Topics

Sensitivity, Spare-Parts and Quality Questions #ubitx #v6.1 #ubitx


DC3AX
 

Hi!

A friend of mine asked me to help her getting the ubitx v6.1 running. It was only giving very low audio, even it seems to receive. I checked all solderings and they looked good. I got some audio but a sensitivity of around -57dBm at 14.200MHz SSB @ 12dB SINAD.

It was suspichious that touching the volume knob makes the speaker "humm"... So I re-soldered some through holes around the audio circuit. I have never had such a bad solder in my life... It doesn't flow good with any of my rework solders or flux pastes. And it hadn't flown correctly when produced originally as many solder points have not soldered through the hole in the PCB. It just looked good, but never connected inside the hole. A combination of flux and lead-free solder was just sucked into the hole at many places.

After that, I got a sensitivity of -95dBm... I still had the issue, that the signal drops in and out if I touch the display or wiggle the Radioino board. So I reflowed that board, the connector on the RF boad and then I found out, that the volume knob has a broken lead. So I unmounted it, set 100R for the volume and a short for the power switch. That brings the unit to -116dBm SSB at 12dB SINAD. That is still not, what I expected to find. 

So my questions are:
Does anyone know a part number for the pot and where to order?
Has anyone measured the sensitivity of his unit and as some values to compare for me?
As this unit was one of the early v6.1 PCBs, does anyone have the same quality issues with this unit?

Thanks for any help!

73 de Ulrich DC3AX / AG1U


Gordon Gibby
 

Wow, that’s some great detective work!



On Aug 9, 2020, at 18:27, DC3AX via groups.io <ulrich.prinz@...> wrote:

Hi!

A friend of mine asked me to help her getting the ubitx v6.1 running. It was only giving very low audio, even it seems to receive. I checked all solderings and they looked good. I got some audio but a sensitivity of around -57dBm at 14.200MHz SSB @ 12dB SINAD.

It was suspichious that touching the volume knob makes the speaker "humm"... So I re-soldered some through holes around the audio circuit. I have never had such a bad solder in my life... It doesn't flow good with any of my rework solders or flux pastes. And it hadn't flown correctly when produced originally as many solder points have not soldered through the hole in the PCB. It just looked good, but never connected inside the hole. A combination of flux and lead-free solder was just sucked into the hole at many places.

After that, I got a sensitivity of -95dBm... I still had the issue, that the signal drops in and out if I touch the display or wiggle the Radioino board. So I reflowed that board, the connector on the RF boad and then I found out, that the volume knob has a broken lead. So I unmounted it, set 100R for the volume and a short for the power switch. That brings the unit to -116dBm SSB at 12dB SINAD. That is still not, what I expected to find. 

So my questions are:
Does anyone know a part number for the pot and where to order?
Has anyone measured the sensitivity of his unit and as some values to compare for me?
As this unit was one of the early v6.1 PCBs, does anyone have the same quality issues with this unit?

Thanks for any help!

73 de Ulrich DC3AX / AG1U


 

Ulrich,

the PTH holes are not soldered but plated. Of the many boards tested I never had a bad connection. Only some
bad solders on components.

Raj

It was suspichious that touching the volume knob makes the speaker "humm"... So I re-soldered some through holes around the audio circuit. I have never had such a bad solder in my life... It doesn't flow good with any of my rework solders or flux pastes. And it hadn't flown correctly when produced originally as many solder points have not soldered through the hole in the PCB. It just looked good, but never connected inside the hole. A combination of flux and lead-free solder was just sucked into the hole at many places.


DC3AX
 

Hello Raj,

I know that the through-holes and vias are plated. And the plating is fine, without any problems. But the solder-work was not optimal. On several through-hole mounted components, the solder was only on the bottom side of the through-hole, it had not flown into the hole, through to the other side. 
However, that looks like I repaired most of it.

But I still wonder, if a sensitivity of -116dBm at SINAD 12dB ist all the device can do. I don't think so, but I do not have any comparision. Can anyone tell me more about the sensitivity of the ubitx v6.2 board?

