Radio Transmitter Frequencies

D-Generate

Just wondering what frequencies people use for their iTrip and other small transmitters. There seems to be a lot of frequencies in use from Today FM and above. A huge variety of pirate stations are stopping me from listening to my music in my car. Help me out folks!

dogg_r_69

I use about 88.5 I do have to change sometimes depending where exactly you are (When I've gone Limerick direction) but never have to change that much

Owen

96.7 mostly.

Antenna

87.5 to 88.0 is generally clear, but unfortunately some of these small transmitters can't be set that low.

trixter

Antenna wrote:

87.5 to 88.0 is generally clear, but unfortunately some of these small transmitters can't be set that low.

most of these devices are made for a global market, so they take the smallest set of frequencies allowed. I dont know about other countries, but the US 88.1-108.1 are the FM radio stations, which increments in 200kHz steps. As such many devices that are fcc approved will not go below 88.1MHz.

88.1-98.1 is designated low power there, I have no idea if that is the same here. If it is, then you should find that there is less RF competition.

Additionally, if you have any electronics skill (and a tiny bit of mechanical skill to open and reassemble the transmitter) *MOST* of those devices have horrible antennas. The ones with a magnet that you affix to something metal in your car generally work better 'out of the box'. There are instructions on the net for some transmitters to improve range simply by making a small coil that is placed over the internal antenna. Placement of the transmitter in relation to your car antenna might help as well (which is usually outside the vehicle, so your vehicle body will attenuate the signal some, making external sources appear stronger, FM will lock onto the strongest source (relative to others), it may fade back and forth, but at any given time it will lock onto the strongest signal).

If you picture the radio signal as ripples in water, starting from the transmitter source and going out, they will generally be about 2.7 meters peak to peak in height. Your car antenna is a tiny bit of that, so it can miss some of the signal as it crests or dips above/below your car antenna. This is why sometimes when you are stopped at a light you dont get good signal from a real station, but you creep foward a few cm and it comes in clear. This is also what causes the fade in/out of other stations compared to your little transmitter.

If you can improve the antenna just a little bit the relative signal from that compared to other transmitters will be greater, and your radio will lock onto your transmitter. Placing the transmitter itself as close to the car antenna should also help. Of course if you have no competition with another station, yours always appears to be strongest, but play around with location in the car as much as is safe to do (you dont want your mp3 player to fly out the window or hit you in the face when you stop suddenly).

These are all the generic tips I can offer, short of knowing exactly what you have, how its set up, etc I cant offer more specific advice. Ultimately everything is a little bit different, and what works for one person may not for others.

Help support me in starting a boards.ie radio forum to discuss such matters radio can be fun, from getting free satellite tv (legally) to astronomy (did you know that you can hear radio signals from jupiter created naturally? many stars have radio signals a hobbiest can hear too!) to personal communication, to just the science and theory of transmitters and receivers!

Winning Hand

88.6 here, get some interference on high ground but otherwise works pretty well

D-Generate

87.9 seems to be serving me just fine now i find. No competition on that frequency I don't think.
I did the theory of telecomms and RF this year in uni but that doesn't exactly help me build the old transmitters other than the maths involved. Damn that lack of practicality!

I have the latest iTrip for the nano, http://www.griffintechnology.com/products/itripdock/

Its working a treat at the moment so no problems anymore. Cheers for the help folks!

trixter

D-Generate wrote:

87.9 seems to be serving me just fine now i find. No competition on that frequency I don't think.
I did the theory of telecomms and RF this year in uni but that doesn't exactly help me build the old transmitters other than the maths involved. Damn that lack of practicality!

I have the latest iTrip for the nano, http://www.griffintechnology.com/products/itripdock/

Its working a treat at the moment so no problems anymore. Cheers for the help folks!

http://www.binaryelysium.com/itrip_amp/ maybe that will help with building something to give you more power. Although odds are that is illegal here ... I dont know irish law that well, especially the radio laws, just the common universal law, if the government can tax it they will

There is a typo at least in that document, they state that wavelength = speed of _sound_ / frequency, which the abbreviated algorithm is speed of light not sound. The real one for the fellow geeks out there is wavelength = C/f*sqrt(E) where C is speed of light, f is frequency (in Hz) and E is the dielectric constant of the propagation medium. A vaccuum is 1.00 dry air is 1.06, sqrt(1)=1 so its often omitted. Another cheat is to use the 300M meters per second speed of light (as opposed to some other distance unit) divide by 1,000,000 and divide the frequency by the same (so express it in MHz), thus the really short and easy way is wavelength = 300/F_in_MHz, so 150MHz is 2 meters in length

Google should be able to help you find other things. http://www.chrisgunton.com/?page_id=19 shows how to expose the antenna, and I know that someone wrote an article about placing a coil (homemade out of a specific length of wire) around that antenna to dramatically improve range.

Just remember, if you break it at least you created a fashionable paperweight

daveirl

This post has been deleted.

trixter

daveirl wrote:

This post has been deleted.

hehe. I am trying to get a new forum for this type of stuff, so that it doesnt interfere with non-geek types lives Even volunteered to moderate it but havent heard anything back in about a month, so I guessed there wasnt enough perceived interest. help to push the boards.ie admins into creating such a place so that you dont have to see this stuff if you dont want to

gimmick

99.1 I use. Used always use 94.7, but some shítty knacker station is around that now in and around town.

coolmoose

i use 100.6, been working fine for ages, have to change if you hit fermoy though usually