Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

[SOLVED] Radiation issue on one frequency

Status
Not open for further replies.

dharithothi

Junior Member level 3
Joined
Dec 19, 2014
Messages
27
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
229
Hello Guys,

In my board I am facing issue of radiation emission of particular 74.25MHz frequency harmonics of 7th number and getting maximum radiation on 520Mhz. Trace length is about 2168 mils and having ground plane on second layer. I have tried by putting RC filter as well putting bead also. But I cant get benefit. Help me to reduce the radiation level.

Dharit.
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
49,148
Helped
14,387
Reputation
29,038
Reaction score
13,141
Trophy points
1,393
Location
Bochum, Germany
Activity points
283,276
How do you know that the said trace is radiating the unwanted signal and not e.g. the power and ground nets of the driving IC? The fact that you "see" a signal with a field probe in one place doesn't mean that you have found the major radiation source.

For a serious discussion, we need to see circuit schematic and layout.
 

jiripolivka

Advanced Member level 5
Joined
May 21, 2010
Messages
2,832
Helped
832
Reputation
1,662
Reaction score
803
Trophy points
1,393
Location
Santa Barbara
Activity points
22,012
Open structures like yours will always radiate , also harmonics. Enclose your whole structure in a metal envelope, use good DC and low-frequency feedthroughs blocked with capacitors, and a RF connector for RF output. Then you may need a low-pas filter for the RF output to cut down harmonics.
 

criterion456

Member level 2
Joined
Sep 13, 2015
Messages
49
Helped
6
Reputation
12
Reaction score
6
Trophy points
18
Activity points
731
If the trace is impedance-controlled.
The resistance of RC filter and internal resistance of bead will affect the impedance of the trace.
And the radiation emission perhaps becomes more serious.....
 

biff44

Advanced Member level 5
Joined
Dec 24, 2004
Messages
4,950
Helped
1,368
Reputation
2,732
Reaction score
1,045
Trophy points
1,393
Location
New England, USA
Activity points
37,185
like they said, you have to solve this at the source, not along some 2" long trace.

Start with bypass caps right a the chip that is making the signal. 1000 PF in Parallel with 0.1 uF, as close as possible to the power supply pin and the ground pin. that will keep the circulating ground currents to a minimum. If you do not have a decent ground under the chip (such as a ground plane), or if your ground plane is cut under the chip, then stich over the cut with short soldered on wires.

After that, maybe near the chip output, you put a series L-C circuit to ground that is tuned to 520 MHz.
 

criterion456

Member level 2
Joined
Sep 13, 2015
Messages
49
Helped
6
Reputation
12
Reaction score
6
Trophy points
18
Activity points
731
In addition to L-C filter, you can also make use of pi-type filter, i.e. C-L-C, to reject the noise.

Because pi-type filter has better noise rejection than L-type.

However, for pi-type filter,

there is one important thing you should pay attention to.

You can NOT make the 2 capacitors share the same ground on top layer.

Otherwise, the pi-type filter will nearly be unable to reject noise.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top