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Old Apr 23, 2009, 01:50 PM
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FPV Backpack, mounting high gain whip antennas

hey guys I need help on finding an antenna mount or relocation kit for the stock 900mhz high gain whip antennas.

I am building a backpack that holds all my FPV gear, such as the Diversity box, lead cell batteries, two 900mhz Rx, and video glasses. it's a little clunky but more comfortable and better than tripping over cables.

I will have everything inside an alloy framed hiking back-pack. What I need to do is find the antenna extension cables, to go from the two Rx's and connect to a mounting plate or adapter, so to afixed to the high gain antennas to the top of my backpack.
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Old Apr 23, 2009, 03:38 PM
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Backpack antennas

that's what sticking out of my backpack
AWM635 diversity receiver gets power stright from HDD recorder
yesterday got 2km range with AWM633 onboard my Beevolution flying wing
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Old Apr 23, 2009, 05:02 PM
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Don't use antenna extension cables. Just mount the receivers high
and use RCA extensions for the A/V. You lose a lot more signal
using long coax than you do long RCA.

ian
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Old Apr 23, 2009, 05:30 PM
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really?

well then if that's the case it looks like a total redesign if that's the case. Unfortunatly I have the really big 4 channel selectable rx's, I wish I bought the smaller version.
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Old Apr 23, 2009, 05:39 PM
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Quote:
Originally Posted by JustinONE
really?

well then if that's the case it looks like a total redesign if that's the case. Unfortunatly I have the really big 4 channel selectable rx's, I wish I bought the smaller version.
I was tossing around an idea just like this in my mind lately. Glad to see someone is actually giving it a try! Please post photos of your final setup!

I have a dream of doing some hiking in my local hills and just pulling out my little FPV T-Rex 250 at any time to fly up and down the hills to "scout" out the trail ahead. The heli could also be good to clear a path through a herd of cattle. They're big animals but skittish.
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Old Apr 23, 2009, 06:58 PM
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JustinONE, I use rg58 cable and rp-sma connectors to connect the biquad antenna with receiver. I think it's enough for shorter extensions. If you need to put the RX and RX antenna further away from you, do what Daemon says and use the A/V cable as extension, not the antenna wire.

fmkit: where can I buy AWM635 diversity package? (very small unit count, I want only one maybe two) do you have specs for the antennas you connect to it in the picture?
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Old Apr 23, 2009, 07:53 PM
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Quote:
Originally Posted by WEREE
I was tossing around an idea just like this in my mind lately. Glad to see someone is actually giving it a try! Please post photos of your final setup!

I have a dream of doing some hiking in my local hills and just pulling out my little FPV T-Rex 250 at any time to fly up and down the hills to "scout" out the trail ahead. The heli could also be good to clear a path through a herd of cattle. They're big animals but skittish.
I'll take some shots of it get the ideas flowing, definatly need to rethink the entire layout again, I could shave a lot of weight off my current set up. I wish I could find a smaller rigid back pack. we;ll see what happens.
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Old Apr 23, 2009, 08:05 PM
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Originally Posted by JustinONE
I'll take some shots of it get the ideas flowing, definatly need to rethink the entire layout again, I could shave a lot of weight off my current set up. I wish I could find a smaller rigid back pack. we;ll see what happens.
Check out this small 17" rolling back pack. I have been using this exact model for several months now for commuting on the train. Good build quality and its under 2lbs empty weight.

http://www.overstock.com/Luggage-Bag...519095-000-005

All rolling backpacks have a hard bottom and back -- it is required for the sliding handle. The handle comes up and out and could act as a perfect antenna mount because the handle is very rigid and sturdy. You just need to find a way to lock it up because it will slide down easily otherwise. I could guess a small drilled hole and a wing nut or something similiar could work.

The photos of the handle here shows the handle coming up only half way. I know for a fact it goes twice as high as the photo shows.

