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Re: si5351 crosstalk
#radiuno
Hi Allison,?
would you be willing to try your load testing again, with the Si5351a driving a set of high impedance loads? say something perhaps 10k Ohms or higher.? -Justin N2TOH? P.S. I'd like to see what the Si5351a would do driving the crystal tube oscillators in the Heathkit SB/HW101 series rigs.? |
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Re: Antenna Loops
#off_topic
David
A copy of your post to the uBITX group has been forwarded to the [email protected]?discussion group.?? This group was formed to move the long and multiple off-topic posts, mostly about EFHW antennas,? to a place where antennas would be?more on-topic.? If not already on that group you can join at and post to [email protected]?. Arv? K7HKL _._ |
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Re: uBitx Antenna
#ubitx-help
Gordon Gibby
¿ªÔÆÌåÓýI¡¯m using one there is almost identical to the one he suggested. ?Works fine all bands as far as I can tell. ?I have used boatloads of different ones throughout the yearsThose that use toroids (instead of the old parallel lines) probably use this basic circuit: You can tell the ones that use the parallel transmission line pick ups: they are longer. ? Those with a toroids ?can be more square shaped boxes
I¡¯ve used them both, they all work
Cheers?
Gordon
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Re: Simple spur fix
Warren Allgyer
Allsison It is not clear to me what advantage a 9:1 transformer would have over what I have advocated and tested. It certainly would not present a better match. |
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Re: uBitx Antenna
#ubitx-help
Output of the uBITX is 50 ohms.? Your CB SWR meter should work for the upper end of? HF range (20M through 10M) and maybe acceptably good for 80M through 10M.? Many? of those old CB SWR meters were just copies of ham radio SWR meters of the era.?? If the CB SWR meter is not performing well, it does provide a case, meter, and knob to? use in building a more modern bridge type SWR and power meter. Arv _._ On Sun, Sep 9, 2018 at 1:12 AM, <gonewiththeego@...> wrote: Thank you very much for your nice "Welcome aboard", indeed I appreciate all of the answers above and I'm pretty sure that this topic will have some "echo" throughout community. These are maybe the most common questions asked by those with just the license of operation in hand and a few basic knowledge of electronics. I can't wait to see the uBitx on my desk. Meanwhile, I can't find some genuine information about the output impedance of the uBitx itself. Is it 50 ohms ? Gordon Gibby previously sugested that a CB SWR-Meter will do the job on HF also. I found one but it's rated to 11m band only, or at least that's what on the label. Can someone tell me what can go wrong it I start using it ? And by experiment, does anyone know how much SWR can uBitx handle without permanent damage? |
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Re: Simple spur fix
Paralleling filters is not a safe thing to do.? Many too many unpredictable things happen.
Also the filter impedance is around 500-650 ohms.?? A 9:1 impedance transformer would get you close and efficiently.? Next integer version is 16:1. A 9:1 would be close enough for low loss (under 1.5db for two using 61 material). An L network works easier. Allison |
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Re: More PA Putzing ..
Arv,
Its not DC resistance its RF resistance and RF inductance.? Flat conductors are? better for the latter and need to be wider for the former.? That is the wires with RF. The grounds are to the plane under the amp through a few tiny holes. Also look at the routing, not at all pretty at even low VHF. Allison |
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Re: More PA Putzing ..
Re Jerry ..Donno... need to start making some transconductance measurements too anyway ?? I was looking at the gate voltage on the mosfets ..4 V at 100 ma bias ...More swing that +/- 4 volts and distortion rears its ugly head (more like 3 volts, but who's counting?
