Re: Modular uBitx - "Ex: Harmonics"
I already started to do "my" improvement on the µBITX, but then stopped, after reading and trying to understand all the issues involved and going back to ideas about a spec and blocks to be designed.
As I am an retired electrical engineer specialized in RF and
communication techology (I started my profesional career in 1980
at the company Hagenuk in Kiel Germany designing part of the
ship´s main communication receiver RX 1001 and later RX1001M, then
working on the RF part of the ST900 cordless telephone)
As I posess a "good equipped home lab" witrh used commercial equipment (spectrum analysers, networt analyser, signal generators and so on), I can test my disgins properl.
Before going to design something we first should think about a specifiaction and wirte it down. Yes I know seldom engineers like it, but this will give some insight into what has to be designed. Very important are also level diagrammes of the bolocks involved to see if the to be designed unit will fulfill the desired spec.
From this point of view Glenn´s way of doing a new design in first to test sub modules is a brilliant idea as it was also used in the industry (and my last occupation within a physics high energy research lab). We often only developed a single unit wioth the use of connectorized "Mini Circuit modules" and built into a case.
As SMD compoents are used the size of the "cheap" chinese pcb´s should be < 100 * 100 mm.
I believe that this forum including Farhan can and shuld be a
good potential for an optimized new µBITX!
My previous ideas:
modular design on pcb´s (<100 * 100 mm)
frequency range 10 kHz to 30 MHz
first IF > 45 MHz (to avoid the 2*IF - LO problem) using four
pole xtal filters e.g. 70 MHz (if easily avaliable)? Another
"popular IF could be 58 MHz or 58.1125 MHz (used in Hagenuks
cordless phones) My be enough NOS filters are laying around.
1) receiver/exciter pcb
2) xtal filter board for the second IF (e.g. 5 MHz) with filters
for SSB; AM; FM(?), CW
2) input lowpass filter (corner freq. 1.6 MHz) plus overlapping
bandpass filters (e.g. 1.6 - 4MHz; 4 - 8 MHz, 8 - 16 MHz; 16 - 30
3) driver board
5) PA board
7) VSWR bridge
8) VFO (several SI5351 ? to avoid crosstalk between outputs of a single SI5351 driven from a single reference (TCXO; or VCXO which could be synchronized to a GPS reference?)
RF signals to be routed via SMA connectors
For the mic amp I remember that for maritime ship transmitters there is a requirement to limiting the max RF output via a Mic compressor. Chips like the SSM2167 could easily fulfill such a (similar) spec!
Comments are welcome
Am 15.08.2018 um 02:37 schrieb Nick VK4PP:
Hi Allison/ Kees/ Glenn/ other technical competent hams...