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extremely poor range..... why?

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Well, I have FINALLY gotten the chance to use the wireless video system I bought close to a year ago. Testing the system revealed a good, stable image with the electric motor at various throttle positions so I figured I would give it a go... Well, for some reason video begins breaking up about 30 feet out and is totally gone by 50 feet. The system has been tested in 2 different locations to rule out local anomalies. I am using the stock whip antenna on both the TX and RX. The only possible issue I can see as having possibly caused this is that I put a very small amount of solder near the base of the antenna since the original solder had cracked from the antenna flexing too much.

I am about to give up one this project since I can't see any excuse for a system that’s supposed to go at least a 1/4 mile out performing so poorly... any suggestions or ideas?

Pete

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Pete,

What system did you buy? Try and be as specific as possible. Model number, watts, frequency etc.

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Hi Pete,

The lawmate equipment is pretty well respected for putting out the amount of power they state, and 100mw should get you a lot farther than 50 feet, even with the stock antennas

If you got the equipment from me, please email me and we can work out something where I can get you some new antennas. I wouldn't trust the antenna you repaired, since there could be something going on with the center conductor. Here are a couple of good tests to perform on the antenna:

1) Test for continuity between the center pin and the outer shell of the connector. There should be NO connection between the two.

2) Carefully pry off the plastic top of the whip antenna, and you will find a small pcb dipole soldered at the end of the coax. You should find that one side of the dipole is electrically connected to to the center pin of the antenna, and the other side of the dipole is electrically connected to shell of the connector.

Even if the antenna tests out, the moment you start diddling with the solder connections all bets are off, so still email me and we'll talk about the antennas.

The 100mw transmitter runs at 12v, are you getting 12v to the tx? Same with the receiver.

The standard whip on the receiver is generally NOT considered a good selection for our mobile aerial applications. A better choice would be a moderate gain commercially available patch antenna (circular polarized preferred), or one of the homemade antennas discussed here on the forum, like the double-quad or the 'Goof-proof' antenna.

Also, range with the stock whip antennas will NOT be 1/4 mile, perhaps closer to 600 to 700 feet. If you need 1/4 mile then consider one of the higher gain antennas I mention above.

And finally, don't give up! Either myself or other members of the forum can help get you going. If you suspect that something got fried during your experiments, still email me, we'll get you going somehow.

Regards,

Bill

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I have a feeling that one of the aerials or their feedlines are shorted or open. Either failure mode will result in short range. As Yb2normal also suggests, verify that you are getting 12V to the Tx.

Don't forget that tests inside or around the house may give poor results. You need to go to an open field for real data.

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Although I had tested everything when I build this system up about 6 months ago I went ahead and rechecked everything. TX is getting a solid 12.1v and there are no apparent inappropriate continuities and the antenna checks out for appropriate continuities as I understand them.

One possible source of problems is the fact that I removed the metal casing from the TX shortly after I got it. In retrospect this yielded very little weight savings and was not a good idea. I took care to reground all points on the board that had been soldered to the case however I am wondering if the case is somehow integral to proper operation of the TX. I created a shielding container in which to place the TX to see if this made any difference however no change in range was noted. If need be I suspect I could fit the original case back on without great difficulty.

The only other possible source of the problem stems from my confusion regarding the proper use of capacitors. Please see http://www.national.com/ds/LM/LM2940.pdf According to the application diagram Cout should be “at least 22uF”… so what should I stick on it? I have been using a 100uF electrolytic cap because it was available, is this a possible problem source? Also, C1 is to be used if "regulator is located far from power supply filter" so I have nothing here... do I need it?

Pete

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Well, I've played around a bit more and just decided to scrap my current system so while I appriciate the help there is no need to take this thread any further. I think I would be best advised to get one of the newer 600mw 5v systems and since that is ultimatly what I am going to do anyway why fuss over something that is going to be replaced... I might as well do it sooner rather than later.

Pete

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I'll respond anyway because I think you asked some good questions :)

Your implementation of the regulator should be fine. Or at least, the way you implemented it should not have caused the problems you were seeing.

There are two things that could be going on with your case removal. If you used enough heat to melt those blobs at the corners, you very likely unseated an SMD component in the process or delaminated a trace from the board and then broke it. Another thing to keep in mind is that at these frequencies, everything about the design of the system is important, including the case.

It sounds like you are ready to call it a loss however, so I shall stop beating this dead hourse ;)

Kind Regards,

Bill

Edited by yb2normal

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You would have a good hypothesis on a possible source of the problem however I used mechanical means to remove the case (wire cutters) and never applied any heat with my iron. It was actually a relatively gentile process as I remember it so my guess would be the issue stems from the case removal as an integrally tuned part of the system.

This will not be a total loss however, I think I will use the system to broadcast images of my lipos (they scare me) as they charge in my car. That will allow me to occasionally take a peek at them while watching tv. I think I will also use this system on the front of my Honda Civic at autoX events. That'll give me those cool speedvision type shots without having to mount my handicam on the front bumper. Rather, I can just broadcast the signal to my handicam in the trunk.

Anyway, I'll probably be ordering up a new system here within the week.

Pete

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