HI all,
I've started on that in the wiki and its not a small task.
Also some of the fixes are not "settled" with conflicting approaches.
Right now the best and most complete is Ubitx.net.
Allison
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Farhan,
Yes, Si5351 crosstalk may not be a problem worth chasing for most.
Though a hack to the 6dB pads would be quite easy to do, if that does help.
In addition to RX birdies, I can believe si5351 crosstalk might contribute to spurs on TX.
Though Raj's extra 45mhz filter seems to bring down all spurs well enough, and that occurs
before clk2 enters the mixer.?
Having 12mhz get into clk1 will contribute to carrier leakage on TX.
But residual carrier is not a deal breaker for most of us.
I'm thinking of you and your parents.
I know from experience that these health issues can be all consuming.?
Wishing all of you the best.
Jerry, KE7ER
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On Wed, Sep 12, 2018 at 11:16 AM, Ashhar Farhan wrote:
the si5351 cross talk is not causing either distortions or harmonics. it can result in the birdies, but that's about all.
?
the spurs in the 57 MHz and the 12 Mhz clocks are confined by the following filters at 12 Mhs and 45 Mhz. The only spurs that you have to actually bother about (only on the rx side) are those in the first mixer's oscillators.
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On Wed, Sep 12, 2018 at 10:50 AM, <terryhugheskirkcudbright@...> wrote:
hi
i am still waiting for the delivery of my bitx40 but while waiting i am pondering
i have 40 and 20 using my trio ft520 and dipoles.
but i do not have enough room for an 80 m dipole so i have built a qrp atu and erected an end fed long wire for 80.
there is no way to reduce the 200w from the trio to use a qrp atu so the answer is the bitx40. 200 wats would be like a pan galactic gargle blaster to my atu !!
but i need to hack the bitx40 for 80
nd6t has published a hack for 60 m which involves adding parallel caps to c2, c4, c6 and across l7
so i modeled the bpf and lpf using aade program with 560 pf across c2,c4,c6 and 390 across l7 and the plots look good for 80 m . the sketch also has to be hacked but that is not a problem as i am a retired computer programmer.
What do people think about the? thoughts of an idle fellow.
73 de terry gm4dso
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the si5351 cross talk is not causing either distortions or harmonics. it can result in the birdies, but that's about all.
the spurs in the 57 MHz and the 12 Mhz clocks are confined by the following filters at 12 Mhs and 45 Mhz. The only spurs that you have to actually bother about (only on the rx side) are those in the first mixer's oscillators.
On Wed, Sep 12, 2018 at 11:19 PM, Vince Vielhaber <vev@...> wrote: I've always used an ADA-4789 for DDS buffering.? 50 ohm in and out, single supply and good to 2.5 GHz.
Vince - K8ZW.
On 09/12/2018 10:40 AM, Jerry Gaffke via Groups.Io wrote:
I suspect it is more critical that we have sufficient drive into the
mixer LO port
than to have that 6dB 50 ohm pad.
This sort of thing is best evaluated by somebody with a spectrum analyzer.
A series cap plus series resistor between the si5351 and the mixer may
be sufficient,
the resistor value is a compromise between sufficient drive to the mixer
and minimizing how much power we demand from si5351.
Could also add a resistor from mixer port to ground to bring source
impedance there down,
though that further reduces drive available to the mixer
? ? /g/BITX20/message/35206
The CMOS buffers previously mentioned are good down to about a 100 ohm load,
? ?/g/BITX20/message/59200
Use separate devices for each clock to avoid crosstalk, and filter Vcc
well.
If you insist on driving 50 ohms with CMOS buffers you might put two
such gates in parallel:
Often you see an MMIC in that position, but we don't have to be linear here.
The diode mixers work well with a square wave.
Jerry, KE7ER
On Wed, Sep 12, 2018 at 12:08 AM, Tom, wb6b wrote:
? ? How critical is the impedance the mixer sees?
? ? Possibly another good reason for a buffer where you can control the
? ? impedance better.
? Michigan VHF Corp.? ?? ?
? ? ? ? ? ? ? ? ? ? ? ? ?
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Distorted audio is easy enough for us to be aware of,
even if we cannot all measure it accurately.??
