Mod 2.4ghz microphone receiver. Advice on sma connections

[cristhemuso]

Hi all. I am new to this forum so please be gentle.
I am planning to add an external aerial to improve reception of my camera wireless mic. I believe I can add an sma connector by removing the load resistor thus disconnecting the pcb aerial and attach a fine coax to sma connector.
I am not certain exactly where to make the connections for the attached picture. Any advice very welcome.
I think I attach the shield to the ground plane and the core to where the resistor is removed.
I cant fathom out exactly what the connections are in the picture....
Cris

 

[betwixt]

The bottom two pads in the picture are the antenna connection. The internal antenna is the zig-zag extending beyond the ground plane.

The connector does need to be between the ground plane and end of the existing antenna (which should be isolated by cutting the track) with the inner where the component is missing but beware that the components between the small IC and the antenna are partially for impedance matching and may not be optimal for driving a cable and external antenna.


Brian.

 

[danadakk]

Usually the chip manufacturer has recommended PCB layout recommendations,
maybe get some good clues from that. Usually in datasheet and/or user manual.

Regards, Dana.

 

[cristhemuso]

Wow that was quick gents. At the risk of getting out of my depth I have looked at the datasheet here https://www.ti.com/product/CC2592#tech-docs and I cant see any commentary on meandering aerial / impedance matching. Maybe I should just connect to the two solder blobs, cut the existing aerial trace and see how it performs. Saves me trying to mess with smd resistors.
Really appreciate your feedback.
Cris

 

[vfone]

Most of the people would say that doesn't matter, but was happen to me when the same meander Inverted-F antenna (as the one you have on your PCB) was also covered with black soldermask. I just scratched the paint from antenna and the radiation performance improved a lot.
However, this was a 5.6GHz module (yours is 2.4GHz), and maybe was just a bad paint, but doesn't cost you anything to try to remove it.
One thing I know for sure: most of the black, white, and red colors are made using oxides (iron, magnetite, zinc, etc.)

 

[cristhemuso]

Thanks for the tip vfone. I will try it but am I correct in thinking any protective paint should be non-conductive and not metallic based or else it could cause shorting issues.

--- Updated Jan 28, 2021 ---

Ok note to self. Google something before asking a daft question (mask over aerials) and wasting time. Thanks all. Really appreciate your help.

 

[FvM]

I cant see any commentary on meandering aerial / impedance matching. Maybe I should just connect to the two solder blobs, cut the existing aerial trace and see how it performs

The matching network in the photo has the same topology as the 50 ohm matching network shown at page 9 of the data sheet. But it has not necessarily the same component values and may be matching an impedance other than 50 ohms. You should try as intended.

Useable Receiver sensitivity is often limited by background noise (WiFi, Bluetooth devices) rather than antenna gain. In so far, a better antenna must not necessarily improve microphone reach.

 

[cristhemuso]

Great spot FvM. I will try and measure the values and see if they are the same as in the datasheet. If they are I will assume there are no impedance matching adjustments and the datasheet shows an sma connector so I should see the benefit of stronger receive signal strength. I note we do have quite a few 2.4 WIFI APs near here so I hope a more efficient and accurate aerial will help on range.

 

[cristhemuso]

Slight concern is that if I go ahead and cut the pcb aerial to evaluate an external aerial but decide to revert to stock will soldering the cut connection wreck the pcb aerial performance? / impedance / efficiency.

 

[biff44]

1) remove the components in red

2) replace the components in green with a zero ohm resistor chip

3) scrape away the solder mask in the red areas. CUT the board all the way thru along the green line

4) solder this type of connector on the freshly cut edge of the board.

note that is not necessarily the correct digikey part number. you need the gap in the connector to match the board thickness.

odds are you threw away an output lowpass filter somewhere in steps 1 and 2, so this is only for experimentation....it will not pass an emissions test due to second and third harmonics without a filter

--- Updated Feb 3, 2021 ---

btw, if you are a newbie, removing a chip component without lifting the copper pad under it requires TWO soldering irons. one on the left, one on the right, and when the component gets free, keep pressure with both soldering irons and lift it straight up. clean up with solder wick, and you are good to go