To: | RFlabnotes@aol.com |
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Subject: | Re: [Amps] Power combiners and antennas??? |
From: | Rob & Terri Sherwood <rob@sherweng.com> |
Date: | Wed, 21 Jan 2004 21:24:39 -0700 |
List-post: | <mailto:amps@contesting.com> |
After 25 years in commercial broadcasting maintaining both 50 kW AM and
50 kW FM transmitters, there was nothing I disliked more than combining
two 25 kW FM transmitters to get 50 kW out. When you use a hybrid
combiner to sum two amps, you have to have a reject load that can handle
at least 1/2 the power of one of the amps. If for some reason one amp
goes down, half the remaining power will go to the antenna and half to
the reject load. So in this case 12.5 kW to the antenna and 12.5 kW to
the reject load. So if you have two 250 watt 2 meter amps, and one
faults, the reject load will have to dissipate 125 watts. K8LV is correct that you have to be able to adjust the delay to get the amps to combine properly. Slightly different lengths of cable feeding the input will work, but it is tedious. Considering the complexity of the Harris transmitter I dealt with, there were more failures in all the combining "junk" and logic to handle it than with the transmitters themselves. Personally I would rather have had one big transmitter and a lower power standby. Since VHF and UHF brick amps are not especially clean on SSB, I suggest someone wanting high power on 6 or 2 meters consider a good tube amp that will put out the desired power rather deal with the headaches of trying to combine lower power "brick" amp. Rob Sherwood NC0B RFlabnotes@aol.com wrote: Jim: _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps |
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