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 /> <table style="border-top: 1px solid #D3D4DE;"> <tr> <td style="width: 55px; padding-top: 13px;"><a href=" target="_blank"><img src=" alt="" width="46" height="29" style="width: 46px; height: 29px;" /></a></td> <td style="width: 470px; padding-top: 12px; color: #41424e; font-size: 13px; font-family: Arial, Helvetica, sans-serif; line-height: 18px;">Virus-free. <a href=" target="_blank" style="color: #4453ea;">www.avast.com</a> </td> </tr> </table><a href="#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2" width="1" height="1"></a></div>
On 9/8/18, gonewiththeego@... <gonewiththeego@...> wrote: Oh, thanks! I'm looking for an SWR-meter meanwhile. And about the balun ? Is
it a "MUST HAVE" ?
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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
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On 09/08/2018 03:32 PM, gonewiththeego@... wrote: Oh, thanks! I'm looking for an SWR-meter meanwhile. And about the balun
? Is it a "MUST HAVE" ?
--
bark less - wag more
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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
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Re: Right-sided relay harmonic attempted fix for v3/4 ubitx
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
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On 9/8/18 12:43 PM, Brent Seres/ VE3CUS wrote: 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
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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
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Re: Right-sided relay harmonic attempted fix for v3/4 ubitx
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
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Thank you very much, sir. You just made my day now that you said this.?
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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
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Warren,
>>1) 120 mVrms is far above the audio level that caused unacceptable IMD before the filter mod. IMD must be checked and the audio levels adjusted to make it acceptable.
The problem is the balanced mod easily takes that but the gain after it means the 2nd mixer gets
hit with a very high level.? With that the output of that mixer is high and that leads to the next
mixer getting overloaded.? There is too much gain after the balanced mod.? This is why the
balanced mod needs such a low input.
Allison
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Now that I know how to make one, I like doing that if I¡¯m going to do digital. ? Common mode and unbalanced currents wreck havoc with digital systems.
But for the first 35 years that I was a ham, I didn¡¯t even know what they were. ? Somehow or another I made thousands of contacts and had a ton of ?fun.?
Here are some references that might help you with baluns (there are many good ones)?
Cheers,
Gordon kx4z
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Oh, thanks! I'm looking for an SWR-meter meanwhile. And about the balun ? Is it a "MUST HAVE" ?
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Oh, thanks! I'm looking for an SWR-meter meanwhile. And about the balun ? Is it a "MUST HAVE" ?
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Get an SWR meter. ? old CB types work fine. $15
Most people use 50 ohm coax , but even 75 will work fine.?
Make a dipole, test the swr, adjust as necessary
That¡¯s how many of us started out over the years.
read, read, read, read, and learn, because there are lots of myths that float ?around. ?ARRL ?has good books.
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Hey! I'm Daniel and a few days ago I ordered a uBitx from . I'm quite new to ham radio and I'll appreciate some advices about a suitable antenna for this transceiver. Of course I count for a dipole but I don't actually understand some facts: Shall I need a 1:1 balun or it will easily work without
? Shall I use a 75 ohm coaxial cable or stick to 50 ohm? I know that the impedance of a dipole is close to 73 ohm or so ...? I also do not have any antenna tuner, SWR-meter or antenna analyzer for the moment. Is there any chance to get on air with a properly
dimensioned antenna without these tools? Thanks!
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Actually - that makes a lot of sense Raj b/c the two ends of the filter seem to be capacitively coupled internally according to the spec sheet. It would be great to see the ultimate results of that. Could you share those results?
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I searched for this problem to no avail. So I am posting in case someone has an answer.
I bought a new uBitX, and installed it in the case from Amateurradiokits.in.
Upon powering up the display shows:
uBITX v4.3
LSB A: 7.149.950
If I turn the encoder to change frequency, the display shifts from 7.149.950 to 7.149.900. back and forth as I turn, either CW or CCW.
If I push the encoder, the display shows Band Select >
Turning the encoder does nothing
Push encoder again and I get display showing Band Select:
Turning the encoder now changes display between 7.349.900 and 7.149.900.
If I power off, then back on, sometimes the frequencies shown in the display are a little bit different (some times when in band select, the display will change from 7.149.900 to 6.949.900, or similar).
With an antenna attached I can hear signals from the speaker (noise, occasionally someone¡¯s transmission). So I know the receiver works. If I push the PTT the relays click. I assume transmitter works too.
I thought I had a bad encoder, so I bought a new one from Digikey. Same results.
Power supply is 13.27 volts.
Power to raduino is 5 volts.
Someone suggested pin 3 may be shorted to ground causing raduino problems, but I checked and not grounded.
All wiring triple checked (or more).
Any thoughts are appreciated.
Thanks
73
Mark
W3MSR
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Thanks Jerry! ?
On Sep 8, 2018, at 14:02, Jerry Gaffke via Groups.Io < jgaffke@...> wrote:
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Those messing with 45mhz filters might want to revisit the code of post:? ?
That post provides an easy an intuitive way to put your USB or LSB signal into a desired spot in the 45mhz passband.
If there are two 45mhz filters involved, they should be matched.
If that code is puzzling, then check out this post:??