This 17" size I think is on the small end but they go up to 24" and above if you need more room.
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Old Apr 24, 2009, 01:34 AM
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Quote:
Originally Posted by Jack_LaLanne

fmkit: where can I buy AWM635 diversity package? (very small unit count, I want only one maybe two) do you have specs for the antennas you connect to it in the picture?
http://www.nghobbies.com/cart/index....products_id=23
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Old Apr 24, 2009, 10:18 AM
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thanks vrflyer.
can AWM635-RX receive AWM633-TX signal?
edit: yes
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Old Apr 24, 2009, 04:02 PM
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OK this is my final layout before I start putting it together. I might mount my patch antenna on the upper frame later.
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Old Apr 24, 2009, 08:37 PM
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I read somewhere it is better to have your video rx antennas further apart
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Old Apr 25, 2009, 01:38 AM
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Originally Posted by David22
I read somewhere it is better to have your video rx antennas further apart
imagine both antennas pointed toward plane(no reception),
1st you have to have the antennas polarized 90degree (H/V)
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Old Apr 25, 2009, 01:40 AM
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you are an expert
but even if one is not in use it can cause interference especially if it is in close proximity to the other

having your antennas further apart is a better aproach
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Old Apr 25, 2009, 12:53 PM
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they are about 2.5 feet apart as they are mounted on my backpack frame. how much further must they be?

I'm not gonna walk around with a 10 foot pole across my back..

I'm not going for long range flight as this system will be used with a Spectrum radio, and FPV Helicopter. the Tx antenna stays verticle all the time so no need to 90 degree polarization.
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Old Apr 25, 2009, 01:05 PM
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Not sure exactly what you mean?
Quote:
Originally Posted by fmkit
imagine both antennas pointed toward plane(no reception),
1st you have to have the antennas polarized 90degree (H/V)
I was thinking more like leave one antenna on the back pack so you can turn with the plane and another antenna on a tripod 5 or 8 feet away but connected with a video cable
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Old Apr 25, 2009, 10:54 PM
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The poles will cause multi-pathing sitting next to the antennas like that.
The antennas should have nothing else at their level.

ian
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Old Apr 25, 2009, 11:29 PM
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can you eleaborate on the positioning of the antennas.

the muti path thing I have just heard of.

Quote:
Originally Posted by Daemon
The poles will cause multi-pathing sitting next to the antennas like that.
The antennas should have nothing else at their level.

ian
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Old Apr 26, 2009, 12:15 PM
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Quote:
Originally Posted by fmkit
that's what sticking out of my backpack
AWM635 diversity receiver gets power stright from HDD recorder
yesterday got 2km range with AWM633 onboard my Beevolution flying wing
Hey fmkit. could you detail a bit how you wired the AWM633 and how you made the antennas? Also what is the recorder you use? It outputs clear 5V ?
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Old Apr 26, 2009, 02:23 PM
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Quote:
Originally Posted by Daemon
The poles will cause multi-pathing sitting next to the antennas like that.
The antennas should have nothing else at their level.

ian
Ok I'll check it out, I can easily cut the poles off. fortunatly the frame of the pack sits high on my shoulders so my big head is below the antennas line of sight.
I just finished the whole backpack yesterday, everything is just zip tied together for right now. I'm dying to try the "FPV-Backpack" in flight.

My ground testing was a success, as I was able to leave my AP heli transmitting outside, I recieved great video signal when I walked around, then went into my concrete warehouse with a distance of about 200 feet away from the heli still good clean reception.

what do you guys think, maybe a couple speakers for sound should be added next aye?...
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Old Apr 26, 2009, 02:51 PM
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Quote:
Originally Posted by Jack_LaLanne
Hey fmkit. could you detail a bit how you wired the AWM633 and how you made the antennas? Also what is the recorder you use? It outputs clear 5V ?

