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I would recommend putting the voltage regulator in the supply line to the TDA2822.? I did that before applying power to my kit and have not had a problem since then.? I have very high volume levels if I need them.? The TDA2822 is a good amp when supplied this way. I have also put a mod in to minimize the click and pop produced between transmitting and receiving, and an AGC circuit with RF gain attenuation control that has been a great help.? To my ears the receiver is very acceptable now.??
73, Dan, W2DLC

Here is the link to that regulator mod:
/g/BITX20/message/44099

Tom,

Go back and read what I've posted.? Any load that creates a current flow increases the crosstalk.
Using a CMOS buffer with minimal capacitive loading to the 5351 as we want NO current flow.

Actual testing with 50, 100, 240 ohms all proved it got better but 1k and higher was much better.

Allison

Great find!? That information is not in the most recent datasheet.? Current limited output buffers would explain a lot.? However, having a low Rload with current limited outputs would mean slower edge rates on the output clocks.

I knew that the output drivers could be programmed to 2, 4, 6, or 8mA (which oddly is in an app note, not the datasheet), but the latter 2 settings are inconsistent with the current data sheet's claim of an Ioddx max of 5.6mA per output buffer.? I'm not sure what to make of that...

The good news is that the current limited buffers makes excessive ground bounce from power starvation unlikely.? So Allison's test results may, indeed, be valid.?

73,

Carl, K0MWC

I would try any of the mobile whip antennas mounted to the balcony railing and use a quarter wave wire spiral wound on a 4'X4' wooden or PVC frame as the counterpoise.? Just notch the frame to wind the wire in a spiral from center out to the end of the arms.? You could wind one for the lowest band with jumpers at the quarter wave length for higher bands, just open the jumper to go to a higher band.? The mobile whip can be a single band or a multi-band, just change the counterpoise to match the frequency.
I have used this kind of counterpoise in mobile installations to get a good match with the shortened antennas involved.

Allison,

I agree with everything you have said here.

I really don't have anything new to offer at this time. I've moved on
to other, more pressing projects. Perhaps I'll get back to the ubitx as
the weather gets colder and the yard needs less work.

tim ab0wr

On Fri, 07 Sep 2018 10:58:54 -0700
"ajparent1/KB1GMX" <kb1gmx@...> wrote:

Tim,

Known problems:
Amplifier power vs frequency.
IMD extremely poor for power over 2W
Output Low pass filters.
Spurs, unwanted and unfiltered mix products that show above 20mhz.
Carrier leakage that is not related to modulator or 12mhz filter.

I was the first to try adding an mmic after Q90 to

help with making output more constant if you remember. Because of
physical limitations all I could get it to do was cause an oscillation
that destroyed the IRF510.<<

Both Jerry and I tried that.... instability was rife. I used my HP
current limited power supply didn't fry things.

FYI the IMD issue is related to the first item on the list.? The amp
is struggling to work because of poor choice of transistors for most
of the stages before the finals. Put decently capable parts with
reasonable bias elements and you get a significant improvement.

Do offer what you have as its part of a total set of things that need
attention. However fixing it tends to be for the brave as things like
cutting traces, rewinding coils, are needed.

Hope that helps.

Allison

Yep! That's the whole point of a single point ground! Run the negative
lead from the radio to the battery!

tim ab0wr

On Fri, 7 Sep 2018 12:44:35 -0700
"iz oos" <and2oosiz2@...> wrote:

Ok Tim, in that case the chassis of your rig is not connected to the
chassis of the car. If bonded to the chassis of the rig and the
negative of the battery one would create a ground loop. I think you
connected directly the chassis of your radio to the negative of your
battery with a wire of at least the same size of the 'red' cable.

Il 07/set/2018 20:49, "Tim Gorman" <tgorman2@...> ha scritto:

Respectfully, having fought noise problems in several different cars
and trucks, dependence on the dash to provide a ground or even
depending on the floor pan of the vehicle is a good way to introduce
noise into the rig. Not all body parts are properly connected
together and then connected to the battery and physical stress
during car movement can cause noise generation because of high
resistance grounds. Similar to single point grounds in places like
telephone switches or power substations, a negative lead from the
radio directly to the battery has always worked best for me.

tim ab0wr

On Fri, 7 Sep 2018 09:40:13 -0700
"iz oos" <and2oosiz2@...> wrote:

Ok. Think to an audio amplifier in a car. Often you need just the
red wire to turn it on. When the metal case of the amplifier is
connected to the chassis of the car which in turn is connected to
the negative of the battery (please correct me if I am wrong, I
think it is correct). If you add another ground wire (the black
in our example) is a nuisance that may make a ground loop. The
same applies in the uBitx, if the case is all metal some wires
are nuisances that may lead to ground loop issues.

