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Re: Amplifier chain design - best practices
On Sun, Sep 23, 2018 at 11:23 AM, ajparent1/KB1GMX wrote:
Gilles, |
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Re: Ubitx evolving fixes updated to wiki?
#ubitx
#ubitx-help
Gordon Gibby
Very cool.
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I plan to get external filters for the 160 m band. Or, since I really don¡¯t use the higher bands, maybe switch them around a bit. Neat little rig, will do all kinds of cool things for me. On Sep 23, 2018, at 13:31, Bill Cromwell <wrcromwell@...> wrote: |
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Re: Amplifier chain design - best practices
Hi,
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I always heard "like pushing string". It's the same level of frustration. 73, Bill KU8H On 09/23/2018 12:25 AM, K5ESS wrote:
If there was ever an appropriate comparison, the now overused phrase --
bark less - wag more |
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Re: Ubitx evolving fixes updated to wiki?
#ubitx
#ubitx-help
Hi Allison,
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Little details seem to need a lot of refreshing here - as you often point out. I am using my uBitX on the air primarily for CW up through 17 meters (but no QSOs higher than 14 MHz so far). I use an external filter and will be using a better one (more convenient for field portable use) while I am working on an internal fix. Yes, one of the mods. I just got the board when I returned from a vacation. The external filters might be a good idea even with internal mods to reduce trash even more. The external filters are pretty much painless AND being external may be re-used with other radios:) It's nothing new. Hams have been using them since the 40s or 50s - maybe earlier. I am also (ab)using my uBitX as bench test gear :) I used it to identify broken parts in a PFR-3 and make the repairs. Two inductors had fractures in their windings and one transformer was installed backward! The uBitX with a scope probe where the antenna normally goes made the 'divide and conquer" process quick and easy. It served as a $120 signal tracer. And then I re-used my signal tracer as a two way radio :) 73, Bill KU8H On 09/22/2018 10:41 PM, ajparent1/KB1GMX wrote:
Doc sees horse, --
bark less - wag more |
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Re: Amplifier chain design - best practices
Hi Allison I have a factory unmodified uBitx, I wish to remain QRP and not to exceed 5 watts in emission (SSB). Is a simple modification possible? thank you to enlighten me 73 QRO and thanks for your work within this group Gilles - F1BFU /FR Le?dim. 23 sept. 2018 ¨¤?18:57, ajparent1/KB1GMX <kb1gmx@...> a ¨¦crit?: Henning, --
Gilles - F1BFU/FR |
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Re: No Signal on uBit-x
#ubitx-help
On Sun, Sep 23, 2018 at 09:53 AM, KM4TRT wrote:
) I get about 90 mv @ 45 MHZ just before the crystal filter with the amount of hash you'd expect to see after a mixerThe second amp is at ~12mhz.? if the LO to the second mixer is not correct then nothing works. The second LO is in either 33 or 57 mhz (check the docs). The chain from antenna in is 14.0mhz upconverted to 44.985ish mhz and then down converted to 12mhz. If any of the oscillators are wrong you miss the 45mhz pass band or the 12mhz filter pass band (11.995 to about 12mhz) you get nothing as in deaf. Those 45mhz filters are not likely to fail, bad joints are possible. Any? 45mhz filter should work 7.5 or the wider 15Khz.? ? I'd insure that the calibration went well and the 3 digital oscillators are indeed where they should be. IF they are not its? going to be a deaf rock. Allison |
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Re: Amplifier chain design - best practices
Henning,
Just one more part of the picture but less an issue for lower power. I call that saturation thought its something different.? To many I call that the hockey stick region as it really bends sharply. The problem is at 12V you get distortion under about 2V and hit the wall at 12V. To get power you want to vary current to the load without hitting either?you need a minimum of about 2A into not 50 ohms but about 10-12ohms?to do that. I look at the uBitx and the 1:1 output transformer just cannot do that. IT is also why besides all other problems the IMD goes bad at about 2W. Lower the load or raise the voltage(to about 24V) and at least 80m things improve greatly. Whats interesting is others have seen and applied this with good result. As I have three such examples. Allison |
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No Signal on uBit-x
#ubitx-help
After hooking up my new Nextion screen and making several great contacts, I was trying to optimize the frequency calibration and? hit the PPT switch a few times with the antenna switch in the wrong position.
