Signal Fade Within 30 feet......

[hoveringal]

Hello friends,

I purchased a FPV system for my Flame Wheel 450 and am using a Go Pro camera on board. The picture is fantastic and clear but when the quad is 25-30 feet away and further the image blacks out for a split second. Both antenna's are correctly polorized, the FPV runs on a seperate Li-Po and both TX and RCVR are on the right same channel. I've tried rotating the quad in flight to see if the signal was blocked which had no affect. Is it possible the transmitter antenna is within too close proximity of the rotating blades? I am using APC style blades which the tips come approx 1.5" of the antenna. The receiver is a R-5800 and the transmitter is a 400mw TXV584 - all purchased from Hobby Wireless. The antenna's are two Spironets RPMSA. I am only looking for 500-600 feet max for distance and thought this was a good system. Any thoughts or suggestions???

 

[kloner]

since you have it all seperatley powered, can you turn on the fpv only and does it do that then when the rig is unpowered?

just in case, a broken connection is a normal short range drop off like this, make sure the sma connector on the rx and tx aren't loose on the pcb like a broken solder joint on the ground. make sure the antenna are all the way on. make sure if it's reverse polarity sma antennas it is for the rx/tx too

 

[hoveringal]

All great suggestions and I will start looking for wiring issues and solder board issues.. I know I got the antenna's right and was thinking about trying the stock antenna's incase of of the new ones came defective. Also will try walking craft with motors off. Appreciate the tips and suggestions -

 

[Benjamin Kenobi]

I had this problem when my patch antenna broke and I didn't realise so the receiver essentially was connected without an aerial. This fried the receiver and I only got 10m with various antennas. New rx and all good. Have you powered up without an antenna connected and damaged your receiver?

 

[hoveringal]

Interesting - I have not run the equipment without the antenna's attached to the best of my recollection. Of course if the antenna was bad then yes I have.. Luckily I still have the rubber duck antennas and will try to use them on a test this weekend. Are rubber ducks specific to a rcvr or xmtr or can they be swapped??

 

[PeteDee]

I had this problem when my patch antenna broke and I didn't realise so the receiver essentially was connected without an aerial. This fried the receiver and I only got 10m with various antennas. New rx and all good. Have you powered up without an antenna connected and damaged your receiver?

For the life of me I cannot think of any reason that a vRx would fry with no antenna attached, certainly a problem for your vTx though, if your vRx was "fried" much more likely that it was just faulty.

Cheers

Pete

 

[Benjamin Kenobi]

Seriously? All the warnings about not powering up without the antenna attached are just nonsense then? Without the antenna there's nowhere for the power to go so it builds up and pop. At least that's how I see it. Anyone else want to chime in with a proper answer?

 

[Benjamin Kenobi]

I meant a proper answer to my lame explanation. You did make a valid point Pete. I wondered that myself. My vRx was about 6 months old. ImmersionRC Fatshark rx. Broke Fatshark patch antenna but used it for 30 mins anyway. After that severely reduce range regardless of new antennas. New Rx and all good. Seemed conclusive to me. Cool?

 

[OneStopRC]

VTX would fry without an antenna or some form of a load, VRX would not matter if it had an antenna or not. VTX is the one that relies on a tuned length antenna of which would get damaged without one or with an incorrectly tuned length antenna. I.E. installing an antenna tuned for say 1.2Ghz on something tuned for 5.8Ghz would certainly toast your VTX. When buying an antenna, like the Spironet type, make sure you buy the correct length for your TX and the same for the RX.

 

[Benjamin Kenobi]

And the warning that comes in every receiver manual I have about not powering up without antennas attached can be ignored then?

 

[Benjamin Kenobi]

Best explanation is that the antenna acts as a resistor. So far all web pages I've read confirm not to power on a vRX (yes, and a vTX) without antennas attached. This is common knowledge and I don't know why you guys are arguing it. Please power up your vRX without antennas attached and leave then running for half an hour. See what happens. Remember, lots of people read this forum and we shouldn't give them bad advice.

 

[OneStopRC]

Best explanation is that the antenna acts as a resistor. So far all web pages I've read confirm not to power on a vRX (yes, and a vTX) without antennas attached. This is common knowledge and I don't know why you guys are arguing it. Please power up your vRX without antennas attached and leave then running for half an hour. See what happens. Remember, lots of people read this forum and we shouldn't give them bad advice.

I am not arguing, but I am going to ask you your qualifications to tell me I am wrong! Of course "most" people will use the internet as a source of information, it is a wealth of garbage for all to access... you have probably read or heard the saying "everything on the internet is true, the internet said so".

