by SLiM6y
 P: 10 I have a simple question - but I somehow doubt there is a simple answer. 1) I would like to start a small, non-commercial, home transmitted FM Radio Station - mostly for fun and as a hobby. I have seen an 18W transmitter for a reasonable price. I live on relatively flat land in the country side with no buildings around. What is the best case scenario for distance the 18W transmitter will transmit? Is there a simple formula to use to calculate the transmission distances? I do not know the size of the antennae - but does increasing antennae size increase transmission distances or again is it not as simple as that? Thanks in advance if you have the answers. I am looking forward to knowing more! Cheers Slim
 HW Helper Sci Advisor P: 8,962 It's a combination of the transmitter and receiver antennae size and the sensitivity of the receiver. Voyager's transmitter isn't much more than 18Watts and that can be received from quite a large distance! Are there limits on the power of a transmitter at that frequency in your location?
P: 10

Thanks you two...

Firstly, I am in Australia and very aware of the laws - I release it is possible I could be some sort of Pirate Radio - but, I believe there is a lower frequency that is capable of being used without license (I am still checking into that).

The system I have looked at has these specifications listed:

Specification:

Frequency range: 88MHz ~ 108 MHz
Tuning Step: 100kHz
Transmit Power: 18 watts
Stability of Frequency: ±10ppm?-10?~+50??
Ripple or harmonic waves: <= -60dB
Modulate Frequency error:<=75KHz?100%?
Freq. Response: 100~15000Hz
Antenna Connector: BNC type
Audio Input Connector: 3.5mm headphone connector
Power Supply: 12V DC (The current load of power supply should over 4A)

Unfortunately I don't understand a lot of these descriptives - but I understand what it does :)

I really appreciate all your help with this, I am actually thinking of using it as a school resource as well (a school radio station - this will encourage understanding the physics of transmission for us all hehe).

Anyways, I look forward to learning more.

Thanks.
 Mentor P: 37,661 Well, in the US, those are exactly the specs for a licensed broadcast FM band transmitter. The 18W power output would be sufficient for a local area station. You can probably reliably hit about a 10km radius on flat ground, with a vertical monopole mounted 10m up a tower. You should check into getting a license for one of the frequencies (assuming that the Aussie frequencies match up with that US transmitter). It's probably pretty inexpensive for your situation. Let us know what you find out about the license possibilities.
 P: 10 Thanks again berkman... 10km is exactly how far I'd like to try and reach that covers my two main townships. I have written to the ACMA (Australian Communications and Media Authority) so I will hear back from them soon. The antennae would probably be about 4 - 6m up on my shed rooftop. If I got a 50W transmitter does that dramatically improve my signal distance?
 P: 10 It appears the law is quite simple... I have till February 6 to apply for one of three frequencies (cost of application AUD$300) then from there I can get a license from$250 (to a maximum of $2000) depending on residential area. As I live quite rural I think I should be able to get the$250. A maximum of 10W is permitted for broadcast. So I could get away with it cheap enough by the looks of things. I might become a radio station (legal) afterall! A new question though: Assuming someone (not me of course) decided to start a pirate radio station and used the airwaves illegally. Let's assume no one ever complained about it. Could the broadcasting agency locate you? Let's say someone did complain... How then do the broadcasting agencies locate you. Do they really have a nerdmobile with a satalite dish trying to home in on a broadcasting frequency strength?
 P: 10 HAHA... That's cool berkman. Well, my plan isn't to be a pirate radio station - but a fully legit one. I have now under a month to get my application in! It will be very interesting either way. I appreciate your knowledge on this subject. And even at the least, I plan on incorporating transmission etc into lessons during the 'waves' part of the physics course at my local school. I think the students will gain a lot out of it and seeing an actual transmitter will also encourage them greatly. Well, once again, thanks for all your knowledge. It's very much appreciated!
Mentor
P: 37,661
 Quote by berkeman But in the end, it turned out to be hidden inside of a little stuffed bird that looked like it was sleeping on a tree limb about 10 feet off the ground. That took a good long while to hunt down!
BTW, I do have to say that I went on this T-Hunt with one of my Assistant Emergency Coordinators, and she found the transmitter about 10 minutes before I did. She was extremely happy about that part!
HW Helper
P: 1,325
 Quote by berkeman BTW, I do have to say that I went on this T-Hunt with one of my Assistant Emergency Coordinators, and she found the transmitter about 10 minutes before I did. She was extremely happy about that part!
Were you using a 4-el phased array on your foxhunt-mobile? I learned about the usefulness of attenuators during RDF expeditions. I picked up a commercial grade one for $5 from box under a table, at a hamfest one time. I replaced the burned out components and it works like a charm. It comes in handy when you get in close to a transmitter and the signal appears to be coming from everywhere. You can then, knock down the signal by switching in varying amounts of attenuation, to the point where your directional antenna works again. SLiM6Y You mention you're allowed a maximum of 10W for your (FM) broadcast station. You may want to find out how much peak envelope power (or PEP), you're allowed. In other words if you transmit 10W and your antenna has a gain of 3dB, your PEP is close to 20W. An antenna with 6dB of gain, your PEP goes up to 40W. I've seen some collinear antenna arrays with 12db of gain. In this example that would translate to 160W (PEP). Mentor P: 37,661  Quote by Ouabache Were you using a 4-el phased array on your foxhunt-mobile? I learned about the usefulness of attenuators during RDF expeditions. I picked up a commercial grade one for$5 from box under a table, at a hamfest one time. I replaced the burned out components and it works like a charm. It comes in handy when you get in close to a transmitter and the signal appears to be coming from everywhere. You can then, knock down the signal by switching in varying amounts of attenuation, to the point where your directional antenna works again.
Hi Ouabache! I was hoping that you would see this thread. We were just using our handheld 2m transceivers and using body fade. Other T-Hunters in the group had all kinds of directional antennas and attenuator boxes, but my AEC and I were bare bones. It was a walking hunt starting at the convention center, and we had to deal with multipath reflections off of other buildings and chain-link fences, etc.

