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Amplified Ground Plane Antenna

RX Amplified Antenna

How would you like to add an amplified ground plane antenna to your XCam receiver? For about $25 you can make your own.

Preliminary tests suggest that range is about 25% better than the stock patch antenna. The antenna is vertically polarized, so it is best used with a vertical dipole or whip antenna on your R/C model's video transmitter.

This is not an entry level electronic project, so please do not consider it unless you are well versed in antenna construction. You will find that I did not publish my usually detailed construction details either. So, study the text and photos closely before attempting this project.

Inside peek of AntennaThe basic design is composed of a simple 1/4 wave ground plane antenna that feeds into a Linx BBA-322 amplifier IC. This $15 part is available from Digi-Key. It provides 15dB of gain with a NF value less than 3.8dB. I admit that this is not optimum, but it seems to be an acceptable match for the XCam Rx.

The amp is located in the base of the antenna and the vertical 1/4 wave element connects directly to the amp's RF input. Single sided FR-4 PCB board material provides a sturdy base structure. I used a hole cutting tool to obtain the round shape (about 1.25 inches diameter). It is dimensioned to fit at the bottom of a 3/4" PVC sprinkler pipe coupling. It could have been square, but the round shape makes it look less home built.

The eight ground plane elements are 1/16" hobby shop piano wire. They are 1/4 wave (28-30 mm) and are soldered to the PCB's top side where the copper layer resides. They are bent at a 30° to 45° downward angle.

The Linx amp is mounted on its side, so pins 5, 6, and 7 (RF ground) are directly soldered to the copper PCB surface. But pins 1 and 3 are connected to ground via some copper tape that covers the Linx. The copper tape is rigidly soldered to the base's copper surface. You can NOT use jumper wires to connect these two pads. Surface area counts in this exercise. Of course you could mount the Linx SMT style on some copper clad board, but my dead-bug method was easier for me.

A .01uF ceramic cap is used to decouple power. This cap is installed, with minimum lead length, right on the Linx module. Power is supplied by a LM7805 VReg IC (5.0VDC) that was added inside the XCam receiver. The VReg requires two decouple caps, per its data sheet. It gets warm, so I had it share the heatsink that is used by the receiver's other regulator. The DC power cable is tied against the coax cable for a neater look (use heatshrink or wire ties).

To minimize feedline losses, my RG-174 coax is under 30 inches long. I did not use any connectors because they can invite RF losses at these frequencies. It is important to note that the construction techniques must be carefully implemented. A 2400Mhz RF signal can be severely attenuated if you get careless.
Finished Antenna The antenna is enclosed in 3/4 inch PVC sprinkler pipe fittings, per the photo on the left. Total height is 3.5 inches.

The finished antenna is mounted on the little plastic tripod that came with one of my XCam2 purchases. Mine was a free gift during an XCam promotion. Of course you can build your own little stand.

Because the XCam-Ant is less directional than the stock patch antenna, you should plan on using it only in a wide open area. Otherwise reflected signals (multipath interference) may be a nuisance.

Antenna placement is not as critical as the stock patch. It works best if it is elevated a few feet off the ground and is far away from nearby RF reflective structures. Hopefully it will perform well for you too.

If you have technical questions or comments about this project then please post it on the rc-cam project forum.

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