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Need help with FM transmitter "adaptation" in photo

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FMA

Nov 15, 2021
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Greetings. I understand there are ways to increase the range of a small FM transmitter. I understand that one way is to disable and/or bypass the resistor that leads to the antenna. I'm not well-versed in these things so I don't have a clue where on this circuit board those things may be. Not sure if the photo shows enough, but by any chance can you spot it?

FMAAAA.JPG
 

AnalogKid

Jun 10, 2015
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I understand there are ways to increase the range of a small FM transmitter. I understand that one way is to disable and/or bypass the resistor that leads to the antenna.
Where did you get that understanding?

And . . .

What is the original device?
What device does it transmit to?
Why do you need to increase its radiated power level?

Note - the antenna might be a pc board trace on the underside of the board.

ak
 

Audioguru

Sep 24, 2016
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You need a certified circuit, a license from your government and an allowed radio frequency to be a radio station so that you do not cause interference with other communications and other radio stations. Therefore the circuit you have has a short range to prevent the interference problems.
 

73's de Edd

Aug 21, 2015
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Sir FMA . . . . .
Well . . . . .thanks a lot . . .you DON"T even give a brand or model of this unit !
And you need more range ? So, WHAT is your present max range attainable ?

In just examining your photo, for what is able to be seen.

I am seeing the right sides wiring clutter from the Li Ion "mylar bag" battery that the unit uses . . . .
Definitely, no desire of the placement of the RF aspect of components over in that area.
Now, up at right top, we see a somewhat blasé cylindrical time base xtal, that would relate to
the U2 u/P I.C. just below it
( This unit sure ain't gonna be clocking at Superfantastophenomenostupendooutstandocategorical warp speeds ! )
That is being the brains for the unit and its basic programming is being stored in the U3 . . .24C02 eeprom.
That only leaves the 16 pin U4 ( ? are any readable ID #'s on its top ? ) as being the FM transmitter in a chip, with some probable assist / ancillary
RF discrete components being hidden in that totally non viewable area, just to its left.
But, in "reading the board" I would be most suspect of FM RF output to be from its pin # 16 to that 330 Ω load resistor to board ground plane.


73's de Edd . . . . .

Weight Watchers . . . . .
I ate salad for dinner. . . . . mostly just croutons & tomatoes . . . really just one big round crouton covered with tomato sauce and cheese.
FINE, it was a pizza . . . . . . ALL RIGHT ALREADY ! . . . . . I ATE A PIZZA !
 
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FMA

Nov 15, 2021
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Thanks, everybody for the replies. To answer your questions, the original device is a generic mini FM transmitter much like this one: https://www.aliexpress.com/item/32659548233.html

Here are some better photos of the front and the back (not much there, hidden by LCD screen?) Does that help in maybe spotting the "antenna" such as it is and the resistor leading to the antenna?FMF.JPG


FMB.JPG
 

Harald Kapp

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I understand that one way is to disable and/or bypass the resistor that leads to the antenna.
This resistor wouldn't be there to limit the power, it would be there to match the impedance of transmitter, trace and antenna.. Removing this resistor will not improve output power. On the contrary: a mismatch between transmitter and antenna will reduce the power output.
 

FMA

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Could you tell me whether this video is inaccurate then?

This resistor wouldn't be there to limit the power, it would be there to match the impedance of transmitter, trace and antenna.. Removing this resistor will not improve output power. On the contrary: a mismatch between transmitter and antenna will reduce the power output.
 

Audioguru

Sep 24, 2016
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The Englishman "woked" very far away so the modification made the output level be much higher and be very illegal.
Of course, the video might be a fake so maybe not.

The range might be "fauthah ovah wotah"
Sorry for the severe English accent..
 

FMA

Nov 15, 2021
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Thank you, but the question is whether the modification makes sense or not -- specifically, bypassing that resistor.
The Englishman "woked" very far away so the modification made the output level be much higher and be very illegal.
Of course, the video might be a fake so maybe not.
 

Audioguru

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Bypassing the resistor will short the output signal to ground. I think he said that he "soldered in a wire to bypass it" but instead he wrongly connected his new antenna wire to GND which is Ground. He should have connected his new antenna wire the the ANT end of the resistor.

Don't cause interference to other people on FM, use wifi or Bluetooth instead.
 

AnalogKid

Jun 10, 2015
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Could you tell me whether this video is inaccurate then?
Yes, VERY inaccurate.

The resistor he indicated is *not* in series with the antenna. It is a 47 ohm terminating resistor to prevent reflections. The wire to GND that he added probably does nothing to affect the signal range. However, antennas are weird, and it might affect range by creating a small, local ground plane type of effect. Don't know, not my long suit.

NOTE: He did not demonstrate the transmitter's range before the modification. This is a critical omission, and IMO a clear indication of his intent with this video.

ak
 

Alec_t

Jul 7, 2015
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Even if a power-boosting modification were possible (and legal), the transmitter IC might well overheat and have a short life.
 

Audioguru

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The Micromitter was an article in Australia's Silicon Chip magazine and a kit was made for it 16 years ago. It used a Rohm transmitter IC and had an attenuator on its antenna output so that its 20m range was legal. The IC had 14 FM radio frequencies programmed into it and used a crystal for good accuracy.
 

Audioguru

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The FM transmitter in the video is completely different to the one sold by AliExpress.
 

Martaine2005

May 12, 2015
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One other little point.
The video is in open space without the usual walls, ceilings, routers or metal car.
Any device will transmit further under those conditions.
A 1km range radio can transmit 10km if the conditions are right.

Martin
 

FMA

Nov 15, 2021
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I'm just wondering if anyone has any practical advice directly on the subject at hand, about how to make it work, instead of how things don't work.
 

Audioguru

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I'm just wondering if anyone has any practical advice directly on the subject at hand, about how to make it work, instead of how things don't work.
Do people modify their car so it can fly like a jet airplane?
Is the cheap FM transmitter made with enough power to have a range that exceeds the short distance from your phone inside the car to the car radio so that it is legal?

We are not allowed to show illegal circuits on this forum.
 

FMA

Nov 15, 2021
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Do people modify their car so it can fly like a jet airplane?
Is the cheap FM transmitter made with enough power to have a range that exceeds the short distance from your phone inside the car to the car radio so that it is legal?

We are not allowed to show illegal circuits on this forum.

You don't know where I live, you don't know if it's illegal where I am, that's ridiculous, nothing but negativity and naysayers, but what did I expect from an Internet forum anyway
 
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