I received a few days ago finally my FM transmitter from Austria and it seems to work really good so far.
I use it with a stable power supply, a PC as audio source (Forward my radio stream) and no real antenna yet.
Also I bought a case for it, switches, cable sockets etc. which will receive hopefully soon.
The transmitter has 15-20W~ and can send good on the frequency's 80-92Mhz~, I didn't made much tests yet but a neighbour who life about 500 meters away get a clear signal on his pocket radio which seems to be a good range without any real antenna.
Now I have a few questions...
1. Is there a possibility to filter the frequency's 80-87 Mhz? Cause here in Germany the police send on such frequency's and I don't want to disturb their communication.
2. Can I boost the signal a bit with a extra device? I remember that there existed "Burners" for the radio communication (CB) is there anything I could build to get a few Watts´s more? (Amplifier)
3. What is the best Antenna for my transmitter, I have currently no real antenna for it which would increase the sending range feelable.
4. There are quite big heatsinks placed on the transmitter and the biggest one get really hot after 10 minutes, what is the maximum temperature for such electronic parts and would it be good to add a small fan for example from a PC?
5. In which lands is it between allowed to have a "pirate radio"? (That one isn't important, im just curios)
Here a picture how it look currently without a case or anything else, will post later one when it is done.
Well if it were mine I would put it in a mostly air tight case and have a few brushless type PC fans blowing air at the hottest heatsink and have the exhaust hole at the opposite end. I hope you had it connected to a dummy load when testing it or at least some kind of tuned antenna! Turning it on w/o anything attached to the antenna out or even a bad antenna will burn the thing up.
20 watts is actually a good amount of power. That's 1/4 the power of what a lot of high powered commercial stations run. I wouldn't worry about any kind of amplifier on the output at all right now if I were you. Just focus on a good antenna mounted high up and good coax cable feed with low power loss at VHF frequencies. RG8/u would be an okay choice of cable if you need something cheap to get the job done but there are better choices if you have the money. I use RG8/u here and it works great at the lower FM broadcast band frequencies.
Also it looks from the pic that your transmitter is Mono audio only correct? If so you can attach a stereo mpx box to the audio input to achieve stereo sound.
To filter your output you will need a band pass filter or at least a basic high pass filter. This is something that either needs to be built to spec. by a manufacture or made by someone who knows a bit about radio transmitter electronics. You could check ebay or something and see what pops up. As for antennas, there are many to choose from. J poles work really well and will give you a few db of boost, but even a simple dipole or 1/4 (or 5/8) wave ground plane will do well. Just make sure the antenna is designed for FM broadcasting! Check out Ramsey Electronics for some cheap easy to install ones.
Post by crashuncle on Jan 18, 2009 22:55:06 GMT -6
Thank you for your quick help
I have built everything together now and here you see how it look like.
(Front of the case with a power switch + LED) (Backside with 2xchinch input, RF out, manual power input, power supply input and fan holes) (Inside the case, yes could be prettier)
The bigger cooler looks a bit "raped" but it wasn't possible to place it in another solid way cause I had to cut board a bit so it fit in the new case. It hold very strong like that and the fan near it (5000 UPM) cool it good, it is now always only a bit warm (40°C~) everything else stay also only a bit warm.
It looks inside not perfect, but outside I think it looks pretty ok so far and there is still place to add something
I tested it and it generally "Worked" but I have a few small problems...
- The range is quite limited with a small Antenna (I tried a normal small Antenna and noticed if I make it longer the quality goes down? When I plug-in the Antenna when it is "together" then I get a clear signal and my power supply doesn't make any high strange noises)
- My stable power supply make strange noises when I add a bit longer antenna (Very high peep like sound) but it doesn't get hot, is it possible that 2A are not enough and it get a bit overloaded?
Thats it so far, the positive thing I noticed is that the Frequency is quite "clear" now since it is in a case. It send on 87.5 - 88 (Out of the house) no other frequency is affected Also the Sound quality is even on a 5.1 Sound-System very clear and no disturbing noises appear, in a car you don't even hear a difference to public stations.
I guess that I simply use a wrong Antenna, the problem is that I don't want to invest too much money in the small project currently cause I don't want to broadcast 24/7 anyway and also plan to use it in the car. What would the cheapest way for a "Broadcasting Friendly" Antenna in Germany which isn't very huge or expensive? Is there maybe even a possibility to build something myself?
Between, I hurted my finger badly when I touched RF Output (I didn't thought that it has that much power but yes, it was like holding my finger 6-7 seconds in a candle and I really don't overplay here) (See it as a warning for other free radio newbies)
Heh yeah don't touch the RF output unless you want to feel like a lighter is held over your fingers. Be lucky it was only a few watts of power or you could have really fried yourself. I once touched my AM transmitters long wire antenna while the transmitter was on trying to get the darn thing out of a tree branch and almost got nocked on my ass because of that.
You need a proper antenna for sure. With any transmitter you need a tuned antenna. In other words the antenna has to be designed for the frequency or range of frequencies to be used. Anything less is likely to kill your transmitter over time and besides that a bad antenna = bad signal and range.
The most basic form of an antenna you can build yourself is a dipole. Though you could use a whip type antenna as long it's the exact correct length and above a metal surface like a metal building or a car.
For a frequency of 90MHz for example, each part of the antenna would be right around 2.6 feet long, or 5.2 feet total. The ground connector of your coax would go to the bottom arial of the dipole and your main lead would go to the top arial section. You can use many things to make a dipole antenna, even wire as long as it's mounted to something like a PVC pipe or anything that isn't metal. Take a look on google and on that wiki page to get the idea. Dipoles are very easy to make for a beginner.
The Antenna is really a problem for me due to space problems, it should be a bit hidden so it cant be really big. (It would be awesome if it would even fit in a car)
I don't want to kill my Transmitter, but I cant find any real "tutorial" how I build such a Antenna.
I have basic technical knowledge but not much experience with "Transmitting" especially not with the FM band and I already made a Dipole like antenna for my CB-Transceiver a few years ago with the help of a "friend" but it looked totally different ... more like a normal Antenna with 2 loops.
Most stuff here is made of wood, would something like a heater which is connected with the ground work?
The Frequency itself is what I got out 88Mhz, it looks quite complicated to calculate the correct length of the Antenna. What materials do you suggest? (I heard Aluminium works good?)
What is the cheapest way to optimize my transmitter / antenna when I have build everything?
I would be thankful if I could get some help with the final step
Post by HighMountainRadio on May 21, 2018 6:02:48 GMT -6
Greetings from High Mountain Radio !
In order to determine the correct length for a 1/2 wave dipole antenna for FM broadcast, or any frequency for that matter, use this forula:
468/Frequency(MHz) The resultant figure will give you the precise length for a resonant antenna for your given operating frequency. If you divide that resultant number by 2, you will have the correct length for 1/4 wavelength per side of dipole antenna ! It's just that easy !
For instance, if you choose to broadcast on 88 MHz, then just plug in your frequency of 88 MHz into the equation and the result for 1/2 wavelength is: 5.318 feet therefore each 'leg' or 'element' of a dipole antenna would be 2.659 feet.
Figuring antenna dimensions out is really quite easy.
If I can assist you in any other area, please feel free to message me here on this forum, I'd be happy to help !
73... Spooky...
"Knowledge Is Always Made More Valuable By Sharing It With Others !" Always Remember To Be Kind ! True Greatness Often Has Very Humble Beginnings ! Help A Kid Out Today ! *** High Mountain Radio *** "Broadcasting From Somewhere High In The Remote Appalachian Mountains"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
