[Elecraft] Amplifier thoughts
Doug Smith
doug at w7kf.com
Wed Mar 29 13:28:26 EDT 2017
I cast my ballot for NO internal coupler.
1) An internal coupler is NOT needed by many who would rather not pay for something they don’t need. Sure, it could be optional but see points 2 and 3.
2) An internal coupler at 1.5 KW as anything beyond a trivial “line flattener” will be large. If the matching range is extended to the 10 : 1 SWR range then the components will be *quite* large. Feeding 1.5 KW into a 5 ohm load with an L-Network will require an inductor about the size of a K3S if any sort of Q is expected.
3) There exist RF transistors that are built to withstand high power operation with really high SWR values. For example:
http://www.nxp.com/products/rf/rf-power-transistors/rf-broadcast-and-ism/1-600-mhz-broadcast-and-ism/1500-w-cw-over-1.8-500-mhz-50-v-wideband-rf-power-ldmos-transistor:MRF1K50H <http://www.nxp.com/products/rf/rf-power-transistors/rf-broadcast-and-ism/1-600-mhz-broadcast-and-ism/1500-w-cw-over-1.8-500-mhz-50-v-wideband-rf-power-ldmos-transistor:MRF1K50H>
Surely with such a device (or, better yet, a pair), a 3 : 1 SWR can be accommodated with no coupler at all. Thus, no line flattener needed.
If someone is trying to feed a 43 foot vertical on all bands at 1.5 KW then the coupler really should be at the antenna site, not in the shack. That antenna presents a load of about 5 ohms -J500 and the coupler will have to be large at 1.5 KW. (This is RF, not DC. In a high pass L-Net think 18 amps and 9000 peak volts with a staggering 600 watts of losses generating heat in that coil.)
As to the amp itself my wish list would include:
1) 1.5 KW ICAS. (I would accept 1.3 KW but, hey, it’s a wish list.) Must be contest capable, including those crazy RTTY guys. ;-)
2) Separate light weight power supply.
3) QSK at reasonable speeds. At least 40 WPM.
4) Multiple antenna outputs, remembered per band; overridable.
5) FULLY integrated with the K3S. Given proper antenna loads the K3S + KPA1500 becomes a 1.5 KW transceiver.
6) A remote console setup would be cool. That way the amp would be just a power block that could be set aside, out of the way. Or, even operated at a remote site from the console. TCP/IP connectivity for the console to power block.
73,
Doug, W7KF
http://www.w7kf.com <http://www.w7kf.com/>
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