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Another uBITX v5 FT8 success story #ubitx #ft8 #v5

Doug Hall
 

Tonight I did some simulated FT8 testing by going key-down in CW in a 15 second on/ 15 second off cycle for five minutes at full output. At the end of 5 minutes, and with an ambient temperature of 25C I measured the heat sink temperature with my Fluke temperature probe. It was 56C which does not seem like a big deal to me. This is with no fan and stock heat sinks. The case has decent ventilation. Encouraged by this, I installed WSJT-X on my laptop and cobbled together a couple of cables for audio. I didn't use any isolation transformers (don't do as I do) but I did use a resistive divider into the uBITX mic input. I configured WSJT-X to talk to an FT-817 and used CAT PTT. I checked the signal on my main rig for anomalies and everything looked good.

Less than 5 minutes later I had worked ZL1BD. Of course he was +02 and I was -13, but a nod's as good as a wink if it gets you in the log.

Of course I may burn up some IRF510s before this is over, but so far FT8 just doesn't seem to present any problems.

73,
Doug K4DSP




Don - KM4UDX
 

Doug - I clicked the wsjtx "tune" button with a buddy as we looked at SWRs on an external SWR/power meter. I was showing off the ~28 watts produced with 16v going into the  IRF510s into my homemade 80-10 OCFD. The conversation was great I forgot it was in tune mode -- for about 15 minutes. I had a panic attack when I realized my stupidity, clicked it off, grabbed the temperature gun, and read 95deg C on  both little babies. There were a bit totasty. I was sure I cooked'em into RF heaven.  

But, they cooled and came back to fighting form. Amazing how they survived high levels of heat and stupidity. 

Arvo W0VRA
 

Speaking of heat and stupidity, I ran an entire WSPR transmission on 40m with no antenna connected.  I was thinking, "Wow, something smells hot."  It scorched the board, but the IRF510s still work today.

I did add a fan later...

http://ubitx.net/2018/06/28/a-fan-for-your-ubitx/

Don - KM4UDX
 

Arvo -- hahah.  

Q: do you have to worry about the fan current if you hack into the TX 12v line, namely at pin 3 on U2?

Don
km4udx

David Wilcox
 

Does anyone know if overheating the finals causes damage to them if on cooling they still work........ I would wonder if the output is the same as when they were new.

David J. Wilcox K8WPE’s iPad

On Aug 7, 2019, at 10:31 PM, Don - KM4UDX <dontAy155@...> wrote:

Arvo -- hahah.  

Q: do you have to worry about the fan current if you hack into the TX 12v line, namely at pin 3 on U2?

Don
km4udx

Arvo W0VRA
 

Don,

I don't think so, but I haven't done a rigorous analysis.

There is a bit of an issue, as the fan coasts down it generates electrical noise that is picked up by the RX AF chain.  That I don't worry about very much because I've not used it for anything but FT8 for the last year.

But I did put a EZ TR Switch in it so I could use the RSP1A for RX, and I suppose that would be a more elegant solution for turning fans on and off.

https://www.qrpkits.com/ezseries.html#eztrsw