Jerry
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Those messing with 45mhz filters might want to revisit the code of post:? ? /g/BITX20/message/44278That post provides an easy an intuitive way to put your USB or LSB signal into a desired spot in the 45mhz passband. If there are two 45mhz filters involved, they should be matched. If that code is puzzling, then check out this post:?? /g/BITX20/message/44515Jerry
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Unfortunately in the uBitx design all three clocks are feeding impedance is a good bit lower than the maximum one suggested. ?
These outputs are CMOS outputs, are they not?
So they have active device up and active ?device down, and the impedance is constantly changing as one device turns on and the other turns off. ?It¡¯s a digital system made out of analog parts.
So sure, running through a 50 ohm transmission line you would get some reflections, to a higher than 50 ohm load, but the line lengths ?so tiny fractions of a wavelength here that probably doesn¡¯t make that much difference. ??
I¡¯m not familiar with ground bounce, but because of these low impedance loadings, signals are getting coupled ?from one output to the other.
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Allison
Thanks.? You may have just saved me from overloading some of a recent purchase of Si5351a devices.
I too was under the impression that 50 ohms meant 50 ohms, instead of "use a 50 ohm line and a much
higher termination".? That though does raise a question regarding 50 ohm line with significantly higher
impedance termination at the extreme upper frequency limits?? Might this cause higher reflected signal
on that 50 ohm line?? Maybe it doesn't matter?
Arv
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On Sat, Sep 8, 2018 at 10:03 AM RCBoatGuy via Groups.Io <ijnfan-HamRadio= [email protected]> wrote:
Allison,
I'm afraid if you tested the way you described in your original post on this thread, you weren't testing for crosstalk.? I believe what you measured wasn't cross-talk at all, but rather ground bounce due to current starvation of the Si5351 output buffers.
I've attached the Si5351 datasheet.? On page 5, Silicon Labs gives the following specs:
Vddox, output buffer voltage => 3 ranges, 1.8V +/- 0.9V (5%), 2.5V +/- 0.25V (10%), and 3.3V +/- 0.3V (9.09%).? ?The Raduino uses a 3.3V supply for Vddox.
Iddox -? output buffer supply current per output => 2.2mA typical, 5.6mA max
Zo, output impedence @ 3.3V => 50 ohms
Note this is output impedence, which is very misleading.? The spec is not saying to use an output load of 50 ohms (Rload).? It is saying we need to drive thru a 50-ohm impedence to reach the destination Rload.? So we need to calculate the mimimum output load
(Rload) that the output driver can drive.
Rload = Vddox/Iddox = 3.3 / 0.0056 = 589.3 ohms.? This is the minimum load the output can drive, as it gives the maximum allowed output supply current.? Exceed this spec and you enter current starvation on the power supply to the output buffer.
You stated that you used both a 50-ohm load (not impedence) and a 25-ohm load (not impedence) for your cross-talk testing.
With a 50-ohm load, Iddox = V/R = 3.3 / 50 = 66mA, which is more than 10x the maximum allowed output buffer supply current.
With a 25-ohm load, you subjected the part to 132mA Iddox!?
In both cases, the output buffers are so power starved that the chip internally can't supply enough Vddox to control the output buffers.? The result is ground bounce on all the outputs, not cross-talk.? This is typical behavior for digital chip output drivers
whose output specs are violated in such a manner.? It also explains why you didn't see as much signal on the Si5351 outputs as you expected.?
The Zo spec was meant to say that the chip was designed to drive thru a 50-ohm impedence (either a 50-ohm coax or a 50-ohm micro-strip line on a PCB) to its load (Rload), not that you could use a 50-ohm or 25-ohm termination as the Rload.? An example of this
appears on page 22 of the Si5351 datasheet.? Here the datasheet describes using the part to drive 2 clock outputs with 180 degree phase difference, but the example circuit shows driving the Si5341 clock outputs thru a 50-ohm coax to a voltage divider for the
receiving circuit that presents an Rload of 511 ohms + 240 ohms = 751 ohms to each? Si5351 output buffer.? This gives an Iddox = 3.3 / 751 = 4.4mA, well within the 5.6mA max Iddox spec.
I suggest you repeat your cross-talk tests using an appropriate Rload value at the end of a 50-ohm line for each clock output and see how much cross-talk you see.
73,
Carl,? K0MWC
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Warren,
That IMD could be in the IF amps (Too much gain for 2n3904's at 45mhz?? Mixer overload?)
or in the power amp.? If IMD gets worse when RV1 is cranked up, that would suggest it's in the PA.
If it's in the 45mhz IF, the new filter will help but is too wide to clean up the immediately adjacent channels.
Seems it should be straightforward to clean up this IMD on v5, but may take lots of small hacks to?
clean up existing rigs.? Fortunately, at 5 or 10 watts out it seems to not be just too bothersome as
I don't recall any reports of trouble in the forum.? But it should be fixed on v5, and v3,v4
should not be used with an external high powered linear.
Jerry
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On Sat, Sep 8, 2018 at 09:30 AM, Warren Allgyer wrote:
Before the mod the radio showed terrible IMD at any input level higher that about 25 mV and, at that level, the radio produced less than 2 watts. If it turns out the filter is a 'magic bullet' and the radio can actually sustain this level of input with acceptable IMD, then the input audio stages need more gain.
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Brent Seres/ VE3CUS
YO8UFO
George