Lawmate 1000mw tx with DX8 - can this work ? - ArduCopter User Group

I purchased a ready to fly quad from 3DR. with the works. The video receiver was back ordered so I removed the Lawmate TM-241800 Tx, camera, Minim OSD and began my journey. I have years of past RC heli and plane experience and I'm good with computers so I manged many successful flights along with waypoint guided flights using the mission planner. I have been very satisfied with my purchase. The video receiver arrived a week or two later but without a monitor or goggles, I kept the FPV items off of the quad.

My bosses loved the aerial pics I took with my Gopro and had a job for me to perform using the potential of FPV.

I order video goggles, a monitor and some cloverleaf antennas, these items are in the mail.

Christmas Eve day, I have mounted all FPV equipment to the quad and use the TV set to check operation. All seems good so I take a flight in my yard at lunch time, this is great stuff, the wife watches the video live on the tv set and I am ready to demonstrate for my bosses at work. We have a small monitor there that I hook up. Mission planner is running on the laptop and video is playing in the office. So far, I am a hero.....

Takeoff is fine, I head to the back of the property about 50 feet away and start a slow climb to take some photos. Then it happened. My failsafe is set for Return To Launch, the quad climbs to 40 meters and begins to head back, but its over trees and there is some wind causing it to drift. I lower the throttle stick, the quad responds momentarily and drops, then recovers. I am trying to bring it closer, it responds again and perches itself atop a tree and out of sight till the next (Christmas) day. I have not looked at it till today.

What happened?

OK, so there's that range check thing. I put a flag on the servo controlled camera mount so I could monitor it from a distance.

I have now noticed a substantial difference in range when the Video TX is powered on, 12 paces as opposed to an easy 30 paces. I tried it a few times, powered the video tx on prior to the control system as well. Same thing, my RC control system range is cut in half when the video TX is powered on.

Due to my lack of knowledge in FPV, I purchased an already configured system feeling that I was safe. I understand that both transmitters are in the 2.4Ghz range and that the DX8 uses spread spectrum frequency hopping technology, so I thought........

The Lawmate Tx came set on "1CH" all dip switches up, still the same.

Am I alone, can this system work?

All comments will be appreciated, except for "why didn't you range check it first"!

Thank you.

Stan

Aloha Stan,

The problem you are experiencing isn't with corruption of your controls it's with loss of signal as evidenced by your aircraft going into RTL mode. The DX8's FHSS is working hard to maintain a solid connection to your DX8 and does well until the signal of your lawmate vTx overpowers the signal. The signal output of your DX8 I believe is about 500mw and your lawmate vTx is 1000mw, as you fly away from the source of your DX8 signal the vTx overpowers the signal and 'blanks' it out. Even if you had a digital vTx with FHSS or some other form of signal identification, the greater power of the vTx in closer proximity to your RC receiver would cause the same problem. Some lower quality 1.2 GHz and 1.3 GHz vTx's will even cause harmonic interference that can cause the same problem if severe enough. However you can use filters to reduce or eliminate the interference.

A better choice for your vTx (depending on what frequency you are using for telemetry, if your using telemetry) might be either 1.3 GHz, 900 MHz, or 433 MHz. All but 900 MHz require a HAM radio license to operate. It is worth noting that the lower frequencies will have higher performance over a longer distance at the same or possibly lower power output. The need for a HAM radio license shouldn't stop you from considering these frequencies as it is quite easy to get your operators license. The Technician class test is only 35 questions out of a pool of 463 questions and I'd bet you already know the answers to a lot of the questions.

Lastly not to be the wet blanket, but you mentioned

My bosses loved the aerial pics I took with my Gopro and had a job for me to perform using the potential of FPV

If you are working and you provide a service to your 'Boss' you can't take pictures for anything other than your own personal use. Even if you do it off the clock and don't charge anything for the service or get anything in trade and your Boss uses the images for commercial purposes, you would be breaking the law. You would need a Federally issued C.O.A. (Certificate of Operating Authority) prohibitively expensive and not worth the effort unless you want to make this a career. In addition if you are operating on a frequency that requires a HAM operators license you are prohibited from taking any form of compensation for services you perform while using your HAM privileges. That said go get your HAM license and have fun with it!

