hello there. i'm thinking of purchasing either a 5w or 15w FM transmitter with a good antenna. I live in quite populated suburb here, and my house is conveniently at the top of a hill which looks out over much of the suburb and neighbourhoods near by. I would definitely try to stick the antenna as high up as I can to get a better signal out to the houses below.
What I'm trying to find out is, for a good antenna with a 5w or a 15w transmitter, how far on average would they be able to broadcast out? 1km? 2km? 3km? A rough idea? How does one figure out these kind of things?
If you're on a hill overlooking neighborhoods you'd be surprised at how far the signal goes. A 5w (especially a 15w) will probably go a lot further than 1 to 3 km if nothing's in the way to block the signal. I'd go with 5w just to be safe.
as long as i could get about a 3km radius i'd be pretty happy with that. it seems the 5w transmitter is fairly capable of that, and from what I've read, the quality and position of the antenna is far more important. the higher the better.
there is a portable GP antenna included with the transmitter which I doubt is as good as the one cmradio mentioned above, but as I mentioned, I'd be able to get it in a good position as high above ground as possible. I guess I could always get a better antenna later on once I've tried it out.
If it was me I wouldn't bother putting the antenna any higher than a bit above the roof of the house. Trying to improve things by attempting to go higher is pointless if your house is on top of a hill and there is direct line of sight to the homes below. It's also a waste of time, money, and effort.
You have a great location, so take advantage of it by just going for "stealth" with the antenna. Position it so it is hard to see from casual sight by people driving by.
as i will probably end up going with a 5watt box. do you suggest a GP antenna, a colinear antenna or a J-pole.. like the ones you can buy here? --> www.jpole-antenna.com/category/amateur-radio/
The supplied GP antenna is unlike the dipole or J-pole. I'm sure you realize that the second link you provided are antennas tuned to the ham-bands, and will not work "out of the box" for you. The 6 meter version would work, but you would have to shorten it.
Are you able to build one yourself or modify the 6 meter version? Do you have a swr meter to know when the antenna is matched?
If you enter --- diy j-pole --- in a search engine many links will come up including a java script calculator that tells you what length to cut the antenna at for your needed frequency.
thank you so much for the advice links The j-pole antenna links look good. shouldn't be too hard to make something up.
For the 5watt transmitter, what's the advantage of using a j-pole over say a 1/2 wave or GP antenna? Maybe there's advantages to using the others over the j-pole? Would it be something could broadcast out a signal further than the others?
I appreciate your help everyone. I'm sorry for the all the questions.
I've also heard these jpoles require SWR metres to tune or something. Do other antennas like GP's and other dipoles require tuning as well?
i'm more than happy to purchase and make a number of different antennas just to see which gets a better result, but for example...
The GP antenna that comes with the transmitter I assume would be a plug and play affair, but when purchasing or building another better antenna to use with the transmitter, is this something that requires tuning and testing so that it doesn't damage the transmitter itself? are different antennas to a standard 5w transmitter a fairly plug and play affair?
i was either going to build one of the j-poles from the links posted above or purchase one of the following: (please feel free to modify posts if I'm not meant to post links)
i tried looking for suburban pictures on google, places that sorta look similar to my town. imagine a home on a slight hill, looking out over a town like this. like from the hills on the other side. i don't actually know where this place is though.
Yes, all antennas need an SWR meter for proper tuning in the simplest way.
You can use field strength, but if there's hidden problems, that won't show other than a cooked output transistor.
You can use the GP that came with it for now, just follow the instructions exactly... but even that should make use of an SWR meter to get the telescoping sections just right.
Several things can alter antenna SWR... frequency of operation, height, obstructions, proximity, etc.
J-poles have the added benefit of being directly grounded to the tower so that in the rare case of being struck by lightning it acts literally like a ground rod. Also they are nothing more than a pole with a small matching stub on the side so it's not so obvious to onlookers what it's purpose is. You can get away with lying and say it's a CB antenna if need be.
What's really important is gain.. I don't have the exact numbers on hand but a 5/8 wave and J-pole antenna will have substantial gain over a 1/4 wave ground plane or dipole antenna.
Most properly built J-poles will have a gain of around 6db. A basic dipole has a little less than 1db of gain. 5/8 wave antennas are a bit less gain than a J-pole.
Any of these antennas are fine for broadcasting. Of course the higher the gain of the antenna the stronger your signal will appear to be (ERP effective radiated power). Since we want to use lower powered transmitters to save on cost of design and get the most bang for the buck it's best to use the highest gain antenna one can build or buy.
There are people who swear by the J-pole antenna, but then same for the 5/8 ground plane. It's a matter of opinion. Dipoles are okay in a pinch and by far the easiest antenna to design but they aren't going to do much for getting your signal way out there.
I personally like the J-pole because they are easy to build and don't require radials making the design much simpler. It is also possible to make both these types of antennas into stacked collinear types which increase the gain even more. Problem is how much room it takes. Even a basic J-pole and 5/8 wave gp for 96MHz is around 8 feet alone.
If you wanted to you could use multiple dipoles stacked a quarter wavelength apart to increase gain much like antenna bays on large radio stations do but in my opinion it's more work than needed when you can just use a high gain antenna in the first place.
Wow darklife - thank you so much for your detailed response It is so very much appreciated.
The idea of having an antenna with a bit more gain but also not looking exactly like an FM antenna is appealing. Because I do live amongst a number of other houses, I don't want it to be standing out too much, and because I will have to mount it onto a fairly long pole on the roof to get a good line of sight, it does help.
I will look into some designs and materials for 5/8 and J-pole antennas. The J-Pole sounds good though.
You are right about trying to get as much bang for buck as possible. I'll only be using a 5watt transmitter and wanting to do roughly a 3km radius so extra gain is good.
However, does the extra gain on an antenna impact the transmitter at all? If the transmitter comes shipped with a standard GP antenna, are there any risks of using an antenna that's too powerful for a small 5watt transmitter? Or are there transmitters that should be only be used with certain antennas? Or is just a matter of different antennas for different results?