View Full Version : 600 watts on 2m.
ZL2WHO
11-10-2009, 08:10 AM
Hello all. I have 2x 300 watt VHF amps and I wish to split and combine to give 600 watts. I have built a rat race hybrid mixer using 3x 1/4 wave and 1x 3/4 wave lengths of 75 ohm coax. I wsed RG11u and yes I did take into consideration the velocity factor. Has anybody had good sucess with this idea, or can some approach this problem using a different idea. Wilkenson splitter ?. Im in the dark somewhat here, any help would greatly be appreciated. 73. mark. ZL2WHO
Hello all. I have 2x 300 watt VHF amps and I wish to split and combine to give 600 watts. I have built a rat race hybrid mixer using 3x 1/4 wave and 1x 3/4 wave lengths of 75 ohm coax. I wsed RG11u and yes I did take into consideration the velocity factor. Has anybody had good sucess with this idea, or can some approach this problem using a different idea. Wilkenson splitter ?. Im in the dark somewhat here, any help would greatly be appreciated. 73. mark. ZL2WHO
See this post (http://forums.qrz.com/showpost.php?p=1760494&postcount=1).
Cortland
KA5S
CT2JUT
11-10-2009, 11:34 AM
Is it legal to run 600W on 2m in ZL?
What exactly is the problem?
Combining 2 amps with a pair of RR hybrids is standard procedure.
Rege
WB2WIK
11-10-2009, 06:36 PM
What exactly is the problem?
Combining 2 amps with a pair of RR hybrids is standard procedure.
Rege
Should work if the amplifiers are phase consistent. Some aren't. You may have to change the line length to (or from, or both) one of the amplifiers to make sure they're really in phase. I do this using an adjustable coaxial line section ("stretcher") and just peak for maximum output from the combined amps.
I have used Wilkinson power dividers/combiners many times with success. Most broadband multitransistor amplifiers use them to connect each pair of transistors and then again to connect pairs on the input and output stages.
73,
Terry
ZL2WHO
11-10-2009, 09:19 PM
What exactly is the problem?
Combining 2 amps with a pair of RR hybrids is standard procedure.
Rege
Hi Rege. I have been building single ended amps for over 10 years, mainly this one for 88-108MHz http://www.communication-concepts.com/ar313.htm but until now never tried combining. Its just something new. When I compare the output ports there is a slight imballance of power, 5 watts on one and 6.5 on the other. Ill now try the Wilkinson as per KA5S. I understand that a rat race will offer better isolation between the ports, but a Wilkinson seems to be more popular. I have a sig gen and a spectrum analizer, so I now need to spend some time and fiddle with some lengths. Its a possibility that my RG11u does not have a velocity fact of 0.66?. I see some coaxes have 0.80.. Thanks to everyone that posted help. 73. Mark.
ZL2WHO
11-11-2009, 12:36 AM
Is it legal to run 600W on 2m in ZL?
Oh, did i type 600, im meant 400, small typo there ;)
ZL1UZM
11-11-2009, 12:39 AM
Oh, did i type 600, im meant 400, small typo there ;)
It is 500 watts PEP now. All modes.
It was increased in 2004 from 400 watts.
We got more power than our Aussie neighbours, hi!
Should work if the amplifiers are phase consistent. Some aren't. You may have to change the line length to (or from, or both) one of the amplifiers to make sure they're really in phase. I do this using an adjustable coaxial line section ("stretcher") and just peak for maximum output from the combined amps.
Well, the resistors in a Wilkinson make things less critical. But... I think you'd want to adjust the tuning individually BEFORE you adjust the line stretcher, no? Or otherwise you'd change the phase with the tuning.
Cortland
KA5S
CT2JUT
11-11-2009, 01:49 AM
It is 500 watts PEP now. All modes.
It was increased in 2004 from 400 watts.
We got more power than our Aussie neighbours, hi!
That´s cool!
We´re limited to 150W here.
Watch you health mate! :)
73 de Miguel
Hi Rege. I have been building single ended amps for over 10 years, mainly this one for 88-108MHz http://www.communication-concepts.com/ar313.htm but until now never tried combining. Its just something new. When I compare the output ports there is a slight imballance of power, 5 watts on one and 6.5 on the other. Ill now try the Wilkinson as per KA5S. I understand that a rat race will offer better isolation between the ports, but a Wilkinson seems to be more popular. I have a sig gen and a spectrum analizer, so I now need to spend some time and fiddle with some lengths. Its a possibility that my RG11u does not have a velocity fact of 0.66?. I see some coaxes have 0.80.. Thanks to everyone that posted help. 73. Mark.
The resistor will have to be big enough to handle any phase or amplitude imbalance between the 2 amps.
It's too late now, but if you repeat this in the future, about the best way to keep the amplitude and gain the same on the 2 amps is to specify matched transistors from the same manufacturing lot.
And I would never trust the published velocity factor, best to measure each cable as you go. use the sig gen to check the resonant frequency of each .
Do all your testing with the absolute minimum possible voltage, 11v or so for a 13.8vamp and use the absolute minimum drive power. When things look ok, increase each a bit at a time and look for troubles.
Here is what the combiner looks like on a GE Mastr II amplifier, 4 transistor, 100w, 470mhz.
http://www.n9rjz.us/GE%20Mastr/UHF/Repair%20of%20GE%20MASTR%20II%20100%20watt%20UHF%2 0Station%20Power%20Amplifier_files/after.jpg
Note the identical PCB used as a input splitter, and output combiner. Also note the identical lot and date codes on the transistors, and the general symmetry of the circuit.
In this case, the resistors are 2 watt units, in service, the failure of any one of the 4 transistors will cause the output resistors to catch on fire!:eek:
Rege
GM4PLM
11-14-2010, 06:37 AM
Is it legal to run 600W on 2m in ZL?
500w PEP at the antenna
600W with a small amount of feeder loss would be fine
for WSJT etc I would be running the amp at less than 600W however ...!
nice shack heater :D
73 SImon ZL4PLM
Let us know how that works in your case, but be sure to test for stability and out-of-band oscillations.
In many cases, the amplifier will become unstable when combined this way. This is because amps generally have heavy negative feedback, have inconsistent phase shift, and the combiner only has significant port isolation when terminated in the design impedance of the combiner at ALL frequencies. You not only have to properly terminate at the operating frequency, you must properly terminate the combiner on frequencies where external impedances can rotate phase inside the amp to phases that are regenerative.
At times combining outside a PA and filter system will work, but many times combining at the output of filtered amps won't work and the PA system will oscillate.
There is a heck of a lot of difference doing this inside a system before filtering and outside a system after filtering, especially when the amplifiers have high levels of internal feedback that is phase sensitive.
73 Tom
