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Old Oct 25, 2013, 11:20 AM
Agent
Joined Jun 2013
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8w 2.4mhz wifi booster with 9x transmitter mod?

Ok so i wanted a cheap way to get more range out of my stock Turnigy 9x.

I have done some research and found that a frsky module is an excellent upgrade, so i have one on the way. Also I've seen an alternative to expensive LRS such as DragonLink ect is using a 1-2w 2.4Mhz wifi booster. I found one on ebay for about $30 and decided to grab it. I got lucky and the seller ran out of 2w boosters and instead shipped me an 8w booster.

Now I know 8w is waay overkill, but what I really want to know is will 8w work with my 9x and all my gear, or will it be 'screamin' rf so much that my other rf systems will be degraded?
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Old Oct 25, 2013, 11:46 AM
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Most of the LRS systems use 433Mhz, not 2.4Ghz. The frequency lends itself better to non line of sight operation as it's not blocked as easily as 2.4Ghz is. In the USA, you are supposed to have an amateur radio license to use them. I have no idea how many people follow the rules though.

As for your WiFi booster, it's likely illegal to run without a license, even for WiFi. Just FYI. There's not a thing I can do you stop you and the FCC probably won't bother looking for you.

It will probably work, though I expect it will swamp out your receiver at close range. It will also likely cause issues for anything on a remotely close frequency or harmonic. So if your video gear is on 1.2Ghz, it will probably not like it. 5.8Ghz will probably be OK. I'd also be a little concerned about an 8W 2.4Ghz transmitter in my hand. RF heating of body parts close to the antenna might start to be an issue. I'd recommend you remote mount the antenna away from you a bit if you try it. It's likely not a huge issue, but it doesn't hurt to be safe.

You might also be generating enough RF noise to cause issues for other people flying nearby. Please do some testing before firing something like that up at a field where others are doing RC. Modern spread spectrum systems are pretty robust, but operate at about 100mW. An 8W source, that may well be noisy, might be enough to cause issues, even if transient ones.

Honestly, I think with a patch antenna or perhaps a small yagi, you would get more than enough range from the stock power levels. Or perhaps an Orange 433Mhz module from HobbyKing with a directional antenna on the transmitter side. Last time I looked, they had a 1W module for Futaba, I imagine a JR module will be available soon. Or you could just hack the Futaba module a bit to make it work on your 9x.
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Old Oct 25, 2013, 01:56 PM
Agent
Joined Jun 2013
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Legal issues aside, I wont be near any others and will be flying in a very remote area. Although that was all very good info to know.

My video is running off 900Mhz, and occasionally i'll have 915Mhz for telemetry depending on the set up that day. I think mounting the booster out of my hand could be easy enough too.

Because of my location, it is very difficult to any new parts in, so i'm trying to make due with stock and mod it ever so slightly and easily. Mail takes an average of 2 months to get to me, so it gets very frustrating trying to overhual my set up to lets say 433Mhz.

But out of curiosity you're saying stock with an patch antenna/yagi would be adaqute? I want to have at least 7km range as thats my current goal.

The setup i have in process is:
9x with frsky module
frsky patch antenna for the tx
8w 2.4Ghz booster (wanted a 2w but got 8w instead)
900Mhz vtx

Everything is still in the works, I've finally came out my shell and started to post here on RCgroups, so your input is a great help to me ttabbal. Thanks.

Due to the very limited spare parts I can get my hands on in my location, my number one (and everyone else's) concern is absolute reliable RC control over the aircraft. If i lose her, then its months before i could ever get back on my feet.
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Old Oct 25, 2013, 01:57 PM
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With a spread spectrum system the front end of the receiver has to be able to receive all frequencies in the 2.4 G range. If you fire up your 8 watt transmitter it will swap out all nearby receivers including yours.

The FCC rules are not for the governments benefit, they make it possible for all of us to make use of limited frequency bandwidth.

I used to live near a ham radio guy who was trying to see how far he could transmit at 1.44MHz. He was in the Kilowatt range and was killing every TV for blocks. At that power level it just saturated the TV's RF amp. I consider him to be the worlds biggest jerk and considered cutting his expensive coaxial feed to his tower. 8 watts on the flying field would make you the same type of jerk. The only difference was that he was legal at the time.
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Old Oct 25, 2013, 03:13 PM
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Originally Posted by AgentTheFox View Post
Due to the very limited spare parts I can get my hands on in my location, my number one (and everyone else's) concern is absolute reliable RC control over the aircraft. If i lose her, then its months before i could ever get back on my feet.

It sounds like you are a new FPV pilot. Have you learned to fly LOS really well? You need to do that before you attempt FPV.

For FrSky, you have telemetry coming back that tells you if you are getting out of range. If that happens, turn around.

And start small. Make a 0.5-1km flight before you start trying to get gear all set up for a 7km flight. You will be much more likely to fly home. The FrSky gear should be able to get you to 1km without issue in a remote area like you are describing, with perhaps a patch antenna, but even with just the stock antenna you should be fine. Maybe set your RSSI alarm a little conservatively just to be sure...

If you're worried about range, set a receiver on a pole or otherwise up high. Now take the TX and drive away. Use the RSSI indicator to tell when your signal will drop. It's not perfect, as your plane will likely be high enough that you will get more range due to less for the signal to get blocked by, but it will give you some idea.

