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HK 900mhz 200mw FPV issues...

#1
hey guys,

i just bought this 900mhz 200mw kit from hk, and it has never worked. ive spent about 6 hours farting around with it, and cant get it to work at all...

i was running the RX and monitor off a 800mah 3s lipo. i had to open up the video RX and solder a different plug onto the board so i could power both the RX and monitor at the same time.

so ive tried every combination of switches i can think of on the video TX, and every channel on the video RX through each of the combinations of the tx... still no video signal.

i was thinking that maybe the camera is faulty, as i was reading that hk had the + and signal wires mixed up on their prebuilt harness. so i flipped the wires around, and still nothing.

so then i built a custom harness for my gopro hero hd (original hero hd haha) and still have no signal...

for the gopro harness, i used a the original tv-out cable that came with the camera. i cut the end off it, and soldered the included 4-wire pigtail that HK includes with this kit. yellow to yellow, white to white, all the grounds were soldered together, and red to red. for the red and ground, i cut them off the camera, and ran them to my lipo's + and negative, respectively.

fired everything up, and STILL NO SIGNAL... im about ready to pull my hair out...




can anyone help? maybe i wired up my gopro harness wrong? i couldnt find any wiring diagrams or anything anywhere online...

thank you in advance!
 

squishy

Pirate ParkFlyer
#2
Try just using a video signal, like from an old VCR or something, stop switching wires around on your cameras, you prolly already fried it. At this point you need damage control. Find out what works. Get a video signal, test it on the monitor or goggles, then run it through the video transmitter, test each and every piece before bringing it all together. Oh and if you are in the USA, you will not be successful with 900mhz, cell phones, and all those cell phone towers you see in this country are 900mhz. Even when you get the signal working it will have a very short urban range, you will need to go out in the middle of nowhere for it to work, I hope you are far from cities or cell towers..
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#3
GSM-900 isn't used in north america -- it's primarily used in south american countries. Other than the CDMA in Japan, it's the only cell band int the lower 900 Mhz. That all-seeing celphone tower isn't going to bother the 900 band.

That's not to say the band is free -- it's not -- but most of your interference is going to come from low power local sources (older cordless phones, wireless mics, wireless security systems). They're running at that freq because the FCC has opened it up to unlicensed low power use.

The diffrence is you can have good cell coverage far from other people witout RF interfence, but the more populated the area is, the more likely you'll run into interfence.
 

squishy

Pirate ParkFlyer
#4
Where are you getting your info from?

I fly with a Ericson technician, he was very specific about at least the area I live in (central California) and stated all the towers have 900mhz. He told us this after trying for over a year to get 900 to work and failing, 2.4ghz also sucks here, but 5.8 and 1.2 work perfectly...it's all noise...

"In North America, GSM operates on the primary mobile communication bands 850 MHz and 1,900 MHz."
Source: https://en.wikipedia.org/wiki/GSM_frequency_bands#The_Americas
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#6
Where are you getting your info from?

I fly with a Ericson technician, he was very specific about at least the area I live in (central California) and stated all the towers have 900mhz. He told us this after trying for over a year to get 900 to work and failing, 2.4ghz also sucks here, but 5.8 and 1.2 work perfectly...it's all noise...

"In North America, GSM operates on the primary mobile communication bands 850 MHz and 1,900 MHz."
Source: https://en.wikipedia.org/wiki/GSM_frequency_bands#The_Americas
Read the article you just posted.

850 stops at 895MHz. A little further to: https://en.wikipedia.org/wiki/Cellular_frequencies and you'll see that covers only ATT & verizon towers -- a good percentage, I'll grant, but not all.

Depending on the quality of your receiver and your range from the tower, this might oblitertate a 900-even channel (not legal anyways for US amature 33cm band -- bottoms out at 902M), but with 15MHz seperation, 910MHz commonly sold should be clear of tower interference (near center of the amature 33cm band). If Hams can use it to chat, TV, FM and whatever, there's no reason you can't use it on a short range (less than a mile) flight.

It's a bummer to hear he's having such trouble with his equipment, and not a surprise that S-E phones can operate in GSM-900 (they are sold world wide), but if the Cell downlink is to blame, you need a better filter on your base station.

1.2 should be clear-ish -- 23 cm band has a nice wide 600MHz bandwidth without much compitition nearby -- while 5.8 and 2.4 are probably just as crowded with part 15 clutter. You do get an advantage with 5.8, though. Both air and building materials are getting really foggy around that freq, reducing your compition's range. Come out with a strong LoS link with good filtering (5.8G channel filters are crazy small), and your neighbors cordless phone doesn't stand a chance.
 