Spurs and harmonics are more apt to slip by unnoticed,
and can wreak havoc outside the ham bands.
Most of the reports in the forum about bad audio seem to come down to
a BFO not placed correctly with respect to the 12mhz filter,
or a poorly shaped 12mhz filter passband.?
Perhaps some are due to IMD, and we simply have not been aware of that aspect.?
But many here report good sounding audio.
In most cases, distortion due to IMD will go down with lower audio levels into the mike.
This will not help if the issue has to do with the 12mhz filter shape or BFO placement.
These levels of IMD should not be ignored.
I'm hoping there will be a v5 with much improved IMD specs.
We may eventually come to some easy partial fixes on v3 and v4,
but a complete fix may require a significant redesign.
Jerry, KE7ER
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On Wed, Sep 12, 2018 at 10:22 AM, Warren Allgyer wrote:
There is is nothing illegal about putting distorted audio in the air. But I would not do it.?
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Thanks Warren,
That is exactly what I was looking for. It just so happens I have all the parts and will make the mod asap and wait to see what else will be recommended.
Joel
N6ALT
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hi
i am still waiting for the delivery of my bitx40 but while waiting i am pondering
i have 40 and 20 using my trio ft520 and dipoles.
but i do not have enough room for an 80 m dipole so i have built a qrp atu and erected an end fed long wire for 80.
there is no way to reduce the 200w from the trio to use a qrp atu so the answer is the bitx40. 200 wats would be like a pan galactic gargle blaster to my atu !!
but i need to hack the bitx40 for 80
nd6t has published a hack for 60 m which involves adding parallel caps to c2, c4, c6 and across l7
so i modeled the bpf and lpf using aade program with 560 pf across c2,c4,c6 and 390 across l7 and the plots look good for 80 m . the sketch also has to be hacked but that is not a problem as i am a retired computer programmer.
What do people think about the? thoughts of an idle fellow.
73 de terry gm4dso
|
I've always used an ADA-4789 for DDS buffering. 50 ohm in and out, single supply and good to 2.5 GHz.
Vince - K8ZW.
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On 09/12/2018 10:40 AM, Jerry Gaffke via Groups.Io wrote: I suspect it is more critical that we have sufficient drive into the
mixer LO port
than to have that 6dB 50 ohm pad.
This sort of thing is best evaluated by somebody with a spectrum analyzer.
A series cap plus series resistor between the si5351 and the mixer may
be sufficient,
the resistor value is a compromise between sufficient drive to the mixer
and minimizing how much power we demand from si5351.
Could also add a resistor from mixer port to ground to bring source
impedance there down,
though that further reduces drive available to the mixer
/g/BITX20/message/35206
The CMOS buffers previously mentioned are good down to about a 100 ohm load,
/g/BITX20/message/59200
Use separate devices for each clock to avoid crosstalk, and filter Vcc
well.
If you insist on driving 50 ohms with CMOS buffers you might put two
such gates in parallel:
Often you see an MMIC in that position, but we don't have to be linear here.
The diode mixers work well with a square wave.
Jerry, KE7ER
On Wed, Sep 12, 2018 at 12:08 AM, Tom, wb6b wrote:
How critical is the impedance the mixer sees?
Possibly another good reason for a buffer where you can control the
impedance better.
--
Michigan VHF Corp.
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Reasonable people can disagree. At -12 dB IMD distortion products become audible within the signal itself.?
IMD is one component of the Total Harmonic Distortion spec that we see for our audio equipment. Generally it is accepted that 3% THD is the maximum acceptable for any of the components in the consumer electronics world. In the professional world we want to be below 1%. Above that and the distortion becomes noticeable to the consumer ear.?
3% THD corresponds to -30 dB IMD. 12% IMD is nearly 100 times that amount.?
There is is nothing illegal about putting distorted audio in the air. But I would not do it.?
WA8TOD
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Daniel-
I've been studying and building antenna's for 52 years.. Here's some things I've concluded:
With regard to uBITX (under 300 watts) operation:
#1. The guy that tells you, you need a balun for a dipole, Usually is the guy that is selling them. They can be made for $5 or less. Markup is huge.
