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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 |
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 |
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 |
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 |
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 |
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 |
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. |
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 |
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 |
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. |
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 |
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.
|
Re: Amplifier chain design best practices
Jim,
Its not only if you do not meet "x" your problems start earlier. Its the difference between ON and "well sorta on" the latter being conducting but not hard.. For commutating mixers (DBMs and other ) just sorta conducting is not on or off and non-linearity is then the problem. In the end not enough means exactly that. Allison |
Re: Amplifier chain design - best practices
IMD can be caused by two things, saturation at high power and
cross-over distortion near idle conditions. I suspect the high standing current prevents cross-over distortion which is why you get better IMD performance. tim ab0wr On Sun, 23 Sep 2018 14:53:53 +0400 "Ashhar Farhan" <farhanbox@...> wrote: Allison, |
Re: Off-topic posts, Amplifier chain design
Jack Purdum
Mike: I think your criteria may be too narrow. Not all of us are EE guys who understand the nuances of amplifier design. To me, most of the topics you're complaining about seem to make sense to me, perhaps because I'm not an EE person. Even something that appears off topic (e.g., K2 and its price) make sense to me since there needs to be a standard against which things are measured. Personally, judging against a well-known product is more insightful than fitting data to an equation from a book. Often I read posts that I know I probably won't completely understand (like amplifier chain design) because I hope to glean some information from that post. Given that there are thousands of us here and a good chunk are not engineers, "off topic" to some may actually be the post that makes "the penny drop" for others. Finally, we have a very capable monitor for this group who is unafraid to jump in when he feels the nature of a post or its thread doesn't serve the group's interests. I suggest that we leave the policing of this group to his judgement. Jack, W8TEE
On Sunday, September 23, 2018, 12:25:42 AM EDT, K5ESS <k5ess.nothdurft@...> wrote:
If there was ever an appropriate comparison, the now overused phrase ¡°like herding cats¡± fits the bill with regard to keeping these group posts on topic. Mike K5ESS ? From: [email protected] [mailto:[email protected]] On Behalf Of ajparent1/KB1GMX ? Did a count and nearly 50% of the posts in thsi string have nothing to do with: |
Re: Ubitx evolving fixes updated to wiki?
#ubitx
#ubitx-help
Thanks folks!? I found some good pages on filters to study up on.? Doesn't look too bad.? Think I'll go ahead and build them for the experience points :)
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Re: Amplifier chain design - best practices
Farhan,
I am very aware that fewer devices are desired for better IMD.? ?The key is using competent devices at attainable gains.? There are two problems with 3904s in that role, gain compression at higher operating currents and a distinct problem with delivering the desired gain at higher frequencies.? ?If they cannot produce the needed gain any feedback required for?supporting input and output impedance will be unpredictable producing a cascade of performance degradation.? Its not what you may have built in some prior time as we have many tested that do not.? ? Its about how to do it at some production level. First is we do not ask a device to push above it weight class.? 2n3904 is not going to deliver more than 12DB power gain at 3-30mhz and less than 1db gain flatness. The power it can produce is not device dissipation its gain at currents higher than? its peak current gain (about 10mA for HFE peak and HFE is well down at 100mA). This shows well of a curve tracer.? We would deire for linear use a prt that has a more or less flat current gain in the operating range. By measurement we have insufficient drive and gain at frequencies approaching 8mhz. As a result of those factors the IMD measured is seriously poor above 2W even on bands where more power can be delivered.? The key here is power with acceptable IMD from 3 to 30mhz not 3 to maybe 10mhz.? ?We cannot do that with devices that incapable of that for those first three stages.? Note this is not an IRF510 issue as the driver has failed to deliver adequate drive and the prior stages requires overdrive to function at all.? That does not help IMD or spurs. Also bias of 1A for?RD16HHF is not class A above about 3 to maybe 4W and wanders into AB1 above that power.? ?A pair of IRF510s at 12V can achieve that at about 250ma though at higher voltages can easily surpass that.? In general the RD16HHF is about $4.50 more expensive to get maybe 3db better IMD at 12V if everything around it supports that.? To do that prior stages have to built to do that.? The IK4AUY amp (IRF510 pp driving IRF510PP) supports the ability of the part to perform. In either case loading a IRF510 or RD15HHF to 50 ohms Drain to Drain is far too high a load resistance for more than a few watts.? Reason is MOSFETs are voltage driven current sources.? ?If you want power from them the load current must swing in the linear current region without exceeding the available voltage.? So with 50 ohms and not more voltage say 12V peak 2.88W is about it and we are driving devices to saturation.? ?We need s a load line what can support a Drain current in the 1-2A region. for that was need to get to 12.5ohms for a 10W amp without saturating or voltage clipping. At that point we are running near 1A Peak current and likely with 200-500ma of bias we are in the linear region for a push pull amp.? Combined with a reasonable feedback for flatter gain vs frequency the IRF and RD are in the same region.? ?But this will be true only if the drivers and prior stages are not suspect. Allison |