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I have a small 5 watt FM Transmitter I am experimenting with occasionally. I am using about 70′ of RG213 Coax, and My 1/4 wave antenna is mounted on a 20′ pole on the side of my one story house. The other +/- 50′ is lying on the ground (lawn, not electrical) I am only getting about 1 mile of solid signal. My antenna is lightly bent and crooked, but should I be achieving greater range. Or Do I need a dipole antenna? Could anyone help me?
Have a great day!
Travis
Total posts : 45366That does not sound like a good idea to me.
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Total posts : 45366
Total posts : 45366Well, yes. 5 watts into a quarter wave should do better than that. Even lightly bent. Something would definitely seem to be wrong there.
But.. 5 watts is a long ways from part15 operation? You’re a good guy Travis, nobody here wants you to get in trouble.
Daniel
Total posts : 45366Hey Travis,
I know the temptation to get more range is great but like the others said you don’t want to get in trouble. If I was you I would go back to setting up you sstran. I get good range with mine on a 25ft tower which if you spent some time experimenting you should get a good range. You can see my setup and range at http://www.freewebs.com/underdogradio and if you get the word out about your station people will come to your transmitter I have many drive by listeners who are close but not in range of my signal. Its pretty cool to see people driving by at a turtle pace or parked down the road Just to hear my station. So I would keep it legal.Brian
Total posts : 45366I appreciate all of you trying to keep me from getting in trouble, I still am mainly using my SSTran. In fact, I’m listening to it now on AM 1610. But, I still need to know if having a bunch of excess coax lying in my yard is causing poor FM range. Also, I am still involved with my part 15 AM tx. I wouldn’t trade it for anything…. well, mabye a local 6,000 watt Class A FM station.
Travis
Total posts : 45366Travis, if your range from a “Part 15” FM setup is one mile, maybe you shouldn’t be worrying about reducing the losses in your system, including that of your coiled-up coax.
Maybe you should be worried about how to increase those losses, so as to reduce the risk of FCC detection and a possible NOUO?
A legal Part 15 FM setup over a line-of-sight, reflectionless path does not produce a useful signal one mile away. It falls below a useful value to all but the best FM receiver+antenna systems at about 1,000 feet away from the tx antenna (and that value is about 3 µV/m).
Sorry.
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Total posts : 45366Travis,
100′ of new RG213 coax at 100 MHz. will deliver 72% of the power into the cable to a 50 ohm load.
Neil
Total posts : 45366Quite frankly, it depends on the signal quality when looking at a 1 mile on 5 watts.
If you are getting a city-grade signal for one mile with 5 watts you are doing great.
The excess cable is a problem, on FM the cable should only be as long as you absolutely need for the run. Plus, it could affect the system impedence if it begins winding which can quickly degrade the signal. You are using good quality coax which is a plus; you just have too much of it. Coax is the loss-source in your system, it is the opposite of an amplifier, the more you have the more loss you have.
The antenna being slightly bent (or others at a bit of an angle) is of little or no consequence.
From time-to-time I use a 5 watt t-mitter for event broadcasting and a good wide-band signal is only going to give you so much coverage.
Regards,
Total posts : 45366hello
i saw your comment
i want to ask you a question
i have a 15W amp into a single tuned dipole about 8m off the ground.
i am getting less than a mile with it. I have 17m of standard RG58 coax. do you think upgrading to RG213 coax will help with the range?thanks’
tim
Total posts : 45366The RG 213 will help a bit, but the difference won’t be what you’re looking for.
At 100MHz, RG58 will lose about 5 dB per 100 feet, or 2.5 dB for 17 meters. RG 213 will lose about 2.5 dB per 100 feet, or 1.25 dB for you.
15 Watts would be expected to get out over 5 miles at 25 feet HAAT with a properly tuned antenna, so you would really benefit from checking your SWR, connectors, etc. A 5/8th wave vertical would probably give better coverage than the dipole, too.
I’d be inclined to check SWR with the RG58 and see if that gets you going in the right direction before investing in 50 feet of RG213.
If you were to locate your transmitter at the base of the tower you could also cut your losses in half without buying any cable.
Remember to be polite to the FCC when they drop by and make sure you’ve got some extra $$$ handy for the NAL. Once you get that 15 watts performing properly a field agent will be along in no time. He or she will also measure your field strength for you, so you’ll get an idea of your efficiency, too
Experimental broadcasting for a better tomorrow!
Total posts : 45366Tim wrote: I have a 15W amp into a single tuned dipole about 8m off the ground. I am getting less than a mile with it. I have 17m of standard RG58 coax. do you think upgrading to RG213 coax will help with the range?
Hi, Tim –
It is a “given” that systems compliant with Part 15 FM as defined by the FCC may radiate no more than 250 microvolts per meter as measured 3 meters in any direction from the transmit antenna.
If your goal is to meet Part 15 FM, then you may use whatever combination of transmitter power, cable loss, and antenna gain as produces that peak field strength at that distance.
If FCC Rules are of no concern to you then anything you do to increase your radiated power will improve your distant field strength in that direction (other things equal).
BUT… a reality of physics is that about 11.43 nanowatts (0.000 000 01143 watts) radiated from a 1/2-wave dipole will produce this maximum Part 15 FM field.
Obviously, even if your cable loss meant that you radiated only 1 watt from a tuned dipole, that would still produce fields far, far in excess of the legal limit.
Even a power level of 1 milliwatt radiated by a 1/2-wave dipole will produce fields.that are non-compliant with FCC Part 15 FM.
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