11380	2015-07-30 11:25:30	peter_dl8ov	The Problem of the 'T2 Pro' Output Stage
Message	Date	From	Subject
I have a problem with one of the circuits shown in EMRFD. Since I have three different circuits and only one transmitter I would appreciate some help with my dilema. 1) In EMRFD First Edition, Section 9.10 page 9.46 there is the output stage of a high performance SSB exciter. Figure 9.83 shows the RF split using a bifilar transformer, no capacitors and a 100 ohm resistor. 2) The design for the Micro T2 published in QST December 2006 (which appears to be very similar) shows a bifilar winding and two capacitors of unequal value, 390pF and 39pF and a 50 ohm resistor on one port. This design is duplicated in the commercial design marketed by Kanga US and I'm guessing that this works as Bill has sold a lot of them. 3) The classic design for the quadrature hybrid has a bifilar winding, two capacitors of equal value and a 50 ohm resistor on one port. Please could somebody tell me which design of RF splitter is correct for use in the EMRFD circuit? Also, nothing is shown of what happens after the RF leaves the two TUF-3 mixers. Do I just join LI and LQ together and feed the result to an amplifier? Regards Peter DL8OV
11381	2015-07-30 12:23:22	Claudio Girardi	Re: The Problem of the 'T2 Pro' Output Stage
Hello Peter, 1) is the in-phase combiner, to sum the RF output of the mixers. The LO is applied to the mixers on the LI and LQ inputs, and these two have to be 90 degrees apart. 2) and 3) are the quadrature splitter for the LO. As far as I know, the capacitors need not to be equal (but need to have the right value, hi). If they are equal the two outputs are at +45 and -45 with respect to the input, independently of frequency (only their amplitude changes). If they are not equal the phase shift between the two outputs is still 90 degrees but the shift with respect to the input changes (which is not important in this application). There might be advantages regarding the splitter bandwidth, but I am not sure. As explained above, in 1) LI and LQ are for the local oscillator, the RF output is on the combiner, labeled RF. 73 de Claudio, IN3OTD ----Messaggio originale---- Da: emrfd@yahoogroups.com Data: 30-lug-2015 20.25 A: Ogg: [emrfd] The Problem of the 'T2 Pro' Output Stage ----Messaggio originale---- Da: emrfd@yahoogroups.com Data: 30-lug-2015 20.25 A: Ogg: [emrfd] The Problem of the 'T2 Pro' Output Stage I have a problem with one of the circuits shown in EMRFD. Since I have three different circuits and only one transmitter I would appreciate some help with my dilema. 1) In EMRFD First Edition, Section 9.10 page 9.46 there is the output stage of a high performance SSB exciter. Figure 9.83 shows the RF split using a bifilar transformer, no capacitors and a 100 ohm resistor. 2) The design for the Micro T2 published in QST December 2006 (which appears to be very similar) shows a bifilar winding and two capacitors of unequal value, 390pF and 39pF and a 50 ohm resistor on one port. This design is duplicated in the commercial design marketed by Kanga US and I'm guessing that this works as Bill has sold a lot of them. 3) The classic design for the quadrature hybrid has a bifilar winding, two capacitors of equal value and a 50 ohm resistor on one port. Please could somebody tell me which design of RF splitter is correct for use in the EMRF D circuit? Also, nothing is shown of what happens after the RF leaves the two TUF-3 mixers. Do I just join LI and LQ together and feed the result to an amplifier? Regards Peter DL8OV
11382	2015-07-30 13:17:40	peter_dl8ov	Re: The Problem of the 'T2 Pro' Output Stage
"(1) is the in-phase combiner, to sum the RF output of the mixers. The LO is applied to the mixers on the LI and LQ inputs, and these two have to be 90 degrees apart. (2) and (3) are the quadrature splitter for the LO." Ah!! Now I see it. Just put this down to a moment of 'brain fade' at the end of the day. I have now relabelled the schematic and things now look much more reasonable. I'm going to use my own values in the quadrature splitter though as the TX will be working at 45 MHz, Tnx. Peter DL8OV
11384	2015-07-31 09:27:50	kb1gmx	Re: The Problem of the 'T2 Pro' Output Stage
You are confusing hybrids and combiners and their function in a phasing transmitter (or receiver). The MicroR2 and the classic are the same thing for the hybrid. The total capacitance bridging the windings is critical not the distribution. That's a 90 degree hybrid. The R2Pro what your looking at (in figure 9.83) is a lumped form combiner the resistor is there to both balance and absorb imbalance. It is also a 0 degree split. This is not the baseband or LO path. The hybrid is not shown in the drawing and is discussed elsewhere. Its important to keep the block diagrams in mind as all three designs mentions are largely the same at that level and the differences are the level of refinement with the resulting level of performance. A reminder that many of the schematics presented in EMRFD are incomplete or part of a larger set of drawings. In the case of R2Pro generating the LO and its quadrature output are up to the user and there are a lot of example of how this would be done. Allison
11385	2015-08-01 05:06:23	peter_dl8ov	Re: The Problem of the 'T2 Pro' Output Stage
Thank you for the reply Allison but it looks like both of us are slightly confused :) Section 9.10, page 9.46, Figure 9.83 is the output mixer stage of a transmitter, not the R2. I have now committed the cardinal sin of writing in ink on figure 9.83 the pinouts of the mixers, the two IQ Local Oscillator signal lines and the RF output but at least I can now wire everything correctly. The 90 degree hybrid is a work in progress, as you will see in a previous email I am having difficulties but experimentation is fun. Peter DL8OV
11386	2015-08-01 08:05:36	kb1gmx	Re: The Problem of the 'T2 Pro' Output Stage
Hi Peter, I was sitting there with EMRFD when I commented to be sure I was looking at the right pages. The R2, R2pro, and even miniR2, miniT2 tor the mixers and combiner are identical just reverse the signal direction. Transmitters and receivers are mirror images and for the mixers with combiner and quadrature that whole section up to the audio processing can be used for TX or RX. The microR2 and the microT2 depart from the others by simply connecting the two mixers together at the input(output) for a 25 ohm node and skipping the combiner. By skipping the explicit combiner which has a lower frequency limit makes for a circuit simplification that is not so easy to understand. To me there is no sin of marking the book. Not like its rare and your notes may be significant. Allison