Jim, Also the transconductance of the mosfets is around .2 S? fairly high.? You need to bias for about 100-300ma per device and the Drain load must be low enough to stay on the load line for the device.? Keep in mind from about 2 to 6V gate voltage you see at DC near 0 current to over 4A so it not like you need more than a volt maybe 2 P-P especially push pull.? That requires a load at the output that does not allow the drain to swing to zero or 12V at full power out (linear load line).? To get that?we need a low impedance load and translation to 50 ohms.? Typical load say 25 ohms and 20V PP swing [why not 24V?? Never go to zero or max V saturation or voltage clipping.] barely?nets 10-11W. We move lower to about 12.5ohms and we get 22w but we are still near saturation but at 10W we are not and the result is much cleaner.? So we need to develop power from the mosfet with minimal gate swing and maximum safe drain current.? Both happen with about 2A drain current and conditions that keep the gate at less than 4V peak (at the device.).? ?For push pull that means each mosfet can go to near zero current point (best not to for IMD) but not near the power supply max (also IMD).? Its also why parallel internal architecture hexfet, LDmos, Vmos, Tmos] or hybrids of multiple discrete are used.? IRF510 is hexfet, essentially many parallel little MOSfets in parallel. MOSFET is a voltage controlled current generator.? That's the general model where the current is Vgs* GM. So when I see people getting high power I know one of two things either they have transformer loading the drains to under 15ohms or they clipping heavily.? The IRF510 (is not alone with this) however runs better at 20-28V where much more power is possible without exceeding peak current.? FYI the current stock transformer barely has the drains Push-pull at 50 ohms which is way too high.? It should be a 2:3? [maybe 4:6 turns] where 2:3 ratio nets about 22ohm drain load and it likely to have a chance at 10W IMD?being acceptable at 12V.?? Back of the napkin for current stock transformer is 50ohms and we push to the edge at 12V (22V P-P) and we get... 9.68W peak (6.7rms)!? ? Its ohms law, power law, and that simple. More than that it will be very unclean. Things you have to do to generate /clean/ power. Allison |
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Surprised by generous and kind act
#bitx40
Today I was greatly and pleasantly surprised.? I'd mentioned that I was thinking about converting my BITX20 to 40 meters, and I'd related some stories of frustration with the local ham community (generosity and willingness to help others seems to be a rarity in this area).
When I got our mail, there was a package in it - with a BITX40!? The housing it was in is very attractive as far as my wife and I are concerned - and perfect for our car.? The neat part was that you could see the circuitry in it - and the case also would lend itself to portable operation! I won't embarrass the sender, but I will say it came from another state.? For many years, I've insisted that there was no such thing as Karma... but this suggests otherwise! To the sender (not named) - a big Thank you! from both of us, and (laugh) no worry about "paying forward" - we do things all the time like that, whenever we can (we may not have much money, but we do have skills and knowledge we share).? Generosity and helping others is not a big price for gifts like this - in our opinion! |
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Re: More PA Putzing ..
Allison can the "wimpy ground paths" part be helped by overlaying fairly heavy wires in? parallel with existing wimpy grounds? Arv _._ On Sun, Sep 9, 2018 at 9:06 AM, ajparent1/KB1GMX <kb1gmx@...> wrote: Jim, |
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Re: More PA Putzing ..
Jim,
Yes the big thing is developing a voltage across the capacitive gate, takes power to do that. Also the impedance of the source (driver) has to be low at low HF as at 3mhz the gate looks like about 220ohms reactive with whatever resistive values are applied across that. At 30mhz its 22 ohms plus that same set if Rs and Ls.? A crappy driver can push 3mhz but at 30 the layout and current for less than 22 ohms becomes significant. FYI I have 4 of the the QSX amps and several I've built proving flat to 30mhz or beyond with IRF510 is very doable.? However the board layout has to look like a VHF layout not long thin traces with wimpy ground paths.? Also the drivers have to be able to push a bit of power optimally about a watt.? While delivering the same gain at 3 and 30mhz. All the at is to help you understand why it doesn't.? IF you fix drivers,, transformers, and biasing, your still stuck with board layout.? That not to say it can't be improved greatly. Work I did said 10-12W at 80m and 5W at 10M is very doable but to take advanage of that you have to clean? up spurs and low pass at a minimum. The problem was I was peeling a very pungent onion. Allison |
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Antenna Loops
#off_topic
There have been many posts regarding end fed?antennas. I hope these posts were helpful.?
