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Mr.RC-Cam

Low Cost DiY 900Mhz Omni Dipole Antenna

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Be sure & mount the dipole in a vertical position if you want omni directional radiation. In a horizontal plane it has directional radiation Foreward & Backward) & the polarization will be 90 degrees out of phase with a vertical Tx antenna.

Have you or any of your audience here come up with a way of driving 3 dipoles on 90 degree planes? the goal is to prevent dropout when the aircraft is in a tight bank close to the reciever(relatively, as in on the overhead pass).

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The goal is to prevent dropout when the aircraft is in a tight bank close to the reciever(relatively, as in on the overhead pass).
If you mean to do that on the Tx end, then the crossed dipole (Turnstile) antenna would do a decent job. These are very difficult to build correctly at 2.4Ghz and require careful co-phasing. Cyberflyer used a quadrature hybrid module from Radite to build his. It is a very old project posted at the old rc-cam MSN site.

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If you mean to do that on the Tx end, then the crossed dipole (Turnstile) antenna would do a decent job. These are very difficult to build correctly at 2.4Ghz and require careful co-phasing. Cyberflyer used a quadrature hybrid module from Radite to build his. It is a very old project posted at the old rc-cam MSN site.

Turnstyle sort of, one beam straight aft, one vertical, and one horizontal. Can the same matching methods for 200MHz television yagi antennas be used @ 2400MHz? Ie. 1/4 wave seperation 180 Degree beam.

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It's the same principal, but I doubt construction would be a practical because the build is much more critical. That is, the DiY techniques that mortals can do with VHF/lower-UHF just aren't practical at 2.4Ghz.

I'd recommend you search the old site and try to find cyber-flyer's turnstile discussion. He worked on two different versions, one with coaxial co-phasing and the other with the quadrature hybrid modules -- the module version worked. It was year 2002 or so.

Orig rc-cam archive site (will go away in Feb): http://groups.msn.com/rccam/_homepage.msnw

New archive site: http://rccam.multiply.com/

If you find it please post the link to the topic. The photos are easy to find, but the discussion will require some digging.

Many of the issues that are solved with these kinds of antenna tricks are mostly solved nowadays with careful A/V installations, good RF links, and perhaps diversity Rx's. Rarely does anyone go beyond a rubber duck dipole on the Tx end; generally speaking the video link reliability is very good with that.

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I bought an SMA-SMA cable to hack apart to build a couple of these antennas. In the plane, does it need to be pointing up or down or doesn't matter? It needs to point up in my installation.

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It can point up or down. However, like most rubber duckies, best operation is often found when the antenna is below the model pointing down and away from the model's structures.

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It can point up or down. However, like most rubber duckies, best operation is often found when the antenna is below the model pointing down and away from the model's structures.

Makes sense to do that. With full-scale aircraft, the antenna for the radar transponder is placed below the fuselage so the ground-based ATC receiver can "see" the transponder with less chance of the aircraft's structure blocking the signal.

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Do you need to use an sma connector? I am trying to make a transmitter as light as possible, so I have an airwave tx module, and I will make a pcb to take care of all the pins/power supply/signals. However, it would seem unnecessary to me to put an sma connector on the pcb, then have a mating one on the antenna - if I dont need to disconnect the antenna. My questions are:

1) Can I do the coax dipole antenna (2.4GHz) and solder the coax core/shield directly onto the module pins?

If so:

2) Does the coax core solder directly to the "ANT" pin?

3) Does the coax shield solder directly to a ground trace on the pcb?

4) Are there any tips/requirements for the pcb - eg large ground plane trace etc...

Cheers,

Rob

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1. Yes.

2. Yes.

3. Yes. It connects to the RF ground.

4. It would take a book to cover all the aspects of good RF PCB layout. Two main tips: Unless you know how to correctly implement microstrip design, do not connect your PCB trace to the module's RF output pin. I recommend that the ground plane occupy an entire PCB layer and have lots of via connections to the grounds on other layers.

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1. Yes.

2. Yes.

3. Yes. It connects to the RF ground.

4. It would take a book to cover all the aspects of good RF PCB layout. Two main tips: Unless you know how to correctly implement microstrip design, do not connect your PCB trace to the module's RF output pin. I recommend that the ground plane occupy an entire PCB layer and have lots of via connections to the grounds on other layers.

Thanks Thomas (hope that is correct),

Excuse my naivity...do you work for/own dpcav? Just curious... I bought my modules etc from that shop

Anyway, I have attached the airwave module connection suggestion.

1) When you say RF ground, do I assume this is the two gnd pins on the ant side of the module, adjacent to the ant pin?

