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sigma_fr

1.2 GHz video and GPS

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Hello,

I recentely move my video system : 2.4 GHz to 1.2 GHz.

3ch=1160 GHz

I have 2 FPV plane:

Easy Star : RVOSD gen 2 (GPS 5Hz)

Flying wing : Intelligent flight OSD (GPS 5Hz)

With EZ: I don't have more problem to lock GPS but I lost GPS signal easily (when I turn for exemple).

With flying wing: I need 15 minut to lock the GPS (2 minutes with 2.4 GHz) ... And I lost GPS signal during flight.

Do you have this problem ?

Should I move to other freqence ?

1ch=1080

2ch=1120

3ch=1160

4ch=1100

5ch=1140

6ch=1180

Any idear ?

On picture : red arrow is GPS and blue arrow is TX

If I move to chanel 1 (1080) and I mount an 900 Mhz filter ... does it will works ??

http://www.dpcav.com/xcart/product.php?productid=16417&cat=266&page=1

I found also this one ... but the shipping cost is expensive to france about 90 $ !!

http://www.minicircuits.com/pdfs/VLF-1000.pdf

Thanks

Julien

post-4801-086104900 1286915769_thumb.jpg

post-4801-033003900 1286916122_thumb.jpg

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The 1.2GHz low pass filters do not have tight enough band limit, so they are not expected to solve serious GPS interference issues (they are designed to reduce interference to nearby 2.4GHz R/C links). Of course they may help your GPS, but the only way to know is to just try it.

The 900MHz filter has very good attenuation on the GPS related noise. It could be used with 1010MHz (small decrease in the Tx's RF power will occur). However, I haven't seen any commercially made antennas that work well on 1010MHz, so you will have to build your own. A properly matched Tx antenna helps reduce the radiated RF noise, so don't install one designed for other frequencies.

But there is more to the problem than just filtering the Tx antenna. That is because typical interference is rarely due only to radiated noise from it. There is also significant contribution from the conducted noise that travels through ALL the wires. These two noise sources (radiated and conducted) exist together and both contribute to the poor GPS operation. Good solutions require that your attack both, as explained in this white paper:

http://www.dpcav.com...tepaper_RFI.pdf

General comments:

(1) On the flying wing model I would recommend that you move the GPS to the other side, far from the Tx.

(2) On both models, a Toroid type common mode filter on its 4-wire cable is mandatory. Like explained here:

http://www.dpcav.com...tepaper_GPS.pdf

(3) If you still have problems then please post some photos of the Toroid filter that you have installed on the GPS cable. And provide better close up photos of the models (can't really see any details in the two photos that were posted).

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Thanks Mr.RC-cam,

Using twisted cable is equivalent to tore to prevent conducted noise ?

Thanks

Julien

The 1.2GHz low pass filters do not have tight enough band limit, so they are not expected to solve serious GPS interference issues (they are designed to reduce interference to nearby 2.4GHz R/C links). Of course they may help your GPS, but the only way to know is to just try it.

The 900MHz filter has very good attenuation on the GPS related noise. It could be used with 1010MHz (small decrease in the Tx's RF power will occur). However, I haven't seen any commercially made antennas that work well on 1010MHz, so you will have to build your own. A properly matched Tx antenna helps reduce the radiated RF noise, so don't install one designed for other frequencies.

But there is more to the problem than just filtering the Tx antenna. That is because typical interference is rarely due only to radiated noise from it. There is also significant contribution from the conducted noise that travels through ALL the wires. These two noise sources (radiated and conducted) exist together and both contribute to the poor GPS operation. Good solutions require that your attack both, as explained in this white paper:

http://www.dpcav.com...tepaper_RFI.pdf

General comments:

(1) On the flying wing model I would recommend that you move the GPS to the other side, far from the Tx.

(2) On both models, a Toroid type common mode filter on its 4-wire cable is mandatory. Like explained here:

http://www.dpcav.com...tepaper_GPS.pdf

(3) If you still have problems then please post some photos of the Toroid filter that you have installed on the GPS cable. And provide better close up photos of the models (can't really see any details in the two photos that were posted).

