Date   

Re: uBITX v5 TX IMD measurements #ubitx #v5 #two-tone

Gordon Gibby <ggibby@...>
 

Thank you so much for making those measurements!   Better than I would’ve expected and your power output data is also very interesting, I’ll have to save up for a version five.  




On Aug 4, 2019, at 00:00, Doug Hall <k4dsp.doug@...> wrote:

On Sat, Aug 3, 2019 at 08:34 PM, Ashhar Farhan wrote:
Much appreciate the measurements. What is your measurement setup?
 
I used my laptop and the Audacity application to generate the 700/1900 Hz two-tone signal. This was fed from the laptop audio output through a variable attenuator with a 10-turn pot.  This feeds the mic jack and prevents overdriving the uBITX mic amplifier. The uBITX RF output goes to a dummy load with a 60 dB attenuator output. The attenuated output goes to a Rigol DSA-815 spectrum analyzer, and that is used for the IMD measurements.

The uBITX has been a very enjoyable project.

73,
Doug K4DSP


Re: Audio isolation w/ digital modes #ubitx

Gordon Gibby <ggibby@...>
 

Sure.  Take a look at public schematics and you’ll often see a bunch of resistors to cut down the levels


Especially on the input to the transmitter microphone, you are  going to want to have some way to adjust it....




On Aug 4, 2019, at 08:58, Rob French (KC4UPR) <robert@...> wrote:

I'm looking to use my uBITX on digital modes.  So, on the one hand, I should probably just plug the inputs in and go... on the other hand, I've seen plenty of discussion about isolating the audio I/O via transformers, to mitigate digital noise on the lines.  Question:  would 4:1 audio transformers be acceptable for this purpose, instead of 1:1 isolation transformers?  My rationale includes:

(1) On the output... it seems to me that the LM386 output (I have a V5 board) is way too high to be sending straight into a computer soundcard line input.  (I don't actually know this, it just seems right...)  Obviously I can turn the volume down, but what about using the 4:1 transformer, with the "4" on the LM386 side, and the "1" on the computer side?

(2) On the input... I'm thinking here that computer sound card line output would be higher than the mic input for the uBITX.  So in this case again, the "1" would go on the computer side, and the "4" on the uBITX side of the transformer.

Thoughts?  (My real rationale, of course, is that 4:1 transformers are what I actually have on hand...)

Regards,
-Rob


Audio isolation w/ digital modes #ubitx

Rob French (KC4UPR)
 

I'm looking to use my uBITX on digital modes.  So, on the one hand, I should probably just plug the inputs in and go... on the other hand, I've seen plenty of discussion about isolating the audio I/O via transformers, to mitigate digital noise on the lines.  Question:  would 4:1 audio transformers be acceptable for this purpose, instead of 1:1 isolation transformers?  My rationale includes:

(1) On the output... it seems to me that the LM386 output (I have a V5 board) is way too high to be sending straight into a computer soundcard line input.  (I don't actually know this, it just seems right...)  Obviously I can turn the volume down, but what about using the 4:1 transformer, with the "4" on the LM386 side, and the "1" on the computer side?

(2) On the input... I'm thinking here that computer sound card line output would be higher than the mic input for the uBITX.  So in this case again, the "1" would go on the computer side, and the "4" on the uBITX side of the transformer.

Thoughts?  (My real rationale, of course, is that 4:1 transformers are what I actually have on hand...)

Regards,
-Rob


Re: amatureradiokits enclosure question #ubitx-help #ubitx

Ian Reeve
 


Image


Hi Dean, sorry for the delay,I had to find my spare board to photograph for you.the board is unsoldered and without the link but hopefully you can see from my hand drawn diagram that you join the unused pin on the pcb to the one that comes from the connector.  I suggest you place the Jack socket in place and then turn the board over printed circuit side up and make a short link and place the wire in the appropriate hole.you only then need make one solder joint for each.  Good luck with the project and any more questions do get in touch.Best 73. Ian M0IDR


From: BITX20@groups.io <BITX20@groups.io> on behalf of Dean Souleles <dsouleles@...>
Sent: Sunday, August 4, 2019 12:35:05 AM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] amatureradiokits enclosure question #ubitx #ubitx-help
 
Thanks Ian - for a newbie - what did you jump exactly?