The closest we got to attenuators was when I bummed a paper clip off of person at a hotel front desk, and I cut it into various length small sections for my AEC and me to use for way-off-resonance antenna stubs for our HTs. When we got near the fox (or bird in this case), we just used the open SMA connectors for our antennas, with no antenna at all.

A directional antenna and switchable attenuation would have made that hunt a lot easier! But it was still fun, and we learned a lot about how 2m radio propagates in areas like that.
 HW Helper P: 6,774 From what I understand, the FM frequency range you quoted is line of site, so curvature of the Earth is an issue. Distance is a function of how high the transmitting antenna is, combined with sufficient power to receive at the desired range.
 P: 2 I am in need of help with the same question of this original post. I am trying to find out how to calculate the estimated broadcast range of both FM and AM radio stations. I have all of the information that I can imagine necessary to calculate this considering I am pulling some of the data directly from the FCC website. Can anyone help me in learning how to calculate the broadcast range of both FM and AM radio stations? Thank you!
Mentor
P: 37,661
 Quote by drewski22785 I am in need of help with the same question of this original post. I am trying to find out how to calculate the estimated broadcast range of both FM and AM radio stations. I have all of the information that I can imagine necessary to calculate this considering I am pulling some of the data directly from the FCC website. Can anyone help me in learning how to calculate the broadcast range of both FM and AM radio stations? Thank you!
Ignoring multipath issues, you should be able to calculate it based on transmit power, TX antenna gain in azimuth, power decrease with distance (what is it?), and receive sensitivity of the RX device. What equations have you been starting to work with so far?
 P: 2 I have not been working with any formulas to this point. I did go through my physics book from college (i took the class about 3 years ago) and found information on calculating wave lengths and such but didnt think they were completely relevant. For starters, the calculations were not specific on radio waves and more directed toward light waves or general wave length calculation. They as well did not take into account factors including line of sight, penetration, transmission power and other areas I felt important. At this point I believe i am lacking any relevant formulas or calculations. I can assure I do have the calculus and physics background to be able to use the necessary formulas. Thank you for your reply!

 Related Discussions Introductory Physics Homework 1 Electrical Engineering 9 Electrical Engineering 8