to get fairly good coverage without the FCC having the urge to bust me in less than a days time. I would prefer to be able to build the transmitter myself, as I have plenty of access to components and such, (have recently built a bug transmitter...) and some electrical knowhow, but could use a little assistance when it comes to the more complex stuff as far as acronyms and certain components go...
Also, as I'd like to build my own transmitter/amplifier/stereo encoder etc. I would prefer to keep everything free of tube technology... IC's and the like are the way I'd wish to go, and if anyone would be able to point me to a good, self-explanatory (as in doesn't leave any IC numbers or resistor values etc to the imagination) design it would be appreciated...
Well that schematics section should be of some help. You can use something as simple as the BA1404 chip as an MPX generator (stereo encoder). There are a few schematics around on the internet for more complex ones built from multiple ICs and they will give much better stereo separation but problem is they aren't easy to build unless you are well experienced with radio/digital electronics building.
Building an exciter to generate the FM VHF signal isn't as easy. You can use a VFO but it's definitly not recommended because they drift badly at VHF. Digital signal generator chips are available. Take a look at some of the digital FM transmitters and you can get an idea for some PLL circuits to get on the channel you want.
For the PA section you can use an assortment of RF transistor amplifiers. You will need to boost the exciters RF output to some usable level. FETs work good for that purpose. Then simple string of transistor stages will get you to a few watts or more. Anything beyond 5 watts is going to take some detailed experience in RF electronics and you will need to filter the signal when all is built.
It's a hell of a project you are taking on. Though it's fun to homebuild your own gear I would recommend sticking to prebuilt stuff unless you're that serious. Start with building for Part 15 power levels. In other words flea power. It won't broadcast very far but is the first step to take. There are lots of Part 15 FM transmitter kits you can solder together available. Ramsey Electronics and Panaxis come to mind.
Forgot to mention, with 150ft and a good tuned antenna you probably need much less than 10 watts to cover 10+ miles! Even a single watt at that height can get some incredible range.
Post by Ozone Express Radio on Nov 8, 2010 21:42:45 GMT -6
I second the purchasing your equipment. There are some really good deals out there and building your own can be an intimidating task. I've only built a few items myself for other projects and I still have tons to learn. Its a never ending learning curve and it can get very time (and income) consuming.
If you are serious and have the time and skills then go for it though. Nothing like saying you did it yourself!
I wish I could get an antenna up 150 ft. About 30 ft is where I am at now with 25 Watts and I can easily reach 5+ miles with lots of trees, and some hills off in the distance. Once the leaves are fully down I may get more. We will see.
Post by Ozone Express Radio on Nov 10, 2010 15:46:05 GMT -6
Generally I am not an advocate of anything made in China, but as it goes, the HLLY transmitters offer a fair amount of bang for the buck and seem to last pretty well.
Others may have different opinions or experience, but I can say mine has done quite well.
If you can run an extension cord up there, use a regulated power supply and you'll be all set. Those transmitters come with a generic laptop-like power supply, but I prefer a stable regulated supply for my 13.8 volts that these units require. A good 15 AMP power supply will run you around $80-90 bucks.
You'll probably want power there anyway to run your audio equipment unless you are planning on short broadcast times. Its surprising how fast this type of equipment will eat batteries.
I have that exact transmitter and it's pretty good, but doesn't get much range with the supplied ground plane antenna. Then again, I haven't tuned mine.
amnesiac...I would highly suggest including a low pass filter for that HLLY unit. Although most of them do include one on the final, they are NOT tuned except for the center of the band (100Mhz).
In most cases they need a bit of tweaking to optimize, which would require access to a spectrum analyzer. I have 5 of these units ranging from the mere 50mW unit up to the hefty 30 watt unit and each one had different specs on the output purity...even when tuned to the same operating frequency.
These things can get you into serious trouble unless filtered properly. Lots of filter info on the web. Recommend a 7 pole minimum filter for these HLLY units.
Do not use the junky 1/4 GP antenna. Build a J-Pole, or simple dipole will perform better than the 1/4 GP cheapo.
Also I agree with the height and power issue. 1-3 watts at 150' height will provide about 5-10 miles of coverage...spotty at the outer rim. Combine 2 or more dipole antennas phased about 6* on the top array and you can "bend" that signal down to the horizon and extend that fringe range out another couple miles. ARRL Antenna handbook is a must and filled with info on doing this.
Good Luck!
RFB
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
Post by Ozone Express Radio on May 14, 2011 20:14:37 GMT -6
Good info regarding the HLLY units.
They also like to interfere with TV broadcasts on analog channel 6. Probably not a huge issue given the switch to digital if you don't have anyone on that frequency in your area, but some sound still resides there, and if you step on it, you will get noticed.
An LPF is a must on any transmitter, no matter the claim of a built-in, etc. Its too much of a chance to take not filtering the output.
I have, (had) a Chinese 15 watt transmitter that I ran for twelve hours a day for about a year. It ran cool into a quarter plane antenna and I had a perfect signal at 3 miles, an acceptable signal at 5 miles and heard my signal sitting in an Offce Depot parking lot more than 10 miles away. The transmitter had excellent frequency response and unbelievable stereo separation. I have a friend that builds, (illegal) linear transmitters. He checked for sideband interference and harmonic frequencies. Apparently the sideband filter works. None of my neighbors reported music on their phones and not a single airplane fell out of the sky.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
