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Old Aug 25, 2011, 08:13 AM
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Question
CP Omni antenna gain

Hugo and IBCrazy;

What kind of gain levels do your antennas have?

I ask because I am moving to ground-based fpv due to lifestyle and location constraints (2 kids with one on the way and living near the great lakes where it is *always* windy and hard to fly.)

Since in ground FPV making banked turns really isn't something we worry about, we "ground pounders" can take advantage of a much "flatter" TX radiation pattern than the flyboys can. I'm hoping that you guys can help me out by either selling me, or assisting me in making some really high gain Omnis for my FPV truck project. Not only should it help increase range, but it should really help in cutting through or wrapping around ground clutter.
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Old Aug 25, 2011, 08:29 AM
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The highest gain CP omni that I know is OMM's variation of the SPW at 1.7db, still fairly spherical for a truck however. My solution would concentrate on the Rx end, with an open biquad (9.5db) and a turbine on the truck (0.9db) to maximize multipath rejection.

-Hugo
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Old Aug 25, 2011, 08:35 AM
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Quote:
Originally Posted by Hugeone View Post
The highest gain CP omni that I know is OMM's variation of the SPW at 1.7db, still fairly spherical for a truck however. My solution would concentrate on the Rx end, with an open biquad (9.5db) and a turbine on the truck (0.9db) to maximize multipath rejection.

-Hugo
I'm just concerned about beamwidth on an open Biquad. I don't have and can't afford an antenna tracker right now, and it's really easy to drive out of a narrow beam as you have to navigate around obstacles on the ground.

Most of the ground guys are trying to deal with the "blocking" issues by using ever more powerful transmitters. As you can imagine, this has an upper end of utility where one simply can't go any higher. I'd like to see if we can avoid using absurdly over-powered TX units by focusing on gain and multipath rejection to increase our limited range.
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Old Aug 25, 2011, 09:15 AM
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The beam of an open-biquad is 60deg, but 90deg. is usable.
When driving a truck, does manually pointing the antennas seem realistic?

-Hugo
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Old Aug 25, 2011, 09:28 AM
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You could even go linear and build an AMOS antenna. If you drive in a fairly flat area, you could put an AMOS a few inches off the ground and have 11dbi with 120 degree beamwidth.

CP is excellent at penetrating objects. If you want to drive behind stuff, take Hugo's suggestion. I would sooner use a helical over an open BiQuad, but that's just my personal preference.
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Old Aug 25, 2011, 09:38 AM
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Originally Posted by Hugeone View Post
The beam of an open-biquad is 60deg, but 90deg. is usable.
When driving a truck, does manually pointing the antennas seem realistic?

-Hugo
Not terribly. While ground vehicle travel much slower than air vehicles, knowing where they are in relation to you when driving around obstacles can be tricky. Even a spotter won't help if there is a house or half a forest between you and the vehicle.

However, a 90 deg beamwidth is probably doable. the open biquad is CP, correct?
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Old Aug 25, 2011, 09:40 AM
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Originally Posted by IBCrazy View Post
You could even go linear and build an AMOS antenna. If you drive in a fairly flat area, you could put an AMOS a few inches off the ground and have 11dbi with 120 degree beamwidth.

CP is excellent at penetrating objects. If you want to drive behind stuff, take Hugo's suggestion. I would sooner use a helical over an open BiQuad, but that's just my personal preference.
I'm not familiar with AMOS antennas myself. I just want to ensure that I can have good object penetration.
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Old Aug 25, 2011, 10:53 AM
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I must have wrecked dozens of times since switching to circular polarization due to loss of control by flying behind objects. I used to use my video as an indicator, but it really doesn't do it anymore. CP tends to punch right through houses, hills, ect. Sure if you are a mile away you won't get signal penetration, but for close-by CP does the job.

If you want pure punch with high gain, the AMOS is the way to go when coupled with a 3/2 or 5/2 wave dipole. You can build them for up to 13 dbi and they have an incredibly wide beamwidth.

Either will work. If you want to build the AMOS, I'll make the 4:1 balun and cable connection for you.

-Alex
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Old Aug 25, 2011, 10:57 AM
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I think there's a faulty premise here, which is that the ground is flat.
An R/C truck rolls and pitches all the time, going over relatively minor
terrain features, including vegetation.

ian
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Old Aug 25, 2011, 11:25 AM
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I would sooner use a helical over an open BiQuad, but that's just my personal preference.
I suggested the OB because high gain helical tend to have a narrow beam. However they are much easier to build than the OB. Furthermore, I forgot that you'll probably use 1.2ghz, which I'll don't make OB for, at least not now.

-Hugo
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Old Aug 25, 2011, 11:38 AM
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I suggested the OB because high gain helical tend to have a narrow beam. However they are much easier to build than the OB. Furthermore, I forgot that you'll probably use 1.2ghz, which I'll don't make OB for, at least not now.

-Hugo
Actually, I'm going 5.8g. Many of the ground guys are starting to go that way. it seems to match up well with the 2.4g control systems. Less range, but a more stable signal than either 1.2 or 900. Could be that it has less ground plane issues than the lower frequencies.

As far as the "pitch and roll" issues of ground FPV that you mentioned earlier, you are correct. But I'm not looking for gain so high it turns the signal into a "washer". I'm thinking more "flower" vs "Apple" shape. something like a 20-30% flattening and widening of the radiation pattern. Nothing more. Just something to slightly increase the range and give the signal a bit more "punch" when dealing with ground clutter.
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Old Aug 25, 2011, 06:04 PM
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Originally Posted by Wearyman View Post
Actually, I'm going 5.8g. Many of the ground guys are starting to go that way. it seems to match up well with the 2.4g control systems. Less range, but a more stable signal than either 1.2 or 900. Could be that it has less ground plane issues than the lower frequencies.

As far as the "pitch and roll" issues of ground FPV that you mentioned earlier, you are correct. But I'm not looking for gain so high it turns the signal into a "washer". I'm thinking more "flower" vs "Apple" shape. something like a 20-30% flattening and widening of the radiation pattern. Nothing more. Just something to slightly increase the range and give the signal a bit more "punch" when dealing with ground clutter.
Remember how your mother use to say "if everybody jumped off a bridge, would you jump too?" That applies here. You want a LOWER frequency for object penetration. Go 900 or 1.2. 5.8 cannot penetrate trees let alone hills and structures.

I was referring to the AMOS as an RX antenna, not a TX antenna.

-Alex
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