Regards,

Nathaniel ~KD2DEY ← my call sign

Replies

Moderator

Nathaniel Caner December 29, 2012 at 4:42pm

Stan,

Here is a copy of the HAM radio frequency chart, it shows all the frequencies available to a HAM radio operator licensed in the USA by License Class. You will see that all the frequencies we have been talking about are available to a HAM radio operator that holds an entry level HAM radio operators license. The test only cost $15 and the license is good for 10 years!

Regards,

Nathaniel ~KD2DEY
Moderator

Nathaniel Caner December 29, 2012 at 4:24pm

I didn't mention 5.8 GHz which is kind of funny because I currently use a 600mw 5.8GHz system LOL. This is a valid frequency for use in the USA, if you have a HAM license. However it's not great, it has good bandwidth but it isn't great if you have any kind of terrain (Mountains, buildings, trees etc) it doesn't take much to disrupt a 5.8 GHz signal and multipath interference is really bad on this freq. CP antenna sets like a cloverleaf on the Tx and a Skew Planar on the Rx will all but eliminate the multipath issue. 5.8 GHz will however have the shortest range of all the options for a given power level.

Regards,

Nathaniel ~KD2DEY
Moderator

Nathaniel Caner December 29, 2012 at 2:54pm

Aloha Stan,

The problem you are experiencing isn't with corruption of your controls it's with loss of signal as evidenced by your aircraft going into RTL mode. The DX8's FHSS is working hard to maintain a solid connection to your DX8 and does well until the signal of your lawmate vTx overpowers the signal. The signal output of your DX8 I believe is about 500mw and your lawmate vTx is 1000mw, as you fly away from the source of your DX8 signal the vTx overpowers the signal and 'blanks' it out. Even if you had a digital vTx with FHSS or some other form of signal identification, the greater power of the vTx in closer proximity to your RC receiver would cause the same problem. Some lower quality 1.2 GHz and 1.3 GHz vTx's will even cause harmonic interference that can cause the same problem if severe enough. However you can use filters to reduce or eliminate the interference.

A better choice for your vTx (depending on what frequency you are using for telemetry, if your using telemetry) might be either 1.3 GHz, 900 MHz, or 433 MHz. All but 900 MHz require a HAM radio license to operate. It is worth noting that the lower frequencies will have higher performance over a longer distance at the same or possibly lower power output. The need for a HAM radio license shouldn't stop you from considering these frequencies as it is quite easy to get your operators license. The Technician class test is only 35 questions out of a pool of 463 questions and I'd bet you already know the answers to a lot of the questions.

Lastly not to be the wet blanket, but you mentioned

My bosses loved the aerial pics I took with my Gopro and had a job for me to perform using the potential of FPV

If you are working and you provide a service to your 'Boss' you can't take pictures for anything other than your own personal use. Even if you do it off the clock and don't charge anything for the service or get anything in trade and your Boss uses the images for commercial purposes, you would be breaking the law. You would need a Federally issued C.O.A. (Certificate of Operating Authority) prohibitively expensive and not worth the effort unless you want to make this a career. In addition if you are operating on a frequency that requires a HAM operators license you are prohibited from taking any form of compensation for services you perform while using your HAM privileges. That said go get your HAM license and have fun with it!

Regards,

Nathaniel ~KD2DEY ← my call sign
Mike Boland December 29, 2012 at 2:14pm

Yes, I must concur with jeff,

I have always had range issues when trying to use 2.4 for both video and RC, Spectrum being the worst, Futaba being the best but still not adequate.

If you are going to use 2.4 RC then you should be using 5.8 for video (at least in this country, Australia, as it's the only legal one we can use).

I actually keep some 36MHz equipment for FPV, so my RC is 36MHz, data is 900MHz, and video is 2.4GHz.

Just think of the RF soup around your video Tx on the copter and your poor Tx at only 10mW or so trying to get through to your RC Rx. It hasn't got a chance at any sort of range.
JeffBetts_KK4MTC December 29, 2012 at 2:00pm

I believe you need to use a different frequency for video tx/rx and rc controls. Even though the DX8 is FHSS, I've read to always use a different freq for each signal transmitted, and separate the antennae as much as possible to get best reception/range. Also filter the power supply if using the flight battery to power the video transmitter to eliminate back-emf/motor-noise.

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