5W HF PA and U3S #5wPA #u3s

Bertel Andresen - SM6OES


I'm about to build the 5W HF PA to go with my U3S transmitter.
I hope to be able to fit it behind everything else.
I have the U3S board, a LPF relay board and a GPS board.
Everything will be tucked into a kit case.
I will be tight, but I hope it will all fit.

Apart from that, I would like to fit a 12V-5V DC-DC converter in there.

But what about heat considerations with such a configuration?
I'm currently running with the standard synth.
With that heat sink warming up inside the case, close to the synth seems to be asking for freq drift.
I could try the TCXO and maybe even the OCXO.
What would be my best bet in this case?
Could it be a good idea to use the case itself as a heat sink?
Maybe mount the heat sink outside of the case?

I'm sure that someone have invented this wheel before me.
Any input will be highly appreciated.

Bertel - SM6OES

Curt wb8yyy


your path should be okay.  i suggest starting with the kit assembled without the PA, operate it QRP to see that everything is working.  at this point you ONLY need a 5 volt supply - the current is something on the order of 300 mA - so it would not be taxing a 7805 (large size) regulator. 

the 5 volt PA can be added later - it operates from 12 volts - so the regulator is not involved here. 

carefully check your chosen regulator - but likely the device body can be grounded.  I imagine if you search for U3S regulator you may find some pictures. 

by the way, into a decent antenna 200 mW will propagate to ZL, VK etc on the middle bands (20 to 40 meters).  but the higher power will help on the other bands. 

I am not using the TCXO here - just GPS.  possibly things may still be okay with the PA.  Note the GPS has an antenna on the circuit board - it does not make sense to me to put it inside the U3S case - I have it in a separate plastic case. 

be patient and enjoy your journey - the U3S is a simple circuit board with a huge number of settings - and just two push buttons (-:

73 Curt wb8yyy