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Video Transmitter 910MHz 20Watt for ultra long range

antenna I made for this system look here Antenna 1/4 wave for 940 to 980MHz easy homemade

The main transmitter module is a 200mW type 12V from rangevideo, called TX-900-200
its 4 channels was measured : to 910, 980, 1010, 1040MHz
the output power was from 23.0dBm to 23.8dBm depending on channel.
voltage vs output power was measured to:
12V 140mA 23dBm, 11V 120mA 22dBm, 10V 100mA 21dBm, 9V 90mA 20dBm.

the lowpass filter C1 1p8, C2 2p2, C3 NM, C4 1p8, L1 8nH, L2, 8nH (A03T)
at 910MHz 0.0672dB, at 960MHz 0.145dB, at 2.43GHz -36dB

Output power vs supply voltage and current, at CH1 910MHz:
28V 2.0A 21Watt (MAX !!! dont do this for a long time)
26V 1.9A 19Watt
24V 1.8A 17Watt
22V 1.8A 15Watt
20V 1.7A 13Watt
18V 1.7A 11Watt
16V 1.6A 9Watt
14V 1.2A 6Watt
12V 0.6A 2Watt

the rangevideo datasheet

heatsink measurements: length 145mm, height 38mm, width 116mm

R5 = 330, R2 = 330, R4 = 18, input attenuator, signal level fix
the tx module voltage is 9V from LM7809 and the bias for PA unit is 15V from LM7815
the PA module used is from Motorola called MHW916 designed for GSM band basestations, 925-960MHz
luckyly this module can handle a lot wider frequency span, than said in the datasheet, works fine at 868MHz too :-)
and also this module if found to deliver a bit more power too.

with covers on, total weight of this unit is 830 grams

video and audio input connectors RCA also called phono connectors.
RF output is N type from Suhner.







Light weight version for long range FPV !

All metal parts was drilled to remove as much weight as possible

length 155mm, width 75mm, height 31mm, weight all inclusive 200gr.




in the hottest area I keept more aluminium to cool the PA stage better.

all the holes will save weight, but they will also let cold air in and cool the unit from both sides.

the red wire that goes to the PA stage bias voltage can be moved from Vin (pictured)
to the 12.7V output of the LM317, this will change the output and input voltage range on this unit, see this table:

Bias Vin selected   -  Bias 12.7V selected:
Vin  Ain  Watt out  -  Vin  Ain  Watt out
10V  0.2  0.1W      -  10V  0    0
11V  0.4  0.7W      -  11V  0.2  0.07W
12V  0.6  2.5W      -  12V  0.4  0.7W
13V  1.0  5.4W      -  13V  0.6  2.4W
14V  1.3  7.7W      -  14V  0.8  4.6W
15V  1.7  10.1W     -  15V  0.9  5.3W
16V  dont do this   -  16V  0.9  5.9W
17V  dont do this   -  17V  1.0  6.7W
18V  dont do this   -  18V  1.0  7.4W
19V  dont do this   -  19V  1.1  8.0W
20V  dont do this   -  20V  1.1  8.6W
if your unit gets too hot to touch ! you need to air cool it better or lower the output power !
at output power up to 5W no problems even with no fan cooling, if located in plane with plenty of air cooling
I expect you can output 7-10W if you are lucky !
(the PA stage block is rated for 28V supply and 15V bias and HUGE heat sink to give full output)




the heawy RCA connectors can be cut off and wires soldered directly in the plane to save weight.


I wonder how much power this little antenna can handle :-)


www.cpemma.co.uk/317calc.html good link about LM317 regulators

-Thomas Scherrer OZ2CPU this page was last updated: Dec. 4th 2008