2.4Ghz Tx blockout with 1.2Ghz VideoTx - RC Groups
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Sep 20, 2010, 06:42 PM
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Discussion

2.4Ghz Tx blockout with 1.2Ghz VideoTx


I've setup an FPV system on two platforms - both crashed due to the VideoTx blocking the RcTx signals.

Here is my FPV Setup:
Platform 1: 450 'Alone' (Align/Clone) Heli
Platform 2: AXN CloudFly Foamie Glider


RcTx: RadioLink 6Channel
RcRx: Radiolink 7Channel

Similar item: http://www.lowpricerc.com/product_in...products_id=60

VideoTx/Rx: 1.2Ghz 700mw
Actual item: http://www.lowpricerc.com/product_in...roducts_id=986

Lessons learnt from these two incidents - test and range check on the ground first before flying.

Range is not the problem however since the first crash, which was on a heli, was flown very close (about 10yards) and about 20feet off the ground in an open field.

The second crash was in an open field/airport but the distance was a little bit further (about 100yards) - this was on a foamie glider.

Bothe crashes were using the same exact system, I transferred the VideoTx from the heli to the glider after it had crashed.

Both systems were flying great before the installation of the VideoTx.

In the first crash(heli) the VideoTx was about 3inches away from the RcTx.
In the second crash(glider) the VideoTx was about a foot and 2 inches away from the RcTx - although the RcTx was imbedded inside the cockpit of the foam plane.

Now the question:
How do I prevent the VideoTx from blocking my RcTx signal?
Would changing my RcTx/Rx to a branded one like a JRDSX9 Tx with an AR6200 Rx prevent the blockout?
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Sep 20, 2010, 07:15 PM
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Daemon's Avatar
Answer 1: Get the dpcav 1.2-1.3Ghz low pass antenna filter. Done.
See this post https://www.rcgroups.com/forums/show...0#post16094264
and subsequent Q&A.
Answer 2: No. Without a filter, the 1.2Ghz video Tx's first harmonic will always
splash on the 2.4Ghz control frequency and seriously reduce your range. With the filter
you'll get full range of the 2.4Ghz system (which still may not be all that far, depending
on the brand).

ian
Sep 20, 2010, 11:33 PM
Registered User
Thanks for the suggestion.

Placed an order - can't wait to test it.
Sep 21, 2010, 01:29 AM
MK Addict
GC9N's Avatar
where can i find low pass antenna filter?
Sep 21, 2010, 01:59 AM
Post # 20 million
Kev.au's Avatar
http://www.dpcav.com/xcart/product.p...8&cat=0&page=1
Sep 27, 2010, 09:03 AM
Registered User
Ok so I got the DPCAV.com lowpass filter delivered today.

Installed it straight away in the videoTX (placed it to bridge between the VTx body and whip antenna).

I did a range check on the ground.

Went about a hundred yards or so, and found that the VideoTx is still blocking my RcTx signals.

Whenever I plug the VideoTx the RcTx signals get blocked.

I did my rangecheck by having a person move the cyclic on the heli constantly whilst I walk away down the street.

The heli would still respond to the RcTx signals by the time I got to the end of the street (about 100yards) but as soon as I plug in the videoTx the heli would stop responding to the RcTx signals.

I would then unplug the VideoTx and the heli would once again respond to the RcTx signals of the cyclic being constantly moved around.

Would this be because I'm using a park flyer RcTx/RcRx?

That seems a little odd, because unless I plug the VideoTx the heli gets perfect signal from the RcTx.

Has anyone used the VideoTx/Rx from Low Price (link in the first post) with success? Could this be the problem?
Sep 27, 2010, 09:47 AM
Registered User
I am using 1.2GHz video TX with 2.4GHz control TX.

To use those lowpass filters are an effective solution but there is some simple things if you keep in mind will never have the interference problems.

When you are using any kind of radio systems, you will have the main frequency harmonics, the first harmonics are x2 and 1/2 of the main frequency.
Example: in case of using 1240MHz video TX your first harmonics will be at 1240x2=2480MHz and 1240/2=620MHz.

The most annoying tested and proofed problem for FOX video TX is the strong second harmonics, it was 24dB power on 31dB output power TX.

If you notice just by selecting a channel with second harmonic out of your control spectrum you can avoid of that interference, like F>=1280 or f<=1160
(The examples are chose in your FOX TX channels).

Another thing you must keep in mind is that all 2.4 modules always scan the band spectrum then chose free channels for transmitting, so if you simply turn your video TX first then turn your radio control unit, you let the 2.4 module to select most clear channels to transmit on.

Habib
Last edited by Talajouy; Sep 27, 2010 at 09:54 AM.
Sep 27, 2010, 10:02 AM
Registered User
I just found this photo to show you the second strong harmonic that can kill your control signals if it comes to over cover



Now I'm using Lawmate 1.2GHz video TX that appear to have cleaner output and flow the simple two things explained above and flying very long distances without interference problem.

I have lost a very nice scratched built FPV plane to realize what is wrong



Sep 27, 2010, 10:13 AM
Registered User
Hi Habib,

Thanks for the reply. A bit too technical for me - haha.

