<<<What if you have one of the 200w or new 400w output rigs? What if you have one of those radios that shoot out a spike of greater than 100w at the beginning of every transmission?
Do people blast the inputs of their SS amps with 200w or 400w? You bet they do. They fry the FETs immediately too. We see them on a fairly frequent basis and we have gotten adept at swapping out FETs quickly - at significant expense to the owner of the amp. In the vast majority of cases, they had ALC disconnected and made a mistake when switching antenna outputs from these high-power transceivers. So, if you feel confident that you won't make a mistake, then go ahead and take the risk of not having ALC connected and adjusted properly. But, keep in mind the costly consequences that can result if you make a mistake. >>> A word of additional caution.... While external ALC might force a long term power reduction, the external ALC system generally does not correct overshoot in radios. It almost never reduces power spikes on leading edges. The reason ALC does not normally affect the spikes, and why typical external ALC systems cannot reduce the spike, is the response delay in the ALC system inside the radio. There is group delay in filter, and there is propagation delay through the radio. There is also delay in the actual ALC system. The gain control system is up front in the radio, almost always ahead of filters and the delays. The ALC sampling is after filters, and in the case of amplifier derived ALC it is no better than the directional coupler that samples power inside the radio. It is a serious mistake to let the external ALC, derived after the filters and group delay in the radio, do primary power control. What the ALC does buy people is gain control or power limiting if the knob on the radio is adjusted wrong, but it most certainly will not correct leading edge spikes. It's my understanding the K3 uses a two stage system, and handles the sampling before passing through filters. I'm still trying to get my head around how it works and why I am uncomfortable with how the meters act, but at least it addresses the overshoot problem. The amplifier ALC should be connected, if the manufacturer requires it, but don't expect it to make something like an IC 775 not pop FET's. The correct approach would be an attenuator pad so the radio could run at near full power and not have a chance of overdriving the amp, or better yet buy a radio that does not spike to 250 watts at the leading edge. Now there is one exception to this. If the amplifier has a memory on ALC, and holds the ALC at the highest value and reduces ALC until power comes slowly up to the correct value,, then there would be no overshoot. I'm not aware of any amplifiers that do this, and I expect customers would complain about the slow power response and lack of compression or reduced average power with a system like that. Without an attenuator to "match levels", people are gambling with or without the ALC connected. 73 Tom ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
