Topics

BFR93w availability in US

barry halterman
 

Any one know of a source in the US for these BFR93W transistors as used in the V5 ubitx?
Thanks
Barry

Paul KL7FLR
 

Curt
 

I am also thinking try everything else first. If and when we establish a best recipe for curing v3 and v4 mixer spurious, maybe some of our merchants in various spots in the world could kit the parts, perhaps. Or maybe you have tried all those? But I see more signal might reduce the spur level when it sneaks in after this amplifier, if is really needed.

Curt

Evan Hand
 

Here is the explanation of the v5 spurs and the v5 solution.  Not that in this thread, Ashhar has not yet gone to the BFR93W devices for the 45 MHz IF.
https://groups.io/g/BITX20/topic/28982939#63695

Interesting background on the problem. 

73
Evan
AC9TU

Curt
 

Evan

I am remembering that the v5 board contains different transistors for the 45 MHz amplifier with a higher Ft (aka higher gain at 45 MHz).  I get it that he worked the spur level in bite sized pieces.  I can't speak too loudly since I have not have time to fix my own v4 in this problem, but sensing the pain of ordering 2 parts is why I suggested to Barry to try everything else first, and that shielding the leakage into the 45 MHz may be a bit more important than this amplifier type.  I haven't looked at the 45 MHz filter on v5 - does it still use toroids? 

I am thinking that implementing all of the v5 fixes on a v4 board will not necessarily - or likely cure its ills.  my conclusion is that it is easier to cure a v4 board if you are willing to sacrifice several watts of CW output -- I decided I could not do that, and I don't need 15 to 10 meter SSB just yet with scarce sunspots.  So I suggest that fixing the harmonics is a higher priority now - and here in the US we do have a supplier selling a kit to do that. 

enjoy your radiations

Curt WB8YYY

Evan Hand
 

Curt,
I agree with your assessment.  The harmonics are the larger issue, and need to be addressed.  Changing to the shielded inductors before and after the 45 MHz crystal worked for some, and is a much easier repair than changing out the 45 MHz if transistors.  

The only issue with the above is that you do need a way to measure the spurs.  The harmonics are easy and can be done with either a separate receiver or a low cost spectrum analyzer (SA).  I have found that measuring the spurs is more difficult, as you need a better RBW (resolution band width) SA to do so effectively. 

(asbestos suit ON)
I would assume that it would be of interest to this group to post a how to verify the issue with minimal equipment.  Having been a retread ham after 31 years away from the hobby, and starting with only a vom and cheap oscilloscope, I can identify with the issues that some might have with testing.  I did not have another receiver to test the uBITX with, and was not a member of a club when I first built the uBITX.  I found out afterwords that there were emission issues.

I have since made part of my hobby to add the more test equipment, however I still do not have what I would call a good spectrum analyzer.  I have tried most of the low cost alternatives that have been listed in this forum (it is fun to test them out and not too expensive to me).  As stated above, I have found them to be great at one type of test or another.  None seem to meet all of the needs to vet out the uBITX.  I have just recently received the Antuino, however have not had the time to go back and redo the spurs testing.

The last point is that I would feel safe with sticking with the low power of the bare uBITX in working SSB on all bands.  The reasoning is that the 10 db of attenuation missing with the spurs is way below a similar rating for a 100+ watt rig.  The risk of interference is small.  I would only use it for CW if one of the low pass filter modes was done, as the harmonics are much higher and in general CW is a lower power mode.  I would not connect the uBITX to a power amp without vetting the signal purity.

As always, the above are my observations and opinions.  You will need to verify for yourself.
73
Evan
AC9TU

Sudanthiram N
 

Dear ,
I purchased 10nos in AliExpress com for my ubitx v4, and installed .it works well.
Thanks and regards
Sudanthiram
Vu2nsk

On Thu, 26 Sep 2019, 7:45 pm Evan Hand, <elhandjr@...> wrote:
Curt,
I agree with your assessment.  The harmonics are the larger issue, and need to be addressed.  Changing to the shielded inductors before and after the 45 MHz crystal worked for some, and is a much easier repair than changing out the 45 MHz if transistors.  

The only issue with the above is that you do need a way to measure the spurs.  The harmonics are easy and can be done with either a separate receiver or a low cost spectrum analyzer (SA).  I have found that measuring the spurs is more difficult, as you need a better RBW (resolution band width) SA to do so effectively. 

(asbestos suit ON)
I would assume that it would be of interest to this group to post a how to verify the issue with minimal equipment.  Having been a retread ham after 31 years away from the hobby, and starting with only a vom and cheap oscilloscope, I can identify with the issues that some might have with testing.  I did not have another receiver to test the uBITX with, and was not a member of a club when I first built the uBITX.  I found out afterwords that there were emission issues.

I have since made part of my hobby to add the more test equipment, however I still do not have what I would call a good spectrum analyzer.  I have tried most of the low cost alternatives that have been listed in this forum (it is fun to test them out and not too expensive to me).  As stated above, I have found them to be great at one type of test or another.  None seem to meet all of the needs to vet out the uBITX.  I have just recently received the Antuino, however have not had the time to go back and redo the spurs testing.

The last point is that I would feel safe with sticking with the low power of the bare uBITX in working SSB on all bands.  The reasoning is that the 10 db of attenuation missing with the spurs is way below a similar rating for a 100+ watt rig.  The risk of interference is small.  I would only use it for CW if one of the low pass filter modes was done, as the harmonics are much higher and in general CW is a lower power mode.  I would not connect the uBITX to a power amp without vetting the signal purity.

As always, the above are my observations and opinions.  You will need to verify for yourself.
73
Evan
AC9TU