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Old Oct 22, 2009, 03:04 PM
JettPilot's Avatar
Miami
Joined Apr 2005
10,325 Posts
Quote:
Originally Posted by webdr
question, why does DPCAV sell the extensions as "Ideal for remotely mounting 434MHz - 1300MHz wireless video (A/V) antennas."

http://www.dpcav.com/xcart/product.p...cat=261&page=1
Pratorian,

12 inchs and 23 inch extensions are relatively short and wont hurt to badly, but it will hurt. The higher the frequency, the worse the loss. The amount of Loss at 435 MHZ is not bad at all, its very little. By the time you get to 2.4 GHZ everything changes, even short lengths have a lot of loss Just each connector at 2.4 GHZ has loss, which is probably why DPCAV is saying up to 1300 MHZ.

So I would say for those very short coax extensions, if it is for 900 MHZ video, it probably will be OK, not great, but usable..... For 2.4 GHZ video, I would not use any extension no matter how short it is.

One rule of thumb at our frequencies, do whatever it takes to mount the receiver itself at the antenna. You will get best performance if there is no coax at all.

Mike
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Old Oct 22, 2009, 03:09 PM
The Fixer
Martin Y's Avatar
Canada, ON, Milton
Joined Jan 2009
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Pick your type of cable and run it here. As you think you know better.
http://www.timesmicrowave.com/cgi-bin/calculate.pl
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Old Oct 22, 2009, 03:12 PM
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pratorian's Avatar
Quebec, Canada
Joined Sep 2007
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Quote:
Originally Posted by JettPilot
Pratorian,

guess you meant Webdr ?
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Old Oct 22, 2009, 03:13 PM
The Fixer
Martin Y's Avatar
Canada, ON, Milton
Joined Jan 2009
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Thats why I wont use that DVCAP cable.
http://www.dpcav.com/xcart/product....&cat=261&page=1
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Old Oct 22, 2009, 03:19 PM
JettPilot's Avatar
Miami
Joined Apr 2005
10,325 Posts
Quote:
Originally Posted by pratorian
guess you meant Webdr ?
Yep, I meant Webdr, hhahaha, to many responses and got them mixed up !

Mike
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Old Oct 22, 2009, 03:24 PM
JettPilot's Avatar
Miami
Joined Apr 2005
10,325 Posts
Quote:
Originally Posted by Martin Y
Pick your type of cable and run it here. As you think you know better.
http://www.timesmicrowave.com/cgi-bin/calculate.pl
That is the table I was talking about, Times Microwave cable is the best you can get that is practical for FPV uses. Remember , some of the very low loss cables in that chart are very large hard line, like pipe, so many are unusable for our purposes. There are many very hard to deal with, and very large pipe like coax listed in that chart, make sure you know what you are buying ! LMR 100 is the best small cable, and LMR 240 ultraflex is about as large a cable that is practical for our ground stations.

Then dont forget to add in the connector losses, assuming someone used the best connectors and did a perfect job of solding them to the line By the time you get to 2.4 GHZ, any type of extensions are just a bad idea and wont work well.

Mike
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Old Oct 22, 2009, 03:37 PM
The Fixer
Martin Y's Avatar
Canada, ON, Milton
Joined Jan 2009
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I using LMR-300 on my antenna(s). And I have a bit of M27500 cable to use also. This is also good to use http://www.xagyl.com/store/product.p...cat=252&page=1
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Old Oct 22, 2009, 09:50 PM
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North vancouver, B.C. Canada
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solder the rx to the antenna for best performance, so it is dirrectly in the centre behind it.

from there use high quality cable so you can sit down comfortably away from the antenna. which is clear and free

distance is not a big deal, test out far away compared to being very close.

With a good "powered" video splitter connected close to the oracle your video will be better. dvr etc.

If you use only one antenna even better , say a 10 foot cable, video audio, to your goggles or tv screen would be best "for your eyes only" lol
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Old Oct 22, 2009, 10:22 PM
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Matt Gunn's Avatar
United States, OH, Parma
Joined Jul 2009
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Quote:
Originally Posted by JettPilot
How long does your battery power that 15 inch TV ???

Mike
I had my first flight with the 15" tv today.
After a 30 minute flight, with a 3s 2200mah pack powering the tv and the oracle, it was at 73% remaining.
Not bad...
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Old Oct 23, 2009, 01:30 AM
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QUIKSILVER's Avatar
UK
Joined Sep 2002
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Quote:
Originally Posted by webdr
I had my first flight with the 15" tv today.
After a 30 minute flight, with a 3s 2200mah pack powering the tv and the oracle, it was at 73% remaining.
Not bad...

Wow, good result
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Old Oct 23, 2009, 02:53 AM
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UK
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General ground station Q, is it an advantage to mount your omni-directional Video Rx high up, for better reception?
ie: So would it at 3 metres off the ground be more effective than a foot off the ground? Cheers in advance.
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Old Oct 23, 2009, 05:43 AM
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Switzerland
Joined Oct 2006
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Yes, it can make a big difference, especially if you're flying low! Line of sight is only half the truth, you need also free space over and UNDER this line. Otherwise, you can loose up to 6dB, which results in half the range, even if you have direct sight to the plane.
See here: http://en.wikipedia.org/wiki/Fresnel_zone

Cheers, Roman
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Old Oct 23, 2009, 06:27 AM
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UK
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Quote:
Originally Posted by Hueber
Yes, it can make a big difference, especially if you're flying low! Line of sight is only half the truth, you need also free space over and UNDER this line. Otherwise, you can loose up to 6dB, which results in half the range, even if you have direct sight to the plane.
See here: http://en.wikipedia.org/wiki/Fresnel_zone

Cheers, Roman

I started to cry when i read this part

Fn = The nth Fresnel Zone radius in metres

d1 = The distance of P from one end in metres

d2 = The distance of P from the other end in metres

λ = The wavelength of the transmitted signal in metres

The cross section radius of the first Fresnel zone is the highest in the center of the RF LoS which can be calculated as:


My ears are bleeding
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Old Oct 23, 2009, 06:39 AM
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UK
Joined Mar 2009
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Roman, cheers thats great info - the wikipedia link.
This helps ALOT, as I'm currently re-vamping my Ground Station.

I take it a Patch Antenna will also benefit being higher up, for a greater opportunity to have LOS of the plane with no ground obstructions? Hence why you see them mounted at the top of masts - however, contradicting info people have posted here, where its best close to the ground!
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Old Oct 23, 2009, 06:47 AM
FPV addict
Giske, Norway
Joined Aug 2009
521 Posts
I've started to place my antennas (11dB patch and 3dB omni connected to Duo Diversity) on the roof of my car and I've got much better signal/range now.

Kristian
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