when use metal case then jack sleeves have ground at case an
yellow wire isn't need any more and use thick black ground wire
and and and..then big written 'be aware of ground loop

Il 07/set/2018 17:50, "iz oos" <and2oosiz2@...> ha scritto:

Not in Germany but not that far away, I have qsos on VHF with
German stations only during contests with big big stations like
DR9A... I mostly use qrp and minimal equipment on higher bands as
well. Not every time an increase of noise level is due to ground
loops. But it happened to me I solved noise issue using for
instance isolating audio transformers between the rig and
external accessories and especially PC soundcards. My case is all
metal except for the front and the back panels so it is surely
different from yours. I didn't notice annoying noise that could
be due to ground loops. All installations are different. Ground
loops may become a problem when too many things are connected
together and are not bond together to a common ground point. I am
not an expert on this, read the ARRL or equivalent handbooks that
treat this topic.

Il 07/set/2018 16:36, "sdr freak" <sdrfreak55@...> ha
scritto:

ok thank you!

would you life in germany, too? if yes, we should try to
transmit with the vhf radio when you want it too?

ok by the way, in your post you mean the increased noise is a
sign of ground loops.. ok something new i have learned by
this.. very thankfully about these kind of knowledge!

when the ground loops you say, isn't the problem in ubitx by
wire up the v1.9 shematic in a metal/aluminum case without
extra ground cable to the case and less cable for the sleeves,
how i should i understand the words in shematic v1.9 which says
the things that makes me crazy.. there is written when use
metal case then jack sleeves have ground at case an yellow wire
isn't need any more and use thick black ground wire and and
and..then big written 'be aware of ground loops'...

this is the problem i doesn't understand and how have you make
your project by this, by the using of or not using these whole
points sayes in shematic v1.9? you dont have a metal box only
front is metal ?

hm here again the shematic v1.9 which i have to understand..
/g/BITX20/photo/49276/0/uBITX_wireup_v1.9.
png?p=Name,,,20,1,0,0



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Here is a slightly older revision of the Si5351 data sheet before some marketing person possibly demanded that the data sheet had too much technical gibberish and scary numbers in it, and that needed to be fixed.?



The output drivers are current limited with programmable levels of 2, 4, 6, and 8 MA.

Also, the spec sheet claims the DC output impedance is 85 ohms when the 8MA drive is selected. Maybe they think that is close enough to the 50 ohm transmission line they use in the examples that it provides a source side impedance match. In moving data across transmission lines, ribbon cable, twisted pairs and such (usually more like 100+ ohms) you only need to match the source with a series "termination" resistor or the load with a parallel terminating resistor.?

Tom, wb6b

Richard

I would see what HF antennas might fit on or next to your largest window. A dipole with ends bent, or a moxon come to mind. Try to google high rise indoor antennas for ideas. You will be limited to the direction of your window, but your antenna would be much higher than most of us. If you don't have blockage from another large building you might have a decent circumstance.

Curt

Daniel

Great questions, a ham license is an opportunity to keep learning. Good answers here.

Best to get 50 ohm coax, but as others suggest 75 ohms will work. I have never used a balun on a dipole. You can make a center support from a scrap of PVC, as strain relief between coax and the wires is vital.

A dipole interacts with the ground and everything else around, so cutting it for 468 divided by frequency in MHz provides total length in feet, but almost always needs some adjusting. Make wire a few feet longer, and wrap the extra back around to shorten it. You will need a swr meter to adjust this, see what you can find or borrow from a nearby ham.

Be patient with the low power bitx but you can make contacts.

73 Curt

Daniel

Great questions, a ham license is an opportunity to keep learning. Good answers here.

Best to get 50 ohm coax, but as others suggest 75 ohms will work. I have never used a balun on a dipole. You can make a center support from a scrap of PVC, as strain relief between coax and the wires is vital.

A dipole interacts with the ground and everything else around, so cutting it for 468 divided by frequency in MHz provides total length in feet, but almost always needs some adjusting. Make wire a few feet longer, and wrap the extra back around to shorten it. You will need a swr meter to adjust this, see what you can find or borrow from a nearby ham.

Be patient with the low power bitx but you can make contacts.

73 Curt

On the assumption that leads to a buffer board out of the Si5351 outputs being a good idea, I drafted one up that fits onto the uBITX board as shown.? Requires 3 track cuts on the uBITX, pcb is fitted using existing thru holes for the ground points and short links to the input and output sides.
Buffer chips 74LVC1G04GW. Board is tiny and parts are also, so not for everybody.

