开云体育

This is a continuation of an old conversation that deserves its own thread.
? ??/g/HBTE/message/942
? ??/g/HBTE/message/944

Summary:
Driving a level 7 mixer such as an ADE-1 or SBL-1 with 20dBm may damage it.
It is definitely too much when driving the SAW filter in signal generator mode.
The code used to set the transmit power level in the Jan 17 tinySA.ino firmware
may not be correct for an Si4432, it appears to be written with some other part in mind.

I think that all writes to the transmit power level register of the Si4432 should follow this pattern:
? //? drive:? 0x0=-1dBm? 0x1=2dBm 0x2=5dBm 0x3=8dBm 0x4=11dBm 0x5=14dBm 0x6=17dBm 0x7=20dBm
? SI4432_Write_Byte(0x6D,? 0x30 | (drive&0x7));


Erik's build instructions explicitly state that the mixer should be chosen to handle 20dBm:

> The mixer is preferably a level 13 or better mixer. An example of a good mixer is the ADE-25MH
> but any passive double balanced diode mixer (such as a ADE-1) that can be used till 500MHz
> on its RF and LO port is usable. The mixer should be able to handle +20dBm input on the LO port.

A level 7 mixer such as an ADE-1 could work fine if power into the LO port is reduced to 8dBm with:
? ? SI4432_Write_Byte(0x6D,0x33);
as per post 944.? Too much power can damage such a low level mixer.
Also, I suspect that asking for more power from the Si4432 than needed may create extra noise
in the Si4432, and perhaps in the mixer.

I doubt the Si4432 has any way of directly connecting the TX port to the RX port
using the lna_sw bit as the Si4431 does.? ?So that bit may not be an issue.

The B3730 SAW filter that Erik uses can deal with an absolute max of 10dBm.
So if going into signal generator mode with the "P6 3" command, be sure to
reduce transmit power for the RX Si4432 before enabling the transmitter.
No reports yet of this damaging a B3730 SAW filter.

The B3790 SAW filter I plan to use can deal with an absolute max of 5dBm.
So quite likely that 20dBm would damage it.

There are Si4431 modules available, capable of a maximum of 13dBm instead of 20dBm.
That may be a safer choice for most of us, but has not been tried.
The power levels available are down 7dB from what the Si4432 can provide:
? //? drive:? 0x0=-8dBm? 0x1=-5dBm 0x2=-2dBm 0x3=1dBm 0x4=4dBm 0x5=7dBm 0x6=10dBm 0x7=13dBm
? SI4432_Write_Byte(0x6D,? 0x30 | (drive&0x7));

We could choose to have the variable "drive" be calibrated in dBm rather than arbitrary numbers.
This might be more convenient, but is definitely more confusing:

#if USESI4432
#define? MIN_DBM? ?-1
#else
#define? MIN_DBM? ?-8
#endif
SI4432_Write_Byte(0x6D,? ?0x30 + (((drive - MIN_DBM)/3) & 0x7));

Disclaimer:
I have not verified any of this by trying it out on hardware,
just reading datasheets for now.

Jerry, KE7ER