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about VCO Noise - RF Cafe Forums

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lifan

Post subject: about VCO Noise Posted: Fri Feb 17, 2006 6:06 am

Captain

Joined: Fri Feb 10, 2006 1:20 am

Posts: 10

Hello,

all.

I have a TX vco circuit,osc at 2.4GHz,I use it TX Video signal. I found that the video in the RX have very big noise.

the noise is from TX VCO,how to reduce it ?

thanks.

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IR

Post subject: Posted: Sat Feb 18, 2006 7:11 am

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

Hello lifan,

There are many details missing in your description, could you please elaborate if your circuits are assembled on PCB?

In general such problem might be caused by poor PCB layout. Please provide more information so one might be able to help you.

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lifan

Post subject: Posted: Sun Feb 19, 2006 9:24 pm

Captain

Joined: Fri Feb 10, 2006 1:20 am

Posts: 10

Hello IR,

Thank you for your answer. I don't know how to elaborate my circuit. If I can upload the circuit here then you can get more information,but I can't.

Thank you the same!

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lifan

Post subject: another questionPosted: Sun Feb 19, 2006 11:46 pm

Captain

Joined: Fri Feb 10, 2006 1:20 am

Posts: 10

I found another very oddity phenomena.

That is : when I close to the TX module (body or hand),see the monitor which video signal is from RX module,I found that the video is distortion

very easily. I stand here or there near the TX module,I always can find some point that makes the video distortion. That's very oddity !

What does my body acts here ? Am I like a magnetic field ? If yes,what can I do to resolve this problem?

Thanks.

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IR

Post subject: Posted: Mon Feb 20, 2006 5:16 pm

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

Hello lifan,

You need to shield your circuits and by that to prevent coupling between them. You should shield your circuits by using shielded cans that have to be soldered to the PCB and sealed with covers. This is a common solution for RF circuits.

http://www.masach.com/

Look at this company, this is an example to what I mean.

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- IR

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Peter Raynald

Post subject: Posted: Tue Feb 21, 2006 10:36 am

Captain

Joined: Tue Sep 07, 2004 3:09 pm

Posts: 11

How are the TX and RX modules connected together?

Are you making a transmission reception test?

Are there some antennas involved?

Are you blocking the signal with your body?

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lifan

Post subject: Posted: Wed Feb 22, 2006 1:29 am

Captain

Joined: Fri Feb 10, 2006 1:20 am

Posts: 10

Hello Peter Raynald,

Thank you for your attention.

1.Tx module is far away RX module about 10 meters.

2.Yes,I have made a transmission reception test.

3.TX module and RX module have a attenna each other.

4.No.I just stand between the TX module and RX module.

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fred47

Post subject: VCO NoisePosted: Wed Feb 22, 2006 4:00 pm

General

Joined: Wed Feb 22, 2006 3:51 pm

Posts: 104

A few questions and comments:

1. Is your system AM or FM? If AM, is it positive or negative modulation?

2. How is the video modulation accomplished?

3. Multipath is a perennial problem with video - it generally results in lower received signal strength, hence noise (and possibly distortion, based on the type of receiver and the quality of video sync). Standing between Tx and Rx reduces the strength of the direct path signal (you absorb RF energy, being mostly salt water), but doesn't affect the reflections.

4. What power level are you running? Is receiver overload an issue?

5. When you say "noise" do you mean "snow" or some kind of pattern?

Thanks, and

Good Luck!

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lifan

Post subject: Posted: Thu Feb 23, 2006 12:04 am

Captain

Joined: Fri Feb 10, 2006 1:20 am

Posts: 10

Thank you !

The problem of noise is resolved. The 4 MHz crystal modulates with the signals.

fred47,thank you !

1. the system is FM

2. vco oscillate at 2.4GHz, the video signal through varicap diode to

change the frequency.

3. thank you.

4. TX power is about 20 dbm. I am sure the RX isn't overload.

5. Now the distortion is the main problem. Maybe I really absorb the

power.That's funny.

I think I possibly need to re-consider the antenna.

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