Investigating transmit gain in UBITX V3 using LTSPICE, Aug 28, 2018

Caveats:

all modeling done at 13.8vdc

For simplification:

q90 collector circuit modeled as parallel feed with 400 ohm load

q911-q912 collector circuit modeled as parallel feed with 200 ohm load

q92,q93 and q96,q97 collector circuit modeled as parallel feed
??????????????????? with 50 ohm load,each side

observations:

in the bidir amps the 2n3904 gain rolls off 1.2 db from 5MHz
to 45 MHz...not real bad; I believe 2n3904s are quite usable
in the bidir amps at 45 MHz.

In the TX:
q90 rolls off less than .5 db from 5 to 30 MHz

same for Q911-Q912

same for Q92,Q93,Q96,q97

so, adding q90 rolloff, and q911-912 rolloff, and q92,q93,q96,q97
rolloff I get (.5+.5+.5)= 1.5 db rolloff from 5 to 30 MHz.

My most recent ubitx v3 has 10W out on 40M, but less than 2W out on 15M.
That is more than 7dB drop.

I take it from the above that replacing the TX driver transistors with
higher Ft devices may not substantially improve the 15M performance.

WARNING: q911,q912,q92,q93,q96,q97 all dissipate at least 296 mW. That
means 250 mW transistors are not acceptable.

So, in searching for a better Ft device for the TX chain:
the BFR106 has the dissipation, but the 3.5 to 5GHz Ft invites instability
the MMBT10? ?? lists dissipation at 225 mW, so it may not be a good candidate
the MMBT2369 lists dissipation at 225 mW, so it may not be a good candidate
the DTX2222A has the dissipation, but the Ft is not better than 2n3904, and
the footprint is not compatible with the board.

So at this point, I do not see a real winner for 2n3904 replacement.
I am sure open to suggestions on this front.

All of the above really leads me to question the power amp circuit..
and I do not have the wherewithall to model that successfully.

Any ideas there?

Rod KM6SN

Yes, but we know this is not perfect.? Wrong word should been reasonable.

开云体育

Here are photos of the assembled board. ? I did break down and use shielded microphone cable for the relay control wires. ? Soldering those SMT inductors was a bit of a thrill with a Walmart soldering iron. ? As some of you suggested, I put the relays on the ground plane side. ? The extra circuitry unused is for a regulated voltage.

The question would be then can it be changed, and did the ubitx exist when the group moved from yahoo?

I'm guessing no and no. So then you would have to create a new group and move thousands of members over a trivial thing like removing 20 from the group name. Clearly the problem isn't people finding or using the group.

For several hours now I have composed and edited this message, now
before anybody adds any other comments to this thread I should probably
send this and piss everybody off.

It sounds to me that some people think the group is too big and needs to
be broken up. Now the one thing that attracted me to this group was the
community, people helping other people with various radio problems.
Personal opinion here, break up the group you may kill the community.

How to handle the flow.

Digests have been mentioned. My personal experience with digests in
another group in the past was that the digest pretty much trashed all
threading and made everything hard to follow. My eventual solution was
to take the entire email flow and have my email client do the threading.
It was much easier to follow that which was interesting to me.

Here are the top tags that have been used, you can try searching on some
of those.

#ubitx 418 threads
#ubitx-help 84 threads
#bitx40 75 threads
#bitx40help 57 threads
#parts 30 threads
#radiuno 22 threads
#bitx20help 18 threads
#w8tee 18 threads
#firmware 13 threads
#bitx20 13 threads

I read this group via email, my email client has no problem threading
messages, it also has search and filtering capabilities on a couple of
levels. I have filters, pretty much inactive now, that put certain
addresses and subjects right straight in the bit bucket. If your email
client does not have those capabilities then use the web page, you can
do searches from there.

There are related groups on groups.io as well. This is not a complete
list, just some of those that I find interesting so far.

SoftwareControlledHamRadio 1107 members 44 messages this month
HBTE (Home Brew Test Equipment) 156 members 124 messages this month
antennas 168 members 130 messages this month

And of course.