beside supporting antenna pole(75cm CF rod from HC) there is no need for a backpack - whole ground station fit in pocket.
You.ve seen diversity receiver already, here is the rest:
160GB HDD recorder
4000mAh 3S lipo to power the recorder,RX and video goggles(one battery for all)
5v 3A UBEC
and custom (molex) connectors, it looks like a mess on photo but simple at use: just two connectors: gogles and antenna, and 3rd for battery.
none of original AV-IN, AV-OUT and power connectors used in field
Note for those soldering power to AWM633: power has to be 3.3v sharp, even 3.5v may kill the module. I used 5v ubec with modified feedback to output 3.3v so no power gets lost unlike linear regulator.
I don't have a car yet so riding bicycle with flying wing and pocket sized ground station works for me.
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Old Apr 26, 2009, 02:58 PM
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Quote:
Originally Posted by fmkit
beside supporting antenna pole(75cm CF rod from HC) there is no need for a backpack - whole ground station fit in pocket.
You.ve seen diversity receiver already, here is the rest:
160GB HDD recorder
4000mAh 3S lipo to power the recorder,RX and video goggles(one battery for all)
5v UBEC
and custom (molex) connectors, it looks like a mess on photo but simple at use: just two connector to connect gogles and antenna, and 3rd for battery.
Note for those soldering power to AWM633: power has to be 3.3v sharp, even 3.5v may kill the module. I used 5v ubec with modified feedback to output 3.3v so no power gets lost unlike linear regulator.
I don't have a car yet so riding bicycle with flying wing and pocket sized ground station works for me.
actually the recorder is on the helicopter, the black box is holding the Diversity controller and two Pb batteries. you can see the heli in my blog.

let me know when you start mass producing it in a nice clean package, I'd love to have a smaller system, but it has to be on 900 mhz. can't use 2.4 tx
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Old Apr 26, 2009, 03:00 PM
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hey JustinONE, you gonna get arrested with outfit like this
it happened to me once in Arizona and here in Israel people may freak out even sooner
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Old Apr 26, 2009, 03:06 PM
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Originally Posted by fmkit
hey JustinONE, you gonna get arrested with outfit like this
it happened to me once in Arizona and here in Israel people may freak out even sooner
I was thinking about growing a bushing beard, that'll scare the piss out of the Conservative blue hair hags in my nieghborhood. Unfortunatly I live in a super conservative Navy town so I expect to get a little flack, we'll see what happens.
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Old Apr 26, 2009, 03:39 PM
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Quote:
Originally Posted by JustinONE
actually the recorder is on the helicopter, the black box is holding the Diversity controller and two Pb batteries. you can see the heli in my blog.

let me know when you start mass producing it in a nice clean package, I'd love to have a smaller system, but it has to be on 900 mhz. can't use 2.4 tx
I also have recorder on board also everyone needs a backup, if the plane fly away ground video may help to trace it.
BTW, check my ebay feedback (same username fmkit) I sold custom built electronics to thousands, always taking orders from people who can explain what they need / know electronics basics. My UHF system is unbeatable, no one else came up with -120db sensitive receiver as far as I know.

edit: all components "pocket" ground station. Only missing is a pole to support antennas. I soldered small alligator to RX body so the receiver with antennas can be clipped to a hat thus getting rid of backpack
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Old Apr 26, 2009, 05:59 PM
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Quote:
Originally Posted by fmkit
I soldered small alligator to RX body so the receiver with antennas can be clipped to a hat thus getting rid of backpack
now you are talking, rx antenna on your head


But if Justine leaves one antenna on his back pack and have another on a tri pod it should be ok

If he upgrades his video wires it should help
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Old Apr 27, 2009, 10:46 AM
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I don't have any problems with my video cables, they produce clean crisp images, yet I did chop off those two pipes that where sticking up and blocking the two antennas.

I would like to hack the video goggles for direct powering off the backpacks battery. also want to install a headband from a set of skiing goggles next, as the video glasses are not very tight fitting.

