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Old Jan 28, 2011, 11:28 PM
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Daemon's Avatar
Lakewood, Colorado
Joined Aug 2002
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Quote:
Originally Posted by Old Man Mike View Post
But for a max distance, low flight objective like the example that started this discussion, the higher mounted patch is far better.
Yet nobody has *ever* asserted that a patch on the ground was the best tool
for that particular objective (long range, low to the ground), but you were the one to
bring patches on the ground into the discussion. Guess it was just a straw man argument.

ian
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Old Jan 28, 2011, 11:56 PM
BEOWULF
North vancouver, B.C. Canada
Joined Apr 2008
18,828 Posts
You guys should try a yagi or patch or omni on your head, it works great for flying fpv

No need for your body or objects to get in the way

You can do high speed passes all around yourself

You can peep under or over the goggles to see if clear LOS is there as you fly
even if you are very far away. like 5 km
your orrienteering is spot on etc.

with 1.2 there is very little antenna tuneing needed, you will be able to fly far away and turn the antenna with small increments

sit back in a lawn chair and put a yagi or a patch on your head
if you fly behind yourself just stand up and move with the plane

fly into the wind at all times and stand up for landing
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Old Jan 29, 2011, 12:56 AM
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Old Man Mike's Avatar
Joined Oct 2007
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Quote:
Originally Posted by Daemon View Post
Yet nobody has *ever* asserted that a patch on the ground was the best tool
for that particular objective (long range, low to the ground), but you were the one to
bring patches on the ground into the discussion. Guess it was just a straw man argument.

ian
What spun me up was the comment "..when a patch is mounted on a tripod high into the air, it's only yeilding ~3-4dBi of gain at most..." and that the 8 dB is only possible when the patch is on the ground. It bothers me to see such disinformation.

And never say *ever* when referring to RCgroup discussions.

OMM
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Old Jan 29, 2011, 01:56 AM
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Virgis21's Avatar
Kaunas, Lithuania
Joined Oct 2007
1,527 Posts
Quote:
Originally Posted by Old Man Mike View Post
Excellent! You can now show everyone how much worse it is when you put it on the ground. It is amazing how many people believe that a patch on the ground works better than one up in the air. There is a small angle where this might be true (depending on ground conditions) and I suppose that is what started the popular but generally false believe.

OMM
Hi Mike,

I could believe then flying far and very high (American style ).
but then i go very low? Patch on the ground and patch on the top of car (2.5m above) gives much more clearance over terrain! So I believe to go very low and far, must build yours own communication tower


Quote:
Originally Posted by Eganwp View Post
Virgis, those are great videos! I'm very impressed with the quality of signal that far away, so close to the ground. Is it a home made patch? (GP or fast patch if so?). I get a lot more multipath interferrence when far away low to the ground on my modified l-com patch. I thought it was just the snow causing it (5" off the snow), which it might be, but we haven't had a break from the snow yet to be able to test. I might try mounting mine up higher on vehicle as you've done for an effective ground plane, and see if the lack of snow gives less multipath interferrence. My guess is it should.

Thanks for the great videos!

Egan
Egan,

That patch antenna is one of two very similar. I am using frequency above 1200mhz. So must choose one with correct frequency build for.
Ones are very popular are 1080-1200mhz, they don't work for 1280mhz at all (tested, not more than 1.5km).
So I went for another one, 1180-1300mhz. I think Hobbywireless.com sells them:
http://hobbywireless.com/cart/index....roducts_id=343
they do have another with 1080-1200mhz (does fit my frequency range).
And another way to have this quality is to match antennas. I've never had time to try to build my own (inverted ... antenna yet). For now have tried as many as 6 omni 3dbi (stock) antennas on video tx to find the best matching for my frequency. And got this lucky number to play with!.
So This setup as you have seen now (6km so far). works the same good over 20km (tested):
Far FPV test (4 min 2 sec)
(testing, if landing could be done over 20km )

