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Old May 06, 2012, 08:55 PM
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Question
Video TX kills 2.4 ghz RC link

Hi all,

My Video TX (Lawmate 1.2 ghz 1000mw) kind of kills my 2.4 ghz RC link. I already added a 1400 mhz low pass filter (LPF1400 from Bevrc) but it doesn't help at all. (Any idea why it doesn't help btw? It's NOT this cheap low pass filter that aparently isn't very good...)

I did notice that at 1010 mhz the lawmate doesn't limit my RC range quite as much (maybe 10% reduction - acceptable) but on that channel the video range is really poor...(not even 150 meters line of sight) even with a custom tuned antenna! When I try higher frequencies, the video range gets much better, but the RC link gets worse... at around 1160 mhz to 1200 mhz the RC range is really crappy and at 1280 mhz it starts to get better again.

So for the moment 1280 mhz seems to be the best, but my RC link clearly still suffers with about 40% reduction in range. My RC link is the hobbyking GT-2 system by the way. I already added this 2watt wifi booster which helps a lot, but it's not a very elegant solution. Also I still lose RC link way before the lawmate loses signal...

Any idea for a solution? I know those UHF systems will probably work great, but they are expensive and so are the TX's that you need. Not the mention the complete overkill feature wise of those transmitters, since this is just a RC car on the ground.

Another option would be 35 or 72 mhz transmitters, but I was hoping there might be 2.4 ghz RX/TX systems that work better with the Lawmate at 1280 mhz. Perhaps the hobbyking GT-2 isn't the best system to use and another brand works better with the lawmate?
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Old May 06, 2012, 09:47 PM
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Hm.. apparently this guy has had good success with a lawmate 1.2 ghz and a minicircuits 1400 mhz low pass filter. But would it be worth it to replace my bevrc one with the minicircuits one? I mean assuming the bevrc does its job correctly the interference I still encounter won't be solved by another brand.
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Old May 06, 2012, 11:45 PM
Project Tormentor is flying!
United States, WA, White Salmon
Joined Nov 2005
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Have you separated the Vtx as much as possible from the rc Rx? Distance can make a big difference. Also, you could build a patch antenna tuned to 1160. Very easy. And build an inverted V tuned for 1160 for the Vtx. Then you would have good video range and your rc range wouldnt be hit so hard. I also don't trust the filters from Hobbyking. I strongly suggest you order one from Readymaderc or DPCAV.
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Old May 07, 2012, 02:03 AM
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What do you expect for such a hobbyking radio?

The problem is not with 2.4 GHz is with the awful brand you use.

See what happens with Futaba:

http://www.rcgroups.com/forums/showp...81&postcount=9
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Old May 07, 2012, 06:14 AM
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Thanks for the suggestions. I might be able to separate the video TX and the RC link RC on the car a tiny bit more, but I already got them separated as much as practically possible. I ordered a low pass filter from Rangevideo. It's the minicircuits brand. Not the cheapest though and even 20 dollar shipping (!) but hey, all for the hobby right? :P I'll let you guys know if it makes any difference. Else i'll try another radio.

By the way, the hobbyking GT-2 got excellent reviews (it even gets praised for its long range!) and value for money though... I'm a bit confused how this radio is 'bad'?

Anyway, any suggestions for a 'simple' radio for a car? I really don't need all those bell's and whistles. Just forward and backwards and steering. That's all! Thnx!
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Old May 07, 2012, 06:18 AM
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United States, FL
Joined Oct 2005
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As a general rule of thumb - 2.4 control + FPV = not that good.

You would be better off getting a 72 module if you can. Many times the harmonics (the second one specifically) will crush the 2.4 link. A 1W is a bit.... much as well.
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Old May 07, 2012, 06:43 AM
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Will look into the 72 mhz module, but this guy did have succes with a 2.4 ghz transmitter and 1.2 ghz video.

Quote:
I'm very happy with my FRSky+Argtek booster. I use a Minicircuits VLF-1400 low pass filter on my 1280MHz VTx and the 2.4GHz Rx range is unaffected. Without the filter though, a range test returns less than 1/3 of what it should be
So in my logic either my low pass filter is faulty (or not doing its job very good) or the specific (cheap) RC link RX/TX that I use isn't a good choice with my 1.2 ghz video.

Replacing the low pass filter is the cheapest although the filters are not very cheap If that doesn't help I'll look around to borrow another 2.4 ghz RX/TX for testing purposes. If it works out i'll stay with 2.4 ghz, else I'll look for the 72 mhz.

Any suggestions for 72 mhz transmitters. I really only need simple forward/backward and steering, but al those TX's are for airplanes.
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Old May 07, 2012, 07:03 AM
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Quote:
Originally Posted by Bram1982 View Post
Will look into the 72 mhz module, but this guy did have succes with a 2.4 ghz transmitter and 1.2 ghz video.



So in my logic either my low pass filter is faulty (or not doing its job very good) or the specific (cheap) RC link RX/TX that I use isn't a good choice with my 1.2 ghz video.