#2. You need no better than RG-8X coax... Unless:
?????? A. Your coax run is over 75 feet? and used to 148Mhz. (27ft per dB loss -under 3dB which is 1/2 power) negligible loss.
?????? B. Your coax run is? 150 feet or less? under 30Mhz. (63ft per dB @28.4Mhz- under 3dB or less on lower bands) negligible loss.
?????? C. You are not running over 650 watts (approximate)
#3. There is no "secret sauce" when? buying a manufactured antenna.
?????? A. One manufacture makes antenna's in colors and that is their #1 selling point.
?????? B. Virtually none come assembled, so you have to put them together anyhow and tune them.
?????? C. Markup on materials is 4-10x, so you get a "kit of parts" they put together for you. (and pay for the "secret Sauce"
#4. If you can't afford Antenna books, your local public library will get you any Antenna Book with an Library of Congress number.
????? A. My antenna books stacked on the floor are Knee high.. 20+ years ago I paid $52 for John Krause's Antenna Theory.
????? B. Authors such as Lew McCoy, John Krause, R.L Cibek, Joe Carr, anything sold by ARRL are authoritative. This is a start, there are others.
#5. Regarding coax in #1... Reference QST October 2017 page 72.
#6. Remember? 3dB loss can be measured with instruments but never detected by ear.
#7. An antenna constructed with sound engineering plans will get you on the air.? Having the test equipment/ tuners is optional (OCD frankly)
#8. Watch them bash my sound advice.. Yet some will also agree with me.
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Re: I find This Shorted Circuit on Raduino, here the pics..plz Help?
#ubitx-help
Hello Armin nice to see you!
Ok thank you! I have a little bit wondering about that and the voltmeter test between both pins says that they are shorted circuit..? but then it should be ok when yours look the same.
Have you a picture or vor video from your ubitx and its case with wiring up? I would happy to look at yours.
In an other post i was wrote a large answer text to you but then windows was shutdown to update.. but after this all was delete all i wrote.. it was incredible how bad is this day at all today...
But i write you again next few ours again in the other post from me...?
Till then bye..
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Warren did us a service by showing that IMD on the uBitx is worse than it should be
and where that is coming from.?
I agree it should be fixed.
However,? some IMD and some residual carrier are relatively minor sins
compared to strong harmonics and out-of-band spurs.
Looking at Warren's screen shots, the two highest peaks are 1khz apart,
and in a perfect rig are the only peaks that would be in the display.
We see one fairly strong peak 1khz beyond on each side,? and some lesser peaks
20dB down from those strong unwanted peaks.
As shown, that signal is taking up less bandwidth than an AM phone signal.?
At QRP power levels, some will consider this acceptable.
Warren's screen shots only show as far as the D1,D2 mixer,
not shown is how much worse this gets after going through the power amp.
He has reported that "On 40 meters the best IMD achievable was 12 dB"
That was likely with RV1 gain set quite low, not much power out.
But if those lesser peaks remain 20dB below the strongest unwanted peaks,
then the uBitx likely remains within the acceptable bandwidth of an AM phone signal.
For now, evaluate your rig carefully for splatter, especially if goosing the mike gain.?
Acknowledge reports that your signal is splattering into adjacent channels,
and perhaps report such events to the forum.
Do not use an external high power amp with the uBitx, keep it at 5 or 10 Watts.
We should all find the time to fix the transmit LPF's somehow, perhaps just
adding an external filter in line with the antenna.
Also do the simple 45khz filter fix for spurs once a preferred mod is arrived at.
With that, it appears this rig may be ok wherever AM phone is legal.?
Especially when operating at QRP levels.
Jerry, KE7ER
On Wed, Sep 12, 2018 at 08:59 AM, iz oos wrote:
ndeed it shows some mess on the SSB mode. It is not a K3. I am curious how the MFJ SSB hf transceivers, like the 9420 which have a powerful average power, behave on this respect (IMD). And also how ham transceivers behave with external speech boxes.
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On Wed, Sep 12, 2018 at 07:40 AM, Jerry Gaffke wrote:
Could also add a resistor from mixer port to ground to bring source impedance there down,
though that further reduces drive available to the mixer???
