kc2tj@ky2d-2.UUCP (John) (01/21/86)
During the last vhf contest there were a lot of 70 kc wide amps on the air who seemed to feel they had a right to be that widebecause they were running high power. i see nothing in the rule book that says this. maybe an official observer in the area during a contest would help. i would like to hear comments on this both pro and con. 73 john kc2tj marlboro.
Borton.Henr@Xerox.COM (01/23/86)
Your comment hits right at home. Here in Western New York (Rochester), I have the same gripes about both the manners and use of high power during contests. Maybe it is because I only run 5 watts but I quit participating in these contests on 2 meters just for that reason. The question is what can be done about it. Mike KA2AFE
wjc%ll-vlsi@tgr.UUCP (01/23/86)
It's not just during contests. I mainly operate on 6 meters, and there are some noteable examples of wide amplifiers. Part of the problem is probably due to improper operation. However, a great part is due to non-linear amplifiers! If you look at the specs for something like a Mirage 100-watt solid-state amp, you will see that they claim something like 40 watts out for 2 watts in and 100 watts out for 10 watts in. Clearly, this is not linear and leads to some distortion. Also, many of the tubes used in amateur high-power amplifiers leave something to be desired in terms of linearity. For example, Eimac claims that a 4CX250R running 295 watts PEP plate power output will have a 3rd-order IMD suppression of only 25 dB. Thus, you would be outputting almost 2 watts of 3-rd order distortion. A 3-400Z has 28 dB of 3rd-order suppression and a 3-1000Z has 29 dB. I believe the 4CX1000 series falls in this range, too. For better linearity, you can use tubes like the 4-400 (35 dB), 8873 (35 dB), 3CX800A7 (36 dB), 8877 (38 dB), 3-500Z (40 dB), 4CX1500B (43 dB), and the 8938 (44 dB). It probably doesn't make sense to use tubes with better linearity than these unless we start using cleaner exciters. A quick exam- ination of equipment reviews in QST shows that most modern rigs have about 32 to 36 dB of 3rd-order IMD suppression. Also, "ultra-linear" tubes are quite expensive. All of the above is on my mind because I'm starting to plan a 6-meter amplifier that will run within 2 dB of the legal limit, and I want it to be clean. Anyway, I will post any interesting findings. Bill N1CPK