My favorite portable antenna are?various loops, either full-wave?loops,?quads, or Miniature Magnetic Loop Antennas. Why do I like loops:
I wrote an article about Miniature Magnetic Loop Antennas for the Elecraft.com team way back in 1999 when they were not yet so popular (i.e., I was a builder of the early K2 and beta tester for the 100 watt?linear). Check it out at?. You can build these antennas with materials from any home improvement store. I hope they inspire some antenna building from among the uBitx?building family. David Posthuma, WD8PUO |
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Re: uBitx Antenna
#ubitx-help
Richard Chan
I appreciate all the support I have received and thanks. I will work on some of these but the whip antenna will not work I'll the magnetic loop antenna.? Thanks for sharing. Richard Chan? On Sun, Sep 9, 2018, 9:24 AM Warren Allgyer, <allgyer@...> wrote: Daniel |
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Re: Lcd nextion generating qrm
with 5 ohms and with 100 brightness level , is there no qrm, Junior !!!\ ?Congrats. sarma ?vu3zmv On Sun, Sep 9, 2018 at 7:44 PM J¨²nior PY2ADA via Groups.Io <aaj280174=[email protected]> wrote:
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Lcd nextion generating qrm
The nextion 2.8 "display is generating qrm, when I adjust the brightness control to less than 100 I have qrm at the reception, if it is 100 without problems. I installed a 5 ohm resistor in series with the power of the display, it was nice the brightness of the lcd. ? 73 de J¨²nior |
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Re: More PA Putzing ..
jim
Yep?? all true ... minor circuit/device constraints
Jim
On Sunday, September 9, 2018, 6:30:33 AM PDT, ajparent1/KB1GMX <kb1gmx@...> wrote:
jim, input C for irf510 is in the 150-180pf range, drain to gate about 20pf. Classic case for Triode miller effect.? Feed impendance must be low of you get the? output voltage divided across the input 20pf and 180pf as negative feedback. You seen this will all mosfets only the degree of it varies. FYI the drain to gate C varies with DC drain voltage for all mosfets. The circuit for the driver has issues: Output impedance is not constant or low enough. The stage voltage saturates (high emitter resistor)? THe stage current limits due to high Collector L(transformer). The 3904s loose gain with increasing frequency. Allison |
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Re: Simple spur fix
Warren Allgyer
And a correction to clear up any confusion: I wrote: " Clearly we need these transformers to be impedance matched in the circuit." It should have read: "Clearly we need these FILTERS to be impedance matched in the circuit". Wish I could blame autocorrect but it was lack of proofreading.
WA8TOD |
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Re: Simple spur fix
Warren Allgyer
John
It is 7:2 or a 3.5:1 ratio. The impedance ration is the square of the turns ratio. I honestly don't know the answer to your question about paralleling filters. I guess you could try it..... but some bad karma and icky things might result. I would have to test it to be sure. If you are going to use a transformer anyway I would just adjust the turns ratio and use one. WA8TOD |
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Re: Simple spur fix
I don't think paralleling the filters will impact the nominal input
impedance of each filter. If you have a SA and have something to generate a 45Mhz signal you could sweep the filters in parallel and see what it does. tim ab0wr On Sat, 08 Sep 2018 12:41:16 -0700 "John KC9OJV" <greusel@...> wrote: I rolled the dice on a pair of filters and received Toyocom 45E1A9Fs |
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Re: Simple spur fix
Should the pad after the balanced modulator be changed to add more loss?
That should be easy to do. tim ab0wr On Sat, 08 Sep 2018 12:39:46 -0700 "ajparent1/KB1GMX" <kb1gmx@...> wrote: Warren,The problem is the balanced mod easily takes that but the gain after1) 120 mVrms is far above the audio level that caused unacceptable |
David Posthuma
J¨²nior PY2ADA
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