? ? /g/BITX20/message/35206
Hi Jerry, The simple voltage divider you suggest in the linked message could provide a simple solution. No reason that the drive to the mixers needs to be set with a pad, as the Si5351 is not a lab frequency generator. Buffers may still be a good idea, but the divider may get close to the goal. Tom, wb6b
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Published on the IMD thread but wanted to include here for continuity:
?
Here is what I did. I did not try with a second transformer because the results were good enough. After the IMD measurements I would be even more concerned about adding a second transformer because the Q22 emitter follower is operating at an impedance of about 400 ohms and, as such, is one of the major contributors to the IMD issue. Adding a low impedance transformer to this source is likely to make that problem worse. But I have not tested it so I cannot be sure.
WA8TOD
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WHOOPS!!!! Forgot a critical component. You need a capacitor in the low impedance output of the transformer. WA8TOD 
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Joel Here is what I did. I did not try with a second transformer because the results were good enough. After the IMD measurements I would be even more concerned about adding a second transformer because the Q22 emitter follower is operating at an impedance of about 400 ohms and, as such, is one of the major contributors to the IMD issue. Adding a low impedance transformer to this source is likely to make that problem worse. But I have not tested it so I cannot be sure. WA8TOD 
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Jeff et al:
There are multiple proposed fixes for the multitude of issues. For
example, for the harmonics on CW I have redesigned the filters so
that the existing artwork can be used. Others have added external
filter boards. Both work. The spur issue is still a works in
progress.
My suggestion to anyone that is not skilled enough to do the
design and testing themselves is to wait. Enjoy your uBitx and in
a few months clear solutions should arise, and HFSignals will
probably make the appropriate modifications. Then you can decide
if you want to tackle the upgrade yourself or get another uBitx
with all the fixes.
Howard
On 9/12/2018 11:23 AM, Jeff Omundson wrote:
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I have been following the work everyone is putting in to solve the
various issues with the ubitx.? The threads addressing the
harmonic and spur issues are getting really long and trying to get
a handle on it can be tough, especially for those of us who are
not seasoned electronic wizards.? Is there enough consensus on
working solutions so that we could write something up for each
problem on the wiki?? It seems like solutions are still evolving,
so may be this would need to be updated over time.? It sounds like
the spur issue might have a fix at this point.? For the harmonic
issue,? I know some people propose building separate boards.? I
think another solution was to cut traces to the existing filters
and re-wire them.? I don't know if I am the only one grappling a
bit with understanding the best course of action.??
-Jeff
AG7NW
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Indeed it shows some mess on the SSB mode. It is not a K3. I am curious how the MFJ SSB hf transceivers, like the 9420 which have a powerful average power, behave on this respect (IMD). And also how ham transceivers behave with external speech boxes.
Il 12/set/2018 17:37, "Gordon Gibby" < ggibby@...> ha scritto:
Very helpful information, thank you! ?
On Sep 12, 2018, at 11:00, Warren Allgyer < allgyer@...> wrote:
The generally accepted limit for SSB intermodulation products is a minimum of 24 dB between the lowest of the twin tones and the highest of either the third order (products immediately adjacent to the twin tones) or fifth order (products next over above
and below the third order) products. My uBitx shows -12 dB at 3.6 MHz. Conditions are: 30 mVrms audio input and RV1 set for 5 watts RF output through a 4 MHz LPF. My board has the onboard PA filters removed and strapped and has the additional 45 MHz filter
with 12:1 output impedance transformer in place of R27.
In order to better understand where the IMD is being introduced in the radio I started all the way back at the balanced modulator output and measured IMD at thoughtfully provided test points up through the driver output. In general, once IMD products are
introduced at early stages they tend to only get worse as the signal progresses down the chain. The key to fixing it is finding the root cause as early in the process as possible.
TP17 is the output of the balanced modulator and the 12 MHz SSB filter. IMD products here were below the noise floor of my measurement configuration and I did not chase them down into the mud because they are at least 40 dB down and do not pop up through the
floor.
TP16 is the output of the first bi-directional amplifier and IMD at this point measured -35 dB, already much too high and and indication of non-linearity in the amplifier that must be addressed.