2) These "RF gnd" pins shouldnt be connected to the ground trace/plane on the pcb?

post-3068-125669858161_thumb.png

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Yes, I'm with dpcav, so I get to play with this stuff all day long. :)

1. On Airwave modules, the PCB is an RF ground with several solder pads available for bonding to your custom PCB. For convenience, the coax shield from your feedline can connect to the pads on both sides of the RF port pin.

2. ALL of the Gnd pads on the Airwave module should be bonded to your PCB's ground plane.

The discussion is going a bit off topic since it is for building a low cost 900Mhz omni dipole antenna. If you have Airwave specific things to discuss then it would be best try to find a related Airwave module discussion or simply start up a new one.

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Yes, I'm with dpcav, so I get to play with this stuff all day long. :)

1. On Airwave modules, the PCB is an RF ground with several solder pads available for bonding to your custom PCB. For convenience, the coax shield from your feedline can connect to the pads on both sides of the RF port pin.

2. ALL of the Gnd pads on the Airwave module should be bonded to your PCB's ground plane.

The discussion is going a bit off topic since it is for building a low cost 900Mhz omni dipole antenna. If you have Airwave specific things to discuss then it would be best try to find a related Airwave module discussion or simply start up a new one.

Ooops, sorry about that. I might start another one...

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The elements consist of brass tubing with a diameter of 0.9". The length of the elements are 3.09", measured from where the conductor emerges from the ferrite bead.

post-5231-1231744370_thumb.jpg

Pardon for dredging up a thread started ten months ago. This dipole implementation looks almost ideal to my needs - for a helicopter even smaller than DCSensui's. I would replace the tailfin with a radio-transparent one, raise up the centerpoint so it's definitely not hitting the ground, and maybe put the centerpoint to the left by an inch to further expose it and move it away from the aluminum tailboom.

Two critical questions: (1) Am I to understand the coax shielding is soldered to the tubing, not to a wire inside the tubing; and the same with the coax core on the other tube? And (2), where do I source the appropriate ferrite bead at the centerpoint for 910MHz?

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Two critical questions: (1) Am I to understand the coax shielding is soldered to the tubing, not to a wire inside the tubing; and the same with the coax core on the other tube? And (2), where do I source the appropriate ferrite bead at the centerpoint for 910MHz?

Replying to myself here. I am very happy with the brass tubing dipole - three flights yesterday on a T Rex 250 helicopter. The whole connector, feed line, mount, and antenna was just 11 grams, less than half of the weight of the stock rubber duck dipole I use on larger craft. I got the tubing at a hobby shop's railroad department, where lots of very fine metal extrusions are sold for scratch-built bridges and towers. I stripped about 15mm of coax, used half of the shielding and all of the core. I tinned and tucked the strands into the ends of the tubing and soldered as close to the root of each branch as possible. At this point, I have no bead at all. I have no method of measuring the gain, but had good signal everywhere except when I flew directly behind a utility van.

Edited by halley

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Well I've read the two pages and joined the forum. I've learned a lot in the last few minutes. I have been using Range Video equipment and was going to venture into 5.8Ghz a I have the 900mHz and 2.4Ghz systems. i am ground based with RC Cars and there is very little in the way of interest as opposed to FPV flying RC's. I'm learning to fly a quad so one day I'll do FPV in the air. My question is what is ground plane and how does it relate to a plastic body of RC's. I looked at the discussion of building your own patch antenna. My 900mHZ TxRx from Range Video comes with the vee antenna. I've mounted it horizontal and vertical. I have two of their receivers with the rssi module and I can't see an improvement in reception with the two receivers about a foot apart. They both have the standard Duckie antenna. I get better reception with a vertical orientation with the transmitter vee antenna placement. My field of range is around a 100 foot square more or less field. I'm loking for clear no banding reception and am planning on getting the Range Video patch antenna for the 900mHz system and use a standard Duckie on one of the recivers. I've seen their circular skew antennas but I have limited room in my car body and I can't really put anything out of the body as i am into the rough crash and bang environment of bumper cars. 2.4Ghz FPV used to work pretty well before the new crop of radios and I have gotten pretty good resulta as a ground based RCer. Here is a sample video of the 900mHz that I recently did on YouTube.

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5.8GHz with CP antennas is worth exploring if you give up on what you have. But if you want to improve your existing 900MHz diversity setup, I'd suggest a pair of L-Com patch antennas. Elevate the patch/vRx combinations (do NOT extend the antenna coax) at the track's corners so the patch's beamwidth can "see" the entire layout. The vTx should use a good quality standard dipole rather than the RV V-dipole. All antennas should be installed vertically, not horizontally. This should work much better than what is seen in your video example.

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I just ordered a 3dBi whip to try your suggestion

There's a lot of poor performing antennas being sold. So hopefully you ordered one of the good ones.

I doubt you'll experience any significant improvement by only changing the vTx antenna; Please note that I also suggested patch antennas on the vRx's (positioned strategically).

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