Dean
KK4DAS


Re: Cool cheap oscilloscope for troubleshooting

David Wilcox K8WPE
 

Thanks everyone.  Will get a low cost scope and do some looking around in my QRP rigs.  

David J. Wilcox K8WPE’s iPad

On Aug 3, 2019, at 10:16 PM, Tom, wb6b <wb6b@...> wrote:

Hi,

Oddly enough this video by a person who has claims to have little experience using a scope may be of help. Or at least interesting as he is poking around the innards of a CD player to see how it works.

https://youtu.be/7olNiMCz9to?t=255

Tom, wb6b


Re: uBITX - super touchy low end volume #ubitx-help #ubitx

Kobus ZS6CHK
 

Yes it is a log pot. The human ear hear in a log fashion. Using a linear pot one will notice that, on a dvm you wll notice there is a change in voltage as you turn it up and down in a linear way. Now if the change is relative small, the dvm will show it. But your ears will not detect it. That is why for audio applications a log pot is to be used. The change in resistance at the bottom end is quite small. Going to the higher end the resistance change is quite steep. If you are using for example a 10K pot and and the change in audio level is to harsh to your liking, change it out for say a 20K pot. And here is the reason. Most pots have around a 260° turning angle. So  some simple maths.  10K / 260° = 0.385 ohms per degree. 20K / 260° = 0.077. Ok this is based on a linear pot. But the principal is the same for a log pot. But there is more to it to calculate the exact resistance of a log pot per degree. Also bear in mind that as the resistance of the log pot is not linear, connecting the pot the "wrong" way around. (The 2 outer connections) will effect the responce of the middle connection. How to know if the pot is linear or log. Look on the casing of the pot. The resistance of the pot is written on there. 20K for instance. And followed by an A or B. The A is a log pot. The B is for a linear pot.



Sent from my Samsung Galaxy smartphone.

-------- Original message --------
From: "Rob French (KC4UPR)" <robert@...>
Date: 03/08/2019 16:43 (GMT+02:00)
To: BITX20@groups.io
Subject: Re: [BITX20] uBITX - super touchy low end volume #ubitx-help #ubitx

Yeah, I thought about that, but from what I can tell, the stock pot is audio taper.  I measure it at a few points w/ my multimeter and it seemed to fit a log profile. 


Re: Elmer Needed

Dexter N Muir
 

Ask here. In the Ham Radio fraternity there is no such thing as a "dumb question". Here and in any other Internet forum you have answers at your fingertips for recall, and a history you can research (or others can point you to).
p.s. there's not much 'Brit' about a BitX :)
73 de ZL2DEX


Re: uBITX v5 TX IMD measurements #ubitx #v5 #two-tone

Doug Hall
 

On Sat, Aug 3, 2019 at 08:34 PM, Ashhar Farhan wrote:
Much appreciate the measurements. What is your measurement setup?
 
I used my laptop and the Audacity application to generate the 700/1900 Hz two-tone signal. This was fed from the laptop audio output through a variable attenuator with a 10-turn pot.  This feeds the mic jack and prevents overdriving the uBITX mic amplifier. The uBITX RF output goes to a dummy load with a 60 dB attenuator output. The attenuated output goes to a Rigol DSA-815 spectrum analyzer, and that is used for the IMD measurements.

The uBITX has been a very enjoyable project.

73,
Doug K4DSP


Re: uBITX v5 TX IMD measurements #ubitx #v5 #two-tone

Ashhar Farhan
 

Interesting,
Now a days, the TX IMD is the most critical parameter on SSB mode. Consider the best on class IMD (called Splatter by the old timers), it is about -35 dbc. Thus, this is what you will hear on the opposite side band. On the other hand, claiming a -60 db opposite side band suppression is useless : you are subsitituting the other sideband with splatter. 
Now, consider a receiver trying to receive an S 5 level signal adjacent to an S9+10 db signal. However good your receiver is, the splatter of the loud signal is going to ruin your reception.
Much appreciate the measurements. What is your measurement setup?

