Powered by Invision Power Board


Forum Rules Forum Rules (Please read before posting)
  Reply to this topicStart new topicStart Poll

> Increase Fm Transmitter Output
Kanoonoo
Posted: April 18, 2011 10:47 pm
Reply to this postQuote Post


Newbie
*

Group: Members+
Posts: 2
Member No.: 34,893
Joined: April 18, 2011




K so i just recently bought a new FM transmitter for my ipod and have found it to be less than satisfactory. I wanted to open it up to see if i could add my own antenna onto it but i do not have a lot of experience with this and dont know what to look for. i have some pictures of the boards inside of my transmitter but could someone help?

Images:
http://img809.imageshack.us/g/img2103eh.jpg/

PMEmail Poster
Top
Nothing40
Posted: April 18, 2011 11:44 pm
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 3,510
Member No.: 181
Joined: October 05, 2002




Are there any numbers visible on that chip? BH141_ or something?


--------------------
"we need an e-kick-in-the-nuts button" -Colt45
PMUsers WebsiteYahoo
Top
CWB
Posted: April 19, 2011 01:26 am
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 21,216
Member No.: 15,154
Joined: May 15, 2008




ehhh ... the ic in those little units have about 10 mW output (on a good day) .

trying to connect an antenna to the output coupling/matching circuit will cause detuning and can actually make the range lower .
the signal quality sucks ... i checked it out on a spectrum analyzer and a inovonics fm signal monitor .

i have one sitting in the bone-pile i was experimenting with .
it resides somewhere near the lower level . dry.gif

if you want more range and decent signal quality google for a "license free"/"part 15" fm transmitter kit .
the specs on some of these units is pretty decent for what they are .



--------------------
"Know how to solve every problem that has been solved"
R. Feynman '88
PM
Top
Kanoonoo
Posted: April 19, 2011 04:58 pm
Reply to this postQuote Post


Newbie
*

Group: Members+
Posts: 2
Member No.: 34,893
Joined: April 18, 2011




Ok so i just realized that i DID leave out one of the sides, so here are two more photos. Thank you soo much for your replies! i dont know if this will make any difference but thank you for your advice ill look that up too.

Images:
http://img820.imageshack.us/g/img2106o.jpg/
PMEmail Poster
Top
Village Idiot
Posted: April 19, 2011 09:42 pm
Reply to this postQuote Post


Forum Addict ++
*******

Group: Trusted Members
Posts: 1,563
Member No.: 11,398
Joined: October 08, 2007




The important component is the 20 lead chip, but the part number is completely unreadable in all of the photos. If you can tell us the part number, we could probably give you a bit more info.
PM
Top
Nothing40
Posted: May 07, 2011 08:35 am
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 3,510
Member No.: 181
Joined: October 05, 2002




I got bored and managed to glean some info on this..

The 20-pin chip appears to be a "AS6002C"
Datasheet: http://maxdat.eu/_data/15=Letoltesek/Tuner...Transmitter.pdf

Okay <looks over datasheet> Pin 9 is your RF output,I can't tell where it goes from the pictures provided,but if you wanted to you could trace it out with a DMM and find out what it's connected to.
I'm going to guess it goes through a capacitor,and maybe to the ground of the audio input? No idea.

If you're handy with soldering to SMD devices,you could probably just hang a length of wire (quarter wavelength; ~30inches) off of Pin 9,and boost the range. Putting a small cap in series wouldn't hurt (0.001uf?) to block any DC that may be on Pin 9...just in case your antenna wire ever touches anything,you don't want to cause a short.

This IC looks alot like the BH1417:
http://www.datasheetcatalog.org/datasheet/rohm/bh1417f.pdf


--------------------
"we need an e-kick-in-the-nuts button" -Colt45
PMUsers WebsiteYahoo
Top
Village Idiot
Posted: May 08, 2011 01:41 am
Reply to this postQuote Post


Forum Addict ++
*******

Group: Trusted Members
Posts: 1,563
Member No.: 11,398
Joined: October 08, 2007




QUOTE (Nothing40 @ May 07, 2011 01:35 am)
The 20-pin chip appears to be a "AS6002C"

Good find on the datasheet. I tried searching a few different number combinations too, but wasn't good enough at deciphering the numbers on the chip and eventually gave up.

QUOTE (Nothing40 @ May 07, 2011 01:35 am)
Okay <looks over datasheet>  Pin 9 is your RF output,I can't tell where it goes from the pictures provided,but if you wanted to you could trace it out with a DMM and find out what it's connected to.
I'm going to guess it goes through a capacitor,and maybe to the ground of the audio input?  No idea.

If you're handy with soldering to SMD devices,you could probably just hang a length of wire (quarter wavelength; ~30inches) off of Pin 9,and boost the range.

