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uBitx Blowing Fuse on 20 Meters

Scot McMath
 

My uBitx 4.3 blows the fuse in the 12 volt power line on 20 meters transmitting CW into a dummy load. None of the other bands will do this. Power out on 40 meters seems high, about 15 watts. Will backing down RV1 help?

Scot WB7AVU

Curt
 

Scot

that sounds like an excellent idea to back down on the primary drive control -- yes RV1.  your signal should be cleaner if you can get the 40m output down to say 7 watts or less.  most power meters (even the WM2 I use) can't be trusted to extreme accuracy.  a factor of 2 in output power is about one half a S-unit -- so better to be more clean. 

I am very surprised to blow the fuse into a (hopefully) 50 ohm load.  possibly a higher current fuse is encouraged.  I don't myself see danger is using a fuse that is 2X the expected current.  most of the time I use a ~ 3 amp power supply to feed by ubitx.  not sure what fuse Sunil supplies but that is what I have in place. 

there is a greatly diminishing return on output power versus DC supplied -- if you ever operate using battery - less drive via RV1 is highly preferred - with little loss on the receive end. 

73 Curt

Scot McMath
 

Thanks Curt,
I was surprised myself about the output. I'm going to dial back RV1 as you suggest and try a 3 amp fuse.

Scot WB7AVU

 

As far as I remember, a fuse at the rated current should hold out for 10 hours and blow at
double the current with some seconds depending whether it is Slo-Blow, normal or fast blow.

Raj


At 09/07/2019, you wrote:
Scot

that sounds like an excellent idea to back down on the primary drive control -- yes RV1.  your signal should be cleaner if you can get the 40m output down to say 7 watts or less.  most power meters (even the WM2 I use) can't be trusted to extreme accuracy.  a factor of 2 in output power is about one half a S-unit -- so better to be more clean. 

I am very surprised to blow the fuse into a (hopefully) 50 ohm load.  possibly a higher current fuse is encouraged.  I don't myself see danger is using a fuse that is 2X the expected current.  most of the time I use a ~ 3 amp power supply to feed by ubitx.  not sure what fuse Sunil supplies but that is what I have in place. 

there is a greatly diminishing return on output power versus DC supplied -- if you ever operate using battery - less drive via RV1 is highly preferred - with little loss on the receive end. 

73 Curt