Eric,
Great Stuff!!!
I assume "the switch" is the small IC on the Si4432 module (a PCB assembly that we buy)
that selects either the TX or RX port from the Si4432 to be connected to the module antenna port.
And "set the first IF to zero" is done in the software, as we no longer have a front end diode ring mixer.
This was even more cryptic to me at first, just now getting my head around it all:
> If you flipped the switch before init, the LO?one would become the RX, the rx ?one will?be the LO one but it¡¯s tx goes nowhere...
By "one", I'd guess that means a Si4432 PCB module.
And the only "one" we need in single Si4432 mode is the
module that is normally used to drive the diode ring mixer LO port.
I had been assuming that the Si4432 only worked in half duplex mode,
not using the transmitter and receiver at the same time.
Very curious if you can use both simultaneously and get results good enough
on the receiver for it to be used as a spectrum analyzer.? All on one die!
Perhaps it's been updated, but the build documentation specifies a matching network
for the SAW filter, but doesn't bother to say exactly what SAW filter was used.
I'm looking at the B3790 in the RF360 series from Qualcomm.
It's cheap, Mouser has it in stock, 40db down at 500khz out and headed for 60db down.
But passband is only about 120khz wide, will this work with the current software?
? ?
Build photos appear to show two SAW filters directly connected, would it not be better
to have 2x the recommended matching inductance between the two?
Appears to me that top end of the 5dbm absolute max spec going into the B3790 SAW filter will be
the limiting factor when using the ADE-25MH.? Not clear at what power level the SAW filter
will perform well, I assume? 2 or 3 db lower.? If so, the ADE-1 could handle the same power level,
though will need an attenuator between it and the possibly 20dbm TX pin from the SI4432.
I think we're at around 10dbm max into the 250mhz filter, regardless of which mixer.
Though I suppose running an ADE-25MH with 7dbm going in may be cleaner than 7dbm into an ADE-1.
And the ADE-25MH is surprisingly cheap and easy to get.
Amazing these Si4432 modules can be sold for $2us.
Mouser's best price is $4.20us each, if you get the 2500 piece reel.
So the cheapest way to get the Si4432 chip is to heatgun them off of the modules?
Anyways, the tinySA looks revolutionary.
An excellent complement to a nanoVNA, and about as useful.
If a board were fabbed to take the 250mhz filter, mixer, SAW filters,
and sockets for the two Si4432 modules plus a Nano, it should be
very easy and cheap to duplicate.
All them SMA connectors and cables in the rig Eric built dominate the cost!
Jerry, KE7ER
