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Smoked my 900mhz vtx I must be missing something!

#1
I got the hobbyking 200mW 900MHz fpv system. Seemed to work well, so I made the Clover leaf and Skew Planar antennas from David's instructions. Got one flight on that with a great improvement on picture clarity. I went to fly a few days later, and it was like the frequency had shifted. instead of being on ch3 in the rx it was ch1 and the range was literally 3ft. Then I stopped getting any signal. Took it inside to troubleshoot and plugged it in again and smoke...

The best I can figure is that I made the clover leaf wrong or something. The original Dipole antenna measures an open circuit when I try to measure resistance, but my clover leaf (and the skew planar) measure a short circuit.

What am I missing?

That all said, I can't find a cheap replacement for the vtx. HK only has the full system (and that on backorder). Everywhere else has the transmitter for the cost of the full system on hk.

What are the frequencies that the 12ch receiver that comes with the system can pick up? Will it pick up 1.2 or 2.4GHz?

Also, is anyone familiar with the components on this receiver? I know which component died and can post pictures if someone could tell me what it is.

I would appreciate any help that ya'll could give me.
Thanks!
 
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Tritium

Amateur Extra Class K5TWM
#2
Your antenna Ohm measurements are correct. Dipoles measure open with an Ohm meter. Cloverleaf and Skew Planer will measure shorted but RF power doesn't see it that way. If there was a break to the antenna or if the Transmitter was EVER powered up without an antenna then the Xmitter would smoke. Also if the Antennas were not measured correctly then your SWR may have been too high and this could also smoke the transmitter. Your 900MHz receiver is for that band only and will not work with 1.2 or 2.4.

Do post a pic please.

By the way. To fly in that frequency range between 902MHz and 928MHz requires a Technician Ham License to be legal and the new head of the FCC is a "Bulldog" for enforcement.

Thurmond
 
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#3
Thanks for the information. I would say it is that I must have measured the antenna wrong.

Thanks for the heads up on the regs. That is an area that I have done some research, but haven't found much on. Where can I go to get the official rules, what frequencies can be used, and when I would need a HAM license. To get going, do you know if there are frequencies/powers that are legal without the HAM?

Here is a picture of my vtx. I know for sure that the circled component is blown. I remember i could see smoke coming from it. there is also a heat discoloration on the cover right above it. I don't know if there are others that might have died too?

Thank you very much for the help. I have been in RC for many years, but FPV is a totally new thing for me. Also, I know just enough to be dangerous. I am a ME not and EE or ECE... :p

Blown Component.jpg
 

Tritium

Amateur Extra Class K5TWM
#4
Man is that some "trashy" soldering. Resistor, Cap or Inductor. Going to be very hard to tell without a look at a good transmitter. A guess would be inductor but I will see what I can find out.
There are MANY ham radio resources online. As a matter of fact there is a sticky thread on this forum concerning licensing. Do a search for the thread Hams of FliteTest.

The user jhitesma is very good with Ham radio and electronics in general and may be of assistance to you as well.

Can you post a closeup pic of your antenna?

Thurmond
 
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