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JetPilot

900 MHZ 1 Watt or Higher Video Transmitter needed

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I need to find a 1 Watt or higher power 900 mHZ video transmitter. I see at one time Lawmate made a 1 watt cased 900 unit, but no one seems to have one. 5 watts would even be better, but I dont know if they were ever made.

Does anyone know where I can get one of these higher power transmitters, or maybe a small amplifier for a 500 mw transmitter ?

Thanks,

JetPilot

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I'm having a look for you, I will try and find a DIY job if I can as it will be much cheaper and you can make it to your own spec.

Have a look at this ready made amp, I'm sure it could be reduced in weight a fair bit if you lower the power level but I will keep looking.

http://www.teletronics.com/amplifiers90010w.html

Terry

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Thanks for response Terry,

I was searching and ran across that same amplifier, but its more for wireless networks and is quite expensive and large. But your other link took me to Down East Microwave and they have some 40 Watt kits, I could drive it to only 10 watts and do away with the large heat sink....

I was hoping not to have to build, but the kit is only 180 bucks, so I might try it. If anyone comes across the 1 watt or more 900 MHZ transmitter avialable anywhere, let me know !

JetPilot

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http://www.rangevideo.com/900mhz_transmitters.html

Edit: duh, I misread your post. I thought you said 1W or .5W. I see now that it was the period from the sentence before and that you really want 5W. Never mind...

Thanks for looking Mr. Pibb,

I need at least 1 watt to bet more range than my 2.4 stuff, and 5 watts would be great !

JetPilot

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http://www.technologysales.org/servlet/the...h--Audio/Detail

Is one I found that is supost to be one watt.

http://cgi.ebay.com/2-Watt-915-MHz-ATV-FM-...tem140067137556

2 watts.

I know, it's ebay, but it looks pretty legit, not from china, lots of specs.

I see lots of 900mhz amps on ebay, real units. a lot cheaper than 2.4 ghz. may be heavy.

Best of luck!, I have been looking at 900mhz, and have posted questions on most of the boards, but just haven't found anyone who can demonstrate a real world advantage over 2.4ghz. In an environment with lots of 2.4ghz noise, it probably makes sense. On paper, it sure looks better.

Looking forward to your videos in 900mhz.

Ken

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NICE !!!!

The 1 watt and the 2 watt look great. :D I will probably try the ebay one at 2 watts, its designed for Amateur TV and ham operators usually look for high quality stuff, and quickly find out if the specs are not acccurate. Thanks for finding that for me.

JettPilot

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I may get one myself. They look pretty nice. Any thoughts on powering the tx? it calls for 12-13.8v at ~800ma, probably won't run right on 3 lipoly. The anyvolt mini is probably a little too small.

Don't you use a switching reg on your stuff?

I have been using a linear reg for a 5v tx up to this point, so don't have any experiance with this stuff.

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Seems there are prettty accurate specs, never see that many.

However I'd ignore that:

SPECTRUM-FM1200DIG2.jpg

Center frequency: 1.252 GHz... Guess he took the graph from another one... even appears in the image URL actually.

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Yes, I noticed it too, seems there is a spec page for the 900mhz rx, and the low power 70mw 900mhz tx, but he refers to the same spec page for both the 1200and 900mhz high power tx's. I tried haking the URL, and it looks like a page for the 900mhz unit isn't up yet. It is interesting to note that the current specs are not the same, so he isn't just spouting the same specs like we see so often in the chinese junk. It's interesting to note that if you shorten the URL

http://www.mobicomm.com/store/DFM1200TSIM1W.pdf

to

http://www.mobicomm.com/

their products page link makes no refrence to any of these modules. They look like they are mostly into selling expensive stuff, so this might be a side line??

1240 - 1325 MHz

500 kHz

30.0dBm Typ.(1 Watt) (1240 - 1325 MHz) 27.5 dBm Min. 31 dBm Max.

