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Combine 300 watts transmitter and 300 watts amp

 
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Combine 300 watts transmitter and 300 watts amp
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stylzmovement
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Post Combine 300 watts transmitter and 300 watts amp Reply with quote
Hi pcs I will like to know if I can combine a 300 watts transmitter with a 300 watts RF amp to get a total of 600 watts.
Do you sell combiners?
Wed Apr 04, 2007 6:05 am View user's profile Send private message
intertech
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Hi S,

You cannot combine 2 signals at different frequencies into the combiners. The signals must be at the exact same frequency and in phase.

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Thu Apr 05, 2007 12:41 am View user's profile Send private message Visit poster's website
Norwalk Electronics
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Hello Stylz,

I just wanted to give you some technical input since it seems InterTech did not understand your question. The RF splitter and combiner are exactly what you use to add a pair of equal power amplifiers together. The splitter divides the output from the exciter in to a pair of 50 ohm half power outputs. The combiner is used on the output to add the two 50 ohm 300 watt signals together.

Driving both amplifiers from the same exciter eliminates any frequency difference and reduces phasing problems. One common mistake made here is people reverse one wire on either the splitter or combiner and have zero output. Both amps would then be running 180 degrees out of phase and cancel each other out. Wire lengths feeding the splitter and combiner must be short and equal for correct phase.

The fact is you have the right idea however, you do not have the correct equipment in my opinion to attempt this modification for several reasons. First, for this to work both amplifier stages must be matched. This means they have to be the same design made with matching RF transistors. The requirement goes beyond them just being the same 300 watts. If they are not perfectly matched they will not share the drive power equally. One side will work harder then the other and burn out.

You would also have to isolate the exciter from the internal 300 watt amplifier since they are not two separate amplifiers (one is part of a transmitter). You would find there is not going to be enough drive power available to feed both banks and the power supply would need to be larger. Techniques used for combining high power VHF are different then the simple toroid devices we see at HF frequencies and this complicates design.

Chances are with the amplifiers you have, one would fail before you got them to work together. Don't even try it since you would only gain 3 db if it worked perfectly. Even if they were matched you would still need a good deal of test equipment to insure both amps were operating balanced without harmonic content or oscillations. VHF amplifiers can often break into self oscillation during the modification process. Without a current limited power supply and spectrum analyzer, you won't even see the problem before the output transistors burn up. Sell what you have......buy what you need
Thu Apr 05, 2007 7:52 pm View user's profile Send private message Visit poster's website
stylzmovement
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so in this case will it be better to get a new amp the same model same power , so now i will have two amps identical . i will reduce the power on the transmitter to about 10 watts to drive both of the amps into the combiner.
will you say thats a better setup?
do you have combiners here for sale
Thu Apr 05, 2007 8:45 pm View user's profile Send private message
Norwalk Electronics
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No, it's not possible to get a "matching" amplifier to the one you already have. The key here is all of the components have to be exactly the same. Most importantly are the matching power output transistors. All transistors with the same part numbers are not the same. Their gains and several other parameters must be equal to work together. Even two new amplifiers will not have transistors that match in both units. My advice is NOT to modify VHF amplifiers unless you have extensive RF knowledge and test equipment.
Sat Apr 07, 2007 2:52 am View user's profile Send private message Visit poster's website
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