73, f

On Sun 4 Aug, 2019, 5:04 AM Doug Hall, <k4dsp.doug@...> wrote:
All,

I just finished measuring the two-tone TX IMD on my v5 uBITX. These are 3rd order products, and I measured relative to either tone. Since the ARRL states their measurements relative to PEP I have included that as well, for those who sleep better at night secure in the belief that their radio is clean :-)

This is at 10W PEP using 700 and 1900 Hz tones. My radio puts out 10W from 80 through 20 meters, and falls off to 5W on 10M:

80m -25.5 dBc (-31.5 dB PEP)
60m -22.5 dBc (-28.5 dB PEP)
40m -22.0 dBc (-28.0 dB PEP)
20m -24.5 dBc (-30.5 dB PEP)
17m -21.0 dBc (-27.0 dB PEP)
12m -25.5 dBc (-31.5 dB PEP)
10m -22.0 dBc (-28.0 dB PEP)

As my flight instructor used to say after one of my landings, "I've seen worse, but I've seen a lot better." This is probably not atypical of IRF510s.

Now I'm going to hook up the 'scope and look at the CW waveform.

73,
Doug K4DSP


Re: Elmer Needed

Biju Apkrcl
 

Of course, we will help you


On Sun, 4 Aug 2019, 00:17 , <mtngentleman@...> wrote:
Hi All
I have been following this group for some time and have begun assembling a Britx 40
I am sure I will encounter problems and have questions.
Rather then bother the whole group is there someone with experience I might contact directly?

Tks
Shep AA7MH


Re: Cool cheap oscilloscope for troubleshooting

Tom, wb6b
 

Hi,

Oddly enough this video by a person who has claims to have little experience using a scope may be of help. Or at least interesting as he is poking around the innards of a CD player to see how it works.

https://youtu.be/7olNiMCz9to?t=255

Tom, wb6b


Re: amatureradiokits enclosure question #ubitx-help #ubitx

Dean Souleles
 

Thanks Ian - for a newbie - what did you jump exactly?

Dean
KK4DAS


uBITX v5 TX IMD measurements #ubitx #v5 #two-tone

Doug Hall
 

All,

I just finished measuring the two-tone TX IMD on my v5 uBITX. These are 3rd order products, and I measured relative to either tone. Since the ARRL states their measurements relative to PEP I have included that as well, for those who sleep better at night secure in the belief that their radio is clean :-)

This is at 10W PEP using 700 and 1900 Hz tones. My radio puts out 10W from 80 through 20 meters, and falls off to 5W on 10M:

80m -25.5 dBc (-31.5 dB PEP)
60m -22.5 dBc (-28.5 dB PEP)
40m -22.0 dBc (-28.0 dB PEP)
20m -24.5 dBc (-30.5 dB PEP)
17m -21.0 dBc (-27.0 dB PEP)
12m -25.5 dBc (-31.5 dB PEP)
10m -22.0 dBc (-28.0 dB PEP)

As my flight instructor used to say after one of my landings, "I've seen worse, but I've seen a lot better." This is probably not atypical of IRF510s.

Now I'm going to hook up the 'scope and look at the CW waveform.

73,
Doug K4DSP


Re: uBITX finals get hot very fast #ubitx-help #ubitx #v5

 

Hi Rob,

I don't think anything unusual is happening in your case.  Just making some general observations:

The heatsinks provided are probably good for about 20C/W dissipation; meaning the heatsink temperature will rise 20 degrees C above ambient temperature per W dissipated.

Ambient in these situations (a hot day, no fan, heatsink in enclosed or semi-enclosed area) is best taken at 50C.

At 10W out and the PA 50% efficient, each transistor would have 5W to get rid of on constant keydown or about 2.5W during morse sending.

So that makes 20C/W x 2.5W + 50C  =  100C (burn your finger temperature for sure)

This is a worst case example as ambient is high (you may have better air circulation around the heatsinks and a cooler room), the power may be lower, and the PA may be more efficient.  But it gives you an idea of how hot the heatsinks may get.  With no fan, the stock heatsinks are not good for more than a watt or so if you want the transistor and heatsink to stay at "just warm" temperatures (less than 60C).  And no way would they be good enough for digital without fan help.  Bigger heatsinks will allow for cooler tempertures, or you can run a fan on them as I think many do here.

Remember the transistor tabs need to be insulated from grounding through the heatsinks/housing.

73,


Mark.


