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Sustained Transmit Power #firmware

Larry Plummer
 

I have ordered but not yet received a uBitX which I plan to use for 40 meters WSPR.  I have two questions:

1.  Is the simple crystal for the Si5351 sufficiently stable (at least after warm up) for digital modes?  I build WSPR transmitters using the Si5351a for timing but use a Fox TCXO module which costs less than $2.50 instead of a crystal.

2.  WSPR has long 1 minute 52 second key down transmit times.  I plan to transmit on alternate cycles, i.e 2 minutes transmit and 2 minutes recieve.  Will the uBitX support sustained output of 5 watts sith this duty cycle?

Larry
W6LVP

Tom, wb6b
 

I ran a WSPR beacon with my uBITX for several weeks. I found that it was rare for the TX frequency to drift during a transmit cycle. And only a HZ if it did.

I ran a fan on the heatsinks and the heatsink temperature was warm but not hot.  I ran a 20% TX/RX duty cycle. But 50/50 may not be much different. 

It was tricky to get the PPM adjustment right in the WSJT-X WSPR software. The big source of confusion was I could not get the PPM adjustment to converge on the desired frequency. That turned out to be, when using the CAT interface from WSJT-X to the uBITX, the uBITX would only step in the same step size as programmed for tuning with the frequency dial. Setting the frequency step to the minimum step size fixed that issue.

Tom, wb6b

ajparent1/KB1GMX
 

On Sun, Sep 2, 2018 at 05:42 PM, Larry Plummer wrote:
2.  WSPR has long 1 minute 52 second key down transmit times.  I plan to transmit on alternate cycles, i.e 2 minutes transmit and 2 minutes recieve.  Will the uBitX support sustained output of 5 watts sith this duty cycle?
Depends on what band and how big the fan is.  Seriously it does require moving air to cool it.
I wonder how many are in tight boxes and cooking the finals. 

I never noticed frequency stability issues. TCXO is better but I have no proof its needed or required.

Allison