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Author Topic: Testing some different antennas on goggles with linear on a quad  (Read 538 times)

CurryKitten

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Testing some different antennas on goggles with linear on a quad
« on: November 16, 2017, 10:50:44 AM »

This video isn't public yet - I'll make it so in the next few days (I want to space them out so I don't release lots in a big lump).  But I thought it was an interesting test, and I'm keen to hear any feedback/explanations you guys have.

The idea behind this test was the fact that a lot of micro quads, and even the larger ones are getting shipping with little linear dipole FPV antennas.  It's generally a decent idea as it was very easy to squish the little skews they had in a crash (and crashes come often).  But given that everyone uses a skew on their goggles, this will mean a loss shouldn't it ?

TommyD also sent me over a prototype of a linear patch he's been developing, so I thought I'd test the little linear on a micro quad with a 25mw VTX against a skew, rubber duck and Tommy's patch on my goggles.  Here are the results

! No longer available


So why does a linear->linear perform worse than linear->circular polarised.  I thought maybe it's multipathing, but the reason the skew rejects multipath well is that a reflected signal comes in the opposite circular polarisation.  Linear reflected signals would be (I presume) received on the skew.

So why is this happening ?

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Testing some different antennas on goggles with linear on a quad
« Reply #1 on: November 16, 2017, 10:57:09 PM »

So that’s basically what I am using at the moment on the goggles: la Forge diversity, TBS patch and BigNose skew. However...... I am using a Pagoda on the quad. So please do the test again with a pagoda on the quad 😀😀


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CurryKitten

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Re: Testing some different antennas on goggles with linear on a quad
« Reply #2 on: November 16, 2017, 11:02:13 PM »

So that’s basically what I am using at the moment on the goggles: la Forge diversity, TBS patch and BigNose skew. However...... I am using a Pagoda on the quad. So please do the test again with a pagoda on the quad 😀😀

I predict that the rubber duck would be crap again.  I would like to try the rubber duck Vs a coat hanger.  This a reference lost on the young, but was a quick fix for your car radio aerial back in the day*

*day referring to sometime in the 1970's

English Turbines

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Re: Testing some different antennas on goggles with linear on a quad
« Reply #3 on: November 16, 2017, 11:17:59 PM »

  I have flown Fixed Wing extensively on 5.8G using a RD on the Plane....I use a matched Pair of 14dbi Vertically polarised patch antennas on my diversity Monitor.....It works a LOT better than Skews.
  The reason is, is that Im always in the beams as Im not wearing goggles and can track it by hand easily.

 If and when I start flying my Quad though, I will be using a pair of skews with a skew on the Quad because the flying style is lower and nearer where we know the skew will do better overall.  That said, if I could hand track it, (and fly the quad at the same time) the linears would doubtless give a better signal.
  You can't aim a patch accurately whilst wearing goggles, its that simple.

 If you would fly the Bflight 210 as a comparison, I think the linear would do a lot better because its antenna is way longer and clear of the Quad body..?

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CurryKitten

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Re: Testing some different antennas on goggles with linear on a quad
« Reply #4 on: November 17, 2017, 12:43:02 AM »

  You can't aim a patch accurately whilst wearing goggles, its that simple.

I beg to differ, I've done quite a lot of flying on a 3 turn helical on a plane and after you get out to 3 or 4km it becomes very easy to turn your head accurately to the sweet spot as you can spot the drop off in the signal as you do a quick back and forth scan.

If you would fly the Bflight 210 as a comparison, I think the linear would do a lot better because its antenna is way longer and clear of the Quad body..?

I didn't quite get this point.  The little linear which doesn't stick out that far - was still the same for the skew, and that did better than the RD.  What is the issue linear to linear that linear to skew doesn't get ?

English Turbines

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Re: Testing some different antennas on goggles with linear on a quad
« Reply #5 on: November 17, 2017, 09:39:17 AM »

I beg to differ, I've done quite a lot of flying on a 3 turn helical on a plane and after you get out to 3 or 4km it becomes very easy to turn your head accurately to the sweet spot as you can spot the drop off in the signal as you do a quick back and forth scan.

I didn't quite get this point.  The little linear which doesn't stick out that far - was still the same for the skew, and that did better than the RD.  What is the issue linear to linear that linear to skew doesn't get ?

