Antenna for RDA5807M FM tuner chip

Thread Starter

Piotr Mackowiak

Joined Aug 17, 2019
9
FM.jpg


I got the module of FM tuner (picture above) working properly with Arduino. This is small 1x1 cm PCB containing only RDA5807M chip (I2C control) and quartz crystal.
The problem I have is poor sensitivity because of antenna. At this moment I just solder piece of wire to ANT pin.
Poor sensitivity exist due to the temporary antenna. At the moment I just soldered a piece of wire to the ANT pin.
I'm not a specialist in antennas, hence I wanted to ask more experienced colleagues.
The same chip is used in many smartphones, where the headphone cable is used as the antenna. I use it in the Arduino project as a "desktop" device. I tried to connect the telescopic antenna to the pin but it did not increase the sensitivity of the tuner. At least to a small extent.
So how should the antenna be properly connected and what other (most likely) elements to use so that the whole device has the same good sensitivity as in a smartphone.
Anyone can help me?
 

ci139

Joined Jul 11, 2016
797
if the MCU interface --and/or-- Vdd introduces noise that "saturates" the input amp - the antenna may not be the primary issue
 

Janis59

Joined Aug 21, 2017
812
The hobnail is the best antenna ever if signal is strong, but if not, the nail`s length must be adjusted with network analyser as well the counterpoise too. If even that is not enough, the next step is to enroll a J-pole antenna because of it unical quality of narrow diagram, shining only aside but never upside and downside. We have no need to make a light in the head-up, therefore this antenna gives hard ster forward inspite it is till omnidirectional. However the gap distance between it both branches have a critical in bounds of micrometers. To change say 5 mm distance toward the 5,05 means catastrophe in characteristics, therefore still the good construction for HF RF is in the search. Pcb is not applicable there because of FR4 has tan delta so high as about 0,3%, but better materials as Duroid(TM) is bit expensivish with it 650 USD per A3 sized sheet (tan delta 0,0003 at 1 GHz). Next step forward is to condemn the omni, and then for 2,4GHz the fine idea is "can-antenna" (may find a plethora designs in the web) of for lower freq the Yagi-Uda. In the last case it ought to use the metal-less electrotech cabling pipe of styrene, where resonators are fixed by own isolation, I mean cheapest alu or Copper electrotech monolite wires with thick insulation. Then isolation is fixing it not fall out (drill the holes in pipe by copper diameter) as well preserves it against an atmospheric waters and oxidation. But my experience tells the work for passing it is just damn, as all the insulators carry within the certain unknown shortening factor dependant on insulator material and even thickness.
 

ci139

Joined Jul 11, 2016
797
it is also dependent on your relative geo location to nearby stations , time of the day , weather , indoor antenna location/positioning , indoor antenna geometry & "direction" . . . Earthing your SG (signal ground) to central heating/separate grounding rod/conductor may have some benefit occasionally
 

Thread Starter

Piotr Mackowiak

Joined Aug 17, 2019
9
Replying to everyone, I am aware that distance from the transmitter, weather conditions etc. are important, and of course the length of the antenna. I count it to myself. 1GHz corresponds to a wavelength of 30 cm. Hence 100MHz is 3m.
Antennas should have a quarter of wavelength. Hence the optimal length for the FM range is something about 70 cm.
But. My smartphone has exactly the same RDA5807M chip. Any headphone here serves as an antenna - specifically - literally any Chinese no-name, bought for a few cents. Headphone cable length - whatever. How much Chinese have cut. Plug quality, connection capacity, inductance - no further known.
And I compare the sensitivity of the receiver in the smartphone with that bought in the form of a module. The smartphone receives everything possible. The module only has the 5 strongest stations. The rest is noise.
Hence the question. How to make an antenna for such a module ...






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Audioguru again

Joined Oct 21, 2019
270
The radio in a smart phone has a good pcb layout so it works properly.
The module made in China with no proper pcb design works poorly.
Maybe the Chinese module uses a cheap copy of a real chip.
 

ci139

Joined Jul 11, 2016
797
you can try to pack your '5807 PCB into a tin foil or mount it into Al+ casing ... which likely has no effect coz there's no much pickup traces on the tiny board . . . what i kept in mind is that
(-1-) the I/O wiring data/power may bring/pass noise to your module that is stronger than ANT.inp try the ferrite HF supressors around power lines
(-2-) the attached cables also work as antennas that may result 0° phase difference in your ANT amplifier input (FM.in , GND)
i thought something as a loop of wire that
. is attached (soldered) to amplifier side of ant. cable
. runs some length along it then curves back and goes through series RC or C only to the GND
/// i doubt ↑ it ↑ has any significant effect but is worth to try
 
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