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Using twisted cable is equivalent to tore to prevent conducted noise ?

It is NOT the same. Any effect from twisting the wire is much too small and will rarely solve the common EMI/RFI problems that affect the GPS module. To do it correctly you must use a properly installed common mode filter (often at several places in your installation), use a good Tx antenna, reduce the Tx's radiated noise, and so on. The RFI whitepaper mentions these things.

Read the RFI whitepaper several times (do not quickly skim it). Do not improvise; follow the suggestions very closely. I only say this because many people claim to have read it and fully followed the advise. But later when I try to help them with their ongoing noise issues I usually find that they did not follow the information that was written.

So, read the RFI whitepaper several times until every word is burned into your brain. Then implement the suggestions. If the problem continues then post clear photos of the various RFI solutions you installed, plus better photos of the overall installation.

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Ok, Thanks again Mr RC-cam.

I will read the RFI whitepaper every evenig before sleep .. during one month

Julien

It is NOT the same. Any effect from twisting the wire is much too small and will rarely solve the common EMI/RFI problems that affect the GPS module. To do it correctly you must use a properly installed common mode filter (often at several places in your installation), use a good Tx antenna, reduce the Tx's radiated noise, and so on. The RFI whitepaper mentions these things.

Read the RFI whitepaper several times (do not quickly skim it). Do not improvise; follow the suggestions very closely. I only say this because many people claim to have read it and fully followed the advise. But later when I try to help them with their ongoing noise issues I usually find that they did not follow the information that was written.

So, read the RFI whitepaper several times until every word is burned into your brain. Then implement the suggestions. If the problem continues then post clear photos of the various RFI solutions you installed, plus better photos of the overall installation.

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sigma_fr

Possible option ...... if you can open up the metal box that contains your video transmitter electronics and take a high res/close up digital photo of the circuit board, I may be able to point out to you exactly where you can solder on a surface mount component type filter. Many analogue video transmitter-receiver kits are based around the same or very similar generic circuitry & boards, and from manufacturer to manufacturer you often find certain components deemed not essential for the application the product is designed for left off the circuit board to save production time and money. Many of these video transmitter-receiver kits are not designed with placement longside GPS hardware in mind, hence certain filters are left out - even if there is a designated placement point on the circuit board for them! This is common with hardware from the Far East.

While at it, check your video receiver - filtering the antenna input on the receive side can also realise benefits by limiting the amount of rf rubbish the reciever circuitry has to deal with.

Surface mount filters do the same thing as the coaxial type filters you have considered, they are cheaper, can incurr less signal loss, take up less space and weigh less.

Alone a filter added may not solve problems completely. Maximising the physical distance between the video & GPS hardware remains important, as well as following through on other points highlighted out by folk e.g. location/run of wiring, placement of antennas etc etc....

A steady hand and sufficient space to solder surface mount parts is required - or someone to do it for you.

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Julien,

You can have a perfect transmitter with absolutely no signal emitted in the GPS band and still have poor GPS reception. This occurs when the GPS receiver design has poor out of band filtering to prevent desense or overload from a nearby transmitter. For example, the older popular EB85 GPS module has this problem resulting in over 20 dB reduction of GPS satellite reception when it is within half a meter of a pure 1280 Mhz transmitter. The newer (and smaller) GTPA010 GPS module has less than 2 dB reduction of GPS satellite reception for the same distance. Range Video has shipped different GPS modules for their OSD system. What is the marking on your unit? While I know the GTPA010 units are well designed, I do not know about the earlier versions.

OMM

Edited by Old Man Mike

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Hello,

I have 2 Locosys 5Hz GPS Module.

Humm, I juste order 2 DPCAV filter if it doesn't I will try to change GPS ............

Many thanks for all your help

Julien

LS20033 series products are complete GPS smart antenna receivers, including an embedded antenna and GPS receiver circuits, designed for a broad spectrum of OEM system applications.

