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Antenna upgrade for flight RX?

#1
I am looking to do a clover-leaf / planner-wheel style antenna for my TX & RX (Turnigy branded 9x w/stock module). I am handy with the tools required & have two RXs to work with.

I know these RXs have a di-pole antenna under the heat shrink & I was thinking of making a base mount for the leaf/wheel to stick into the plane next to the RX to avoid any stress on the coax.

Has anyone done anything similar?

~psguardian
 

lobstermash

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#2
CP antennas are generally low gain/high fidelity. For the small amount of data being transmitted between tx and rx, you're better off with having 2 antennas on either the tx or rx (generally it's on the rx) and mounting them perpendicular to each other.

Still, feel free to give it a go. At the very least it'll be good practice for making video system antennas...
 
#3
Could I add a second antenna? Or replace with a full loop antenna? Or add two loops? I don't want to ruin an RX buy I'd like a better 'ear' up there.

~psguardian
 

lobstermash

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#4
The pcb doesn't have the circuitry for a second one; neither a diversity controller or a second pair of soldering pads for a second antenna. If you're flying LOS, you shouldn't have any issues with range. If you're thinking FPV and want to stick with 2.4Ghz, I can strongly recommend FrSky, which has 2 antennas on the rx, telemetry that beeps at you when signal is low and the option for a 7db patch antenna that seems to have a good balance of increased forward range while leaving a couple of hundred metres behind you too.

The most common issue with the stock 9x rx antennas is that the coax tends to break after a little while where it exits the box. I reinforce mine with a collar of hot glue. Aside from that issue, you should have control as far as you can see if your antenna is mounted vertically and away from the ESC.
 
#5
I have been thinking about the FrSky 2.4ghz unit with the telem RXs. The only thing That I wonder about is the output power, 60mw isn't much.

~psguardian
 

lobstermash

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#6
Yeah, but like they say, it's not how much power you have, but how you use it ;)

I've got beyond 1.5km without any worries with the patch. With the 2db stock antenna I got over 1km with the occasional beep from the tx. Apparently it has excellent filtering and high sensitivity, which is why it doesn't need such a high output power. There are a number of 2.4Ghz boosters out there, of which I've seen video of someone flying 42km combining it with the patch antenna and 1W boost. I haven't used a booster but I've heard of plenty of people getting 4-6km with just the 7db patch. I haven't been game to push my video that far yet.
 
#7
I have seen the patch cause issues, guy was flying within 300m & tracking model with his head but not his TX. It moved out of the patches beam & lost signal, at 200m. Nasty blind spot that one has. I ask familiar with RF Fromm my days as a CBer. I'm toying with getting my ham ticket also. Would be a nice perk to legally run higher power RF gear. Have a field box with a 5w flight & fpv amps... Ah the possibilities.

For now I may create a wheel antenna & replace the RX current one with it. That should do better than the stock coax.

~psguardian
 

lobstermash

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#8
That's not the antenna's fault... From my experience with it, there's about 200m behind you, 400-500m to the side and a long way in front.

You should be able to use the stock antenna to make your wheel. However note that your rx antenna will be cp and your tx will be lp. There's a couple db loss for not matching polarisation.
 
#9
No it's not the antenna fault, & he quickly swung the TX around to recover, but a scary thing LoL.

Good point. If I do the RX I'll do the TX also, but then there is the question of that brace on the back detuning my TX antenna by proximity. Why do they design these things without taking any RF constraints into account hehe. Maybe I'll just do away with that.

~psguardian
 
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lobstermash

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#10
Haha, they're designed to a price, that's why... You can remove it with some long nosed pliers. I've just made my stock module a plug-in system this afternoon:

IMG177.jpg

Now in the tx this came from, I have a FrSky, OrangeRx DSM2/X, OrangeRx LRS and stock module. My other 9x has become superfluous...
 
#11
No, your other 9x has become the loaner/buddy-box LoL.