Radios, Transmitters and Receivers are something I have dealt with, worked with and worked on in the past. Sure some 20 years plus ago, but radio is radio, nothing has changed, it is still the same as it has been for many years.

Poor reception comes from several sources, (1) No antenna or incorrect antenna, (2) Damaged RX, (3) Damaged TX, (4) Poor line of sight, (5) Structures (line of sight again), (6) Bleed over or interference.

(1) Speaks for itself, no antenna on the RX will shorten its receive range, incorrect wave length antenna will do the same.
(2) Damaged RX, did you know, powering up your TX too close to your RX WILL damage the RX? probably not, but I bet you all do it.
(3) Damaged TX could come from overheating caused by a lack of an antenna, incorrect wavelength antenna, antenna being grounded and much much more.
(4) Line of sight, Radio waves travel in straight lines, trees, houses, objects and structures can cause weak signals.
(5) As above, Structures like tall buildings made of steel, concrete, bricks etc also diminish radio signals.
(6) Interference from other sources, MIMO operating on the 5.8Ghz spectrum can interfere, WISP or Wireless Internet Service Provider operates on 5.8Ghz, might not be on the same channels but bleed over "could" happen. This is just a for-instance.

I would say the OP probably has a bad TX, I have heard of people buying the 600mw VTX from Immersion and people have found solder related issues on the board. It is an electronic item and can arrive bad, become bad or work for ever. If the OP has not damaged the RX by placing the TX to close, I would return it for a replacement along with the TX to have both tested or replaced.

You can't damage a receiver if there is no antenna connected to it, it does not transmit anything over its antenna, unlike the TX that can and will get damaged by not having an antenna. The TX relies on its tuned length of wire to stop Standing Wave Radio (SWR) which in most cases will damage the TX over time. This happens when the radio signals return back to the TX causing damage, not instantaneous, but it will damages it.

As mentioned, a receiver is just that, it does not require a powered radio signal on its antenna, the antenna is there for one purpose and one purpose only, to bring in as much noise as possible on the tuned length it was designed for.

I also looked at and read the PDF's for both of my ImmersionRC 600mw VTX and my ImmersionRC Uno VRX. The VTX does state the following "Must be used with an antenna at all times", whilst the VRX has nothing about operation with or without the antenna.

I try my very best to provide accurate information, I don't on the other hand type just to hear my keyboard click.

 

[Benjamin Kenobi]

See, now that's a proper answer! Not just 'I don't see how it could...' Etc. As you said, you can find anything on the web to support either view point which is why it's so important for you to give a good answer in these threads. I rely on the posts in this forum to guide me.

The manual for my diversity monitor says 'never power up without antennas attached' and I had it in front if me when posting. It's so badly written in general that I guess that doesn't mean anything.

So maybe my old vRX is still good to go then. That would be nice as a spare.

Thanks for taking the time to answer and sorry to the OP for wittering on. I shouldn't post before morning tea I guess!

Cheers!

 

[OneStopRC]

See, now that's a proper answer! Not just 'I don't see how it could...' Etc. As you said, you can find anything on the web to support either view point which is why it's so important for you to give a good answer in these threads. I rely on the posts in this forum to guide me.

The manual for my diversity monitor says 'never power up without antennas attached' and I had it in front if me when posting. It's so badly written in general that I guess that doesn't mean anything.

So maybe my old vRX is still good to go then. That would be nice as a spare.

Thanks for taking the time to answer and sorry to the OP for wittering on. I shouldn't post before morning tea I guess!


Cheers!

LOL, it should be fine, in all my years I have never had an RX fail on me, well not due to lack of an antenna anyway..

Now diversity could be another matter in itself, diversity does antenna switching and could cause premature failure of the diversity circuit.

 

[MombasaFlash]

Best explanation is that the antenna acts as a resistor. So far all web pages I've read confirm not to power on a vRX (yes, and a vTX) without antennas attached. This is common knowledge and I don't know why you guys are arguing it. Please power up your vRX without antennas attached and leave then running for half an hour. See what happens. Remember, lots of people read this forum and we shouldn't give them bad advice.

It is only the transmitter which stands to suffer if there is no antenna attached. If the receiver has no antenna you just get poor reception.

That said, it is the receiver antenna that is the most important element when it comes to sensitivity, range and quality of video reception. It is more important than the output power of the transmitter.

 

[mutley2]

Had great distance with my current set-up until a few days ago, when I looked the SMA end-board connector on my 600mw VTX from ImmersionRC had broken ground pin's (two top and one bottom) and the last was just about to fail. Will get a replacement 50omh con from work Monday but when I've finished refitting I will epoxy around the ground pins (keeping away from the feed pin) to give some mechanical strength. Might be worth having a look to see if all is as it should be