With my radio license, I am allowed to transmit up to 1500 watts. I've never come close to that, not even within an order of magnitude. A very good rule of thumb is to use as little radio power as you can get away with. Not just to be nice to others, but amplifiers also amplify noise and can cause receivers that are too close to be overpowered to the point that they can't decode the signal. I get that on the bench with my Taranis and FrSky receivers. If I get too close, telemetry drops out because there's too much energy going into the receiver and it overloads. RF output power is one of those areas where more is not always better. Ideally, these long-range radios would scale their power output as needed based on telemetry data, but many of the cheap modules can't do that.
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Old Oct 26, 2013, 01:09 AM
Agent
Joined Jun 2013
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Originally Posted by ttabbal View Post
It sounds like you are a new FPV pilot. Have you learned to fly LOS really well?
Yes I am making getting into FPV for the first time, I have enough LOS under my belt, i'm not new to flying, just FPV.

Quote:
Originally Posted by mjsas View Post
I used to live near a ham radio guy who was trying to see how far he could transmit at 1.44MHz. He was in the Kilowatt range and was killing every TV for blocks. At that power level it just saturated the TV's RF amp. I consider him to be the worlds biggest jerk and considered cutting his expensive coaxial feed to his tower. 8 watts on the flying field would make you the same type of jerk. The only difference was that he was legal at the time.
Like i said earlier I will be flying in a remote area free of any others. I wish i has the privilege to fly with others, I could probably learn some things off them. Even so I kinda figured 8w was overpowered and I wouldnt want to operate it near others, I'm not trying to be "that guy", but if it is only my equipment then its different. Originally i was going for 2w not 8w but its what i got stuck with.

I'm glad I settled with the telemetry enabled Frsky then. The whole flying out of LOS is really unsettling for me but i just want to make sure i'm properly and adequately equipped for it.
I think i'll use the Frsky and patch antenna for starters and maybe in the future i'll play around with the booster and see if anything other than trouble comes out of it.
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Old Oct 26, 2013, 03:36 PM
Stuart
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Originally Posted by ttabbal View Post
It will also likely cause issues for anything on a remotely close frequency or harmonic. So if your video gear is on 1.2Ghz, it will probably not like it
Why ?
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Old Oct 26, 2013, 03:44 PM
Stuart
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Originally Posted by AgentTheFox View Post
Ok so i wanted a cheap way to get more range out of my stock Turnigy 9x.
So dump it and get a cheap 35\72 Mhz system off eBay.

The main reason for the difference in ranges for the various frequencies is the attenuation of free space, it rises significantly as frequency rises.

If we imagine we had a 100mW transmiiter on 72Mhz, to get the same range, assuming similar RX sensitivity, you would need about 600mW at 434Mhz and 3W at 2.4Ghz.
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Old Oct 26, 2013, 03:51 PM
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The Frsky telemetry will cut out at the range of the normal FrSky operation, since the power was only increased on the up-link side.
You also have to be sure the down-link telemetry data will actually come back through the booster.Probably will since wifi is also two way?

A better/safer/more legal route would be to use a directional patch antenna on the transmitter, which will increase range for both uplink (controls) and downlink
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Old Oct 26, 2013, 04:51 PM
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Why ?
There are two main ways a receiver can receive interference.

The first way is for the receiver to be overloaded. In this case the signal is so strong the output of the RF amp is being slam-ed from rail to rail and cannot amplify anything. In my case of TV interference, I live in a poor reception area and need a large antenna on a tower with a tower mounted amplifier. The TV band, at that time, went from channel 2 to 69 which is 50Mhz to 1 Ghz. So the antenna, preamp and cables all were open to the 1.44Mhz interference. The high power interference just slam-ed the preamp output from rail to rail.

If you ever read the FCC, part 15 warning that is printed on just about everything, it says that you have to be able to accept interference from legal transmitters. The "@#$%^&" jerk with the 1.44Mhz, 1Kw transmitter was legal so it was my problem. I still do not have much liking for any ham operator.

The second way for interference is for the interfering signal to be a multiple of the IF frequency away. For example my 433 MHz receiver with a 11Mhz IF frequency can receive a 315 MHz transmitter. It turns out 315 plus 11 times the IF frequency equals 433 MHz. Usually the two frequencies have to be closer together but if the interfering signal is large enough it can get through.

Some cheap FM radios can receive a station at two or more places on the tuning band. Usually one or two times the IF frequency away from the actual frequency.

Anytime the receiver's RF circuits are overloaded enough to get out of their linear region, strange and interesting things can happen. Basically the circuits start to mix everything together in a mad brew various frequencies.

A simple example is multiplying two signals together. Given two signals at frequencies A and B.

sin(A) * sin(B) = ˝ {cos(A-B) - cos(A+B)}

The result is two synthetic frequencies of A+B and A-B.
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Old Oct 27, 2013, 04:29 AM
Stuart
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Originally Posted by mjsas View Post
The result is two synthetic frequencies of A+B and A-B.
Yes sum and difference.

However whilst a possibility, I would suspect that if the 1.2Ghz input stages are so overloaded by the 2.4Ghz, to be driven into non-linear operation, the effect of AGC etc would make the 1.2Ghz RX as deaf as a post to the incoming 1.24Ghz video signals.
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