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Old Mar 14, 2012, 07:39 AM
FPVing for fun...
rcall's Avatar
Joined Jul 2003
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I've got a 200mW module from FPVHobby and I mounted it to the back of a mini 420tvl camera for a quick test... both are 5V and I'll connect them directly to the receiver...

the Tx came with a simple wire for antenna and before I change it to a CL I'll do some tests with a rubber duck on the receiver...

the antenna is 17mm long, should I trim it to a proper length for the frequency I am using, 5705MHz?
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Old Mar 14, 2012, 09:17 AM
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Quote:
Originally Posted by rcall View Post
and I'll connect them directly to the receiver...
Expect terrible noise in the picture as soon as you turn on the motor. The ESC causes big spikes in current which change the "level" of the vidoe signal relative to ground as seen by the transmitter. For this configuration, you need a dedicated lipo cell to power the tx and camera.

Quote:
Originally Posted by rcall View Post
the Tx came with a simple wire for antenna and before I change it to a CL I'll do some tests with a rubber duck on the receiver...

the antenna is 17mm long, should I trim it to a proper length for the frequency I am using, 5705MHz?
Does not make much sense since you intend to change it anywaysy. The limitation of this setup in it's current configuration is not range (here tuning the antenna could help provided you could measure what you do), but reflections and they are not influenced by such a change. Safe yourself the hassle and switch to CP antennas.

Remember, if you use a CP antenna, to solder the mesh of the coax to BOTH pins on the sides of the pin where right now the antenna wire is soldered to. Splice it up accordingly. That's important to shield the signal and also to somewhat maintain the impedance. Make this connection as tight/short as you can. The center of the coax then would replace the current antenna wire.

HTH

Markus
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Old Mar 14, 2012, 09:22 AM
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@ rcall

5V for the VTx module is really too much, it should be 3.3v and some are using a single cell LiPo @ ~3.7v

Seriously, for long life you should run it at 3v3 - HK sell a little v-reg suitable for powering it.

Nigel.
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Old Mar 14, 2012, 10:15 AM
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+1 on this ^

I overlooked it and unless you have one of the rare modules with internal regulator, you definately WILL fry it if running at 5V. Been there, done that....

Markus
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Old Mar 14, 2012, 12:05 PM
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He wrote in OP is the FPVHobby module, so should have embedded regulator.

Anyway, keep a finger on module when first time power, if it heats in some seconds at more than 50C (max the human skin can support without issues) then power off imediatelly.
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Old Mar 14, 2012, 12:09 PM
FPVing for fun...
rcall's Avatar
Joined Jul 2003
561 Posts
Quote:
Originally Posted by markus123456 View Post
Expect terrible noise in the picture as soon as you turn on the motor. The ESC causes big spikes in current which change the "level" of the vidoe signal relative to ground as seen by the transmitter. For this configuration, you need a dedicated lipo cell to power the tx and camera.



Does not make much sense since you intend to change it anywaysy. The limitation of this setup in it's current configuration is not range (here tuning the antenna could help provided you could measure what you do), but reflections and they are not influenced by such a change. Safe yourself the hassle and switch to CP antennas.

Remember, if you use a CP antenna, to solder the mesh of the coax to BOTH pins on the sides of the pin where right now the antenna wire is soldered to. Splice it up accordingly. That's important to shield the signal and also to somewhat maintain the impedance. Make this connection as tight/short as you can. The center of the coax then would replace the current antenna wire.

HTH

Markus
bench tests didn't show any noise with motor and servos running, let's see what happens on the field... it will be a 3rd person flight recorded

I will change to CP but I wanted to make a quick test to compare...

as for the 5V, FPVHobby says it is regulated and I have it running for several minutes without problem... it gets a bit hot but not excessively...
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Old Mar 16, 2012, 07:16 AM
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My buddy has now built the DIY SWR meter to find out if our antennas are any good.
We were suprised after we found out that most of the antennas have a swr between 2.05 and 3.5 instead of ~1.05

One of those Antennas was built on our own, the others were bought from other people.
Is it possible, that the SWR meter is not working correctly or needs some tuning (because we are satisfied with the FPV performance of those antennas)?

Tomorrow we can test one of Marcus antennas which are looking really nice, maybe they will give better results.

edit: seems to be a problem of the SWR...even when we test the same antenna multiple times the result is very different...so we will check the SWR meter to fix it.
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Old Mar 16, 2012, 08:34 AM
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If the measuring of SWR in GHz would be so simple, the xxxx$ units wouldn't sell...
Too many gurus in that swr thread to make them understand this.
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Old Mar 16, 2012, 10:08 AM
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Quote:
Originally Posted by BKMorpheus View Post
edit: seems to be a problem of the SWR...even when we test the same antenna multiple times the result is very different...so we will check the SWR meter to fix it.
Better check environment when measuring..... (close to SWR-meter and antenna)
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Old Mar 18, 2012, 01:43 PM
Pat K
The Netherlands
Joined Dec 2010
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RSSI voltage vs distance

Hi all,
has anyone of you ever recorded the RSSI value of your receiver vs distance?
I just made a flight using 5.8GHz 200mW from FPVHobby (I guess Tx/Rx come from SkyRF) and my brand new DIY CL/SPW. I measured the RSSI values of my video receiver and got the following:
- 10m: 1.19V
- 500m: 0.85V
- 1km: 0.70V (still clear video)
- Noise floor (Tx unpowered): 0.43V

I have not checked my antennas yet at the Lab but will do ASAP.
Are these values consistent with your experience?

Pat
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Old Mar 18, 2012, 01:54 PM
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Question is written on the pic...Although there is minus written above that triangle, but you can't never trust the chinese .
This is the power cable for the video receiver btw.
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Old Mar 18, 2012, 01:57 PM
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Papat would you share how you modified it for rssi?
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Old Mar 18, 2012, 02:04 PM
Pat K
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Quote:
Originally Posted by msev View Post
Papat would you share how you modified it for rssi?
I did not modify anything, just connected the RSSI output to a voltmeter.
Here is the Rx I'm using: Here
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Old Mar 18, 2012, 07:22 PM
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Quote:
Originally Posted by msev View Post
Papat would you share how you modified it for rssi?
Asuming you have an RC-305 or RC-805, if you open it, you see a HF module soldered onto the PCB. Put the rx in front of you such that the antenna connector points away from you. Then, the RSSI output is the sixt connection from the left.

HTH

Markus
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Old Mar 19, 2012, 04:56 AM
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Quote:
Originally Posted by markus123456 View Post
Asuming you have an RC-305 or RC-805, if you open it, you see a HF module soldered onto the PCB. Put the rx in front of you such that the antenna connector points away from you. Then, the RSSI output is the sixt connection from the left.

HTH

Markus
Markus what about my question about the powering cable for rc305? Is there where there is a triangle and a - written, ground? I gotta ask since this is a critical area where I could make a mistake..
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