I get no signal on receive or transmit. I believe I tracked the problem down to the 45 MHz bandpass filter because: 1) I injected a 14.725 signal at 100mv at the antenna. 2) I tracked it through the first filter and the the first mixer and amp( on the scope) and 3) I get about 90 mv @ 45 MHZ just before the crystal filter with the amount of hash you'd expect to see after a mixer 4) Nothing out of the crystal filter. or out of the second amp. Yes I did check voltages on all the concerned transistors Can I use any of the cheap bandpass filters from Ebay as long as they are +/- 7.5 Khz pass https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313.TR0.TRC0.A0.H0.X45+mhz+bandpass+filter.TRS1&_nkw=45+mhz+bandpass+filter&_sacat=0 I looked up the WTL filters and don't see the Z 7? thats stamped on mine. The WTL spec sheet has a 2 pole or 4 pole 45/3OT or a 2 pole of 4 pole 45/fundamental. http://www.wtlcrystals.com/UploadFiles/31.jpg Anyone familiar? with this? Thanks-Andy KM4TRT |
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Re: Amplifier chain design - best practices
¿ªÔÆÌåÓýAllison, one more point: for the load always stay off the "knee" i.e. the
so called ohmic range. Above this point the MOSFET acts like a
voltage controlled (control voltage is the gate to source voltage)
current source. Example: for VGS = 5 V stay awav from the range of VDS = 0 to
about 1 V. As easily be seen the "knee" gets worse for higher
drain currents. A similar condition happens for the RD16HFF1, having a larger ohmic region--? and in addition a limited maximum drain source voltage. The IRF 510 can do better as it can be operated at higher drain -source voltages. The result: as the maximum drain -source voltage swing for the RF
signal is limited the maximum output power can be only achieved
through the output transformer and its transformation value. There is a good explanation of this relationship in the proceedings of the "UKW-Tagung Weinheim" a few years ago by the author Prof. Dr Jochen Jirmann DB1NV. ? Henning Weddig DK5LV? Am 23.09.2018 um 17:21 schrieb
ajparent1/KB1GMX:
Tim, IMD can be caused by two things, saturation at high power and |
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Re: Bitx40 vs. uBitx
R. E. Klaus
Right now we are in a low time of sunspots which is part of the Solar Flux equation that effects our Ionosphere and allows the upper HF bands to work (20 through 10 meters) Until the Solar Cycle starts to raise again, 20 and up will be spotty in whether it's open or not.
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uBitx Manager Question
Hello, I upgraded to the KD8CEC firmware last night and I really like it. I see that there is also the uBitx Manager software.?
Im guessing that I can backup my existing settings with this software? ?I¡¯ve been trying to get everything dialed in as far as the BFO and the calibration settings go and occasionally I really get things whacked out. It would be nice if the manager software allows me to back things up and then restore it to a good point should I mess things up.? Is that that one of the uses of the Manager Software? ?Also, do I use the Manager software with the radio powered up with the 12v power supply or only by having the USB cable attached like when you program the radio? Thanks, Curt |
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Re: Bitx40 vs. uBitx
Jack Purdum
Daniel: I have both and I can't really say there's a big difference. One position is save the $50, buy the BITX40, and spend that extra money to upgrade to the best antenna you can buy. On the other hand, check the bands out when there's a major contest on and you find some activity on all bands. Sometimes, I think thousands of us listen to the band, don't hear anyone, so we say "the bands dead" and we give up. If we all got on and tried a few CQ's before giving up, I'll bet we'd find the only reason the band is dead is because we didn't try. So, do you really want to throw all of your eggs into the 40M basket? Eventually, those dead bands are going to open up and you'll want to be part of it. I just hope I'm around to see it! Jack, W8TEE
On Sunday, September 23, 2018, 11:06:40 AM EDT, Daniel <gonewiththeego@...> wrote:
Hey everyone! I have a uBitx for few days and I can say that it's awesome! it's my first and only HF transceiver. Yesterday I listened all across 10m to 80m with just few meters of copper wire as an antenna. I can say that was... radio silence almost all over except for the 40m band. Now that I can see 40m band as a quite crowded place, I'm wondering... is there any advantage of having a Bitx40 comparing to uBitx? Is the reception or the transmission of the smaller brother somehow better comparing to the other one, giving the fact that Bitx40 is focused for 40m band only? Because now I'm wondering maybe uBitx wasn't the right choice for me and I should opt out for Bitx40. If we speak only about 40m band, can we say that Bitx40 is better than uBitx or not ? Thanks, and I strongly appreciate any kind of information and comment.