#7
well, i went back and tested the camera. it works. i built another wire harness and connected it right to my monitor. i have video. so i hooked up the stock harness to the TX and camera, and hooked up my RX back up to the monitor. i was flicking dip switches, and all of a sudden had static... that is a first... i tried to move the rx so i could see what channel it was on, and it was doing a weird scanning thing and had the . (period) on the LCD display on, then my battery disconnected haha! i soldered the plug on, and got everything fired up again, and no signal again... i cant get the static to come back...

my rx and tx are only about 10" apart. as soon as i get a signal, i will see how far apart i can go before i lose signal. i just want to get this thing working...




any ideas?
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#8
Analog,

Good to hear the camera is working -- not sure about what's going on with the Rx/Tx pair. No experince with your equipment, but flipping the dips until you get static sounds like you're flipping through chanels and found some modulated static (has carrier wave and framing, but random pixels). Might be from your TX, might not, but if it dropped when your Rx lost power, it's a good sign the link worked.

Seriously -- Aiidan is right. Seperation. Too close and near-field effect will make it go wonky. At 200mw, it's designed to reach MUCH further, but will stink at knife range. Put them on opposite sides of the room and if you're using the rubber duckies (plastic whip antennas), point them *both* at the celiing, not at each other.

The static sounds like there's still something wrong in the wired signal path on the Tx side (if the Tx sees static from the harness, then the Tx will transmit static). A pic of your harness/setup might help.
 

Craftydan

Hostage Taker of Quads
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#11
That goes for the transmitter. NEVER RUN A TRANSMITTER WITHOUT A LOAD. (sorry for the emphasis -- it's important).

Squishy's suggestion for the RECEIVER is good, but you still need some distance. The transmitter is developing the waves within the first few wavelengths, and effects can be chaotic in the "near feild". Best send them to the opposite sides of the room (or table), possibly remove the receiver antenna, and they'll play nicer.
 
#13
hey guys, i got more static again tonight! im not sure HOW though... i hooked my gopro directly to it, and then unplugged it and plugged in my RX again... then the static came in (i cant get it to do it again though!) with the static going, i changed the channels, and 0 is fine static, 1 is blocky static, 2 is slightly less blocky, and the higher you go, the finer the static gets... turning off the TX made no difference in static. moving the TX made no difference in static either... im wondering if my RX or TX may be pooched... how would i be able to test one independant of the other? the TX gets pretty warm when its plugged in, but i read that this is normal. the RX doesnt get very warm... is that normal?

i have the RX opened up, and i keep feeling the module itself, and its slightly warm... doesnt get hot, but doesnt stay cool either...

im not sure where to go from here...
 

jaygreco

Junior Member
#14
I also have this kit from HK, and I've had some issues. I've found that the only "legal" band for 900Mhz is channel 1, at 980Mhz. I had the flipped signal wires, flipped them, and the camera worked well for a while. However, after a while, I started getting insane flickering from the video. I assumed it was noise on the video channel, as my wiring was pretty messy. So I made a very clean linear regulator and a custom board for my OSD, still flickering like mad. I finally tested the board camera with no transmitter (directly hooked up to my monitor) and realized it was the board camera that was bad. I'd double check that your transmitter and receiver are on the same channel and that the camera is attached to the transmitter correctly.
 
#15
I cant figure out what channels are the same between rx and tx... i have literally tried every combination of switches on the tx while running through every channel on the rx... they will not communicate... had them in different rooms and everything...

I ordered another one last night. Im building a tricopter for fpv as well, so i will need 2 anyways...
 
#16
well... i have got some good news... progress anyways...

on channel 9 on the RX, and the 4th dip switch up on the TX, i had a VERY faint signal, but just for a second... i got my OSD today, and very faintly, every couple seconds, i could see some of the display show up on my screen. this has only happened for about 2 minutes, then nothing. tried moving the tx right beside it, nothing, tried moving it 30ft away, nothing... both with antenna on and off the rx...

is there any way to tweak the channels on the rx?

anyone else running this setup, what are your dip switch and channel settings?! im really lost trying to get this thing to work...
 

RoyBro

Senior Member
Mentor
#17
Did you get any better instructions than what I was able to find on the HobbyKing site? Specifically, the dip switch settings on the transmitter. Although there are 4 dip switches and 4 channels, they don't necessarily correspond 1:1.

For example, these are the dip switch settings for the FoxTechRC 900 MHz 200mW transmitter. I'm not saying you should use these, I'm just using it as an example.

FVT9020.PNG

If you don't have any better documentation, contact HK customer service and ask for both a dip switch diagram and what channels correspond to which frequencies.
 
#18
i contacted HK, and they said to make a video and they will probably send me a new 'whatever has failed' haha!

thats freaking good service. so, after fiddling with the dip switches, i cannot get anything out of it anymore haha! im hoping my RX is toast, as i have ordered a 2nd kit, for my tricopter.

so i guess ill just wait till my new one shows up and see if i can get this TX to work with the new RX...
 

RoyBro

Senior Member
Mentor
#19
i contacted HK, and they said to make a video and they will probably send me a new 'whatever has failed' haha!
At least they aren't asking you to send back the whole unit for them to evaluate. A video can be sent via the Internet, which is a lot better than putting it on a slow boat TO China. :)
 

xuzme720

Dedicated foam bender
Mentor
#20
Yes but they most likely will have you send back the offending part at your expense for warranty evaluation. That is what I've seen in other posts anyway...