The product is based on the proven technology found in LOCOSYS 32 channel GPS SMD type receivers MC-1513 that use MediaTek chip solution. The GPS smart antenna will track up to 32 satellites at a time while providing fast time-to-first-fix, one-second navigation update and low power consumption. It can provide you with superior sensitivity and performance even in urban canyon and dense foliage environment. Its far-reaching capability meets the sensitivity requirements of car navigation as well as other location-based applications.

Features:

* 5Hz max update rate

* Default 57600bps

* Update rate of 5Hz

* GGA, GLL, GSA, GSV, RMC, VTG, ZDA

* 32 parallel channel receiver architecture

* Fast TTFF at low signal level

* MediaTek MT3318 solution

* Capable of SBAS (WAAS, EGNOS, MSAS)

* 3.3 to 4.2V supply

* SAW filter

Julien,

You can have a perfect transmitter with absolutely no signal emitted in the GPS band and still have poor GPS reception. This occurs when the GPS receiver design has poor out of band filtering to prevent desense or overload from a nearby transmitter. For example, the older popular EB85 GPS module has this problem resulting in over 20 dB reduction of GPS satellite reception when it is within half a meter of a pure 1280 Mhz transmitter. The newer (and smaller) GTPA010 GPS module has less than 2 dB reduction of GPS satellite reception for the same distance. Range Video has shipped different GPS modules for their OSD system. What is the marking on your unit? While I know the GTPA010 units are well designed, I do not know about the earlier versions.

OMM

post-4801-088539800 1287385248_thumb.jpg

Edited by sigma_fr

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....

LS20033 series products ...

Features:

...* SAW filter

Often the most sensitive GPS receivers are the most likely to have desense problems with nearby transmitters. It mostly comes down to testing the GPS module in a controlled environment setup to determine if it is good for our application. The SAW filter provides some hope that it could perform well but without complete specifications you can't be sure. Operation near a transmitter operating close to the GPS frequencies is not likely to be a key concern of the GPS module designers.

OMM

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Hello,

I tested this on my two plane :

Freq : 1160 MHz and Low Pass Antenna Filter for 900MHz TX........... and it work very well.

Less than a minute for 7 Sat with RVOSD GPS 5Hz and IF OSD GPS 5 Hz.............. work better than 2.4 gHz video

Thanks

Julien

sigma_fr

Possible option ...... if you can open up the metal box that contains your video transmitter electronics and take a high res/close up digital photo of the circuit board, I may be able to point out to you exactly where you can solder on a surface mount component type filter. Many analogue video transmitter-receiver kits are based around the same or very similar generic circuitry & boards, and from manufacturer to manufacturer you often find certain components deemed not essential for the application the product is designed for left off the circuit board to save production time and money. Many of these video transmitter-receiver kits are not designed with placement longside GPS hardware in mind, hence certain filters are left out - even if there is a designated placement point on the circuit board for them! This is common with hardware from the Far East.

While at it, check your video receiver - filtering the antenna input on the receive side can also realise benefits by limiting the amount of rf rubbish the reciever circuitry has to deal with.

Surface mount filters do the same thing as the coaxial type filters you have considered, they are cheaper, can incurr less signal loss, take up less space and weigh less.

Alone a filter added may not solve problems completely. Maximising the physical distance between the video & GPS hardware remains important, as well as following through on other points highlighted out by folk e.g. location/run of wiring, placement of antennas etc etc....

A steady hand and sufficient space to solder surface mount parts is required - or someone to do it for you.

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I tested this on my two plane :

Freq : 1160 MHz and Low Pass Antenna Filter for 900MHz TX........... and it work very well.

It's great to here you solved the problem. What 900MHz Low Pass Filter did you end up using?

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Hello,

I used DPCAV filter :

http://www.dpcav.com/xcart/product.php?productid=16417&cat=266&page=1

ju

It's great to here you solved the problem. What 900MHz Low Pass Filter did you end up using?

post-4801-040205300 1289478224_thumb.jpg

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