Replacing the low pass filter is the cheapest although the filters are not very cheap If that doesn't help I'll look around to borrow another 2.4 ghz RX/TX for testing purposes. If it works out i'll stay with 2.4 ghz, else I'll look for the 72 mhz.

Any suggestions for 72 mhz transmitters. I really only need simple forward/backward and steering, but al those TX's are for airplanes.
For ground FPV I use a 75mhz HiTec Laser 6, which out of production, but you might be able to find a good used one.

75mhz is for ground vehicles, but largely has now been replaced by 2.4ghz.
Gotta be lots of 2nd hand 75mhz gear out there somewhere....

My 75mhz Laser 6 works very well with 900mhz video. I've not tried it with 1280mhz.
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Old May 07, 2012, 07:54 AM
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Just to add more relevant info on the subject. This guy uses the Lawmate 1000mw 1.2 ghz on 1280 mhz with Futaba FASST 2.4 ghz with no problems and flew about 1km LOS. 1280 mhz is what my Lawmate 1000mw 1.2 ghz is also currently set to, so it looks like it actually is quite possible to use 1.2 ghz video and 2.4 ghz rc link without problems. No info about a low pass filter, so I'll assume the guy did use one. Also I'll assume he didn't use any wifi boosters.
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Old May 07, 2012, 08:04 AM
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Bram- just an fyi, 1km is really nothing in practical sense. Yes you CAN manage 2.4 on the RC link and people have done it, but its one of those 'you're mileage will vary' type of deals. Especially unboosted. Some people have done fine out to a mile, but others have gone into failsafe at under 1/4 mile. I see you're using this for a car, so solid link isn't as critical, but I guarantee you'll have frustrating issues. I strongly suggest a 75mhz radio or a UHF, you'll enjoy it much more!
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Old May 07, 2012, 11:41 AM
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Quote:
Originally Posted by ashdec87 View Post
Bram- just an fyi, 1km is really nothing in practical sense. Yes you CAN manage 2.4 on the RC link and people have done it, but its one of those 'you're mileage will vary' type of deals. Especially unboosted. Some people have done fine out to a mile, but others have gone into failsafe at under 1/4 mile. I see you're using this for a car, so solid link isn't as critical, but I guarantee you'll have frustrating issues. I strongly suggest a 75mhz radio or a UHF, you'll enjoy it much more!
Thanks for th heads-up! I'm aware of the facts about 2.4 ghz and the UHF being the better (ultimate) solution, but I'm trying to do the economical approach. So if I can (easily) fix the interference from my current set-up I'm happy. By the way I'm not expecting long range anyway, but currently I can't even get more than 30 to 40 meters LOS (!) That's ridiculously short range, even if it's without the 2 watt booster.

So if the hopefully better low pass filter doesn't help, I'll try a futuba FASST radio and if that doesn't help I'll might jump ship to the UHF system. The only thing about the UFH system is I really don't need those fancy airplane transmitters and there don't seem to be compatible TX's for cars. Once again, I really only need forward/backward and steering...
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Old May 07, 2012, 11:49 AM
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Lakewood, Colorado
Joined Aug 2002
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I don't think you've mentioned which cheap 2.4Ghz system you're using, but that's probably
the problem. Generally speaking the cheaper the gear, the less Rf filtering it will have.
When doing 2.4Ghz for FPV it's best to stick to proven systems. Futaba FASST, FrSky,
and some of the higher end Spectrum Rxs. Cheaper Spectrum Rxs and various other
systems range from poor performance to none at all. In the end 2.4Ghz control may
cost you the entire aircraft, so may not be the most economical route.

ian
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Old May 07, 2012, 12:23 PM
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I mentioned it before but I'm using the ultra-cheap (like 15 dollar) HK GT-2 system from hobbyking.

So yes, a better (more expensive brand) might solve the problem, but buying another 1400 mhz low pass filter just to be sure doesn't hit me in the wallet that much and might even solve it too.
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Old May 07, 2012, 02:40 PM
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Ok, I found even more user experiences on this topic. This guy used a Lawmate 1.2 ghz 1000mw on channel 1160 with a low pass filter and a Futaba FASST transmitter (he doesn't say what model)

Anyway, he gets around 150 meters ground range when he put his plane in the back of his car with the 1.2 ghz 1000mw Lawmate turned on too. Adding a 1 watt 2.4 ghz wifi amplifier to his RC TX gives him about 900 meters ground range. That's WAY more range then I currently get with my HK GT-2 el-cheapo!

So I think a Futaba FASST transmitter is the way to go, since it apparently constanly hops between (a whopping) 72 different channels and always selecting the channel with the least interference.

Now I suppose every Futaba FASST radio will do right? Or are there (apart from user programmable features) other technical differences I should care about? Like output power etc?
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Old May 07, 2012, 03:57 PM
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how many channels do you need? For the cost of a futaba tx, you can probably get a UHF or find a used 75mhz tx for about the same or less price.
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