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Micro Sprint 15

Soldering to the tin can?

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Hi guys,

LOVE the new forum, looks great! This is my question.....

The cheapy system I have has what appears like a piece of coax wire for an antenna that is molded into a plastic antenna at one end and soldered onto a circuit board in a metal box at the other end. How do I change the antenna? or can I? my system contains the camera and Tx in one unit with the antenna on the side of the plastic box. I really need to relocate the antenna off the camera so I can mount it on the wing of the race car. I have a real problem with loosing signal every time the car turns and is between the Rx and Tx. Is it possible to have a long lead wire between the camera unit and the actuall broadcasting part of the antenna?

I'd also have the same modifications to do to the Rx to create a better antenna for it as it is a unit in a plastic box as well. But I could mount an antenna right off the box and wouldn't need a long lead wire.

Any help as to how to go about changing the wire in the tin box is apreciated. I'm sure I can build one of the antenna projects listed on this site. I just need to know how I can attach it.

This is a video file of what I have so far http://www.microsprintkarts.com/images/in600.avi I'm happy with the quality of the image if I can just solve the problem of the lost signal.


Mike Ferrell

600cc Micro Sprint "pilot" ;)

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How much coax did you plan on adding? More than a few inches?

At microwave frequencies, the losses through the coax cable can be enormous. It would be best to remove the camera from the Tx and remotely mount the Tx and antenna as a RF system. There are only three or four wires to connect, so it should be an easy task.

I do recommend that you install better antennas on the Tx and Rx. Please see this link: http://www.rc-cam.com/forum/index.php?showtopic=12 for some ideas.

Correctly installing your antenna upgrade is important (RF projects are not at all like working on a simple DC circuit). If you do not have any RF experience then try to find some hands-on help from a local ham.

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How do the 2.4gHz wireless internet antennas work? I'm sure I've seen them that are can type and such that have long leads between the base and the actual antenna. I assumed (and probably incorrectly) that the antennas for the 2.4gHz video systems would be the same type.

Any suggestions on what to use to make an antenna detachable from the tin can box inside the plastic case? I assume I can also unsolder the existing wire from the board inside the can to solder a new connection on?

I'm really learning a lot from this project. Thanks for all the help guys!

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The better wireless lan antennas are active designs -- they have a preamp in them to make up for cable losses. The cheaper antennas just accept the losses since they are used with short range RF apps. There is minimal penality for such issues when your goal is to achieve a range of a hundred feet. But in your case you want all the uumph you can get.

For example, popular RG-174 coax has about -0.7dB loss per foot at 2.4Ghz. An innocent looking five foot length will hit you with over -3dB of losses, which represents a 50% reduction in signal strength! A ten foot piece cuts the signal to 1/4 of what it used to be (assuming a perfect match). Commercial microwave installations use low-loss cable, but it is huge stuff (about as big around as a garden hose). Even better installations rely on waveguides, which are plumbing nightmares.

You will achieve the best range if you eliminate the coax altogether and attach the antenna directly to the Tx. This has the advantage of eliminating matching problems. If you must use coax, then keep it VERY short and experiment with the exact length to miminize the VSWR's.

When it comes to UHF and microwave RF, everything matters.

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