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Wireless Music Transmitter for an Apartment?

R

Robert Bass

Question guys...

Last summer I moved to a new apartment complex. My unit is about 998 square feet (think small house sized). In one of the bedrooms, I set up all my audio and computer gear. What I am looking for now, is a decent wireless audio transmitter / intercom type system to route audio through the apartment. The transmitter needs to have some sort of line input option, such as stereo RCA jacks.

I am aware of USB devices that will transmit audio from files playing direct from your PC's hard drive, but I have some external, audio processing hardware the audio goes through.

I'd like a system that is stereo, if possible.

Any ideas?

So far googling audio intercom systems is only giving me results of systems containing an AM/FM tuner, and in some cases an internal CD player.

Thanks,

R
 
Robert Bass said:
one of the bedrooms, I set up all my audio and computer gear. What I am looking for now, is a decent wireless audio transmitter / intercom type system to route audio through the apartment. The transmitter needs to have some sort of line input option, such as stereo RCA jacks.
Click to expand...

I can tell you what *not* to buy...

Made the mistake of buying a little FM stereo transmitter. It's designed to plug into the earphone jack of a MP3 player etc. and play it through the car radio. Programmable for four channels anywhere in the 88-108 band.

The power output is nearly zero. I hang the darned thing *on* the receiving antenna and it's just barely full quieting. Fresh batteries.

I've tried another model. (that has four fixed choices of 88.1/88.3/88.5/88.7) It's a bit more powerful (I can hang it on the car's rear view mirror and get a full-quieting signal) but equally useless since I have local stations on 88.3 and 88.7 & it can't override those stations' adjacent channel splash when set for 88.1 or 88.5.

There have been quite a few similar devices sold as hobby kits over the years. The power output is adequate but they don't use phased-lock loop frequency control -- and drift all over the place. As in, tune it to 103.9 when you start, and it'll have drifted down to 101-something (inevitably, under a 100kw local) by the time you drive 25 miles.

I've had a lot more luck with AM!
 
See if you can find on ebay a US Robotics "KiMA." It does exactly what you want to do. There must not have been any demand for the device, though. They are out of production.
 
For a small unit, the C Crane modulator seems to work fairly well. http://www.ccrane.com/radios/fm-transmitters/fm-transmitter.aspx

If your aspirations are more elaborate, you might consider something from NRG Kits in England. http://www.nrgkits.co.uk/

Please note that a lot of the NRG stuff is not Part 15 compliant when run at its full output. That's not to say that you can't use it in a fully complaint way, but it is easy to get carried away. For just covering a small space as you describe, a half watt transmitter running into a dummy load will probably be adequate. You wouldn’t need an antenna

The good news is the NRG designs are very clean with six pole filters on the outputs to reduce (or eliminate) interference problems. This is important, especially in a situation like an apartment house. Your next door neighbor may not appreciate hearing your personal radio station on his TV set. A lot of cheap modulators put out harmonics all over the place causing interference to other radios and TV's (as well as commercial communications) in the area.
 
You can always try Ramsey Electronics. They have several models that fall into the FCC rules and regs for non licensed operation. I own an FM 25 which I use for this same purpose. Good Luck.
 
I use a Ramsey FM-25 as well. Be sure you get the external AC supply. Otherwise it has a tendancy to go through 9v batteries. Depending where you are, finding a clear frequency may be difficult.

I also have a 900 Mhz 'remote speaker' system. I connect what would normally be the speaker output jack to the remote stereo input. Don't have any interference problems going through 3-4 walls from transmitter to receiver. Try staying with 900 MHz. Better penetration than 2.4 or 5.8 GHz.

Modern 'boom boxes' don't have external inputs so the FM solution generally works better.
 
RF Man said:
You can always try Ramsey Electronics. They have several models that fall into the FCC rules and regs for non licensed operation. I own an FM 25
Click to expand...

Part 15 FM Rules say nothing about the transmitter power rating, only that the highest field strength 3 meters in any direction from the transmit antenna cannot exceed 250 microvolts per meter.

But even a simple 1/2-wave dipole needs to radiate only about 11.4 nanowatts (0.0000000114 watts) to generate the maximum legal Part 15 field -- and not much more is needed even from a simple, short whip antenna.

So a transmitter rated for 0.01, 0.025 or 0.035 watts (ie, 10, 25 or 35 milliwatts) is massively overpowered for this application. The FCC has cited operators for using such power based on the excess field strength they generate.

This info is offered to inform, not to intimidate. Each person is free to choose how s/he wishes to operate.
//
 
While I appreciate the suggestions thus far, I was thinking more along the lines of some sort of digital transmission system, say in the 900 MHz operating range. Sort of like a digital microwave STL, if you will, but not quite that powerful.

The FM band is pretty crowded in this market (Dallas), including KNTU on 88.1 and KEOM on 88.5. Also, it is not clear to me if some of these FM transmitters being suggested, include the pre-emphasis curve. The processing gear I have, that I intend to use, does not have pre-emphasis generation.

Please keep the suggestions coming. :)

Thanks,

R
 
Robert Bass said:
Also, it is not clear to me if some of these FM transmitters being suggested, include the pre-emphasis curve. The processing gear I have, that I intend to use, does not have pre-emphasis generation.
Click to expand...
Hey Robert,

The NRG stuff does have standard and selectable 50 and 75 us pre-emphasis., but you can defeat it if you wish. I'm fairly sure the C. Crane has 75 us pre-emphasis too, but it is not defeatable. If you want to go 900 MHz, why not just go to Best Buy and pick up a pair of wireless speakers? RCA, Pioneer and a lot of others offer these things at fairly reasonable prices.
 
Chuck said:
If you want to go 900 MHz, why not just go to Best Buy and pick up a pair of wireless speakers? RCA, Pioneer and a lot of others offer these things at fairly reasonable prices.
Click to expand...

Thanks for the tip! I'll check that out.

R
 
RF Man said:
You can always try Ramsey Electronics. They have several models that fall into the FCC rules and regs for non licensed operation. I own an FM 25 which I use for this same purpose. Good Luck.
Click to expand...

A friend of mine (2 way radio guy) used a Ramsey for his apartment and had great luck with it. He really liked DXing AM at night and had his receiver in the bedroom. Used a Ramsey and listened to it anywhere around his apartment with a walkman.
 
If you can find them, buy these:

They're on closeout at Radio Shack but may be available at a local store. There are links to check by zip code on each page.

By the way, the speakers sound GREAT especially if you use them without the built in 50 watt amplifier (think 250.00/pair audiophile mini monitors). Also, you can remove the receiver board from both the speaker and the amplifier, hook up RCA jacks (via a cord) and have a 50 watt stereo amp for 15 dollars or a very decent sounding pair of amplifed speakers for 30 dollars. BUT..the amplifiers (it's the same amp in both the stand alone and the speakers) are good but not great. The speakers thenselves, ARE great! I use mine with a 60 watt/channel Adcom amp.

Speakers: http://www.radioshack.com/product/i...origkw=accurian&kw=accurian&parentPage=search

Stand alone amplifier: http://www.radioshack.com/product/i...origkw=accurian&kw=accurian&parentPage=search

AC transmitter: http://www.radioshack.com/product/i...origkw=accurian&kw=accurian&parentPage=search
 
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