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Apr 01, 2011, 06:53 PM
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Discussion

Low Pass filter on 5.8ghz


I am trying to get a better picture on my 5.8ghz system. I want to try a low pass filter.

I have looked around the normal FPV shops but no luck.

Will this help and who sells them?
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Apr 01, 2011, 08:23 PM
Postcards From The Purple Edge
tuppertn's Avatar
What do you hope to get from the filter?

A low-pass filter will attenuate noise transmitted above its tuned frequency. Generally, you use a low-pass filter when you're trying to keep your device from interfering with another device that operates at a high frequency that corresponds closely to one of your device's harmonics. (Example: low-pass filter on a 1.2GHz VTx to attenuate the second harmonic at 2.4GHz that would interfere with a 2.4GHz RC system.)

I don't think a low-pass filter would buy you anything on 5.8GHz. Poor quality video on 5.8GHz is likely due to multipathing or poor impedence matching on the VTx antenna. Many folks have had good luck building their own circular polarized antennas for 5.8GHz to address both those issues.

kendall
Apr 01, 2011, 09:25 PM
Orlin the fpv-a-holic
bigo66's Avatar
Try a 5 dbi higher gain 5.8 ghz dipole antennas from ReadymadeRC $7.

http://www.readymaderc.com/store/ind...roducts_id=366

-- 500 mw 5.8 ghz transmitter from Bev RC $100

http://www.bevrc.com/bev-58g-500mw-t...fpv-p-233.html

-- 8 DB 5.8 GHZ Patch antenna from DPCAV $59

http://www.dpcav.com/xcart/product.p...cat=268&page=1

There are other options like IBCrazy circular polarized antennas. Just got some but haven't tested them. They are very small on 5.8 GHZ!
Apr 01, 2011, 11:48 PM
Registered User
CaliDave's Avatar
You want a High Pass filter
Apr 02, 2011, 03:49 AM
Registered User
ImmersionRC Duo 5.8 and globe-flights 12DBi Patch antennas will give you a very good image. Best combo i have ever seen on 5.8gHz.
Apr 02, 2011, 03:55 AM
Registered FPVer :)
markus123456's Avatar
Quote:
Originally Posted by hornant
I am trying to get a better picture on my 5.8ghz system. I want to try a low pass filter.

I have looked around the normal FPV shops but no luck.

Will this help and who sells them?
If you want to filter nosie coming from the power line, a low pass filter in fact would help. Let us know what your setup is. If you have disturbance in the picture on 5.8Ghz, then it also can come from multipathing interferances which is VERY common on such high frequencies.

If your "tx" is just this bare transmitter module as it's sold by fpvhobbies, and you power it from your ESC, then you need a very good filter which you can't buy off the shelf. A better aproach in this scenario is to use a dedicated single lipo cell for the tx module and a little linear voltage regulator to come down to 3.3volts as this is what's needed for said module. Like this you get rid of the noise since you use a dedicated power source for the tx. Alternatively you can get a full blown tx (if you don't already have one).

In case you already you use a regular tx that incoroprates filtering (like the one sold in many asian stores), your problem is most likely not caused by noise in the power line, but from the forementioned interferances. Here you best get a circular polarized cloverleaf antenna for the tx and a skew planar wheel for the rx. You can either build one yourself (there is a thread somewhere in this forum) or buy one. IBcrazy sells them, so do I. If you want a pair from me, send me a pm. I charge $25 per antenna plus shipping.

Circular polarized antennas solve the problem caused by multipathing. They are ideally suited for FPV. You will definately have a "wow" kind of experience once you try them out. Video is rock solid and although in theory you would loose 3dB from going from linear polarized to circular polarized, in practice you GAIN range because of the fact that the further you fly out with linearly polarized antennas, the chances for interferences increase. Without them (alas when using CP antennas), the video quality will start to decrease slowly if you reach the limit leaving you enough time to turn around and most importantly giving you a lot of confidence.

Last weekend I flew out 2.5 kilometers with a 5.8Ghz 200mW transmitter using omnidirectional CP antennas. I had to return because of the RC link starting to fail. Video was stilll rock solid....

Markus
Apr 03, 2011, 09:42 PM
Registered User
Thread OP
Thanks for the tech advice guys.

