Belkin Tunecast 2 mod - Contributed by an anonymous reader

Extending the range of the Belkin Tunecast 2

DISCLAIMER: I have not done this mod, and do not support modifying the Tunecast in this way, as it may very well violate some FCC regulation somewhere. This mod should not be attempted unless you have the correct permits and information which guarantee that you are not violating any regulations. Be aware that I take no responsibility for your actions, and this article is for informational purposes only. This was contributed by an anonymous reader, and I thought it was interesting enough to post for others. Please do not email me asking for information on the author, or on how to build this mod. I have not and do not ever plan on performing this mod myself. - Jay

For my original mod, please visit HERE.

And now for the mod...the following text and information is quoted from the original source, so don't ask me how I did it or what I mean, because I don't know.


I'm always looking for a good quality FM transmitter to play my MP3's or whatever and came across the Belkin tunecast 2. This is a cool toy, the fact that it has a phase locked loop and can be tuned anywhere in the FM band with a big radio station sound. The question is how about the battery life and how far will it transmit?

They claim it lasts up to 10 hours so when putting in a new set of AAA batteries the current reads about 100 milliamps then as the batteries drain, goes up to maybe 200 milliamps then quits. Those AAA batteries are quite small and could be gone in about 4 or 5 hours but this has not been tested. Larger AA or D batteries would work much better.

Another bad thing is the 1.5 milliamp continuous current drain while it's off, which would drain the batteries if left sitting in storage in about 3 weeks. They would become totally drained and would eventually leak and ruin the unit. You must remove the batteries whenever it's not being used even if only a few days. It might as well not have a place to put the batteries with a problem like this.

There is an external power jack for automotive use marked DC input 12V 200ma, a total of 2.4 watts. Are they lying? You won't quite need a diesel generator but the battery from your Intel Centrino laptop might not be big enough. Connecting a 12V source with a meter shows it's only 41mA. Not the 200 as marked on the unit. This is still a lot of current.

The signal strength is a little lacking too and even at only 30 feet away gives fading and static. Why is the signal so week this close to the unit? The FCC says only 150uV/meter at 10 meters is allowed so I'm guessing any more power than what this has could not be FCC certified and sold at retail outlets nationwide.

Older gray colored versions of the Tunecast lose their memory settings and reset to 88.1 Mhz when power is lost. This wouldn't work while it's powered from a hard drive connector after doing a shutdown. It would need it's own AC adaptor plugged in all the time. The newer white ones are fixed.

Some good things are the phase locked loop, good sound, and the 12V input that eliminates the need for batteries.

Best of all extending the range of the Belkin tunecast 2 for better reception is possible. The following is a theoretical exercise for educational purposes only, and not a definitive solution for boosting the tunecast output power to get better reception. It cannot be offered for sale. Performing this mod might damage the device and void the FCC certification. Any FCC violations or damages that result will be at your own risk. This mod should not be attempted unless you have the technical expertise and soldering skills needed for such a project. An ESD safe surface mount soldering station and microscope are required.

The first thing to do is disassemble unit to see what's inside.

Take off battery cover.



Remove screw and pop back cover off.

Remove second screw and circuit board comes out.



You can see the blue wire is the antenna and it's wrapped with the other wires in the audio chord. This would attenuate the RF radiation so a separate antenna wire lead would make a good first mod.

This image shows the blue wire has been cut, the blue inductor at the top shorted, and where the coax is attached. When the unit is assembled, the coax can be routed out the hole where the audio cable is stored. The measured signal level is -22dbm at 107.9 MHz and -15dbm at 88.1 MHz. That's not much power if you need it to go very far. Shorting the inductor as shown increases it to about -12dbm across the band, a little less than 1/10 of a milliwatt so you don't need it when driving 50 ohms. The coax is used to drive the RF amp described here. It'll take allot of gain (at least 20db gain) to get any good range, but it's a nice stable stereo signal, and this amp will do the trick.

Here is an easy to build hand wired prototype RF amp that has up to 32 db of gain and is constructed on a piece of circuit board with ground plane on one side. The transistors are 2N5770 (similar to ECG108) and MRF515. I see these listed on RF Parts http://www.rfparts.com/mototran.html#MRF502 for 2.95 each. The coils were made with #24 wire wound around a 3/16-inch diameter screwdriver blade. This photos show a 2N5943 in place of the MRF515 which has 2db less gain and 2db less max power output but still plenty of signal for around the house and it is more plentiful. It operates on 12 volts DC at 60 milliamps.

A network analyzer shows exactly what's going on in an RF circuit and with a little tweaking of the components the hand wired amplifier is flat and has lots of gain. The filter on the output has a good flat band pass and good harmonic rejection. The filter on the output has a good flat band pass and good harmonic rejection. These plots were made with the better MRF515 output stage.







The second plot shows harmonics to be well suppressed by the filtering. Spurs seen in the third plot are present in the original un-amplified output and are probably generated by digital circuits in the BH1415 chip but are low enough not to cause any harmful interference aside from the main signal itself, and are amplified along with it. The marker reads 21.48dbm output power at the center frequency and it's good and strong in the kitchen. If there were going to be a $10,000 dollar fine or 6 months in jail, this would be the reason. Best just to stay with the original un-modified version.

Example of a complete TuneCast system with all cables attached. RF output power is about 120 milliwatts. Although not verified with this setup previous road tests have shown this much power can be heard up to 3 miles away using an outside 1/2 wave vertical transmitting antenna.