On Sun, 1 Mar 2009 09:26:20 -0000, John Stringer wrote: >The linear requires only 20watts drive for 400 watts out (our limit). >In SSB the only output control on the TR7 is the Mic Gain.It is a real >fiddle to adjust this for 20 watts and more so to keep it there. The >smallest touch on the gain control can double the output and also it cannot >cope with peaks. >Modern radios have SSB output level separated from Mic Gain. >Any ideas on how to get around this situation?
A couple of things come to mind. Does tha amplifier have an ALC output? This can be used to limit your drive. You don't mention what kind of amp it is, but if there is no ALC output, you might be able to look at how Drake implemented the ALC in the L-4B/L-7 and add it to your amp. A power attenuator could be added inline. The difficulties there are that you have to find non-inductive resistors of sufficient power rating to soak up the extra exciter power, and provide T/R switching somewhow. A *good* external RF speech processor (SP75 or equivalent) could be used to limit the output level. I've found that my SP75 does a good job of limiting the peak output to a certian level. Or you could try adjusting the ALC control inside the rig for 20 watts maximum output. You might have to change some component values in the ALC circuit, but it should be do-able. The problem with reducing the output from a 150 watt amp to 20 watts is that you are operating closer to the crossover point of the transistors, and you could have higher IMD on your transmit signal. There can also be also other problems associated with using ALC to control your output level as is done in "modern" rigs: http://www.nitehawk.com/sm5bsz/dynrange/alc.htm From a spectral purity standpoint, it's probably better to have an attenuator in the input side of the linear than use any of the other methods. The National NCL2000 comes to mind here. The grid circuit is a 50-Ohm dummy load with two taps - one for high power and one for low power (~20 watts) drive. But that's a grid-driven amp, you may need something a little different if your amp is grounded-grid. 73 -Jim -- Ham Radio NU0C Lincoln, Nebraska, U.S.S.A. TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A, GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time! "Give a man a URL, and he will learn for an hour; teach him to Google, and he will learn for a lifetime." HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/ http://radiojim.exofire.net http://incolor.inetnebr.com/jshorney http://www.nebraskaghosts.org _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