  I think you misunderstood my Mail Wayne, yes, I agree, as I said, hand (head) tracking a plane wearing goggles is one thing, tracking a low, fast flying quad flying around a large field is another...dont you agree..? Try using just your directional on your goggles for example.

  As I said, if and when I get to fly my quad, I will be using a Skew both ends.

 I thought the linear dipole on the Bflight 210 was pretty long..?....If you had someone else hand track that for you using a linear directional (never seen you use a linear directional antenna before) on an external receiver, it would be a different story altogether.  (If they could see it..lol)

 But I agree, the tiny linear on the quad using a skew on the goggles did work quite well, and seems like a reasonable (if unlikely) working combination when flying relatively close in  (when isn't it close in)?..

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« Last Edit: November 17, 2017, 09:50:42 AM by English Turbines »
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Loopdreams

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Re: Testing some different antennas on goggles with linear on a quad
« Reply #6 on: November 17, 2017, 11:13:28 AM »

If you've got a diversity module then a patch and skew works really well.  Many patch antennas have a fairly wide angle so depending on the layout of the field you can usually position yourself so that at least most of the time the patch will be effective and the rest of the time it just uses the skew.

But even without diversity I still found that a lot of the time it was still fine, if you're within a reasonable distance then the patch still works of even if the quad gets behind you.
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DS123

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Re: Testing some different antennas on goggles with linear on a quad
« Reply #7 on: November 17, 2017, 12:19:48 PM »

Have you tried the Menace RC linear patch? I have one but not got the adaptors to attach it to my goggles yet (wait another 20 days). I'd like to see a test of that as I've just changed to a linear on my 5" quad as I've broken so many VTX and skews!
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English Turbines

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Re: Testing some different antennas on goggles with linear on a quad
« Reply #8 on: November 17, 2017, 02:04:35 PM »

If you've got a diversity module then a patch and skew works really well.  Many patch antennas have a fairly wide angle so depending on the layout of the field you can usually position yourself so that at least most of the time the patch will be effective and the rest of the time it just uses the skew.

But even without diversity I still found that a lot of the time it was still fine, if you're within a reasonable distance then the patch still works of even if the quad gets behind you.

   Yeah...I agree... :yeahthat:....I will probably be using a Skew and an old 3 turn helical on my diversity Monitor...It just seems the sensible thing to do..As much as I like a linear antenna, I know it's not going to be much use on a Quad, not on 5.8G anyway.  My 5.8G Linear RX antennas are vertically polarised and at 14dbi present quite a narrow beam to fly in, but not 3kms out when using a pair of them, which is where they really excel.

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Coyote

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Re: Testing some different antennas on goggles with linear on a quad
« Reply #9 on: November 17, 2017, 08:27:52 PM »

Quote
So why does a linear->linear perform worse than linear->circular polarised.

Because of polarization loss.

Linear to linear is perfectly polarized, until either end is not perfectly vertical, then db losses are incurred degrading the signal by up to -26dBi.

With linear to circular polarization, a -3dBi loss is already incurred but because the circular antenna is circular the movement in the linear polarisation incurs no more thereafter.
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CurryKitten

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Re: Testing some different antennas on goggles with linear on a quad
« Reply #10 on: November 17, 2017, 09:24:19 PM »

Because of polarization loss.

Linear to linear is perfectly polarized, until either end is not perfectly vertical, then db losses are incurred degrading the signal by up to -26dBi.

With linear to circular polarization, a -3dBi loss is already incurred but because the circular antenna is circular the movement in the linear polarisation incurs no more thereafter.

Thanks Ian - all explained now.. and with a quad the two linears will almost never be lined up

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Re: Testing some different antennas on goggles with linear on a quad
« Reply #11 on: November 30, 2017, 01:53:09 AM »

Good little test. You need to finish the test with a different Quad that would allow antenna swaps at the TX end, and include mixing LH & RH CP.

Also throw in a couple of slow rolls at the end of the field ;)
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CurryKitten

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Re: Testing some different antennas on goggles with linear on a quad
« Reply #12 on: November 30, 2017, 09:49:22 AM »

That QAV105 has a UFL connector for the antenna, so I was thinking about swapping out for a skew to compare (I have a few with UFL connectors) but because we really didn't get much of a drop off using a linear, it seemed a bit of a waste.  It's like saying - the picture is good, but you could also use a skew that could get damaged easily for a slightly better image ?

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