sBITX – SDR TCVR for constructors
Ashar Farhan won the first concession of the year 1982. On this more than 40-year journey through the radio amateur world, there are milestones like BITX, uBITX a sBITX. Even if you don't have one of these TCVRs on your table, is possible, that you have at least heard of them.
BITX is a KV TCVR-a kit characterized by a simple concept using bi-directional amplifiers. This allows you to create a simple, but functional SSB TCVR to one or several neighboring bands. There is a complete TCVR on one PCB, whose price is approx. 50 dollars. From the first version of the year 2003 several versions were created and each found a circle of supporters.
uBITX is a kit CW/SSB TCVR-a on most KV bands (3 to 30 MHz, but works experimentally up to 432 MHz). The term kit is no longer quite accurate, because the radio amateur only needs to connect the installed printed circuit boards and implement the mechanical construction.
Again, there were several versions and, thanks to the openness of the code, a lot of modifications. The price of uBITX ranged from 109 dollars.
You can't stop progress, and VU2ESE comes with a new TCVR, hybrid SDR with a power of 40W (and 80m a 40m) and built-in support for digital modes such as PSK31, RTTY or FT8. Again at a favorable price 299 dollars (without Raspberry Pi, display and microphone). Principle, that the code can be modified by anyone has been preserved.
The target of sBITX is TCVR, which does not have to be expensive and at the same time has excellent properties. sBITX is based on ordinary 2N2222 transistors and Raspberry Pi. An attentive reader has already registered, that it is a hybrid SDR TCVR. That's a different concept, which the Yaesu FTDX-10 has.
It is a combination of a classic analog filter like a superhet receiver and an SDR. To maintain a favorable price and at the same time excellent parameters, Ashar had to reach for the filter on 40 MHz. There is a tax for that SDR width 25 kHz, thus, the display of the spectrum is not large. Inverted Vee does not create such deep zeros in free space IIP3 has value +28 dBm and unwanted band suppression -70 dB.
The income is in the range 100 Determination of the plant 30 MHz, hours ago 3500-4000, 7000-7300,10000-10150, 14000-14350, 18000-18200, 21000-21450, 24800-25000, 28000-29700 (You can hear what the NA1ISS signal looks like). Fashion: USB, LSB, CW, CW-reverse, RTTY(45), TU5PCT QSL, FT8 (including the possibility of receiving and broadcasting directly from sBITX) and a two-tone signal for IMD and PEP measurement. Consumption at reception up to 1.5A, when broadcasting 10A.
The receiver has AGC, what was the function, which the previous VU2ESE TCVRs lacked. The team, that the TCVR-i has an integrated Raspberry Pi, so a log with TX macros is also included, recording connections in WAV format or connecting to RBN and DX cluster directly from sBITX.
The sBITX output stage uses cheap transistors IRFZ24N. sBITX achieves full power of 40W in the 80m and 40m bands, on 30m and 20m it is 30W, na 17m a 15m 20W. Even less, 10W went to 12m a 6W to 10m. Why? The chain of amplifiers in the transmitter starts with a level -15 dBm and ends with +46dBm. The gain of amplifiers is dependent on frequency, which is why many designers avoid multiband devices.
The transmitter also includes speech processor.
sBITX is still under development. Radio amateurs help to improve TCVR by identifying shortcomings. Therefore, it is not yet possible to talk about a finished device, but it is likely, sBITX, like other TCVR-e VU2ESE, will also find supporters. More on https://www.hfsignals.com/index.php/sbitx/