Virgis
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Old Jan 29, 2011, 02:10 AM
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Lakewood, Colorado
Joined Aug 2002
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Perhaps "ever" was too strong, but I've never seen anyone claim that here, and it's
certainly not a "popular believe". That a patch on the ground can perform well, yes.
Low and long, no. One thing to consider is this
Quote:
Originally Posted by Old Man Mike View Post
I I can assure you that a properly designed patch
antenna will provide the entire 8 dBi gain without any contribution from earth ground
(technically this is called free space gain).
Again, since the belief that a patch on the ground was effective came from the 900Mhz
world, I want to talk about that a bit.
I'm not convinced that the most widely used L-COM 900Mhz 8dB patch is really
properly designed. The well proven Goof Proof patch, for instance
has an 11.2x11.2" ground plane and 5.9x5.9" patch when scaled for 910Mhz,
while the L-COM HG908P has a 7x7" ground plane and 5.75x6.375" patch,
while they both have roughly the same 0.5" spacing between plates.
Since patch area and spacing are so close to each other, it seems like
the L-COM patch is seriously lacking in ground plane.

One more interesting note.. The Wiki article on patches http://en.wikipedia.org/wiki/Patch_antenna
just happens to do a comparison between a couple 900Mhz patches which results in this.

Where Antenna A is basically an L-COM patch, and Antenna B sounds to be pretty
darn close to a GP patch.

ian
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Old Jan 29, 2011, 02:15 AM
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Lakewood, Colorado
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BTW, I suppose I should tear open my L-COM 1208 patch now and
see how it scales to the 900Mhz patch and the appropriately scaled GP patch.

ian
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Old Jan 29, 2011, 02:57 AM
Giant Scale 3D/IMAC & FPV
Eganwp's Avatar
Canada, AB, Calgary
Joined Feb 2008
631 Posts
OMM and Ian, you guys are making me wish this cold weather was gone so I could go test this stuff out again now! :P

Thanks for the info OMM. I too only have a 7" ground plane in my modified l-com 1.2 patch (tuned for 1280mhz). I'm wondering if the ground is causing a larger effect because of this?

I'm going to build a GP Patch and also a Fast patch, all tuned to 1280 to see if I can yield any differing results between them. The comment about 3-5dbi when on a tripod is simply info I'm relaying, nothing to do with my own testing...

Thank again OMM, your knowledge in antenna design is definately welcomed by me.
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Old Jan 29, 2011, 04:48 AM
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Joined Oct 2007
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Quote:
Originally Posted by Virgis21 View Post
Hi Mike,
..... So I believe to go very low and far, must build yours own communication tower ....
I agree. This is my communication tower with FPV and R/C control antennas:





Top antenna on tower is 28 meters above ground.


Quote:
Originally Posted by Daemon View Post
..... it seems like
the L-COM patch is seriously lacking in ground plane.
.... ian
Maybe so. But lower VSWR (shown as Reflection Coeff in the chart) does not necessarily mean significant improvement in forward gain. The difference between 15 dB Ref Coeff (1.5 VSWR) and 25 dB Ref Coeff (1.1 VSWR) is only about 0.2 dB of signal loss. But higher VSWR can be an an indication of a poor radiator or a poor pattern. The only way to know for sure is to do antenna modeling and determine the actual radiation pattern and gain.


And apologies to all for my rather strong earlier response. RF guys are generally temperamental. It is probably due to all that RF exposure over time (more than 40 years of exposure here).

OMM
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Old Jan 29, 2011, 09:12 AM
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Back in Hong Kong
Joined Sep 2003
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Quick question.

Is 1.2 ghz or 1.3ghz legal in Hong Kong or at least a frequency that can be used without upsetting anyone.I have seached for days but cant find anything either way about it on the net.

Thanks
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Old Jan 29, 2011, 09:55 AM
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Luxembourg
Joined May 2009
806 Posts
Hi folks, I would like everybody to focus on a new issue which would help the community with straight solutions I could add on the first page of the Topic.

