Anybody know anything about FM transmitters?

BatteryCharger · Jan 18, 2006

I have several nice sounding stereos thoughout my house, and I was thinking how nice it would be to listen to the same thing at the same time on all of them. Since they all have an FM radio, I was thinking an FM transmitter might be a good way to do this.

Anybody know anything about FM transmitters? I was thinking about something like this: http://www.electronickits.com/kit/complete/radi/ck301.htm

What kind of real life range could I expect to get with that? Would it work well through walls in a house? Would the sound quality be as good as a normal radio station?

turbodog · Jan 18, 2006

Run away!

I've had 3-4 transmitters through the years.

Expect a usable range of *maybe* 10 feet at the power level it indicates.

Expect some hum/static/etc also.

I got the same result will all transmitters across a variety of receivers.

greg_in_canada · Jan 18, 2006

I recently got an iPod and have been reading about FM transmitters for use in my car.
This one http://www.ccrane.com/radios/fm-transmitters/fm-transmitter.aspx got some good mention on macrumors.com forums or ilounge.com forums (can't remember which).

Here's one thread on it: http://forums.macrumors.com/showthread.php?t=27757&highlight=ccrane

Greg

Mike Painter · Jan 18, 2006

The sound quality will be a function of the design and usually related to the cost.
There are other solutions that would probably give you better sound but cost a lot more. For casual listening this will probably be fine.
The power level is low enough but you want to make sure that there is a good clear channel that you can transmit on and make sure that the tuner will not drift after warming up.
It should work through out a hose with no problem. Antenna lenght and orientation will help a bit if it does not, however you want to make sure that you are not broadcasting outside the house, especially if this does not lock in the frequency.

On the other hand you might want to Google "Pirate radio"

turbodog · Jan 18, 2006

In the car, reception can be better or worse. It depends on where your antenna is located.

Also, you need a completely blank station to transmit on. The least little signal will give you pops and static on the receiver.

It's marginal at best.

whiskypapa3 · Jan 18, 2006

If you are comfortable with kits check these out;

http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=FM10C

For a rock stable semi-pro grade go for---

http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=FM25B

Lasernerd · Jan 18, 2006

whiskypapa3 is right on the money this unit is awesome I have been transmitting with this unit for acouple of years it works great !!

http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=FM25B

PhotonWrangler · Jan 18, 2006

I've also used the Ramsey FM25 and it's very stable. If you buy one from someplace other than Ramsey though, make sure it's the FM25B. The original FM25 had an issue with the power supply electrolytics going south and producing hum.

BatteryCharger · Jan 18, 2006

greg_in_canada said:
This one http://www.ccrane.com/radios/fm-transmitters/fm-transmitter.aspx got some good mention on macrumors.com forums or ilounge.com forums (can't remember which).

Here's one thread on it: http://forums.macrumors.com/showthread.php?t=27757&highlight=ccrane

This one looks pretty good as far as low power transmitters go. I don't really want to spend much more than $50 on this. I'm fine with the kits so long as I can buy them pre assembled.

Is there any way to increase the output of this transmitter? Maybe a bigger or different style antenna? I know it's probably dumbed down from it's fullest possibilities to make the FCC happy. Does it make any difference what station frequency you use as long as it's already quiet?

Are there any other options to do this that doesn't cost thousands? Are there any WIFI audio transmitters?

Mike Painter · Jan 18, 2006

As I said originally price = performance and for $50.00 you may not get much.
Increasing the output is not going to happen unless you can design the circuits.
The FCC is spread thin but if they do catch you it's going to cost a *LOT* of money.
Longer antennas are one choice and some colleges actually use water pipes as an antenna. They are very poor radiators but carry the signal a far greater distance. You have to be close to a pipe to recieve.
Wifi transmitters require recievers, one per radio.

MScottz · Jan 18, 2006

No matter how much you spend or how great a transmitter you buy, the *best* is still gonna sound like an fm station, whether it's a cd, md, dat or whatever type media you use.

PhotonWrangler · Jan 18, 2006

I agree with Mike. The highest allowable transmit power is 100mw (a tenth of a watt) abd any modification of an FCC Type-accepted transmitter can bring down their wrath if caught. You're far better off buying or building from a 100-mw kit that's already been approved by Fox Charlie Charlie.

The Ramsey FM-25B can get faairly close to maximum allowable transmit power legally. It also has low-pass filtering in the audio stage to filter out high-frequency CD whine from the sampling rate.

I hooked up an FM-25 with a decent compressor/limiter and the results sounded like a big time broadcast station.
:rock:

BatteryCharger · Jan 18, 2006

Mike Painter said:
As I said originally price = performance and for $50.00 you may not get much.

Well, the C.Crane transmitter is only $60 shipped and so far I've only found outstanding reviews.

I just found this one on Amazon.com:

1) Open up the box,
by removing 3 screws (one screw is in battery compartment and the other 2 are under those circular rubber feet which are adhesive and once removed can be refitted afterwards)

2) Locate the variable resistor marked VR2 on the circuit board. (For those non-technical this is like a volume control that is operated by inserting a tiny screwdriver and turning fully clockwise). Turn VR2 to the fully clockwise position.

Viola! The power output will increase by about five fold.

If you want to go even further, then

a) sit it on a grounded metallic surface, such as a metal tray to form a ground plane.

b) increase the length of the antennae to about 75 cm (29 inches) which is the correct quarter wavelength at these frequencies.

But frankly, you are unlikely to need this once you turn up the boost.
Enjoy

We can't even afford keep real criminals in jail around here, I'm not worried about a black van full of thousands of dollars of equipment and FCC officials somehow finding my driveway by accident...especially considering it would only be on a few hours a week while I'm listening to music.

whiskypapa3 · Jan 19, 2006

Your main worry isn't the FCC sniffing you out, it's some neighbor whose dog you snarled back at or who doesn't like the color of you trash cans turning you in.

Mike Painter · Jan 19, 2006

whiskypapa3 said:
Your main worry isn't the FCC sniffing you out, it's some neighbor whose dog you snarled back at or who doesn't like the color of you trash cans turning you in.

Or the real estate agents who happen to use your frequency for drive by house listings.

BatteryCharger · Jan 19, 2006

According to CCrane, this modification of their transmitter is not only FCC legal, but does not void the warranty and is recommended by them to those getting poor reception. :sssh:

Plus, all my neighbors already know I'm the last guy they want to pick a fight with. :devil:

Anybody know anything about FM transmitters?

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