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Re: Bitx40 vs. uBitx
Daniel,
I'm a bit of a noob, but I have been playing with with various transceivers in receive mode for a few years.? For what it's worth, I can tell you that regardless of the unit, your going to need more antenna to get decent reception.? Even if it's just taped to the ceiling where you live.? Up in a tree is better.? If it's for receiving only, you can use any cheap wire of any size.? Short antenna and bad band conditions = no reception. Do this and I think you'll be pleased. |
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Re: Low Pass filter inductor question.
#filters
Air core has one liability that is mutual coupling.
So if you use air core the parts must be oriented so they will not couple That means one in each plane of X, Y and Z.? Supporting the Z might be? annoying (coil spirals away from the board). Air core want to be no less than 1 coil diameter from any metallic surface or wall. The rule of thumb for good Q is three coil diameters. That and they will be bulky.? Wire size for 10W is anything you can make mechanically stiff for self supporting and at least #28 for wound on former.? Heavier gauge wire is handy for that. For this close wound is likely ok.? Note higher Q may impact filter characteristics. ? Allison |
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Re: Amplifier chain design - best practices
jim
The bother I have with most all those curves is that they start at Amperes ....Not mA's ...Been considering generating some on my own, just for fun and enjoyment ...(conductance curve probably) Jim
On Sunday, September 23, 2018, 8:21:24 AM PDT, ajparent1/KB1GMX <kb1gmx@...> wrote:
Tim, ? load line that reflects input voltage.? Old tube hands likely the curves looking like? many power tubes.? ?It is on the page upper right corner.? Do not let pulsed be a bother as in some cases those curves represent power well above what the device can do sustained.? Needless to say its hard to run the drain to zero volts and remain linear.? It also indicates a Gm of about 1S? IE 1Vgs change causes a 1A Drain current change. Allison |
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Low Pass filter inductor question.
#filters
I'd like to build a few lpfs for my ubitx.? Can I use air core inductors?? I've got plenty of magnet wire and there are lots of inductor calculator online.
If this is doable,? Is close wound ok?? Also, what effect would wire size have? Thanks in advance. |
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Re: Amplifier chain design - best practices
Tim,
IMD can be caused by two things, saturation at high power and cross-over distortion near idle conditions. You missed one.? Anytime the output is not a uniform multiple of the input. Or what is know ans non linear behavior. Good example the HFE of 3904 at 10ma is 100, at 100ma its 40.? So is the? waveform causes it to swing from 10 to 100ma the gain supplied is varying. The base current required to get 10ma and 100 ma is not ten times higher it is more like 25 times higher and the change is varying for intermediate currents.?? For power MOSfets this is pronounced at low gate voltages as first we have threshold where below that there is no conduction. as we go up from that point the curve is markedly curved then straightens and at some high current bends again. For information look at the Ids VS Vds for Vgs curves.? From that graph we can get a load line that reflects input voltage.? Old tube hands likely the curves looking like? many power tubes.? ?It is on the page upper right corner.? Do not let pulsed be a bother as in some cases those curves represent power well above what the device can do sustained.? Needless to say its hard to run the drain to zero volts and remain linear.? It also indicates a Gm of about 1S? IE 1Vgs change causes a 1A Drain current change. Allison |
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Bitx40 vs. uBitx
Hey everyone! I have a uBitx for few days and I can say that it's awesome! it's my first and only HF transceiver. Yesterday I listened all across 10m to 80m with just few meters of copper wire as an antenna. I can say that was... radio silence almost all over except for the 40m band. Now that I can see 40m band as a quite crowded place, I'm wondering... is there any advantage of having a Bitx40 comparing to uBitx? Is the reception or the transmission of the smaller brother somehow better comparing to the other one, giving the fact that Bitx40 is focused for 40m band only? Because now I'm wondering maybe uBitx wasn't the right choice for me and I should opt out for Bitx40. If we speak only about 40m band, can we say that Bitx40 is better than uBitx or not ? Thanks, and I strongly appreciate any kind of information and comment.
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YO8UFO
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