I have an iPod to car radio adapter that uses a BH14xx, and it has the RF out connected via a small cap, back into the power cord that plugs into the cig. lighter. If the unit doesn't have a power cord, then the other option is as you said, through the audio cable. On mine, I rewired the RF output to a short length of wire. It gave a noticeable improvement, but the range was still very short. The problem is that the RF output is a high impedance. So even if you have an antenna of the correct wavelength, the RF out won't be able to drive it properly without adding some sort of buffer stage.
PM
Top
tekwiz
Posted: May 08, 2011 06:34 pm
Reply to this postQuote Post


Forum Addict ++
Group Icon

Group: Moderators
Posts: 28,711
Member No.: 5,746
Joined: July 24, 2006




QUOTE (Village Idiot @ May 07, 2011 04:41 pm)
QUOTE (Nothing40 @ May 07, 2011 01:35 am)
The 20-pin chip appears to be a "AS6002C"

Good find on the datasheet. I tried searching a few different number combinations too, but wasn't good enough at deciphering the numbers on the chip and eventually gave up.

QUOTE (Nothing40 @ May 07, 2011 01:35 am)
Okay <looks over datasheet>  Pin 9 is your RF output,I can't tell where it goes from the pictures provided,but if you wanted to you could trace it out with a DMM and find out what it's connected to.
I'm going to guess it goes through a capacitor,and maybe to the ground of the audio input?  No idea.

If you're handy with soldering to SMD devices,you could probably just hang a length of wire (quarter wavelength; ~30inches) off of Pin 9,and boost the range.

I have an iPod to car radio adapter that uses a BH14xx, and it has the RF out connected via a small cap, back into the power cord that plugs into the cig. lighter. If the unit doesn't have a power cord, then the other option is as you said, through the audio cable. On mine, I rewired the RF output to a short length of wire. It gave a noticeable improvement, but the range was still very short. The problem is that the RF output is a high impedance. So even if you have an antenna of the correct wavelength, the RF out won't be able to drive it properly without adding some sort of buffer stage.

What if the antenna were cut for high impedance? wink.gif


--------------------
Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
PMEmail Poster
Top
Village Idiot
Posted: May 09, 2011 01:04 am
Reply to this postQuote Post


Forum Addict ++
*******

Group: Trusted Members
Posts: 1,563
Member No.: 11,398
Joined: October 08, 2007




QUOTE (tekwiz @ May 08, 2011 11:34 am)
What if the antenna were cut for high impedance? wink.gif

Possibly.

The trouble is that the impedance is in the 50k range, and the signal voltage is only about 2 volts. So even with a perfect impedance match, it's still only going to be a few microwatts into the antenna. I'm not even sure how a person could build a VHF antenna with an impedance that high. You could make a matching transformer, but I expect something with that kind of impedance ratio would have a significant insertion loss. On the other hand adding a single mosfet buffer stage should be simple enough to do, and the output would be much easier to match to a 75 or 300 ohm antenna.
PM
Top
CWB
Posted: May 09, 2011 12:51 pm
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 21,216
Member No.: 15,154
Joined: May 15, 2008




hmmm ...
do the calcs for a 50K folded diplole .
the rough vision in my mind has impractical dimensions .


--------------------
"Know how to solve every problem that has been solved"
R. Feynman '88
PM
Top
tekwiz
Posted: May 09, 2011 06:36 pm
Reply to this postQuote Post


Forum Addict ++
Group Icon

Group: Moderators
Posts: 28,711
Member No.: 5,746
Joined: July 24, 2006




QUOTE (Village Idiot @ May 08, 2011 04:04 pm)
QUOTE (tekwiz @ May 08, 2011 11:34 am)
What if the antenna were cut for high impedance? wink.gif

Possibly.

The trouble is that the impedance is in the 50k range, and the signal voltage is only about 2 volts. So even with a perfect impedance match, it's still only going to be a few microwatts into the antenna. I'm not even sure how a person could build a VHF antenna with an impedance that high. You could make a matching transformer, but I expect something with that kind of impedance ratio would have a significant insertion loss. On the other hand adding a single mosfet buffer stage should be simple enough to do, and the output would be much easier to match to a 75 or 300 ohm antenna.

I'm sure it would be. In fact, I've built a couple of BJT booster amps for TV modulator boxes that used the antenna as the tuned circuit, by mounting it directly onto the transistor. Crude, but it worked. wink.gif


--------------------
Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
PMEmail Poster
Top
Nothing40
Posted: May 10, 2011 07:02 am
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 3,510
Member No.: 181
Joined: October 05, 2002




The output from one of these small transmitters won't ever be very great,but you can usually make an improvement over the stock antenna setup,with a bit of fiddling.

They aren't really suitable for (much) amplification,as the signal is fairly dirty with spurs and crap. I've done it,and it works okay,if you use a crapload of filtering between stages,and on the output to clean up as much of the crap as you can.

Even tacking on a MMIC and the few associated parts for it can give you a pretty good boost in output/range,and a lower output impedance to work with.


--------------------
"we need an e-kick-in-the-nuts button" -Colt45
PMUsers WebsiteYahoo
Top
0 User(s) are reading this topic (0 Guests and 0 Anonymous Users)
0 Members:

Topic Options Reply to this topicStart new topicStart Poll

 


:: support us ::




ElectronicsSkin by DutchDork & The-Force