I still think a set of speakers for onboard sound would be cool.
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Old Apr 27, 2009, 11:00 AM
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Do you need to set the channel on those receivers every time you turn them on ?? Those are HUGE. You can get the same receiver, the single video output versions that work on whatever channel you want as soon as power is applied. They are perfect, no setting channels, and no turning on required, they just work ! Not to mention, they are MUCH smaller and make for a much more compact, lighter portable ground station.

Mike
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Old Apr 27, 2009, 01:47 PM
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Originally Posted by JettPilot
Do you need to set the channel on those receivers every time you turn them on ?? Those are HUGE. You can get the same receiver, the single video output versions that work on whatever channel you want as soon as power is applied. They are perfect, no setting channels, and no turning on required, they just work ! Not to mention, they are MUCH smaller and make for a much more compact, lighter portable ground station.

Mike
yeah they are a pain in the ass, I will eventually buy the smaller rx's.

with this back pack frame there are more possibilities for mounting a manual head tracker, the tracker2 drift issue is very annoying.
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Old Apr 27, 2009, 03:38 PM
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I'd consider the airwave awm635 package for RX. I really don't see the point of diversity on the video level when you can have it on the radio level. and speaking of diversity. I saw Jett has a directional (dish) antenna and a omni direcitonal antenna working together with diversity. Don't know where the picture is right now. Wouldn't that be something for you? One guy in the forum put two directional antennas on a bagpack just like you, just so he can use the directional ant.

edit: I'm waiting for my awm635 at the moment and I am planing on using it with two biquad antennas. I saw one webshop offering the awm635 in a nice housing, complete with sma connectors and dual A/V connectors. but it was 200 USD
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Old Apr 27, 2009, 04:47 PM
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Quote:
Originally Posted by Jack_LaLanne
I really don't see the point of diversity on the video level when you can have it on the radio level.
The point of having diversity on the video level is that it works with
*any* pair of video inputs from any Rx of the same or even different
frequencies. Rf diversity receivers are nice, but they're only
available on 2.4Ghz and 5.8Ghz and generally cost a fortune.
If it was available for 900Mhz or 1.3Ghz I might consider it, but
they're not, so it's moot point.

ian
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Old Apr 28, 2009, 11:00 AM
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I'm not sure I understand the difference between Video diversity and RF diversity that you guys talking about?
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Old Apr 28, 2009, 01:08 PM
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Quote:
Originally Posted by JustinONE
I'm not sure I understand the difference between Video diversity and RF diversity that you guys talking about?
Video diversity = two (any) receivers compared for best output
RF diversity = one receiver programmed to compare it's two antennas

today I was field with friends
tred FPV w/ backpack set but it didn't work out
I hated all the controls in the back, even if wanted adjust volume
somehow I broke video gogles in the first minute

couple hours later I got rid of the backpack completely
soldered longer wires to RX, mounted it on top of CF rod so antennas some 50cm above my head and the recorder with battery sits conviniently on my side, the set is worn as a rifle and I flew with it one hour ago and finely enjoyed it needs no improvement.
BTW, I used USB cable to wire AWM635 to video recorder, the cable had exact amount of wires to connect two audio channels,video and power.
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Old Apr 30, 2009, 05:09 PM
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today I tried FPV with this monitor/recorder
I made a wrist band using fiber tape and velcro and flew couple minutes watching the brilliant screen, it worked better than rangevideo 545 videoglasses also the RX is only good for some 300-500meters because of poor built-in antenna(easy to fix)
So today the backpack was reduced to a single item !
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Old Apr 30, 2009, 06:18 PM
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interesting. is it not distracring during flight to make sure you see everything on the screen? is it one of the cheapo 2.4GHz surveillance kits?
I'm trying to find a reseller of compact 2,5inch hdd dvr in europe. found one in ebay italy but I'm not sure if it can record and play simultaneously. There are plenty of stationary 3,5inch recorders but the small ones are hard to find.
regards
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Old May 03, 2009, 10:11 PM
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I didn't notice the link. VGA on such a small screen is very sharp. But can you see anything with ambient light? Did you mess with the antennas yet? For that price it seems perfect to get into fpv.

