Re: si5351a CLK drive levels in uBITX #ubitx

Jim Sheldon

Michael and all,
I set my signal generator to .5 microvolt @ 7.000 MHz and listened to the sound of it (no accurate S meter here yet).  Compiled my own group's software, Version 6.00R (for the BITeensio card we sell) at 6 and 8 ma.  6 ma gave an increase in sensitivity by a noticeable amount (not a lot but noticeable) and 8 ma brought it up again by a quite small amount but I noticed a marked increase in extra signal artifacts in the RX Audio.  There were a few added artifiacts @ 6 ma also, but not nearly as pronounced as with the drive set to 8 ma.  

This may very well be different for each different uBITX due to the variable nature of the transistors and mixer diode arrays used in the rig.  Not a scientific measurement but I did see some RX gain from setting it to 8 ma.  I left mine at that setting for now and will run it for a while to see what happens.  Might have to get the adapter out and see what it did on TX to the spurious and harmonic output.  I don't TX with this particular uBITX except into a dummy load so may let someone with better test equipment check the TX spurs & harmonics @ 8 ma clock drive.

Jim Sheldon, W0EB

------ Original Message ------
From: "Michael Babineau" <mbabineau.ve3wmb@...>
Sent: 7/24/2018 10:27:01 AM
Subject: [BITX20] si5351a CLK drive levels in uBITX #ubitx

I noticed that in both Ashar and Ian's uBITX code that the CLK outputs of the si5351a are being set to 4ma.

uint8_t  si5351bx_drive[3] = {1, 1, 1};  // 0=2ma 1=4ma 2=6ma 3=8ma for CLK 0,1,2

My understanding is that this translates to an output signal level of about 6dBm. 

What I have previously read is that most passive Double Balanced Diode ring mixers need a LO signal of 
7dBm or greater for optimal performance. 

Has anyone tried increasing one or more CLK output levels to 6mA to see what effect this has on receiver performance ?
A 6mA setting would translate to about 8dBm.

This would be an interesting experiment for someone with the necessary test equipment to verify whether this would be a positive
or a negative change. 


Michael VE3WMB 

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