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Jul 23, 2011, 01:00 AM
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Brand new 1.3gHz Lawmate vtx is NO GOOD


Got around to doing some tests with my new Vtx. Its been a bit of a rough start. I had some horrible audio issues starting out that I was able to more or less get rid off by adding a pot on the audio to vtx line. My problem now is, when the OSD pro voice message engages, the sound is very grainy. Anyone else have this. Its not my amp, its the audio signal generated by the OSD pro, and I can barely understand what its saying now. My 900mhz system always sounded crisp and clear. Anyone have issues like this

Update, Starting to think I may need to take a look at the osd pro board. I may also play with an attempt to shield the whole cockpit. I have some special conducive shield paint somewhere.....
Last edited by Slaphappysamy; Jul 27, 2011 at 12:58 AM.
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Jul 23, 2011, 01:28 PM
fly it high as possible
Quote:
Originally Posted by Slaphappysamy
I had some horrible audio issues starting out that I was able to more or less get rid off by adding a pot on the audio to vtx line..
I'm using audio signal from Immersion EasyOSD through 1280Mhz Lawmate Tx for tracking antenna and w/out 22k in serial it couldn't get working, too. I mean to install 22k between OSD output and Tx input. Tryed 20k, 18k - no, it should be 22k in my case. Now it is OK.
Try it (22k or potentiometr).
P.S. And even more, I had to open Tx for fixing (broken wire) and saw a potentiometr inside, just touched it and move little in one and in other side. Probably it helped, too.
Last edited by IL76MD; Jul 23, 2011 at 01:34 PM.
Jul 26, 2011, 09:26 PM
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Took the suspect Lawmate TX over to a friends house tonight he is a ham and rf Engineer. Put the Tx in his Faraday cage and ran some tests with a Spectrum analyzer. The results make me feel a little better. The Tx's PLL circuit is shot. Its jumping all over the place. Its a miracle I was able to even get video in the first place. I emailed Hobby wireless about it as I just got the thing from them late last week. We'll see how they handle it. Ill keep you posted. In the mean time I am going back to 900MHz.
Jul 27, 2011, 04:20 AM
Zephyr 66" Blunt
mark hitchman's Avatar
Why did you leave 900mhz for originally?

Mark
Jul 27, 2011, 08:12 AM
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Quote:
Why did you leave 900mhz for originally?
I am stupud. lol. 900 has worked really well for me. I just wanted to see what all of the fuss was about with a 1W 1.3gHz tx. And the idea of smaller antennas was appealing. Now that 3.5 foot yagi doesnt seem so long.
Aug 08, 2011, 02:58 PM
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GLADUS63's Avatar
I have same problem with my 2 lawmate 1.2ghz Tx, so noisy that I can't use them for the downlink !
Aug 08, 2011, 06:23 PM
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WBFlyer's Avatar
I wonder if that is the reason my Lawmate 1 watter went out on me mid flight, bring down my plane. Just went black out of now where...
Aug 20, 2011, 04:36 PM
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Serveurperso's Avatar

Lawmate 1W 1.2G audio issue


It's a sound subcarrier oscillator problem on a serie of lawmate 1.2 1W.

Try to remove the smc GREEN trim cap and replace with a bigger one.

It work for me on 2 lawmate 1W 1.2........... you get a new "HiFi" sound without heterodyne noise.........

Just tested with random values caps tonight, and this is the problem...

Pascal
Last edited by Serveurperso; Aug 20, 2011 at 04:45 PM.
Aug 20, 2011, 04:45 PM
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GLADUS63's Avatar
Quote:
Originally Posted by Serveurperso
Try to remove the smc GREEN trim cap and replace with a bigger one.
l
The one just on the left of the ground wire ?
Aug 20, 2011, 04:46 PM
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Serveurperso's Avatar
I just add a picture
Aug 21, 2011, 02:00 AM
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GLADUS63's Avatar
Great !
Aug 25, 2011, 06:21 AM
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Serveurperso's Avatar
instead of removing the variable capacitor, it's better to add a simple cap in parallel
because the tuning is possible with the factory trim cap.

It remains to determine the value that will give the proper range around 5.5MHz.

All brand new lawmate have this problem. DPCAV sell CORRECTED transmitters for 5.5MHz sound subcarrier.

Pascal
Aug 25, 2011, 07:21 AM
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GLADUS63's Avatar
Quote:
Originally Posted by Serveurperso
instead of removing the variable capacitor, it's better to add a simple cap in parallel
because the tuning is possible with the factory trim cap.

It remains to determine the value that will give the proper range around 5.5MHz.

All brand new lawmate have this problem. DPCAV sell CORRECTED transmitters for 5.5MHz sound subcarrier.

Pascal
I haven't thinked about that !! so easy !!! instead I was going to solder an external big old trim capacitor !!!
thanks for the info ;-)

Cedric
Aug 25, 2011, 09:48 AM
fly it high as possible
Quote:
Originally Posted by Serveurperso
instead of removing the variable capacitor, it's better to add a simple cap in parallel
because the tuning is possible with the factory trim cap.

It remains to determine the value that will give the proper range around 5.5MHz.

All brand new lawmate have this problem. DPCAV sell CORRECTED transmitters for 5.5MHz sound subcarrier.

Pascal
It is a good info about the issue, but, how do you know about DPCAV is selling corrected Tx and not just old good working?
I mean m gonna buy from them and to be sure they would send corrected Tx. Did you ask them?
Thanks.
Aug 29, 2011, 04:42 AM
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Serveurperso's Avatar
Hi,

I talked to them (DPCAV), a lot (with my poor english), because I ordered many and many 1.2GHz 1W lawmate TX for "dev&reverse engineering"...

I now know that they will add a 15 to 47pF capacitor between the *right* SMD variable cap pin and the 4MHz XTAL body (ground).
Because the *left* pin of variable cap is the ground, it's the same (caps in parallel).

The oscillator frequency is very approximative from one TX to another, DPCAV use spectrum annalyser to anticipate the choice of the fixed capacitor (15pF to 47pF) Error average is 33pF for all TX (6-6.5 to 5.5MHz mod).

I prefer a bigger SMD variable CAP for DIY mod because tuning is easier.

Pascal


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