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garris2

Noisy transmitter, can it be fixed?

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Hi all, I have a Lawmate 1.2G 1W tx that is noisy on the audio as heard in the attached short video clip.

The photo shows the innards of this tx, I'm wondering if there's a simple adjustment that can be made to quiet down the static noise.

post-4774-128500432273_thumb.jpg

I don't get the static noise with my other tx's but they are not as powerful as this one and I'd like to use it.

thanks

Geoff

Edited by garris2

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Hmmm maybe multi path interference, what rx aerial are you using?

Terry

Hmmm, Hi Terry, bench testing gives the same results. That is, when its sitting on the bench, in the garage, with cam and mic connected there is sporadic audio noise same as in the video. The receiver is 5 feet away so I'm not thinking its multipath or anything like that.

Infact I have another Lawmate tx exactly the same, 1.2G, 1W that is worse.

As I stated my other tx's don't exhibit this noise issue when flying in the same area using all the same other equipment.

What I'm asking is.....

"I'm wondering if there's a simple adjustment that can be made to quiet down the static noise."

I mean in the tx, there's 4 little pots in there or is it just badly designed?

Geoff

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The static noise I hear in the sample video is common to many 900MHz -1.3GHz wireless video systems. But from your info it sounds like you are using the same A/V Rx with several other Tx's and they are quieter. If that is the case then the audio subcarrier on this Tx is probably designed for a different Rx model.

The pot on the far right is for video modulation deviation. If it is set wrong then audio can suffer. You should set it so that full white video is 1Vpkpk, per the instructions posted in the old $50 scope discussion.

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The static noise I hear in the sample video is common to many 900MHz -1.3GHz wireless video systems. But from your info it sounds like you are using the same A/V Rx with several other Tx's and they are quieter. If that is the case then the audio subcarrier on this Tx is probably designed for a different Rx model.

The pot on the far right is for video modulation deviation. If it is set wrong then audio can suffer. You should set it so that full white video is 1Vpkpk, per the instructions posted in the old $50 scope discussion.

Thankyou for your reply, that is very helpfull.

But it compounds my problem a bit.....

This tx is a Lawmate brand and the rx's I'm using are both genuine Lawmate brand. Thats not to say this tx could still be off a little bit couldn't it?

And as I thought it would require some special equipment to make some calibrated adjustments.

Do you think it would be feasible to carefully twiddle the pot and listen for an improvement in the audio at the same time watching for degradation in the video and avoid that?

This method is of course not very scientific or engineeric but I have nothing to loose, If I stuff it completely its cheaper to buy a new tx (hopefully one thats in spec) than to buy a cro to fix this one, but I've been wanting to buy a cro for a long time and its really getting to the point that I need to do it isn't it.

thanks

Geoff

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Adjusting the video level without a scope is not a good idea. Honestly, your audio noise is not as bad as some A/V systems I have heard. Especially after an OSD was installed. If you are happy with the range and video performance, I'd encourage you to just use the Tx as-is.

Since the audio RF signal strength is about -20dB less than the video, you can always use those static sounds as a pre-warning that the signal is getting weak. And of course you can always turn off the audio. :)

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Adjusting the video level without a scope is not a good idea. Honestly, your audio noise is not as bad as some A/V systems I have heard. Especially after an OSD was installed. If you are happy with the range and video performance, I'd encourage you to just use the Tx as-is.

Since the audio RF signal strength is about -20dB less than the video, you can always use those static sounds as a pre-warning that the signal is getting weak. And of course you can always turn off the audio. :)

Thanks for that good advice.

Geoff

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Hi, I note above you said "The static noise I hear in the sample video is common to many 900MHz -1.3GHz wireless video systems4"...

Does that mean that 2.4G (and 5.8) wireless video systems don't seem to suffer this same sort of static noise?

Why would this be?

thanks Geoff

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Why would this be?

Many of the 2.4GHz and 5.8GHz A/V systems use RF modules that were developed for consumer video sender applications (wireless TV room-to-room products). This kind of wireless A/V application demands high quality audio. The 900Mhz-1.3Ghz RF designs are older and did not require high performance audio, so they just did not design them with that in mind.

Just because a design uses 2.4/5.8 GHz does not mean it will provide low noise audio. That is to say, don't expect them all to do any better than what you have now. For sure, I've heard some of them buzz too.

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Hi all, I have a Lawmate 1.2G 1W tx that is noisy on the audio as heard in the attached short video clip.

...

Hi,

I am also running the Lawmate 1.2G 1W TX with the Lawmate receiver. In fact, I have six sets of Lawmate RX/TX systems and have found them to be quite capable of high quality video and audio. However, they are not always adjusted properly which appears to be your problem. First, here is a clip where you can hear what the Lawmate audio sounds like compared to a separate direct recording from a HD video camera:

2x2milesPlay.jpg

The right audio channel is from the Lawmate video in the upper right and the left audio channel is from the HD camera. You can hear a little bit of noise during some signal fades but overall it compares quite well with the HD camera audio.

In your case I think the Video might be overdriving the transmitter which causes interference in the audio channel. There is also some noise corresponding to periods of poor signal reception as you would expect, however this apparently is not the primary issue. Unfortunately Mr RcCam is correct with his caution about attempting to adjust the levels. To do it correctly you need an RF spectrum analyzer to adjust the audio subcarrier level and a NTSC Pattern generator for the video along with a fast scope and video trigger.

After spending a lot time tuning (with all the right equipment) a wide variety of video TX/RX system used for FPV, I can understand the frustration many have with this issue.

OMM

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Thankyou both for your further comments.

I don't want to change to a 2.4G A/V setup, I'll stay with my 1.2G at the moment.

As I mentioned I have another Lawmate Tx that has worse audio noise, I bought the second one in the hope it would be ok but I was disappointed it still had noise.

So it seems its pot luck whether you will get a good one or not, or who has tuned them at the factory determines whether it will be good or not.

Does anybody know of a source of other brand 1.2G 1W tx's or a source of a higher quality product?

Thanks

Geoff

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So it seems its pot luck whether you will get a good one or not, or who has tuned them at the factory determines whether it will be good or not.

It is frustrating. Unfortunately, most of the factories calibrate the A/V systems with little regard to the required accuracy. With some brands I don't think they even try to calibrate them. It's one of the many reasons that the reported experience with some equipment is different for every user.

Does anybody know of a source of other brand 1.2G 1W tx's or a source of a higher quality product?

Although Lawmate may not score well with calibration (as with with some other brands), they have very good build quality. Certainly better than the typical Chinese made A/V systems I have reviewed.

The solution is for the retailer to do the Tx calibration before shipping to the customer. But, it is rare to find a shop capable of doing it (I know of only one that does). So sometimes the customer is stuck with the problem.

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I guess I don't get any prize for guessing but I don't think they have a 1.2G 1W tx, but they do give great service.

I guess you can't have everything.

Geoff

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