That's quite a list of modules. I will likely go with FrSky w/telem & just but a fist full of RXs. Range test with the two antennas... Now if I could just find the $ haha.

~psguardian
 

lobstermash

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#12
That's the attraction of the LRS module. It's the same price as a telemetry FrSky combo, but should deliver omni-directional range at least the same as the FrSky with the patch antenna. And the receivers are cheaper too. I'm just trying to work out how reliable it is at the moment, and will get my HAM licence in the very near future.
 

lobstermash

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#14
It comes stock 433, but can be programmed to be 400-460. It's also frequency hopping (so far up to 6 channel hopping) and the power output is programmable (up to 100mW). It seems like a good medium range solution, however I'm hoping re-flashing will improve the resolution, as servo movement is a bit grainy in stock configuration...

Oh, almost forgot, it only has 1 antenna on the rx. I'm thinking of making up a + antenna as per IBCrazy's build to add diversity.
 
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robschonk

Senior Member
#15
Any "improvements" to your airborne Rx antenna usually affect directionality. Ideally, you want an omnidirectional pattern. This applies to both the receiver and the fpv tx. Given enough time and money, I suppose someone could build a tracking system to control stacked yagis on top the aircraft..

Probably need to concentrate on the ground station, where you can use a combination of increased power and a directional antenna system.

Guys like ibcrazy have lots of experience, and have posted extensively on the net.

Here's a pretty good video from rcmodelreviews:

http://m.youtube.com/watch?v=Bx7gMUw1MGw
 
#16
The antenna i'm thinking of clover-leaf or wheel are omni directional circular polarized. Tracking antenna should only be on the ground. Though the thought of stacks in the air is amusing. I like Davids overkill ground station with the helical beam.

~psguardian
 

robschonk

Senior Member
#17
The antenna i'm thinking of clover-leaf or wheel are omni directional circular polarized. Tracking antenna should only be on the ground. Though the thought of stacks in the air is amusing. I like Davids overkill ground station with the helical beam.

~psguardian
The cloverleaf antennas are great for video to help prevent multipath, but for 2.4ghz, I cant see any advantage over the stock 1/4 wave dipoles.
 
#18
The advantage is circular polarization over horizontal OR vertical polarization.

When you turn/loop/roll a plane out near the end of your radio range you will cause drops due to the movement of the RX antenna. While your TX antenna is situated vertically & your RX is also mounted vertically you get best signal. Now roll the plane 90* & the RX antenna is now horizontal, signal reduced due to mismatching antenna orientations. In the ham/c.b. world this is like two people talking on vertical antennas, & then one of them switching to their horizontal antenna & wondering why the other guy got quieter/silent. Putting a matching circular antenna on both RX/TX will ensure that there is less fluctuation in signal strength out on the edges of its range.

Also if you decide to go with 2.4ghz fpv gear you can do right hand circulars for flight signal & left hand circulars for fpv gear (or vice-versa). Signal rejection between the two antennae will be fantastic, so no need to worry about keeping them apart or interfering with each other.

~psguardian
 

lobstermash

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#19
That's the whole point of having 2 antennas on a rx. If they're mounted perpendicular, one is always oriented the same as the tx antenna.

Flying a 2.4Ghz video and control is risky to say the least, even with different polarisations. The video signal is likely to swamp the control signal, a problem that is exacerbated the further the transmitter is from the plane. The gain on cloverleaf and skew-planar wheels is only around 1db too, so you're losing half your range on your transmitter straight up.
 
#20
On an RX that doesn't have two antennas (Turnigy 9x 8ch for example) I would rather have true omni coverage at a 2db drop in any orientation, vs a 20db drop when the RX antenna is oriented perpendicular or end-on to the TX antenna. With an RX that does have two antenna headers, I would mount them in opposing polarization & axis' (i.e. one vertical along side of fuse & one horizontal across the fuse).

Perhaps a patch on the TX (since its the closest thing to a beam that is portable) & a clover/wheel on the single antenna header RX?

~psguardian