On 3/16/2012 9:59 AM, mark roz wrote: > Interesting. I have build 600W amp with four Motorola MRF150 > transistors and I can easily get 600W output with 7W input.
Well, after a little more research (finding the KPA-500 schematics on the FCC web site) ... there is a fixed attenuator between the input wattmeter and the input matching network (L-net on 6 and an attenuator on HF). The constants don't match those of classic 50 Ohm in/50 Ohm Out 3dB pad but are close. Of course, It is entirely possible that the KPA firmware includes gain measurement will cause a shutdown if the gain is too high 73, ... Joe, W4TV On 3/16/2012 9:59 AM, mark roz wrote: > Interesting. I have build 600W amp with four Motorola MRF150 transistors and > I can easily > get 600W output with 7W input. This was tested with input attenuator removed. > Are those Mosfets in KPA500 that much different? > I also would like to purchase the KPA500 but only if I could get 15 dB gain. > It would be great to drive KPA500 with KX3 10W and get around 300W output > power. > I’m pretty sure that KPA500 has some form of attenuator at the input. > Mark WQ7X > > But I would buy a second KPA500 in a heartbeat if I knew I could > modify it for 10 watts drive for full output! > > I think you're being optimistic about full output with 10W drive. > > The VRF-2933 is rated for 23 dB gain (typical). With perhaps 1 dB loss > in the low pass filter, a dB or so in the output transformer, roughly 3 > dB in feedback to improve linearity one dB in the input transformer, > bias decoupling, gate balancing, and two dB in the input matching comes > very close to the roughly 15 dB gain limit in the US regulations. > > Some of those values are based on application notes from Motorola, > MicroSemi and APT for similar MOSFET designs while some values are > from Elecraft designers. In any case, the inescapable conclusion is > that there is no "magic modification" to get the additional 2 - 3 dB > of gain necessary to get 600W with 10W of driver from the KPA-500. > > 73, > > ... Joe, W4TV > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html