Dan, for QRP work, a balun is not that necessary. A balun helps
greatly in reducing common-mode current that can be created on your
feedline as a result of feeding a balanced antenna (dipole) with an
unbalanced line (coax) or from other factors such as uneven dipole leg
lengths, proximity of the antenna to metal objects in the environment,
etc. If you would be connecting a transceiver with 100w output to the
antenna system this common-mode current can become severe enough to
cause "RF bite" burns on your mic, CW key or equipment cabinets,
disruption of computer operations, burglar alarms and other equipment
in your home, etc.; below 10w this is much less of a problem. You can
build or buy a 1:1 balun to connect dipoles to 50-ohm coax. You can
also create a "common-mode choke" for no money which reduces
common-mode current the same way a balun will, by winding a portion of
your coax feedline into an even coil; there is tons of info on
"common-mode chokes" if you Google that.

-- Rich WB2GXM<div id="DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2"><br />
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Hi,

Welcome to ham radio and the microBitX. Much of what the others have told you is spot on. I only want to point out that a dipoles is close to 75 Ohms when it is high above ground in terms of wavelength. That is easy to do for the higher frequencies. We can almost reach those standing on the ground. Even then it may not be exactly 75 Ohms.

If you have everything specified at 50 Ohms - radio, coax, antenna and then somethings turns out to be actually 49 or 51 Ohms it will not matter. With a chunk of 75 Ohm coax mixed in there some part of the system is going see about 1.5 to 1 - SWRatio. That really is inconsequential. How much of that can be tolerated varies a lot according to how much the various parts of the system can tolerate. Probably 2 or 3 to 1 is still usable. Been there - done that. If the manufacturer specifies 50.00000 Ohms and 50.000001 Ohms will fry the radio and 49.999999 will make it shut then get exactly 50.000000 Ohms. Better yet - get a different radio :)

Getting the best SWR by pruning the antenna is crude and not technically the best way to set up your antenna. Doing it a better way is for some later time. Meanwhile, Get on the air and get your feet wet - the crude way will get you most of the way there:)

See you on the air.

73,

Bill KU8H

--
bark less - wag more

FWIW, I have often used good quality and inexpensive rg6. If you want, you can even use a pre-made 50 or 100 ft length, and then buy some pl259 to F or bnc to F adapters. Although maybe? not 100% matched (75 ohm cable) , the system has worked well for me at HF with 100W, and feeds a dipole just fine. Just make sure you get outdoor rated quality cable.

Welcome to the hobby
73
Brent

Hello Brent...

I'm thinking about the same approach, using the QRPLabs LPFs. I'm only interested in 40/30/20/17 for now so I bought LPFs for those bands along with the relay board. I have them all assembled now and am looking at how to select them. It looks like a fairly simple code change...I'm looking into the wiring now.

Of course it dawned on me after the fact that I could probably do like you suggest and get full coverage from only four filters. It seems to me like that would work. Oh well...

BTW, the relay board uses jumpers to configure it so you can set it up to not keep the first relay in the circuit.

73... Mark AA7TA

Indeed, this does show that the attenuation pads used between the Si5351 and the various transformers at the mixers on the uBitx have too small a load resistance for the Si5351 clock outputs.

Note that when Hans used the Si5351 in his QCX transceiver, he did not drive resistor networks with the Si5351 clock outputs but rather used 50-ohm micro-strip lines on the PCB to drive into the high impedance inputs of other IC's.? Farhan did not take this approach in the uBitx.? My suggestion would be to place op-amps between the Si5351 outputs and the mixer transformers to prevent overloading the Si5351 clock outputs.?

73,?

Carl,? K0MWC

Thanks Jerry

I was thinking of taking Allison's advice and either using the existing parts on a new board, or getting the qrp-labs kits and relay board, and use 60m low pass for 80/60, 30 m for 40/30, 17m for 20/17, and 10m for 12/10. I think this should work, since the even harmonics are already fairly well attenuated, but I'm open to the advice of others. I see the qrp-labs board keeps the 10 meter filter always in line, so it would be simple to change the code so you were only toggling 1 bit at a time.
I have the 45 mhz filters on order, so between that and a better LPF layout, we maybe have a workable solution
Suggestions more than welcome

Brent

Thank you very much, sir. You just made my day now that you said this.?

I rolled the dice on a pair of filters and received Toyocom 45E1A9Fs which show up here as two pole filters at 1200 ohm termination impedance. If I parallel those will I bring that impedance down to 600 and should that be a goal? Should I try both in parallel? I do have a modest spectrum analyzer to take a look at the results with.

John
KC9OJV