Allison is suggesting that the 100pf caps at C217, C218, C219, C220, C221, C222
be swapped out with something smaller.

The board is laid out for 1206 sized surface mount caps, though 0805 sized parts could be used.
These sizes are in imperial units, something near that size in metric should work fine.
? ??https://en.wikipedia.org/wiki/Surface-mount_technology#Rectangular_passive_components
Dielectric should be C0G or NP0.
Voltage rating doesn't matter much here, anything 25v or more should be fine.
Use caps of 5% tolerance (preferably better), or measure them with a capacitance meter.
? ??/g/BITX20/message/52471/g/BITX20/message/52471
Standard values that might be tried include the current 100pf, or Allison's 91pf, or? 82pf.
they lower the value the wider the bandwidth.
Though changing those capacitance values may change the shape of the filter response
with frequency, ideally we would sweep the filter shape somehow to make measurements
before and after the mod.

As you know, crystal filters in an SSB transceiver like this are a trade-off.
A wider filter may sound better, but may not be suitable when there are many
stations operating on nearby frequencies.
?
Would be interesting to measure the capacitance of any 100pf caps removed,
with 10% or worse tolerance parts we would see significant variations n performance.

Jerry

Pat,

I appreciate it but I have no idea what a Nextion screen is.

73,Bill NZ0T

Hi Allison,

Well I think that is the culprit.

I have tried about 7 electrets after my last posting, some sounded a minor bit better others worse.

No significant big improvement.
Also tried playing with the BFO, not much help there either.

Do you have any link regarding the parallel caps? or schematic how this could be done?

--
73' Bj?rn de PD5DJ

The G4HUP buffer amplifier is connected to the 45 MHz IF that is available from C12. I have obtained an SMA "pigtail" that will connect the buffer amplifier output to the SDR dongle.

You may have to move the BFO down more for better audio.?
Its the first thing everyone tries, 100 to 200 cycles may help greatly.?

Also more than a few have narrower than expected 12mhz filters.??
Mine swept on the analyzer at under 1700hz wide and reducing
the parallel caps from 100pf to 91pf got it out to over 2100hz.

Allison

Hi Andy,
did you ever do this mod ?

if so, how did it do ?

Kevin rea
lancaster, calif.
k6rea

This string is 275 entries and counting long for those that use email rather than web site you loose a
huge amount of context and replies never mind the ability to look back.

I stopped writing on improvements over 20mhz as any increase in power makes
the over 20mhz spur a greater issue. Do so at your own risk.

For Q90 the BFR106or a similar high FT part is a winner.? Keep Ie under 20ma.

For the pre-driver and driver....

THe whole point is to get more gain at higher frequencies as the 3904s can be
pretty dismal at 10M.? The 2n2222s are better that but for better 10M you need
2n3866 or 2n5109 and transformer optimizations.? Even with that it wants to
do stupid high power at 80m and less than half at 10M.? So the C81/r83 mod
is needed to tame down 80m (470pf/8.2ohms from memory).

If your not interested in over 20mhz 2N2222A(to18). Ie 20ma max per device.
If you are interested in over 20mhz 2n3866 or 2n5109. Ie can be higher but take care for heating.

The various transformers need help too.? Look back for specific winding info.??
Memory test of what I used:?
T8 (q90) 5t #30 bifilar on FB43-2402??
T9 FB43-302 4t trifilar #28
t10 FB43-302 4t trifilar #26
T11 FB61-202 3T/4T #24

To take advantage of the transformer mods you needs ot make other changes....
See the progression!

2n3866 kitsandparts. com 6.00$ for two.? RFparts.com 1.95ea
2n2222A RFparts.com? 65 cents

Biggest issue with RFparts is I believe the have a 25$ minimum, for me I take advantage of that and
stock up on various other pats like Arco trimmers, metal clad mica caps and other itms useful to a
VHF/UHF RF person.

Other suppliers Mouser, Digikey, Jameco.

FYI MPSH10 kits and parts have them for 25/$5.00 and BS170 25/$5.00? reliable source and they have
Ferrite and toroids!

Allison

Hi Joel,

Thanks I will try that, I think I have a little bag of gathered electreds lying around somewhere.

Will keep you posted.
--
73' Bj?rn de PD5DJ

Farhan, taking a quote from one of our most beloved movies here in the
States, "...you're gonna have to get a bigger boat!" -- Rich WB2GXM

Bj?rn, If you are using the electret element that came with the uBitx, I would try a different one. I haven't been able to use the mics that came with any of my Bitx kits because of bad audio quality. I bought a whole bag of them from a eBay vendor for just a few dollars that work perfect.

Joel
N6ALT

On Wed, Jul 18, 2018 at 07:02 PM, ajparent1/KB1GMX wrote:

In context they worked in that they were marginally better than the 2n3904s, but compared
to the 2n2222A or 2n2219 they were not very good.? ?Compared to 2n3866 they were poor.

Hi Allison,
So it sounds like you found the 2n3866 superior to the 2n2222a ?at some point in the chain. To avoid having to repeat what you have already tried could you share with us at which point in the chain, i.e. driver, predriver & did you use one or two or four? 2n3866’s are pretty pricey but not unobtainium from a reliable source. And do tnis superiority apply to all bands or just to the higher frequencies?

If this is obvious or you have already stated it, I apologize for having missed it (and it’s obviously not obvious to me...) please do not give up, your opinions knowledge and findings are well respected here

and elsewhere.

Thanks. And thank you for your patience.

Sincerely,

Jerry aa1of

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So, what I need to do is measure the voltage at J1 on the AGC at very low and high signals and then guess for what is between those two extremes?? How did you come up with a setting of 217 for the high end based on your 4 volt measurement?

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?So, I'm getting ready to have some number of our Alachua County ARES people built ("install" might be more accurate)? uBitx / Bitx40's.? ?

All these wonderful improvements y'all are developing and testing will be a huge help to us (AFTER we get their stock versions to? work.....).... so this morning I put in an order for?

10 2n2222As

10 2n3866's

100 2n3904's with an Ft of 300 Mhz --- I use these things all the time and it was cheaper to buy a lifetime supply than to buy a smaller number....

I wonder if the higher Ft-version of the 2n3904 would make any significant difference, or if the one that is already in the uBitx has an Ft that high?

Thanks for all the work y'all are doing --- it will help a bunch of Technician licensees see even more reason to graduate up to higher licensure.....we did 5 Extra's last year and hope to do a bunch of Generals this year....

gordon

I have the uBitx for a couple of days now, and have several "issues" with it.

One of them is modulation frequency response.

Monitoring my TX audio sounds like talking through a cloth or something, no high tones are audible.

Is this normal behaviour of this kit?

I have done all the alignments, Masterclock/BFO

?

--
73' Bj?rn de PD5DJ

Got it working!? I tried Ian's settings which were way off for me.? Ended up at 5 on the low end to 60 on the hi end which may still be a bit "Scotch" but I want to try it at that for a while and then adjust.? Thanks everyone for all the help!

73, Bill NZ0T

Yes, it is attached/plugged at J1 which is the positive end of C4.

73 Kees K5BCQ