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Help need with simple FM antenna design

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udhay_cit

udhay_cit

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I have a FM transmitter for 88-108Mhz frequency and the frequency I fixed with 107.9MHz. As per the product description it gives 0.5W transmission gain. The product link is below. Now I need to design a simple and efficient antenna for this transmitter. I can find lot of simple antenna design from google search but one thing I can't understand is about the electrical wiring connection between FM transmitter circuit and the antenna.
​
Both the electronic circuit and antenna inputs are having two terminal that is signal and shielding ground. Both signal and grounds are electrically connected somewhere in the circuit as per my understanding. Is it true? Can anyone give me a paper & pencil drawing to clearly understand the electrical connection?
Also I need suggestion and link for a good antenna design example to fit inside my living room.

https://www.aliexpress.com/item/BH1417-0-5W-Digital-Radio-Station-PLL-Wireless-Stereo-FM-Transmitter-Module-200M/32707320165.html?spm=2114.01010208.3.27.DyULJH&ws_ab_test=searchweb0_0,searchweb201602_6_10065_10068_433_434_10136_10137_10138_10060_10062_10141_10056_10140_126_10055_10054_10059_10099_10103_10102_10096_10052_10053_10050_10107_10142_10051_10106_10084_10083_10080_10082_10081_10110_10111_10112_10113_10114_10078_10079_10073_10070_10122_10123_10124,searchweb201603_2,afswitch_1,ppcSwitch_5,single_sort_0_default&btsid=4ed9b3f6-baf1-4352-9e79-62c453389be2&algo_expid=14397e62-6ba9-4490-a627-dc15d18ba31b-3&algo_pvid=14397e62-6ba9-4490-a627-dc15d18ba31b

Udhay
 

udhay_cit said:
​
I have a FM transmitter for 88-108Mhz frequency and the frequency I fixed with 107.9MHz. As per the product description it gives 0.5W transmission gain. The product link is below. Now I need to design a simple and efficient antenna for this transmitter. I can find lot of simple antenna design from google search but one thing I can't understand is about the electrical wiring connection between FM transmitter circuit and the antenna.
​
Both the electronic circuit and antenna inputs are having two terminal that is signal and shielding ground. Both signal and grounds are electrically connected somewhere in the circuit as per my understanding. Is it true? Can anyone give me a paper & pencil drawing to clearly understand the electrical connection?
Also I need suggestion and link for a good antenna design example to fit inside my living room.

Udhay
Click to expand...

if all you want to do is transmit the signal around the house, then you just want a 1/4 wave wire whip soldered onto the Antenna pad on the output of the transmitter

a 1/4 wave at 108 MHz = 300 / 108 = 2.78 metres
2.78 / 4 = 0.695 metre x 0.98 (for the velocity factor) = 0.681 metre length


that's it
you are done


Dave
 

Just be careful about the regulations in your area. It may well be that it is legal to broadcast on that maximum power in the FM Broadcast band in your area but it may also be illegal and may cause interference to other users (especially if the transmitter signal is not 'clean' and therefore radiates on unintended frequencies).
Susan
 

Silicon chip magazine in Australia had a project like that and a kit was made about 11 years ago. It was called the the Micromitter. Maybe this Chinese crap is the same. It has an attenuator on its antenna output so its range is limited for it to be legal.
I made an older FM transmitter and it uses just one piece of wire about 70cm long for its antenna. The Micromitter also had a single 70cm long wire for its antenna. If the antenna wire is shorter then the range will be less.

I bet the Chinese manufacturer and seller do not know if this Chinese FM transmitter has its audio "pre-emphasis" set for Europe or for USA.
 

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