How to boost FM radio signal inside a steel building

[SharpyWarpy]

My son-in-law listens to FM radio at work inside a steel building and the reception is poor. He uses a pocket radio with earbuds. If I put a cheap plastic T shaped FM antenna outside and run the wires inside what can I use to boost the signal from there so his radio can pick it up? His music is important to him, also it helps mask the noise of the machinery. Thanks ahead of time.

[jcx]

It is a bad idea to use low isolation earbuds and turn up the music to mask noise

get decent sound isolation 1st with IEM or closed back full sized headphones

http://headwize.com/articles/hearing_art.htm

if the noise level exceeds OSHA specs the employer MUST provide ear protection or reduce the exposure

finding a FM radio with antenna connection screws on the back could be a challenge today but they do exist but won't be portable

leaky feeder systems exist for difficult RF transmission environments

today it would be much easier to use a mp3 player or a FM microphone style transmitter fed by a PC audio out streaming a internet radio station

[SharpyWarpy]

Originally posted by jcx
It is a bad idea to use low isolation earbuds and turn up the music to mask noise

get decent sound isolation 1st with IEM or closed back full sized headphones

http://headwize.com/articles/hearing_art.htm

if the noise level exceeds OSHA specs the employer MUST provide ear protection or reduce the exposure

finding a FM radio with antenna connection screws on the back could be a challenge today but they do exist but won't be portable

leaky feeder systems exist for difficult RF transmission environments

today it would be much easier to use a mp3 player or a FM microphone style transmitter fed by a PC audio out streaming a internet radio station

He's not turning up the music to mask the noise, I'm just saying having the earbuds in there helps. Like earplugs?
There are no computers in the work environment, certainly none with an internet connection. Only those that run the CNC equipment and they are not PCs.
He has an mp3 player but he tires of listening to the same thing and wants radio, too.

[gareth]

Hi,
If you know what you are doing inside the fm radio then you could increase the'Q' of the notch filter that accepts the incoming transmission.
Thanks
Gareth

[SharpyWarpy]

Originally posted by gareth
Hi,
If you know what you are doing inside the fm radio then you could increase the'Q' of the notch filter that accepts the incoming transmission.
Thanks
Gareth

Thanks for that, gareth, but I don't have the slightest idea what I would be doing inside an FM radio. My knowledge of electronics is not that good yet. Would such an adjustment help bring in some of the strongest stations? That's all he wants, I think. Just the closest stations.
What I'm wondering is if I connected an FM radio to the outside antenna and put some kind of transmitter -- like the ones used to transmit from player to car radio, only stronger -- on there would that work?

[gareth]

Hi,
Well if you were going to use an FM transmitter of the type you suggest then it would need to be pretty good.
By the sounds of things you work in a machine shop built in a steel frame building. Steel frame buildings like to 'bounce' the signal around and thus dissipating quality signal, basically.
An external aerial/antennae feeding your sons radio would be the ideal solution but is probably impractical due to the obvious hazards in your workplace. Theres no point in wrapping your nearest and dearest around the lathe is there?? ;-)
So, you could try what you yourself have suggested but I would try to get a good quality transmitter (to send onto your sons radio), I say this because I use an iPod in the car. The radio transmitter that I use(d) was probably about the best that was reasonably priced (£30) but I found that it wasn't very high output and was prone very prone to external interference, e.g. the beloved speed camera (not) and traffic lights etc. When the transmitter encountered these then I basically had no reception and this always seemed to coincide with your favourite record which was completely annoying.
Meanwhile back at the ranch, the machine shop you work in is probably prone to emmitting RF noise an d by using the transmitter you mention I feel that you may be disappointed but maybe you will be able to get a better design than I had and everything will be fine.

[SharpyWarpy]

My nephew had the same problem as you with the FM transmitter in his truck, I sent him a headphone amplifier to use between the player and the FM transmitter and it works beautifully now. You have to adjust the volume back and forth between the radio and the player to eliminate distortion but once that's done it's much better.
Back to the shop-transmitter thing, what do you think about this:
http://sound.westhost.com/project54.htm

[gareth]

It certainly seems OK and with transmission up to several hundred metres, excellent. If you are confident then go for it, Rod has some good designs and can wholeheartedly be recommended.
Note what he says about the circuit self-oscillating though, you want to get it right. He even offers design for an RF probe that can detect the oscillations in conjunction with a scope, sounds good. Also, as Rod states, you need to get the inductors right aswell, crucial (in combination with the capacitors) for good operation.
Again, if you feel confident you have nothing to lose, and besides radio is an excellent 'introduction' into electronics.
Thanks
Gareth

[SharpyWarpy]

Will I need to build two of these for stereo? Also the article says I will need a pre-emphasis circuit, I'm assuming for my purposes the line circuit. Do I need to build one of each for each audio signal, left and right?
Would I be able to run a coax from the outside antenna to a radio set close to where he works and use one of those small transmitters from there? Would this require an antenna booster?

[unclejed613]

a good passive way to get better reception inside the building would be to have a high gain antenna outside the building and connect it to a high gain fm antenna inside the building, a pair of dipoles would also work, but not as well, but dipoles are easily built.