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Old Oct 28, 2011, 09:03 PM
Pilot
Ai77's Avatar
Deutschland, RP, Winningen
Joined Oct 2010
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Quote:
Originally Posted by markus123456 View Post
If you fly 5.8G, it's not uncommon to have like zones of interference which ocure in intervals starting out at around 600m to 1km. What I'm trying to say is if the interference is some graininess, maybe some light snow. CAREFULLY try to fly further.
Oh, that sounds strange and quite risky to me...

I found similar problem with a very strong 1W TX and atmospheric inversion. This is scatter interference. I never found this with circular polarization, only with linear or colinear. Over water surfaces there can be reflection and interference on the water (coastline effect, fresnel zone), but again never found this with circular polarization, because circular direction is reversed in reflection or at least converted to horizontal linear on water with 6db loss. So interference in multipathing is minimal to nothing, that's the advantage of CP. Sometimes the signal is bad on narrow field, due to rx saturation, but this gets better within 100m. I'm curious to check the setup...

Maybe a vertical rx antenna could block out the horizontal reflection from the water surface with sacrificing only 3dbi of the direct signal, resulting in overall better link quality.
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Old Oct 29, 2011, 01:22 PM
Flying low is expensive.
pdiddyg40's Avatar
United States, CO, Boulder
Joined Jul 2008
2,398 Posts
I'm looking into building some more antennas for my Skywalker. I need a 20-ish inch piece of RG-316 in order to stretch the antenna from the boom to the top of the horizontal stab. I was thinking I might build a SPW while I'm at it for my RX, as I'm running a CL on the Rx at the moment. If I bought the adapting connector listed below for the Fox Rx and the cable, I'd be set to go, right?

cable- http://videoaerialsystems.com/produc...a-male-jumper/
Connector- http://videoaerialsystems.com/produc...emale-adapter/


Second question: does an excessive run of coax on the Rx side equal the losses on the Tx side?
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Old Oct 29, 2011, 01:38 PM
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Deutschland, RP, Winningen
Joined Oct 2010
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Cable loss is in fact more harmful on the RX side, because it is harder to enhance an antenna than to increase tx power to compensate cable loss.
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Old Oct 29, 2011, 03:41 PM
Flying low is expensive.
pdiddyg40's Avatar
United States, CO, Boulder
Joined Jul 2008
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Okay, then I should just stick with my 3 inch cable run to the antenna on the RX side

But the 2 foot cable run on the VTx side won't kill power radiating from the antenna, right?
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Old Oct 31, 2011, 08:29 AM
Engineer for Christ
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Amherst, VA
Joined Jun 2006
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Quote:
Originally Posted by pdiddyg40 View Post
Okay, then I should just stick with my 3 inch cable run to the antenna on the RX side

But the 2 foot cable run on the VTx side won't kill power radiating from the antenna, right?
No. Cable length increases losses no matter what side it is on. I recommend keeping the cables 12" or less at 5.8GHz. Try moving the TX if possible. If you are on 2.4GHz a 24" run is the maximum I would use.

-Alex
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Old Oct 31, 2011, 10:18 AM
Flying low is expensive.
pdiddyg40's Avatar
United States, CO, Boulder
Joined Jul 2008
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Quote:
Originally Posted by IBCrazy View Post
No. Cable length increases losses no matter what side it is on. I recommend keeping the cables 12" or less at 5.8GHz. Try moving the TX if possible. If you are on 2.4GHz a 24" run is the maximum I would use.

-Alex
Sorry for not providing all the information. Like I said, I need a 20-ish inch run from the flat spot on the boom to the top of the h-stab. I'm on 1.2ghz.
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Old Oct 31, 2011, 12:12 PM
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In that case a 20 inch run is going to cost you about .5db. Not much to be concerned with.

-Alex
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Old Oct 31, 2011, 12:28 PM
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Deutschland, RP, Winningen
Joined Oct 2010
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A cable will always kill power, that's right.

If you need a long cable on TX side, you may compensate the loss by increasing TX power to get the same field strength.

If the cable loss is on RX side, you have to substantially increade antenna gain to compensate some loss and still sacrifice aperture.

So that's why cable loss on TX does lesser harm than on RX side.
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Old Oct 31, 2011, 05:55 PM
Nakelp
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United States, NJ, Union
Joined Sep 2004
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Hi Alex I just got your clover cp and helix antennas today , Thank you so much .
One question, do I keep helix close to the ground or as high as possible/practical?