edit: btw, your car remote is awesome :-) is it easy to produce them for the non electric pro?
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Old May 03, 2009, 11:07 PM
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Quote:
Originally Posted by fmkit
Video diversity = two (any) receivers compared for best output
RF diversity = one receiver programmed to compare it's two antennas
More specifically video diversity (like the Oracle box) actually looks at the
noise profile of the video images. It doesn't care where the video
is coming from. It just picks the one with the lowest amount of visible
noise and can switch between video frames.

Rf diversity actually usually includes two receivers with their own
antennas but they're built into the same box. It looks at the RSSI
(signal strength) or equiv and picks the one that's highest, also
switching seamlessly if possible.

One other advantage to video diversity is that the receivers can
be physically separated (one connected to a patch on the ground, one
on a tall pole connected to a dipole) each a short distance
from its antenna. With Rf diversity you have to extend the antenna
coax (introducing more signal loss than equiv length RCA video cables).

ian
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Old May 09, 2009, 01:06 PM
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I'm about to copy the fmkit minimalistic base station design. Waiting for my super expensive 470uf tantulum smd caps (paid around 6 USD for one) for the transmitter. For the receiver I ordered aluminum thru-hole capacitors. I've noticed those have 20% capacity tolerance as opposed to 10-5% in tantulum capacitors. is that a big distadvantage? all the capacitors are specified for 10V max. Hope that's ok. (the datasheets recommend 25V and 16V but andres martinez uses 6.3 on the tx and it works well)

I will use a thru-hole prototyping board on which I will place the awm635 receiver. I do this for two reasons: I'm not the soldering superstar and would mess up trying to solder the parts directly on the receiver pcb like fmkit. also I want to mount two sma connectors so I can easily change antennas on the field. will use two dipoles like fmkit first and also try one biquad and one dipole. Hope I can mount the connectors solidly while maintaining a very short length of the rf line.

airwave inc. sells the 634 in a readily made with a nice housing. I've been wondering if the housing promotes the overall performance of the receiver a lot. Would it be useful to cover the rx in balsa sheets and put something like aluminum foil around it?

2,5" hdd recorder is on its way too.I will finally get rid of the black screen problem. Looking forward to putting it all together once ups was here I will document the building process a bit with photos.

If everything went well and I have a good a/v setup again I'm looking to add a remzibi OSD.
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Old May 09, 2009, 02:40 PM
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At millimeter wavelengths, the antenna's don't need to be very far apart. Even a few inches is often all thats needed for diversity, both vertically polarised, I assume your TX antenna is vertically polarised? optimal signal strength is usually with the TX antenna facing down on the aircraft, a small ground plane will also boost the downward signal too.

Steve
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Old May 09, 2009, 04:22 PM
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Quote:
Originally Posted by HeliEye
At millimeter wavelengths, the antenna's don't need to be very far apart. Even a few inches is often all thats needed for diversity, both vertically polarised, I assume your TX antenna is vertically polarised? optimal signal strength is usually with the TX antenna facing down on the aircraft, a small ground plane will also boost the downward signal too.

Steve
that sounds like it's not useful to put two sorts of antennas. I think I have a wrong understand of how antenna diversity works. Guess I will just put it like fmkit for the beginning, with the two dipole wire antennas.
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Old May 10, 2009, 01:57 PM
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the backpack became frontpack
3.5mb avi
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Old May 10, 2009, 04:14 PM
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nice! I'll try that. just made the rx antennas. what do you use on the tx? I've been succesfully using the rubber ducky antenna, bottom mounted, with vertical polarization.
edit: and thought about trying a half wave dipole (right one)
edit: found it. fmkit uses quarter wave dipole on the awm633 too http://www.rcgroups.com/forums/showp...0&postcount=52
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Old May 16, 2009, 02:34 PM
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so I just received my 2,5" hdd recorder. here's the pcb. what you can't see: ir interface on the button side, av I/ av O with 3,5mm jacks, mini usb for mass storage, and dc 5v in barrel jack on the other side. 2,5" sata slot on the backside of the pcb. it can be entirely controlled with the buttons, remote is present though. will put it together with rx tomorrow.

