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Current v5 ubitx fixes adequate? Is there a thread about v4 fixes?

Tech Guy
 

Is there a place that lists v4 fixes for improved compliance?

Curt
 

V3 and v4 need reduced leakage through LPF relays. Either add a pc board hosting added relays or switch the relays to axicom. Our club kitted a relay board designed by Gordon Gibby, but no one is yet selling it.

That leaves spurs associated with the mixer from 45 MHz to RF. Shielded inductors said to help, and additional 45 MHz filtering. This issue impacts 21 MHz and higher only.

No clear consensus nor kitting on these.

Curt

 

Either add a pc board hosting added relays or switch the relays to axicom.

Or do Allison's relay mod as described in the wiki.  No need to buy new parts if you don't want to.  Also the Axicom swap relies on the relay having better specifications (which may change with production or if you end up with conterfeit parts) while Allison's mod relies on better isolation of the signal paths and a better switching scheme (like you get with the v5 and probably like is done in the accessory relay board).

73,


Mark.

Evan Hand
 

Tech Guy,

Here is a link to the issues as per the designer Ashhar Farhan:
https://groups.io/g/BITX20/topic/spurs_harmonics_whew/28982939?p=Created,,,20,1,0,0::recentpostdate%2Fsticky,,,20,2,0,28982939

I am still trying to find the thread that Ashhar presented the attached hand sketch for the Spurs fixes: (Note: there are some discrepancies in the text vs the schematic)

The longest thread also delves into the issues of how to measure the emissions without spending >$800 for test equipment.
https://groups.io/g/BITX20/topic/29340928#64194

Lastly, I would look at the differences between the v5 and v4 board for the transmitter circuits to see what was done.  As mentioned by Curt and Mark, the best solution for the harmonics is to either add a daughter board for the LPFs, or cut and rewire the traces on the board to reduce the blow back.  This will not address the spurs above 14mhz, that was only solved by the LPF between the IF and the final mixer (going from audio to PA).  The v5 board also changed the 2n3904 out for that IF stage to BFR93Ws to overcome low gain at 90mhz.

Of note is that the entire spurs and harmonic issues came about by an effort to make the output consistent across all of the bands.  It was during that effort that showed that there was a potential issue.

As far as I know the answer to your question is that there are multiple lists, including one at ubitx.net.  For me, I have reached the conclusion that you will need test equipment that can measure the 2 known issues of spurs and harmonics to verify that the v3 and v4 boards are clean enough to feed into a linear amp, but are probably low enough to not be an issue running bare foot on 12 vdc power to the PA.  This is of course for the US.  For most of the rest of the world, the board as supplied meets their requirements.

Truthfully, the lessons learned has been the most fun of the v4 board fix.  Since I have gotten the v5 board, have not really used it, as I am not really that much into operating, more into the technical solves.

FWIW, Above are my observations and opinions, others may be different.  Please do your own research before you make any choices based on them.  The search function on the board are hard to use (at least for me), however there is information here that is worth the digging.

73
Evan
AC9TU

Don - KM4UDX
 

As you can see this is a very personality driven affair.  Three radio engineers will always have four opinions, all mutually exclusive. Hahah.

My view: operate as is with firm control on drive levels.  The Spurs/harmonic concerns are overdone.  Operator awareness and skill swamp any technical limitations.  Spend time on antenna optimization of anything else that floats your boat.  


When I discovered PSK, i couldn't get enough of chatting with other radio fans.  It was so much fun.  But.  Every other day you would see a PSK signal with echos, Spurs, shoulders, muck and more.   The unfortunate artifacts seem to be attributable to operators, not their gear. 

Work in the V4 board if that floats your boat. But don't be dogged by a fear of US standards compliance.  That issue is largely a red herring.

I might be saying that because I'm not talented enough to do the mods, however. Hahahah.

Don
Km4udx

ajparent1/KB1GMX
 

Its not personality it is a measured thing nor a red herring.  

The question is V5 fixed,  it has the relay fix and generally seems a bit better
with more of them seemingly behaving better with IF fixes.

V4 only fixed the audio amp supplier issues and helped some with pop on tx/rx.

And there are likely many threads on V4 .

Allison

Gordon Gibby
 

The QST report suggested that the version five was just within specs 

My measurements for the daughterboard have already been published here and it was way way way within specs—version 3. 

Anybody is free to take the Gerbers and produce a kit with those.  Or just sell the boards!  I’ll be happy to give you all the rights  you need. If anybody is willing to do it, I would probably be willing to even re-design it to use the cheaper relays that have the opposite polarity coil.   If a few bucks matters anyway.

The external relay board will not fix the spurs of course, but it sure destroys the harmonics.  And most of my operating is on the lower bands anyway. 

Fascinating little rig, I will be buying one of the version five soon, i used my version three in our fantastically successful extra class course just recently and for the first time people got to see every signal inside of a superheterodyne receiver 

When I spun the VFO back-and-forth they finally begin to understand how tuning occurs on a receiver— watching the signal on the spectrum analyzer. 





On Aug 25, 2019, at 20:36, ajparent1/KB1GMX <kb1gmx@...> wrote:

Its not personality it is a measured thing nor a red herring.  

The question is V5 fixed,  it has the relay fix and generally seems a bit better
with more of them seemingly behaving better with IF fixes.

V4 only fixed the audio amp supplier issues and helped some with pop on tx/rx.