Better than -50 dBc

>35 dBc

PLL Typ +/-1KHz (0-20C)

Withstands 30:1 mismatch

SMA

6.5 MHz

1 Voltp-p @ 75 Ohm

Phono/ RCA

Phono/ RCA

12 ~ 13.8Vdc regulated 550mA Typ. 750mA Max.

850 - 950 MHz

500 kHz

33dBm Typ.(2 Watt) (850 - 950 MHz) 32 dBm Min. 33.5 dBm Max.

Better than -50 dBc

>35 dBc

PLL Typ +/-1KHz (0-20C)

Withstands 30:1 mismatch

SMA

6.5 MHz

1 Voltp-p @ 75 Ohm

Phono/ RCA

Phono/ RCA

12 ~ 13.8Vdc regulated 750mA Typ. 850mA Max.

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I bet a 3 cell LIPO would work :D On my smallest plane I use a 3 cell 2100 mah LIPO for my BWAV 12 volt 2.4 GHZ transmitter, GPS, and 12 volt camera. The voltage is right around 12 volts when fully charged, and minimum at the end of the day is around 11 Volts, so no regulator is needed :P Its 2100 mah so it would power the 900 MHZ TX for just under 2 hours with a camera...

For my bigger planes, I use a 15 volt large NIMH pack running through switching regulators, that powers everything on the etire plane for 4 hours plus.

JettPilot

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I emailed him, looks like you are right jett, he said that there is an internal v reg, and that 10.5v is fine. He did mention heat buildup, but that's nothing we haven't seen before.

He quoted $24 shipping for a 2watt tx, Rx and a digital controller. I'm not really sure if the dig controler is really needed for our uses, the RX sig strength reading would be nice, but a cheap volt meter would work the same. It's tempting to buy the 900mhz kit, which includes the RX, dig, and a 50mw tx. for $228 shipped. then Buy a 2 watt tx, $140 which I think would give you a discounted shipping of $10 for the extra tx.

If I did the math right, here are the delivered prices:

~ $378 total with both high and low power tx's, Rx, and dig control.

~ $334 for 2watt tx, Rx and dig control board

~ $280 for just 2watt tx, and RX

Antennas are extra, and at $25 seem a bit much for a cheap 900mhz dipole.

It would sure be nice if someone had some experiance with these units, of any band. It's a lot of $$ to drop on an unknown system.

I might post a question on some of the higher trafic boards to see if anyone has tried them.

For some reason I keep thinking I have seen these systems for sale, somewhere else. Just can't think where.

Ken

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Nice work Lupy !

I wonder what the receivers are like, have you seen any sensitivity specs on them ? That would make a huge difference in range... I would hate to spend a lot on a 900 MHZ system and have poor range due to a cheap receiver. The RC cost in the systems seems kind of cheap...

I will try one of these systems, but I only saw the TX board listed seperately. Where did you see the combo 2 Watt TX, RX, and controller ?

BTW, what does the digital controller do ?

Hyperlink has all the 900 MHZ antennas you could ever want !! Just 8 bucks for a 900 mhz rubber duck :P

http://www.hyperlinktech.com/

JettPilot

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he lists a combo in each band, but it contains the low power TX. The 900mhz rx is available separate.

http://cgi.ebay.com/High-quality-915-MHz-A...tem140067115283

I was simply adding up the various options, and calculating the various shipping discounts.

From what I can gather, the digital display can be used with the tx or rx, it replaces the dip switches to select the chanel. It also shows signal strength. The more I think about it, the less it really seems like anything we need, The last thing I would want is to accidently change the channel on approach. The dip switches are a pain, but as long as both the tx and rx are in the same position, then all should be good.

Sensitivity is a tricky one, in the auction he lists it as -80 db, but in the detailed spec page, it's listed as -92 db at 12db signal to noise ratio. Not sure at what SNR the video is usable. Of course I also note that the auction lists it as tuning in .5mhz steps from 850 to 975 mhz. and the spec page lists it as .125 mhz steps from 900-931.875. I gather that it's a change to the pic chip, which is noted on some ofht eother band's auction pages.