Re: uBITX finals get hot very fast #ubitx-help #ubitx #v5

Rob French (KC4UPR)
 

All good questions!  So, I don't have a power meter, but I do have a QRP Labs dummy load that has a diode for rudimentary RF power measurements with a voltmeter.  I'll try with that, which will also help me verify that the PA's heat up similarly with the dummy load.

I'll measure the overall current consumption of the transceiver as well as the PA section.  

However, one thing I've discovered... I'm using an old Micronta 12V power supply (that's what the front panel says).  When I checked the back panel, it says 13.8VDC output on the spec label, and measured, it's actually like 14.4V.  (I'll double-check that under load.)  So I imagine the higher supply voltage could also be contributing? 

I'm going to wire up a couple diodes in series with the power supply to bring the supply voltage down to ~12V, and see how that affects things.  Then I'll look at the PA section.

Thanks!
-Rob


Re: Cool cheap oscilloscope for troubleshooting

JohnR
 

Dave 
I know meny hams that are looking for the same thing. I know that I could benefit from a simple how to use a scope manual or youtube and it would really help in building and tuning circuits. If you ever find it please post so all us non electronic techs can learn to.
73
John kg4vhv

--

“A single light can banish the darkness”

Lux e tenebris 

"A fool stares at the finger that points at the moon"
I Ching




Elmer Needed

mtngentleman@...
 

Hi All
I have been following this group for some time and have begun assembling a Britx 40
I am sure I will encounter problems and have questions.
Rather then bother the whole group is there someone with experience I might contact directly?

Tks
Shep AA7MH


Re: Cool cheap oscilloscope for troubleshooting

Tom, wb6b
 

On Sat, Aug 3, 2019 at 02:01 AM, David Wilcox wrote:
had a slew of attenuators, tees, and other stuff
Hi,

As long as you are sticking to QRP levels (12 wats or less) like the uBITX you should be able to probe the RF circuits with a 10X scope probe. That would be about 35 volts P-P at the output into a 50 ohm dummy load. Probing the PA Mosfets might be iffy. 

I have some generic P6100 (100 Mhz) probes available on eBay and such. The voltage rating (RMS?) rapidly drops from 600VAC to around 30VAC above 1 Mhz.

The scope probe will cause some loading to circuits that could affect them at RF frequencies.

For anything above a Mhz or so you want to always use the scope probe in the 10X mode. In the 1X setting scope probes only have a few Mhz bandwidth, while in the 10X mode the have the rated bandwidth (in this case 100Mhz).

What may seem interesting to some is that scope probes handle frequencies of 100 MHZ or more and they seem to violate all the rules about transmission lines and impedance matching. So how does a scope probe work at 100Mhz when it is not terminated at the impedance of the coax cable that runs from the probe to the input of the scope? The scope probably is terminating the probe cable at 1M ohm, not 50 ohm, for example. 

The secret is the center wire in a scope probe cable is a thin high resistance wire. The resistance of the wire, as it runs through the center of the cable, provides a distributed damping of the reflections that would normally be present in a normal coax cable. It may have been some genius engineer at Tektronix that figured this out. If you measure the scope probe resistance from the probe tip to the center conductor of the BNC connector you will measure 100 ohms or more. So much for scope probe trivia.

As you are just starting out, you may want to begin by trying out the low frequency, low voltage examples you mentioned before venturing off the the RF power stages of your radio. On receive, go for it. Probe the IF stages, mixers, audio, output of the frequency synthesizers, whatever you want. Even at 10X the probe may put enough of a load to detune something, or lower the amplitude of a signal, but most likely it will be fine. You will not be able to accurately measure signals above the frequency capability of the scope.

Tom, wb6b


Re: uBITX finals get hot very fast #ubitx-help #ubitx #v5

Tom, wb6b
 

Hi,

I found when running digital modes, particularly WSPR, that a fan was a necessity. 

Tom, wb6b


Re: uBITX finals get hot very fast #ubitx-help #ubitx #v5

Curt
 

Numerous opinions here, I run my v4 on cw or ssb without updates. I will add a small fan before doing digital modes, whether its needed or not.

Wait until you discover the hot regulator on the raduino. If your PA heatsink is less warm, I suggest things are okay. If it is warmer, then check out bias current, carefully follow instructions.

Curt