Cheating the rules legally

Hi Jason,

I hope this is on topic for your post.

When I was in college, I worked for a carrier current campus radio station. This station had a transmitter in each campus dorm and they were connected to the studio by leased phone lines...very $$$. We had little money to spare, and needed a new transmitter for a new dorm. I built one from scratch using plans in an ARRL handbook. This unit was a vacuum tube unit and the final input power was 20 watts. Because it had to load into the building power lines, it had a huge coil and capacitor and could load into about anything.

I was in a co-op engineering program where I was at work 3 months and at school 3 months. I built this on work section, and decided to try it out at my parents' home where I lived. I set it up in the back yard, strung about 20 feet of wire for an aerial (a lawyer friend of mine says "bugs have antennas and radios have aerials"), and had no ground. It loaded ok, but the range at full power was just about 1/2 mile on my pocket sized radio. I think this shows the importance of a good antenna and ground.

Back then, we didn't worry about field strength measurements, etc. All you needed to do was check that the range outside the buildings was limited and that the transmitter signal was clean. This was easy. If you had limited range and clean signals all was OK. Not necessarily Part15 compliant, but OK. An experienced tech (me) could set the transmitters without a scope. Just used a VOM and a radio. Even the licensed campus FM station would help us with remotes and let us use their record library. For those who might know the name, Myron Bennett was very nice to work with.

I got too busy with studies, work, and girls to keep working at the station. After I left, some genius decided to string a wire from one football field light post to another and connect the TX to this. Boy did they get out! They got out so well that the FCC monitoring station some 50 miles distant heard them and shut them down, carrier current and all.

After much groveling they were allowed to restart the carrier current operation. As far as I know, this station still operates today at 800KHz. on campus.

Something to consider: If Ebacherville has a school, you might consider operating a P15 station on their site. The rules are different in this situation. If it is a large campus, the field strength limits at the borders apply and not the antenna and power limits. If you get the legal field strength at the borders, it is certainly going to give you more range than the field strength limit for the rest of us which is measured at 30 meters.

Just some memories and random thoughts for you.

Neil

OK so i have been trying to figure out ways to cover a large area of say 5 miles.. frst idea, rangemasters.. expensive but should do the trick...

Even phase-locked Rangemasters will have pattern interference if their coverage areas overlap.

Second idea, multiple TX's on one antenna, it would be cheeting but its the same basic idea of multiple Rangemasters, multiple TX covering a larger area but all TX's are within guidelines set by FCC

No, because this is the electrical equivalent of applying 4X the legal Part 15 power to a large cross-section structure acting as a single radiator. So the system would not be Part 15 compliant.

Increasing radiated power by 4X only doubles field strength (other conditions equal). Probably you could get more of an improvement than that just by installing a very good radial ground system to use with a single Part 15 tx and radiator.

My other idea was wound antenna.. I have seen this on CD and other antenna.. where the antenna is actully a longer wavelength thatit phisically is by windong or looping wire and coating it down in fiber glasss after words.

Winding or looping the wire used to make a linear radiator doesn't improve its radiation efficiency. Consider that a 3-m, hollow copper pipe can be considered as an infinite number of connected rings, but it still has the same radiation resistance as a 3-m length of thin wire used as an antenna.
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Love the story about the campus, Maybe i need to open the "school of har knocks" at my house 🙂

So a rangemester will cancel each outher out in areas .. that sucks.. Screws my idea of lighting up the lacal county seat... a part 15 would not cover enough..

looks like i will have to go underground :).. If im going to break the law i might as well do it in FM.. Seriously , I wont go underground but its so tempting since the laws leave us so crippled...

Any one mess around with a long wire on the part 15 TX, just sto see how far it could get out on 100mw..

I guess many TX that were phase locked would work to cover my goal area.. if is splocht in areas then i guess it is..

Jason

I guess the reason i started this thread is i believe the part 15 rules were thought up figuring some one would run a 3 meter wire antenna and they would get a few hundread feet of range , and us part 15ers took those rules and tried to maximize what we could do with in those rules and were sitting here getting ranges up to miles instead of feet..

I just felt if we brainstormed a bit maybee we could come up with a better way of thinking..

I guess I just don't like the rules and want to push them as far as I can.. like i said i wish the FCC would give a licence for a watt for a hundread bucks i would gladly pay it every year if i could get a quality signal out many miles. I also feel if this was allowed you could run a LPAM station and make some money if you have a range with good quality that can cover a good 10,000 people.. I also think it would make the content, equipment and other related businesses flurish also.

If i can get a good quality signal out with my part 15 compliant system i have here in this tow i will be very happy, but im thinking bigger. not just my small town..

Jason

Hi Jason,

If you want to expand your AM coverage with multiple transmitters, and have read some of the posts here regarding phase enhancement/cancellation, then you know what problems you can have.

I suggest you consider this: Set up remote transmitters on different frequencies. Phase problems and synching rf and audio are gone. If you have programming that your audience wants, they will find the signals.

In my area, an university with a non-commercial FM station (I must laugh at what I just wrote....listen to them acknowledge their their business contributors!) has several translators scattered around southeastern Ohio. It takes them longer to identify these than the time they spend on music intros.

Point is, they are using different frequencies and the listeners apparently find the signals.

As far as linking to remote transmitters goes, I read somewhere where folks are using Part 15 HF transmissions somewhere around 13 MHz. I know nothing more about this, but you might want to check into it.

If you want to expand coverage with FM, you might get away with using the same frequencies for all transmitters. Check out what is known as the FM capture effect in receivers.

Neil

Yes i have contimplated the multi frequency deal.. seams confusing to me...

Now if FM were as liberal with the rules and could cover a mile or so i would go for it.. but rules basicly make it to costly... you would need a FM TX every couple blocks or so..

Jason

I once found a website for a company that markets FCC certified transmitters that are made to be sync'd together. They come is a post-like configuation with solar panels, batteries, recievers for rebroadcasting the signal and a stereo transmitter. All you do is dig a hole in the ground and plant it, move on to your next hole & plant another one. If anyone knows of the company or what the website is please post it!

They cost about $2,000 each. But considering that a new or existing FM station costs in the multi-millions, the cost of this system is quite a bit less...a lot less.