TP14 is the output of the onboard 45 MHz filter following the 2nd mixer. This actually shows a slight improvement but probably within measurement error at -37 dB. This measurement pretty much exonerates the 2nd mixer as a significant contributor to the IMD
issue.
TP16 is the output of the second bi-directional amp and again there is a serious deterioration in IMD with the amp adding 11 dB to the problem.
TP1 is the output of the 2nd transmit mixer (labelled 1st mixer in the text) and is the first time we see a signal at air frequency of 3.6 MHz. The mixer added 5 dB of IMD to the total.... much too much and probably indicative of low injection levels as has
been stated in the past. On the other hand it is not the primary culprit by far.
TP3 is the output of the first pre-driver and of RV1 and it adds a little over 1 dB of IMD. The total IMD at this point is 5 dB less than the acceptable amount and it is only beyond this point that we are able to control power levels with RV1 which would normally
be the adjustment point for controlling PA IMD. In other words we are starting out with an unacceptable signal from the low level stages and only now getting to where IMD is normally introduced. A contemporary radio would show normally show IMD levels at -45
dB or better at this point.
From this point forward, at the five watt level, the combination of pre driver, driver, and PA added 5 dB of IMD. This amount would be perfectly acceptable in most radios starting out with clean drive and would allow the total power to be? increased by RV1
adjustment to significantly higher levels.
The IMD problem is rooted first in non-linearities in both bi-directional amps and then in both mixers.
WA8TOD
<Screen Shot 2018_09_12 at 10.57.54 AM.png>
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Re: Right-sided relay harmonic attempted fix for v3/4 ubitx
All of the recent orders of 25 boards have now been mailed. If I do this again I¡¯ll be a little smarter, and list them as order of one, or order of ?pair of 2; ?I was able to find enough dollar bills to help out the people who bought more than one with
a bit of a refund, but that was a pain.
I improved the inside paper to have a repeat of some of the important information, links, etc
I¡¯ll mark them on eBay as shipped soon. ?I got to see the special stamp as mentioned by Kees I think
On Sep 11, 2018, at 16:28, Gordon Gibby < ggibby@...> wrote:
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Well... now ALL of them are sold.? ?Glad I counted them this morning in the car and they seem to all BE THERE.? ?I'll work on envelopes tomorrow morning and hopefully get them ALL in the mail.? ?
Then maybe order some more.
As folks BUILD this little mod, can you indicate how you installed it,? what the problems or tricks you discovered?? ? i sure hope people can figure out how to do it --- be sure to use the correct relay because these relays DO SEEM TO BE POLARIZED --- Maybe
pay some attention that your relays actuall do work when installed!? ?If you flip a relay to the other side of the board --- YOU CHANGED THE ORIENTATION of the voltage applied to the coil --- and as I discovered the hard way, doing it incorrectly means they
won't operate!? ??
Cheers,
gordon
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Putting them on the Raduino would allow an easy way to upgrade a current radio.
Though the additional signal and ground currents across the Raduino-to-uBitx connector?
might give more trouble than having the buffers on the main board.
If we had coax and SMA connectors between the two boards then buffers on the
Raduino should be fine, but that's significant trouble and expense for a uBitx.
So to answer your question:? I don't know.
To which I will add the weasel words:? Depends on how it gets implemented.
Warren just reported that the? mixer at D1,D2 was adding 5 dB to the IMD problem,
a buffer on clk2 might help some there.? But IF amp non-linearities were?
most of the IMD problem.? ? Makes sense that the D1,D2 mixer would have more trouble
than D3,D4 since the signal is bigger there after the second BiDi amp.?
As I recall, Allison found buffers on the clocks helped reduce the residual carrier
when transmitting, though some of the residual carrier was due to placement and routing.
So adding buffers to the clocks may help somewhat, but is no panacea.
As Allison has said, fixing these problems completely will require changes throughout the radio.
Perhaps buffers on the clocks, plus BiDi amp transistors with higher Ft?
Leave any additional power amp stage (for flat power out) and dealing with layout issues for v5.
Jerry, KE7ER
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On Wed, Sep 12, 2018 at 07:52 AM, Kees T wrote:
Would you suggest mounting those three 74LVC1G04GW parts on the Raduino board, close to the Si5351? ?
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Joel Caulkins/N6ALT
sdr freak