[OKDXA] On Power...

[Roger Simpson]

Kim:

I always run with an amp but I normally don’t run more than 200 watts. My problem is that I run FT8 most of the time and compared to any other mode it has a very high duty cycle.  With FT8 you don’t need really high power but because of the high duty cycle – i.e. 100% for 15 seconds followed by 0% for 15 seconds – you really need a linear. I have found that running several hundred watts on FT8 is “more or less” the same as running 1KW on SSB in terms of duty cycle and the tendency of your linear to shut down due to overheating. 

Here are some examples of what I have learned.

Setup A – ICOM7600 barefoot.  I can run FT8 but I have to keep power down to around 50W or the rig will overheat and shutdown.  Maybe the shutdown will happen after say 15 minutes to 30 minutes.

Setup B – ICOM7600 with ICOM PW-1 linear. The PW-1 is the only solid state linear that I know of that will run FT8 at 300 watts or more for hours on end. 

Setup C – ICOM7600 with Ameritron MFJ 1306 linear. If I run FT8 with this setup at more than 250W the linear will shut itself down due to overheating after about five to  ten minutes. 

Setup D  -- ICOM7600 with ACOM 2100 linear. This linear uses a 4CX1000 vacuum tube final. I usually run a 300W when trying to contact DX station running FT8 F/H mode. I can run for an indefinite amount time with this setup calling FT8 F/H at 300W. I could probably run more than 300W with this setup but I never do. I have been running with this setup for the last year or so. I bought the ACOM from DX Engineering. With this setup I stand a very good chance of breaking even the biggest pileup if I am persistent. This is going to be the setup for trying to work Bouvet and Crozet – both of which I need for ATNO. I have never had a shutdown with my ACOM 2100 due to overheating but it will shutdown right away to protect itself when I have no antenna or wrong antenna for the band I’m trying to run on. .

Bottom line when running high duty cycle FT8. If you get a linear: Seriously consider getting one that can tolerate HIGH duty cycle. Probably the old Alpha linear that advertised “brick on key” at 1KW would be FB for FT8. 

73    Roger   K5RKS 

Sent from Mail for Windows

From: Kim Elmore
Sent: Wednesday, April 13, 2022 10:22 AM
To: Oklahoma DX Association
Subject: [OKDXA] On Power...

I've a question for the group: how often do you QRO for a DX contact vs 
the usually 100 W? I tend to try 100 W first and if I'm clearly making 
no progress, I'll run QRO (except for 30 m). Am I being a masochist? Do 
those of you with almiost all of 'em worked simply turn on the amp when 
you turn on the rig and run full smoke all the time, or do you pick and 
choose?

73,

Kim N5OP

-- 
Kim Elmore, Ph

Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP 
SEL/MEL/Glider, UAS, N5OP, 2nd Class Radiotelegraph, GROL)

/“I occasionally play works by contemporary composers and for two 
reasons. First to discourage the composer from writing any more and 
secondly to remind myself how much I appreciate Beethoven." – Jascha 
Heifetz/
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