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Author Topic: Range over water (need more)  (Read 794 times)

Baldy

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Range over water (need more)
« on: October 25, 2018, 10:17:51 PM »

Hey all,

Some time since I've posted on here but I basically use an fpv rig on a fishing bait boat. I don't use the boat often but had it with me for a week in France last week. It works OK, in fact, boating up to illuminous markers tied to the bank in the night is a revelation! :D but at ranges as short as 40 yards I'm getting broken signal.

The first set ups I made used 5.8ghz Boscam stuff with a 200mw transmitter, with decent los I could just about get to 90/100 yards before image was useless. I have since upgraded to RMRC 1.2ghz gear expecting that to be the answer to my range issues, but it is not proving so. Currently using the standard dipoles that came with the tx and rx as they are compact and look neat, would an antenna upgrade make a significant difference? I'd love a 150/200 yard reliable range over water day and night if possible!

Thanks,
Rob
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ched

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Re: Range over water (need more)
« Reply #1 on: October 25, 2018, 10:22:42 PM »

I am no expert on radio transmission but I am wondering if it's a sort of multipath issue. i.e. the signal is almost swamping itself by bouncing off the water and destroying the signal by being out of phase. Maybe a solution is to use a circular polarised antenna, they need to both be same direction, ie. Right Hand.
Other than that try and get the antenna on the boat a bit higher as that might help.
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Baldy

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Re: Range over water (need more)
« Reply #2 on: October 25, 2018, 11:14:40 PM »

Hi, thanks for the reply. I really want to keep the aerial as low as possible on the boat as the general jist of these toy boats used for fishing is that you can get right under overhanging trees etc  ;D
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ched

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Re: Range over water (need more)
« Reply #3 on: October 25, 2018, 11:48:41 PM »

OK I understand a bit better. Circular polarised antenna on the boat and maybe a directional helical antenna on the receiver. Both same hand i.e. both right or both left handed.
That will probably give you the best chance.
Other than that maybe an increase in power. Although you need 4 x power to get double the range!!!
I would try antennas first.
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Dillwhacker

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Re: Range over water (need more)
« Reply #4 on: October 26, 2018, 11:12:59 PM »

I'm no expert here, but that sounds like there is something fundamentally wrong.
Last week I flew 1 km over the sea and the video was perfect and exactly the same as over land.
So I really doubt that it's the water causing the issue.
You need to  check over land just to confirm.
I was going to suggest broken / shorted / open antennas or LHCP/RHCP or SMA / RPSMA, but if you have switched from 5.8G to 1.2G then you have obviously swapped antennas....
I'm stumped, sorry.
100 yards on 1.2GHz is ridiculous, you should get that without any antennas!!!
Stumper!!


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Ratty

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Re: Range over water (need more)
« Reply #5 on: October 27, 2018, 12:55:54 AM »

I would say fresnel zone issues, but i am no expert either.

Id test it on land at the same distance by placing it on the ground, and then the same distance a meter or two off the floor to see if it improves.

A directional antenna will likely help if you can point it at the boat.

EDIT:

It does sound like something is not right tho. Are you using 2.4 RC control by any chance? If so, do you have a low pass filter installed?
« Last Edit: October 27, 2018, 12:58:00 AM by Ratty »
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Coyote

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Re: Range over water (need more)
« Reply #6 on: October 27, 2018, 11:30:35 AM »

Water absorbs higher frequency RF so the closer an object is to it the worse it is. The boat being on it makes it pretty much as bad as it gets without being in it.



The only improvement I can think is to the the Vtx and Rx antennas on the boat as high as possible from the water. This will only buy you an extra margin of range though, directional antennas will help on the land. The lower the frequencies used for control and video the better tbh. Have you any old 35 MHz kit lying around ?
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Education and schoolin is good, but FPV is gooder :)

Baldy

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Re: Range over water (need more)
« Reply #7 on: October 27, 2018, 01:14:37 PM »

Hi, control is via 40mhz so shouldn't be an issue. I'll give the kit a test over land to make sure everything works as expected in that respect. If I have issues with range on land at those distances I guess I have problems lol I have had it working to maybe 100 yards in the UK with ok picture, little bit of interference. I understand France can do strange things with regards to attenuating signal!
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ched

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Re: Range over water (need more)
« Reply #8 on: October 27, 2018, 01:46:59 PM »

One think to also check is that the antenna connections are compatible. i.e one side of the connection has a in in the middle.
I assume you realise powering on the transmitter without an antenna will destroy it!!!! Maybe not completely but could seriously reduce output.
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Baldy

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Re: Range over water (need more)
« Reply #9 on: October 27, 2018, 02:08:49 PM »

I assume you realise powering on the transmitter without an antenna will destroy it!!!! Maybe not completely but could seriously reduce output.

Yep I I'm aware of this :) never done it! The antenna used are the ones that came with the tx and rx from RMRC, standard dipole things I think, so I guess an antenna upgrade is worthwhile. With the 5.8 I ended up with a circular polarised on the tx and a helical on the rx. Certainly improved things. But as mentioned I went to the 1.2 gear thinking even with bog basic antenna I'd get an easy 150/200 yard reliable range. More fool me lol
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ched

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Re: Range over water (need more)
« Reply #10 on: October 27, 2018, 02:19:33 PM »

Sounds like you are doing all the right things.
I did have a quick look about to see if anyone on the net was having similar issues with vtx being so close to the water. It seems it's a common problem!! I didn't find anyone really saying they had a solution other than getting the boat antenna as high as possible which isn't any use to you.

I wonder if you try putting the antenna horizontally instead of vertical? Reasoning is that the radiation pattern of a dipole is sort of ring donut shaped with the antenna sort of sticking through the hole. So if you position it horizontally you might get more RF sort of firing away from the water. No idea if it would work but might be worth a try.
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Baldy

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Re: Range over water (need more)
« Reply #11 on: October 27, 2018, 02:19:58 PM »

It's a bit of a clunky set up, but would be perfect if I could just get the range sorted :)





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Baldy

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Re: Range over water (need more)
« Reply #12 on: October 27, 2018, 02:25:11 PM »

Sounds like you are doing all the right things.
I did have a quick look about to see if anyone on the net was having similar issues with vtx being so close to the water. It seems it's a common problem!! I didn't find anyone really saying they had a solution other than getting the boat antenna as high as possible which isn't any use to you

It's when you see stuff like this!  :D

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ched

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Re: Range over water (need more)
« Reply #13 on: October 27, 2018, 03:38:17 PM »

That is great. The attention to detail was great. The boats steering wheel and throttle  :D Then the mirrors on the truck  :D
Great fun.

As for your kit, looks like it's made for the job. Dipole is probably safest antenna for not getting stuck in tree branches. I would give it a try horizontally at 90degrees to the boat hull. You could just have the boat a few meters out in the water and walk away with your rx and see what range you can get. Try and have the rx antenna vertical.
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Dillwhacker

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Re: Range over water (need more)
« Reply #14 on: October 27, 2018, 11:46:22 PM »

It's when you see stuff like this!  :D


That is flipping brilliant!! Love it, very well done!
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