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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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Best regards,
-
IR
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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!
[/img]
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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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regards,
- 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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