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SXA-389B replacement - MAAMSS0049?
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Re: SXA-389B replacement - MAAMSS0049?

by sheepke on Tue Jan 06, 2009 5:18 pm

Anyone?

sheepke
 
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Re: SXA-389B replacement - MAAMSS0049?

by nova on Tue Jan 06, 2009 6:13 pm

the rf3809 is 8 soic, whereas the 4089 is sot 89.

In order to use the rf3809 you would need to mod the pcb board.

the gain on the rf3809 is smaller than the 4089, however output power is greater.

the big drawback to the rf3809 is that it requires alot of support capacitor and inductor to make it work which would make the board larger and thus less portable.


the best solution is to use a bga6589. the gain is 22db at 850 MHz and 17 at 1.95GHz.

I tried this amplifier and it put out 20dBm at 1.9GHz and 21 dBm at 850 MHz.

to get the amplifier to work I used different values for the atten pad and a preamplifier.

also I used a 2.4 ohm resistor to bia the amplifier. assume vcc to be 5 volts

then 5v - 4.8v/ .084 A = approximately 2.4 ohms

this amplifier is better than the 4089 because it draws less power and accomplishes the same thing the 4089 does without the cost and current draw.

I hope this helps alot

nova
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Re: SXA-389B replacement - MAAMSS0049?

by sheepke on Wed Jan 07, 2009 7:31 am

nova wrote:the rf3809 is 8 soic, whereas the 4089 is sot 89.

In order to use the rf3809 you would need to mod the pcb board.


This is no problem since i'm completely drawing the board in altium designer 6.

nova wrote:the gain on the rf3809 is smaller than the 4089, however output power is greater.


So if i understand it well you need a bigger input power on the rf3809?

nova wrote:the big drawback to the rf3809 is that it requires alot of support capacitor and inductor to make it work which would make the board larger and thus less portable.


the best solution is to use a bga6589. the gain is 22db at 850 MHz and 17 at 1.95GHz.

I tried this amplifier and it put out 20dBm at 1.9GHz and 21 dBm at 850 MHz.

to get the amplifier to work I used different values for the atten pad and a preamplifier.

also I used a 2.4 ohm resistor to bia the amplifier. assume vcc to be 5 volts

then 5v - 4.8v/ .084 A = approximately 2.4 ohms

this amplifier is better than the 4089 because it draws less power and accomplishes the same thing the 4089 does without the cost and current draw.

I hope this helps alot

nova

sheepke
 
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Joined: Fri Dec 26, 2008 6:14 pm

Re: SXA-389B replacement - MAAMSS0049?

by nova on Wed Jan 07, 2009 12:40 pm

lets understand a few things before you make your final choice

1) the output power from the ros 2500 is 6.5 dbm. assume we remove the -6db pad, then we have 6.5 dbm going into the rf3809. At 850 MHz the gain is 13.5 DB so the output from the amplifier will be 20 dBm at the antenna

now lets see how the gain looks at 1.95 GHz. at 1.95 GHz the gain is 10.5 DB so 6.5 + 10.5 is 17 dBm at the output.

2) in order to use the rf3809 you need more capacitors and inductors to make it work.

this is not worth all the extra work, because the amplifier will never hit the max power it was designed for and you would then be wasting money on something that can't help you.

further more you have to attentuate the power from the vco because the max input to the lmx2430 is 0 dBm, so if you don't attentuate the signal, you'll fry the lmx2430 up(not good and not worth wasting money!!!!!)


the bga6589 is the best buy because at 850 the gain is 22 dB, and 17 at 1.95 GHz.

here's how to use these in the wavebubble.

the output of the bga6589 at 850 MHz is 21 dBm what we need to know is what input signal is this amplifier looking for.

so 21 dBm - 22 DB gain = -1 dbm input. instead of a -6db pad we'll use a -7db pad. this makes sure the input to the amplifier is what we want.

lets see how to handle 1.9GHz. the output of the bga6589 is 20 dBm so 20dBm - 17 DB gain = 3 dBm input signal

that means we attentuate the vco signal by 3 instead of 6. to overcome the input requirement of the lmx2430
(remember the max input to lmx2430 is 0dBm and the min is -15dBm) we attentuate the signal at the lmx2430 by -3db
this protects the lmx2430 from dangerous input level( 3dBm)

and this is how to use the bga6589.

I hope this amplifier tutorial has helped you and others at this forum.

things to remember and in summary.

the input level to the amplifier you choose and at the rf input of the lmx2430 really matters and not the output p1!!!

best wishes to all working on the wavebubble

nova
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Re: SXA-389B replacement - MAAMSS0049?

by nux on Sun Apr 05, 2009 9:17 pm

Can you specify the resistor values you used in the T-attenuators in order to achieve the attenuation required for the bga6589 replacement.
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Re: SXA-389B replacement - MAAMSS0049?

by caffeinatedsoap on Tue Apr 07, 2009 1:12 am

nux wrote:Can you specify the resistor values you used in the T-attenuators in order to achieve the attenuation required for the bga6589 replacement.


Seconding this. This is all a bit over my head.

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Re: SXA-389B replacement - MAAMSS0049?

by enorcrove on Sat Apr 11, 2009 7:17 pm

Like said above you need a -7db pad for the 850mhz and at 1.9ghz we use a -3db pad.

the easiest way to figure out your resistor values for the T-attenuator is something like this.
http://www.daycounter.com/Calculators/PI-T-Pad-Attenuator-Calculator.phtml

the Characteristic Impedance is 50ohms.

If you cant see the T-attenuator on the schematic it uses resistors R23,R24,R25,R26,R31 and R32

Using standard 1% tolerance resistors (which all can be bought in 10 quantity on digikey) i get the following values:

R25 = 19.1 ohm
R26 = 19.1 ohm
R32 = 56.2 ohm

R23 = 8.45 ohm
R24 = 8.45 ohm
R31 = 143 ohm

correct me if i am wrong but i think this should be correct.

good luck.

Mike
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Re: SXA-389B replacement - MAAMSS0049?

by nux on Sat Apr 11, 2009 10:42 pm

Actually the BGA6589 should work fine with the standard components used for the SXA-389, with a slightly higher output gain. However by modifying the t-attenuator pad values, you can wring slightly more power out of the BGA6589, with the caveat that you need to attenuate the input to the PLL as it can only take a max of 0dBm input.

I'll be trying the BGA6589 with the standard parts list shortly and report on how it works.
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