And there are likely many threads on V4 .

Allison

Curt
 

Don

wow 3 radio engineers having 4 opinions - I hope I am not the one with 2 opinions (at least my boss considers me a RF engineer).  our local club has built and tested several dozen v4 rigs - all have significant harmonic and spurious issues as first assembled.  mine is nearly 20 dB out of compliance on one of the bands.  its not a small deal, even at QRP to be this far off.  using Gordon's board my unit is now compliant on harmonics - meaning its okay for CW on all bands, and SSB up through 18 MHz.  while not the only way to fix this, it requires the least surgery in my view.  (I tried to convince at least one merchant to kit Gordon's board - as if many v4 owners in North America are concerned with harmonics it should sell enough to fund a trip to Dayton!  of course don't overly trust my economic forecasting!). 

I still have work to do on the spurious resulting from mixing -- particularly bad on 12m.  I tried adding another 45 MHz crystal filter after amplifier - and found it wrecked 40 and 80 meter CW operation.  my only theory is it is due to stray leakage related to the inductors on the existing 45 MHz crystal filter - at least to the extent that reports of shielded inductors are improving the situation. 

explaining things a bit - there is sometimes more than one solution to something, and one may emphasize sometimes the simple solution or the more effective solution.  RF design requires a healthy mix of theory and experiment - and do appreciate the fine practitioners world-wide on this list. 

I am skeptical that the ARRL lab did not know to look for the high frequency mixer spurious - no hints in the report and other inaccuracies showing limited familiarity with the body of ubitx knowledge reported here. 

enjoy your radiations, and may they be pretty clean.

Curt

Gordon Gibby
 

Ok.  Pretty amazing here.  

Let’s see how many people would be interested in a board or a kit for the daughterboard relay solution


I might be able to pull something off.
The boards are cheap, probably something like a dollar or two each ; the kit would be a little different issue, the relays  were not terribly cheap. And if I have to do this, I’m not going to re-design it —-just going to use the original design.   shipping would have to be on top, and I’m not making any money at this.    I don’t have hours  an hours to pour into this. 

So if you are interested in either the board or a kit, at roughly whatever my costs are,
Email me at

Docvacuumtubes    At.    Gmail.com

With BOARD
or KIT 

as the subject


I’ll give it a week, let the emails build up in my inbox , then search for each word & count up how many there were, and decide if I’m willing to fool with it.    If it looks like something I could do, I can count up what my costs would be and see if people are really interested by return email. 







On Aug 26, 2019, at 20:44, Curt via Groups.Io <wb8yyy@...> wrote:

Don

wow 3 radio engineers having 4 opinions - I hope I am not the one with 2 opinions (at least my boss considers me a RF engineer).  our local club has built and tested several dozen v4 rigs - all have significant harmonic and spurious issues as first assembled.  mine is nearly 20 dB out of compliance on one of the bands.  its not a small deal, even at QRP to be this far off.  using Gordon's board my unit is now compliant on harmonics - meaning its okay for CW on all bands, and SSB up through 18 MHz.  while not the only way to fix this, it requires the least surgery in my view.  (I tried to convince at least one merchant to kit Gordon's board - as if many v4 owners in North America are concerned with harmonics it should sell enough to fund a trip to Dayton!  of course don't overly trust my economic forecasting!). 

I still have work to do on the spurious resulting from mixing -- particularly bad on 12m.  I tried adding another 45 MHz crystal filter after amplifier - and found it wrecked 40 and 80 meter CW operation.  my only theory is it is due to stray leakage related to the inductors on the existing 45 MHz crystal filter - at least to the extent that reports of shielded inductors are improving the situation. 

explaining things a bit - there is sometimes more than one solution to something, and one may emphasize sometimes the simple solution or the more effective solution.  RF design requires a healthy mix of theory and experiment - and do appreciate the fine practitioners world-wide on this list. 

I am skeptical that the ARRL lab did not know to look for the high frequency mixer spurious - no hints in the report and other inaccuracies showing limited familiarity with the body of ubitx knowledge reported here. 

enjoy your radiations, and may they be pretty clean.

Curt

Don - KM4UDX
 

Curt, all points taken and well said.   I'm slinking back to my marginally compliant operation. 

One, of several, reasons I like this hobby is mixing it up with folks who really know their stuff.  I've learned more than I thought I could by reading and re-reading all the posts from all RF engineers here.  As a humble liberal arts major, it is with great humility that I walk the uBITX halls. 

Thanks millions for all the pointers.  

Don
Km4udx

iz oos
 

Regarding the spurs in ver3 and 4 I found that the solution by Farhan helped. If it not enough, for the 10m SSB (there is no spur issue for CW) an external high pass (corner frequency at say 27Mhz) filter should work 100%. There is a residual fixed spur at 12Mhz when you speak, I found it very low in my unit, however I look forward to receiving my Antuino :) to check it more thoroughly.


Il 27/ago/2019 15:45, "Don - KM4UDX" <dontAy155@...> ha scritto:
Curt, all points taken and well said.   I'm slinking back to my marginally compliant operation. 

One, of several, reasons I like this hobby is mixing it up with folks who really know their stuff.  I've learned more than I thought I could by reading and re-reading all the posts from all RF engineers here.  As a humble liberal arts major, it is with great humility that I walk the uBITX halls. 

Thanks millions for all the pointers.  

Don
Km4udx


walt hodges
 

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