But I did understand the last part of your message - which is to turn on the video tranmsitter first berfore the the RcTx/Rx.

How would I be able to figure out which harmonics my videoTx is sending as opposed to my RcTx - so that I can choose a different channel.

And by channel do you mean the channel at the back of my VideoTx (it has 4channels and I've tried channel 1 and 3 both of them blocked my RcTx)?

Cheers.
Sep 27, 2010, 10:30 AM
Registered User
Talajouy, I don't think this is showing the second harmonic in 2.4 GHz band...But it would be an interesting picture to see
Sep 27, 2010, 10:38 AM
Registered User
I don't know the channel frequency of your Video TX.
If you probably know the frequencies, multiple them to two, then select that channel that multiple of two is not between 2400~2500MHz.

Install your Video TX far from your control RX, Speed control, motor, servo wires, and as much as possible from your battery.
Some people install them right at the end of their model wings.

Are you using same battery for your model main power to run video TX?
If so then try to use the balance plug to power your video TX.

Keep your control RX antenna far from your power and servo wires as much as you can.
always lay your control RX antenna straight, do not bend them specially on the unshielded ends.

If you radio RX have two antenna try to fix them on the body upright to each other (not parallel on on one line) and if you have only one antenna then try to fix in on the body somehow to be at the same direction with your radio TX antenna.

These are some suggestion I had in my mind right now

Cheers
Habib

Quote:
Originally Posted by cinemacell
Hi Habib,

Thanks for the reply. A bit too technical for me - haha.

But I did understand the last part of your message - which is to turn on the video tranmsitter first berfore the the RcTx/Rx.

How would I be able to figure out which harmonics my videoTx is sending as opposed to my RcTx - so that I can choose a different channel.

And by channel do you mean the channel at the back of my VideoTx (it has 4channels and I've tried channel 1 and 3 both of them blocked my RcTx)?

Cheers.
Sep 27, 2010, 10:41 AM
Registered User
Quote:
Originally Posted by matttay
Talajouy, I don't think this is showing the second harmonic in 2.4 GHz band...But it would be an interesting picture to see
It is, definitely.
Its the FOX 1.2GHz 1500mw video TX working on 1240MHz and the second harmonic is 2480 MHz (in the 2.4 band)
http://www.webx.dk/rc/video-wireless/1240_1W.htm
What is the reason you think it is not?
Last edited by Talajouy; Sep 27, 2010 at 10:51 AM.
Sep 27, 2010, 11:06 AM
Registered User
Hi Habib,

Sorry to hear about your FPV plane - it looked like and awesome flyer.

What equipment did you use to chekc the spectrum of the signals and where can I get one?

My VideoTx is 1.2Ghz which I bought at Lowprice rc.com (the link to the actual item in the first post of this thread).

The VideoTx is at the far end of the tail boom of my 450heli near the tail propeller - it's the furthest I can place it on the heli.

I've tried using both methods regarding the battery - using one battery to power everything with the videoTx and camera powered through the balanced plug.
I've also tried using a seperate battery to power the camera and videoTx. Both ways still block the RcTx signals.

Will try the other methods you suggested.

Are there any other ideas?

Thanks.
Sep 27, 2010, 11:29 AM
Registered User
Those kind of spectrum analyzer equipment (you see in the photo) are very expensive, when I say expensive I mean over 25,000$.

For a simple one you can buy a WiFi Spectrum Analyzer for less than 100$, it can work only on 2.4GHz band and works fine for you to see if your video TX block your 2.4GHz band.

Before going that deep try the trick, turn your video TX first, wait a moment, then turn your radio on, then plug your model power battery, see if there is still interference, if yes, I suggest you to change your video TX and buy one of these Sunsky 800mw or BOB 700mw.

If you are willing to spend a bit more then Lawmate 1000mw is a good choice.

With a Lawmate 1000mw, Vee TX antenna, BiQuad RX antenna I am flying up to 6KM with stunning video quality and still can go farther.



Quote:
Originally Posted by cinemacell
Hi Habib,

Sorry to hear about your FPV plane - it looked like and awesome flyer.

What equipment did you use to chekc the spectrum of the signals and where can I get one?

My VideoTx is 1.2Ghz which I bought at Lowprice rc.com (the link to the actual item in the first post of this thread).

The VideoTx is at the far end of the tail boom of my 450heli near the tail propeller - it's the furthest I can place it on the heli.

I've tried using both methods regarding the battery - using one battery to power everything with the videoTx and camera powered through the balanced plug.
I've also tried using a seperate battery to power the camera and videoTx. Both ways still block the RcTx signals.

Will try the other methods you suggested.

Are there any other ideas?

Thanks.
Sep 27, 2010, 11:42 AM
Registered User
Talajouy,

I think mattay's point is that you are incorrectly interpreting the spectrum analyzer photo that you posted. That photo is showing the fundamental frequency with the various sidebands (including audio). It does not show the first harmonic because if you look at the photo, the span is only around 40MHz. To see the first harmonic, you will need a span that at least covers 2.4GHz. Yes, there will be harmonics, but you can't use that photo to demonstrate the point.

Daniel


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