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How to get 5W on 10m?
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There are two tricks : 1. BFR93W in the 45 Mhz IF amps, more overall gain. 2. A 470pf in the emitter degeneration of pre-driver instead of a 0.1uf gives more gain at 28 MHz than 3.5 MHz. - f On Wed, Feb 27, 2019 at 1:37 PM iz oos <and2oosiz2@...> wrote:
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The better transistors in the 45mhz IF should help diminish that 90mhz 2'd harmonic of the IF
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that was causing the? (45mhz - DialFreq) spur on 15m,12m,10m. For those curious about the math (arithmetic?) regarding this spur on v3 and v4 uBitx's: The VFO (clk2) into the D1,D2 mixer is always above the 45mhz IF, so at 28mhz the VFO is a 45+28=73mhz If the 45mhz IF into the D1,D2 mixer also has a 2*45mhz = 90mhz 2'd harmonic, that mixes with the VFO also. So transmitting at 28mhz, we have a spur at 90mhz-73mhz = 2*45mhz - (45mhz+28mhz) = 45mhz-28mhz = 17mhz. This only matters on 15m, 12m, and 10m, since on the lower bands the spur is above the transmit frequency and can be taken out by the transmit low pass filter.? ?For 20m, the spur is at 45mhz-14mhz = 31mhz. I'd expect this spur to not be so bothersome on the v5 as it was on the v3 and v4. When transmitting CW, CLK2 is at the operating frequency and the 45mhz IF is quiet (CLK0 and CLK1 are shut down).? So the spur only occurs when operating SSB. Jerry, KE7ER On Wed, Feb 27, 2019 at 12:23 AM, Ashhar Farhan wrote: There are two tricks : |
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Of course, the new low pass filter at L31,L32,C205 would cure the spur
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even if we did have a 90mhz 2'd harmonic present. Adding that filter to v3, v4 rigs is not a bad idea if planning to operate above 17m. On Wed, Feb 27, 2019 at 08:52 AM, Jerry Gaffke wrote: The better transistors in the 45mhz IF should help diminish that 90mhz 2'd harmonic of the IF |
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Jerry
Thanks for pointing out better 45 MHz devices as being a help against spurs, but I wonder if biasing them with a bit more current might help. I do have some eclectic vhf npn devices in my stash. I did install an LC filter, but only in transmit path. Modeling using a Q around 70 per coilcraft catalog conveys enough rejection,? still I am skeptical I might be a little short. I am getting around 4w on 28 MHz CW so not sure I need a mod per this thread. 73 curt |
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I suppose the sch was disclosed? by Farhan,? almost 3 weeks back. On Wed, Feb 27, 2019 at 1:37 PM iz oos <and2oosiz2@...> wrote:
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IZ,
There is no trick, the amp itself is the same so getting 5W is a matter of fixing the problems there. Those being 3904s have far less gain at 28mhz than is needed. As a result most uBitx run short on power at 10M unless modified or very very lucky. Fixing the 45mhz IF was to help with spurs and other trash, it was not more than a partial fix for power out ever as you can only push the mixer so far and it was already pushed hard. This was all cover in painful detail last year and is documented in the wiki.? Remember all of that? Allison |
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Thanks for all the replies. According to the old schematics of my ver. 3 ubitx C81 should be 0.1nF, so I will see what changes with a 470pf as suggested by Farhan. Il 28/feb/2019 23:58, "ajparent1/KB1GMX" <kb1gmx@...> ha scritto: BITX V5 as distriibuted.? I believe its part of the Zip file on github. |
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I replaced the cap at the emitter of Q90 with a 470pf instead of the 0.1nF. In the meanwhile I replaced the bifilar antenna wire with a short coax. Output power on 40 marginally diminished from 15 to 12.5w about. The power on higher bands marginally increased from nearly 2w to nearly 2.5w. But the 'instability' issue with full throttle noise on SSB on 10m has disappeared and I can also not attenuate the Vogad output. Overall I am happy with this one component replacement. Il 01/mar/2019 08:40, "iz oos via Groups.Io" <and2oosiz2=[email protected]> ha scritto:
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What about adding a capacitor (like a 180pf or maybe a higher value) in parallel with r83? Would it increase the 10m power output without decreasing the output in the other bands (I wish I knew how to use LTspice)? Il 02/mar/2019 11:47, "iz oos via Groups.Io" <and2oosiz2=[email protected]> ha scritto:
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¿ªÔÆÌåÓýIz Oos Using LTSpice is not all that difficult (I learned it and I'm not that brilliant). There are two parts to learn.? First is the schematic editor that is intuitive once you know some basic select-and-place moves.? After you have the schematic complete you would select voltage sources and measuring points.? The rest is mostly automatic when you select "RUN" mode. Start with a small circuit segment to get a feel for how it works and then build on that experience.? In a few hours you will be an expert. LTSpice is FREE and will run on Windows or any version of Linux with Wine installed.?? Arv _-_ Sent from my Verizon, Samsung Galaxy smartphone -------- Original message -------- From: iz oos <and2oosiz2@...> Date: 3/9/19 12:04 AM (GMT-07:00) Subject: Re: [BITX20] How to get 5W on 10m? What about adding a capacitor (like a 180pf or maybe a higher value) in parallel with r83? Would it increase the 10m power output without decreasing the output in the other bands (I wish I knew how to use LTspice)? Il 02/mar/2019 11:47, "iz oos via Groups.Io" <and2oosiz2=[email protected]> ha scritto:
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Thanks Arv, I will try it! I had installed under Linux via wine so following your hints I can start with it! Il 09/mar/2019 15:46, "Arv Evans" <arvid.evans@...> ha scritto:
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Iz Oos Many here are users of LTSpice and can help if you have questions.? Feel free to ask us if you run into problems.? In addition to demonstrating how existing circuits should work, Spice simulations can be used for empirical design efforts (try things to see what it does) as an alternative to complex mathematical design and analysis approach. Arv _._ On Sat, Mar 9, 2019 at 9:16 AM iz oos <and2oosiz2@...> wrote:
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Ok, thanks for the hint, I certainly need it. I will start with simulating a dummy load hihi Il 09/mar/2019 22:18, "James Lynes" <jmlynesjr@...> ha scritto:
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What about adding a small cap, say from 180 to 330pf across R911, R96, R941 and R942 to add a little bit more PWR on the higher bands (15-12-10m)? Il 09/mar/2019 17:16, "iz oos via Groups.Io" <and2oosiz2=[email protected]> ha scritto:
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