I will power it with 7,4V lipo battery w/ 5V linear vreg via 5v dc in barrel connector.
Do you think the +5V on the mini usb connector are stable enough for the awm635rx ?

thanks

bummer, the device has the black screen on static problem:
while recording, you have the video-in signal displayed on the video-out, plus two OSD symbols. when the video has a bit static everything is still displayed. but after some higher threshold of static is reached, the dvr only displays a black screen and goes back to displaying the video-in when the signal goes clean again. If the static stays longer, a message is display NO VIDEO SIGNAL DETECTED. once that happens it takes quite long for the video to appear after regaining signal quality.

I use goggles which turn off the displays on noise. When they are used as video-out device they don't turn off because they always get a sync from the dvr, also when it outputs the black screen. so at the end of the day, when I use this hdd recorder my goggle battery draws faster.

so when you are going to buy a similar device look out for that problem. best ask the dealer if the problem exists. I have sent an inqiury about firmware updates to 'Shenzhen Kingzer Electronic Technology Co.,Ltd.'

the hd recorder used by fmkit ( http://www.rcgroups.com/forums/showp...2&postcount=25 ) seems to be produced by kingzer as well. I have DVR-TI-A , fmkit has DVR-BR3000 . I wonder whether DVR-BR3000 has the black screen problem, too.
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Last edited by Jack_LaLanne; May 16, 2009 at 07:36 PM.
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Old May 31, 2009, 04:01 AM
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Norway
Joined Jan 2009
127 Posts
Quote:
Originally Posted by David22
can you eleaborate on the positioning of the antennas.

the muti path thing I have just heard of.
Hi. All metal objects (even if no cables attached like an atenna has) will act like reflectors. In case you have the antennas close to the metal in the backpack, the metal will reflect the signals and cause signal cancellation in certain circumstances (frequencies and angles of arrival). At 2,4 GHz the wavelength is 13cm approx and a small object as small as 13 cm will act like an antenna.

Summarized: keep your receiving antennas at least 50 cm away from metal objects below and no metal objects should be in front of or in rear of the receiving antenna with respect to the planes position. Mount them on non conducting (plastic, wooden) poles sticking up from the backpack...


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Old May 31, 2009, 04:56 AM
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fmkit's Avatar
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Joined Aug 2007
2,639 Posts
@ Jack_LaLanne

My HDD recorder won't start recording without video signal but once started it will continue recording even if video drops completly.
I no longet use HDD recorder at field - too heavy, needs googles or LCD monitor (think wires) and it doesn't deinterlace while recording(playback OK)
Now I use pocket (sd card) DVR, the only wire I have is antenna cable
I'm happy user of AWM635 - it weight almost nothing and can be high overhead with single line (not RF !!) coming down. Extra hight + zero loss in feedlines do more compared to tripods with patches mounted on them, also you can constantly walk, 3 days ago I walked 1.5km while piloting.
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Old May 31, 2009, 07:14 AM
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Germany, Berlin
Joined Feb 2009
896 Posts
yea I figured mine also keeps recording all the time once started. but it blacks out frames with high noise which I was not expecting. (in both, the recording and av out). but the threshold is higher than using goggles directly on rx.
your SD recorder, did it need a lot of soldering in order to accept A/V in? I thought it has 2,4GHz receiver only.
another question: at which voltag do your microphones operate? I wonder if you can sell one or two.
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