Issue is: Servo Jittering with 1.2Ghz

Demo Video and one solution Here:
Servo jittering due to RF Interferences (1 min 58 sec)
(sorry my lens was dirty)

My experience showed that this issue is related to ESC and definitaly servos. But as you can see in the video, picking particular servos solves it completely.

Setup from the Video:

Lawmate 1W on 1080Mhz not connected to the servos at all.
ESC: none (Rx powered with Batteries)
Tested servos: HXT 900 (jitter) - Esky EK2-0508 (no jitter at all)
RC: 2.4Ghz Futaba Fasst

What I want us to achieve: Make a list of servos that don't jitter at all near (even touching) a 1.2ghz Vtx

Because the Eskys servos are not the cheapest and not the best.

Important: test was made with a genuine EK2-0508 (8$ a piece) not the fake ones (4 for 12$, packaged in a bag). Maybe the fake ones would work too but I have no Idea.
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Old Jan 29, 2011, 11:37 AM
Destructive testing expert!
Bill Sanford's Avatar
Bemidji, MN
Joined Dec 2003
908 Posts
Hi Everyone,

Is there a source for just the Fox 700mW transmitters alone like in the BOB combo kit.

I have plenty of RXs and just need more transmitters for more models.

Has anyone found any of these?
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Old Jan 29, 2011, 11:52 AM
Registered User
Luxembourg
Joined May 2009
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No Unfortunately it is very difficult to find a lone Tx

you can buy a lawmate 1W Tx only but its nearly 90USD
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Old Jan 29, 2011, 12:06 PM
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Kaunas, Lithuania
Joined Oct 2007
1,527 Posts
Lawmate does the job, worth 100usd!
Just watch my video will see how it worth..
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Old Jan 29, 2011, 12:39 PM
You can't take the sky from me
Rastislavko's Avatar
Slovakia, Bratislava Region, Bratislava
Joined Jun 2006
754 Posts
About jittering: HXT servos (especcialy HXT500, but also HXT900) jitters like hell. It has nothing to do with your bec or receiver. Make simple test - connect servos to the servo tester and power it directly with 4 NiMh pack. It will jitter as well! For now I don't have any "jitter-free" servos. I've replace all HXT servos with Hitec HS-81, but they jitter as well (but not so much - when I move videotx to the end of the plane as well as on the video, there are no more noticable jittering at all).

I found no proper way to solve this. Shielding or twisting servo wires won't help. Using ferites won't help. I'm going to try some digital servos, I'm really impatient if it will help.
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Old Jan 29, 2011, 01:11 PM
Videopilot
Derek_S's Avatar
United States, NC, Charlotte
Joined May 2009
2,815 Posts
Quote:
Originally Posted by iacei View Post
Hi folks, I would like everybody to focus on a new issue which would help the community with straight solutions I could add on the first page of the Topic.

Issue is: Servo Jittering with 1.2Ghz

Demo Video and one solution Here: http://www.vimeo.com/19322275 (sorry my lens was dirty)

My experience showed that this issue is related to ESC and definitaly servos. But as you can see in the video, picking particular servos solves it completely.

Setup from the Video:

Lawmate 1W on 1080Mhz not connected to the servos at all.
ESC: none (Rx powered with Batteries)
Tested servos: HXT 900 (jitter) - Esky EK2-0508 (no jitter at all)
RC: 2.4Ghz Futaba Fasst

What I want us to achieve: Make a list of servos that don't jitter at all near (even touching) a 1.2ghz Vtx

Because the Eskys servos are not the cheapest and not the best.

Important: test was made with a genuine EK2-0508 (8$ a piece) not the fake ones (4 for 12$, packaged in a bag). Maybe the fake ones would work too but I have no Idea.
Do you also want a list of what does jitter? For me all the 9g blue ones do (rctimer, hextronic, turnigy, towerpro), Hitec HS82MG, TPro MG90s and MG16R (but both much less than the others), the stock ones on my PZ Corsair and Trojan do..
So I have none that are jitter free with 1280 mhz. I would love a list though of canidates.
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