I don't think I have ever seen a sensitivity figure for the super circuits 900mhz rx.

Another thought, given the lower signal loss on 900mhz in coax, it would be relitively easy to put antennas 10ft in the air, which would definetly help out on close to the ground flying.

Ken

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it's the same RX can as lawmate uses, rather than re-type it all, take a look at my post #5 here

http://www.rcgroups.com/forums/showthread....280#post6971003

I started that thread to see if anyone else recognised that rx, but stumbled on it from another tread.

Since they all can be conrtolled by the same digital board, I suspect that they are all comtech cans on various boards.

Still might be a good 2watt tx, but depending on what can is in the common 900mhz rx we see around here, the RX probably is no more sensitive than what we already have around.

Ken

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The lawmate RX is cased, and cheaper no ? I would much rather have a receiver in a nice case than just a board I have to spend hours trying to mount and find a case :angry:

If so, I will just buy the TX from Ebay and buy the RX from range video.

JettPilot

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Thats assuming that the lawmate 900mhz rx uses the same rx, I have confirmed that for 2.4ghz, they are. Since all three mobicomm rx's seem to be compatable with the same digital conrtol board, then I suspect that they must be from the same mfg. THe lawmate 900mhz rx has been around for a long time, they may have updated the 2.4ghz RX to use this RX, but left the older 900mhz unit alone?? No way of telling unless someone has one we can peak into.

The lawmate rx 900mhz is only 4ch, not that we need any more, but it would be nice to confirm that the frequencies will be compatable.

Ken

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If it is an older design I wonder if it is sensitive... If not maybe I would have to get a good LNA to put in before the receiver.

JetPilot

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be aware about:

if you change transmitter power from 0.5W to 1W it is only 3dB more,

if you go from 0.5W to 5W it is 10dB, and this will give you 3 times the range with same signal level if visible.

only 3dB change is close to nothing,

go for 10dB to be able to fell the difference.

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if you change transmitter power from 0.5W to 1W it is only 3dB more,

if you go from 0.5W to 5W it is 10dB, and this will give you 3 times the range with same signal level if visible.

only 3dB change is close to nothing,

go for 10dB to be able to fell the difference.

Thats true but the flip side is 10x more battery drain and the increased chance of interference to your R/C receiver. As with most things it's a compromise.

Terry

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Yep, 5 watts would be better :P But there is no 5 watt unit available... 1 watt is my minimum limit, if I go lower than that, I will just stick with 2.4 GHZ. The idea is to increase performance and range over my present 2.4 GHZ equipment, so I need at least 1 watt at 900 MHZ to do that. The 2 watt unit that LUPY found looks great, double the range of the 1/2 watt units lawmate sells, and given 900 MHZ goes further than 2.4, I think that TX unit is the answer. Im going to buy one, its just a matter of chosing a receiver now.

JettPilot

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I just purchased the 1/2 W unit from rangevideo. I won't be travelling the distances you mention, but once I get things set up I'll report the performance of that setup. My main reason for going with 900MHz is compatability with 2.4 GHz radios like the Spektrum.

I'm also building a 900 MHz version of the goof-proof patch antenna. It's big! (almost 12" x 12")

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900MHz will have much more range compared to 2.4

if the units have exactly the same power and sensitivity.

and the higher the freq is, rx performance will lack, and tx power will be more expensive, antennas will be smaller and also less efective, and distance attenuation will be worse at higher freq.

All radioamateurs know this simple fact:

long range = low frequency

the lower freq the longer you can speak, at even lower power.

my personal record is 3000km at 4mW oneway audio speak contact comfirmed with letter to prove it.

the frequency was 14MHz and antenna length 10meter wire.

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That's just amazing.

I've also heard of a decent bidirectional audio communication between a guy in Switzerland with someone from Brasil, that's at least 7000km, with a standard 27MHz 4W CB radio. He aparently was taking advantage of some strange amplifying effect of being at a certain point under a bridge in the middle of a nearby city.

Wave propagation can be very strange....

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