73 de Ulrich 


Curt
 

Ulrich

Nice work. I am thinking like Raj that issues are few on the circuit board, but maybe others have found faulty potentiometers.

Sensitivity is said to be 0.1 uV but no snr is reported, all of us tend to think our ubitx are as sensitive as most HF transceivers at least through 21 MHz, and likely within a couple dB above that. Fine for amateur radio. I am not familiar with v6, but many use headphones or an external active speaker.

The design uses no preamp but is nicely implemented, and it works. I am making stateside and Europe qsos this week on 40m ssb. I hope the op has some fun with it.

73 curt


DC3AX
 

Hey Curt,

thanks for that reference of 0.1µV but it doesn't help with further reference. So it  sounds more like a wish, not reality. An ICOM IC-736 is known to be sensitive and has less then 0.15µV at a SINAD 10dB with Pre-Amp on. The modern IC-7300 has less then 0.16µV, also with Pre-Amp on.

However, I didn't want to talk the ubitx down, I just need some reference to decide, if the unit I have connected to my test-set is now working or still has problems.
 
And I need a source for the volume / power combination. It has a pin broken off, as I told before and I cannot find a mechanical matching substitute for it. Does anyone know a matching part?

73 de Ulrich


Curt
 

Ulrich

the ubitx was certainly designed for the op of humble means, including youth.  perhaps us hobbyists have purchased many of them.  it is an amazing rig overall.  okay we can wonder if 0.1 uV is exaggerated or more likely the designer has excellent hearing (-:  The receiver clearly was designed with dynamic range in mind.  I expect it hears most everything my K2 hears in most bands.  As delivered the principle need is BFO alignment.  

most of our HF receivers from the past several decades likely have similar sensitivity - its other parameters where they separate.  nonetheless I have numerous CW contacts with my ubitx and I am amazed how well it does on SSB (I got fortunate I think in the particular microphone I found in my leftover stash). 

my ubtix v4 was delivered with a potentiometer, but I also purchased an enclosure kit that contained pots and controls.  my unit does not have an of-off switch in the volume control, so I don't recall if the stock volume pot has that feature.  my power switch is a push button in the back - I suggest finding whatever power switch its op will appreciate. 

does the ubitx in your hands have a commercial looking enclosure?  many came from amateurradiokits.in.  Sunil the proprietor would certainly fill you in on the pot, but it might be difficult to source that particular pot in DL. 

okay this list may be biased but the ubitx is a nice radio adventure.  when we have sunspots again, I am imagining lots of folks enjoying it when its their primary rig.  I have plans to set mine up for WSPR reception.  nothing like this anywhere in its price range - but someday watch for the QSX when it emerges (more assembly required). 

73 curt


Curt
 

Ulrich

Okay a more careful read I see you have a recent v6. I imagine an email to hfsignals reporting quality issue may get you a replacement pot, otherwise the value and taper should be listed on the parts list.

Many of us modify our ubitx, is the YL a new ham? Nearby hams might help with parts.

Hoping you will soon be pleased with your work.

73 curt


DC3AX
 

Hey Curt,

it took a while to add the matching volume control into my digikey orders. I simply forgot to add it multiple times. Now it has arrived and I put it into the unit and it works. 

But to correct some misleading statements:
From the issues I had with my board, I do not state that the whole thing is a bad idea or at general bad manufactured. And I know the difference between this hobbyists self build unit and a four digit cash unit from any major brand.
So the question, if someone has some reference values for my measurements was meant neutrally with respect to quality or expectations. As there was at least one defect, I needed that values for getting an idea if there may ne another cold joint or broken part. 
As it shows, there had been several bad solder joints on my version of the v6 and after fixing them I get a stable -119dBm @ 10dB SINAD. So we are on a good way, I guess.

May be I modify the unit by exchanging the oscillator board with something less noisy and replace the AVR by an STM32L4 for having more options on the display. As you wrote, this unit is for being played with.

The YL is a HAM for many many years, but she likes to buy all sorts of radios, every radio that is new and sometimes a radio that is old or rare or just a curiosity.

73 Ulrich