BITX20 6469 members 2524 messages this month

So this BITX20 group has lots of members and lots of messages every
month. Could some of the traffic here be spread out over some of these
other groups? Yes, and I believe that will happen over time as a couple
of those groups are less than a month old, but this will still be a busy
group and each of us will have to find strategies to deal with that.

There is no single strategy that will work for everybody. I personally
read every single message, I also follow 6 other Ham Radio related lists
and read 200 - 1000 pages of other material most days as well. But I
like to read.

Getting 6469 people to all do things a certain way is kind of like
herding cats. I think I heard that around here recently, not quite in
that context but pretty close I think.

Art N4EZZ <n4ezz@...>
GnuPG key ID 0x6712DD0E
=============================
I need a little tingle once and awhile.
WA0JYD

I vote for subgroups - PLEASE!

Allison

If the IMD were "perfect" you would see two tones, period. :-)

WA8TOD

Nikos,? I do have the 3.5" Nextion display (….T035-011) and would love to have the files (you can send them to jlauber@...).? As for changing the x,y, h and w values, in the Nextion editor, click on any element of the display, and the Attribute page for that element pops up...scroll down to the bottom of the list and you'll find x, y, h and w and you can simply edit them.? But getting the right values to put in those is the devil in these details!

73
John

Warren,

To that we are both in the same pew.? Bandaids are turning to cardiac surgery.
Unfortunate that that is the case.

I've gone back to modernizing a old atlas that was a parts dog for fun.
A display, Arduino, and 5351 can do a lot for that one.?

Allison

开云体育

That assumes that the end users would use them properly. Its already impossible to get a thread to stay on topic. You can always set a thread to be muted if you don't want 300 messages regarding efhw antennas. Besides, who is going to do the labour required, you?

A great example is the same thread coming back even though a group was created for antennas. Nice idea, hard to implement.?

-- If there were only a couple messages a day it might make sense to keep everything together.? But I have received over 3000 digests, and it has become nearly impossible to determine which flavor BITX the messages are for.? I have a Bitx20, Bitx40 and a uBitx , it would be nice to not have to wade through all the messages and ignore the 300+ messages about End Fed antennas to find information related to my Bitx40.? ? I belong to other Groups that have sub-groups and they work well for keeping things a little more organized.
DuWayne? KV4QB

Alison

i have put my uBitx on the shelf and plan no further work on it. Just too many issues trying to make a Ford out of a tricycle. I put these up as an assist for those still trying.?

WA8TOD

Warren,

That is indeed a mess.

One place to look is pull power to the amp.? Look at the output of the 9 element 30mhz filter
peak level should be under -10dbm.? ?The stuff you will see there is not good and varies
with CW and SSB.? ?Then look before the filter (with it disconnected).? IF you look at both
those spots with and with out the power amp operating you also get a different mix of
spurs with different amplitudes.? ?It is especially bad above 17M.? You get at the output
of the 34mhz low pass a mix of signals that changes if the power amp is working into
a dummy load or turned off.

It suggests unwanted coupling and board level current loops.? It appears to be some of it
is signals introduced into the 45mhz wide band amp after the crystal filter.??

The 30mhz low pass was stated as not being adequate from testing then and
would found to be so again.

7/28/2016 part of the email stream at the beginning on freelists.
For myself I'd grab a bag of latching relays and build band specific filters.? That we know
can work but while its repetitive circuits is not always simple to do well (or tune up).

Back then I was told I didn't know shit and so I stopped saying it as was not to beb said
I had all the work and testing on a bench proto to the contrary.? Back then it was
failed TRX Minima as it has all sorts of unwanted outputs using a 20mhz IF and
minimal filtering while trying to cover 3-30mhz.? ?That begat HF1 Dual conversion
with crystal oscillators for CIO and 2nd conversion from a two pole 45mhz LC filter
and morphed into beginning of uBitx by early 2017.? ?The first version only had
2 than a bit later three low pass filters for 3-30mhz.? The goal then was as is
now 3-30 and very few filters.? Parts availability were big divers as in variable
caps and coils.

Allison