Jack
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Old Oct 31, 2011, 07:17 PM
moraesgyn
Brazil, GO, Goi‚nia
Joined Mar 2005
29 Posts
Question about wire

Hi Alex,

I am from Brazil, and I am having a hard time to find the wire you guys use to build the CL/SPW, I have a copper wire about 0.8-1.0mm from a TV coax cable do you think that's suitable?

Thanks in Advance,

Antonio
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Old Oct 31, 2011, 11:31 PM
I can fix that.
United States, PA, Mountain Top
Joined May 2006
278 Posts
Average pre-tuned frequency

I have a question for those who have built these and have tuned them after assembly. Do you find that the pre-tuned freq is lower than the desired center freq or higher?

I have built a few of the clovers, skewers, and OMM pinwheels, using 0.6mm mig wire and a center freq of 5800 MHz (52.9mm lobes). I have built a jig to assemble these. Using a good caliper, all my bends are exact, as well as my takeoff angles (45 degrees). I don't use hooks for the center feed, but subtract 0.6mm from the feed leg. Total lobe loop is right on at 52.9mm. Solder points exact to ground and feed, etc.

Using a 20db attenuator and doing straight line range tests with identical antennas, my best range comes at the lower end, 5740 MHz, consistently among all antennas. Tests were just visual quality, but they were very consistent, confirming my build accuracy.

So, has anyone else found this to be true? If so, what can I do to slightly raise the freq? Solder blob? Hot glue?

-Ken
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Old Nov 01, 2011, 08:12 AM
Engineer for Christ
IBCrazy's Avatar
Amherst, VA
Joined Jun 2006
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Quote:
Originally Posted by nakelp86 View Post
Hi Alex I just got your clover cp and helix antennas today , Thank you so much .
One question, do I keep helix close to the ground or as high as possible/practical?

Jack
Jack, when using a helical there are only two rules that MUST be followed precisely in order for the helical to work effectively.

Rule #1: Aim

Rule #2: Fly

That's it. Put it in the air or the ground. Your choice so long as the Fresnel zone is clear.

-Alex
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Old Nov 01, 2011, 08:14 AM
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Amherst, VA
Joined Jun 2006
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Quote:
Originally Posted by solomonx View Post
I have a question for those who have built these and have tuned them after assembly. Do you find that the pre-tuned freq is lower than the desired center freq or higher?

I have built a few of the clovers, skewers, and OMM pinwheels, using 0.6mm mig wire and a center freq of 5800 MHz (52.9mm lobes). I have built a jig to assemble these. Using a good caliper, all my bends are exact, as well as my takeoff angles (45 degrees). I don't use hooks for the center feed, but subtract 0.6mm from the feed leg. Total lobe loop is right on at 52.9mm. Solder points exact to ground and feed, etc.

Using a 20db attenuator and doing straight line range tests with identical antennas, my best range comes at the lower end, 5740 MHz, consistently among all antennas. Tests were just visual quality, but they were very consistent, confirming my build accuracy.

So, has anyone else found this to be true? If so, what can I do to slightly raise the freq? Solder blob? Hot glue?

-Ken
Adding material LOWERS the frequency. Chances are you are seeing either noise floor or the fact that the transmitter puts out different powers on different channels. The bandwidth on all CP antennas introduced thus far is incredibly wide and thus small variations in frequency have no measurable effect.

-Alex
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Old Nov 01, 2011, 08:15 AM
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Amherst, VA
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Quote:
Originally Posted by chumbado View Post
Hi Alex,

I am from Brazil, and I am having a hard time to find the wire you guys use to build the CL/SPW, I have a copper wire about 0.8-1.0mm from a TV coax cable do you think that's suitable?

Thanks in Advance,

Antonio
No. You must use a copper or brass coated steel. Is there no welding supply store near you?

-Alex
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Old Nov 04, 2011, 08:42 AM
moraesgyn
Brazil, GO, Goi‚nia
Joined Mar 2005
29 Posts
Quote:
Originally Posted by IBCrazy View Post
No. You must use a copper or brass coated steel. Is there no welding supply store near you?

-Alex
Thanks Alex, I will do a little more search, if I am dont find it I will order some assembled ones from
http://videoaerialsystems.com

Thanks again to come up with this great design and open it for the fpv people!
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