I am using this 5.8ghz 200mw TX
http://www.fpvhobby.com/31-8ghz-500m...ansmitter.html


and 2 of these receivers

http://www.fpvhobby.com/33-4ghz-8-ch-a-v-receiver.html

oricale

video booster

fatshark base

The Tx has its own Batt.
I have the same setup in 2 airframes and get the same picture. Its a good strong video link but the focus always looks just not quite right(2 diff cams) no matter how much I adjust it and if you look close you can see what looks like little ripples going across the screen.

The picture is good enough to fly with but it is not great...also the colour looks to be washed out.
Apr 04, 2011, 01:13 AM
Orlin the fpv-a-holic
bigo66's Avatar
The ripples across the screen is motor interferece. Throttle off in flight and notice them go away. Try moving the transmitter close to the tail. It should also help balance the cg so the plane isn't so nose heavy.
Apr 04, 2011, 01:31 AM
Registered User
Thread OP
No...its not the motor. I get them even when the flight pack is not plugged in. They are very small and you wouldn't even notice them at first glance.
Apr 04, 2011, 03:06 AM
Registered FPVer :)
markus123456's Avatar
Quote:
Originally Posted by hornant
No...its not the motor. I get them even when the flight pack is not plugged in. They are very small and you wouldn't even notice them at first glance.
Could you post a video so as we get a better idea of how it looks?

Markus
Apr 04, 2011, 03:09 AM
Registered FPVer :)
markus123456's Avatar
Quote:
Originally Posted by hornant
Thanks for the tech advice guys.

I am using this 5.8ghz 200mw TX
http://www.fpvhobby.com/31-8ghz-500m...ansmitter.html


and 2 of these receivers

http://www.fpvhobby.com/33-4ghz-8-ch-a-v-receiver.html

oricale

video booster

fatshark base

The Tx has its own Batt.
I have the same setup in 2 airframes and get the same picture. Its a good strong video link but the focus always looks just not quite right(2 diff cams) no matter how much I adjust it and if you look close you can see what looks like little ripples going across the screen.

The picture is good enough to fly with but it is not great...also the colour looks to be washed out.
This tx and rx is not that bad really. I made a compatible tx with better noise filtering (there is a dedicated thread about this in this forum).

Without having seen your video, and based on the fact that you use diversity, I would guess you use linearly polarized antennas? If so, switch to circular polarized antennas. You will experience a quantum leap in video quality. Me and others sell those, others make their own. If you are interested in getting a pair (you would need a cloverleaf on the tx and a skew planar wheel on the rx) send me a pm.

Markus
Apr 14, 2014, 02:57 PM
Registered User
I am definitely getting 2.4GHz interference on my 5.8Ghz FPV receiver. My 5.8GHz receiver is mount just above my 2.4 GHz TC Tx, and if I turn it off, I get a clear picture. Turn it on and I get horizontal interference lines. I'm using a BluBeam antenna on my FPV Rx. Any ideas what to try next?

The RC TX is from a stock DJI Phantom V1.1.1 and the FPV Rx is the Neewer 5.8Ghz LCD DVR http://www.amazon.com/Neewer-Wireles.../dp/B00HUL961G
Apr 15, 2014, 03:07 AM
Registered FPVer :)
markus123456's Avatar
Quote:
Originally Posted by cgblack
I am definitely getting 2.4GHz interference on my 5.8Ghz FPV receiver. My 5.8GHz receiver is mount just above my 2.4 GHz TC Tx, and if I turn it off, I get a clear picture. Turn it on and I get horizontal interference lines. I'm using a BluBeam antenna on my FPV Rx. Any ideas what to try next?

The RC TX is from a stock DJI Phantom V1.1.1 and the FPV Rx is the Neewer 5.8Ghz LCD DVR http://www.amazon.com/Neewer-Wireles.../dp/B00HUL961G
I highly doubth that you get it from the 5.8Ghz receiver through the HF path and that any kind of HF filter on the rx side would help . This looks more like your 2.4Ghz tx directly radiates into the low frequency part of the screen etc.

Your best bet would be to either move the rx/screen away or try to shield the screen housing...

Markus


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