Henning and Glen,

Thanks you for the feedback. All interesting questions.

I sincerely hope someone with the test equipment can duplicate and fill in the blanks.

The only test I can think of performing is the 1dB compression point. Since I would use an RF probe with a diode I need a high enough input voltage to make the test meaningful even after correction for the diode's threshold.

So if the gain compression is most likely to be in the final can I measure the output of the driver's stage and the output of the finals while I sweep the RV1 pot for an analysis of the 1dB compression? Also should I measure before or after the LPFs?

All the best,

73, John (VK2ETA)

I got my uBITx wired up today and powered it up this afternoon.  Not much on the air but I did go out to my jeep and fired up my Yaesu FT-817ND on 10 meter and had my wife listen down in the shack.  She said it hurt her ears it was so loud (I had the AF Gain up all the way) but other than that it worked fine.

Now I just need to get the microphone wired up and/or a key wired up so I can test the transmitter portion.  For the key I think I will just make an adapter from the 1/4" mono plug I use on my other rigs.  The mic I will use is a mic that I use with my Baofeng UV-5.  I will modify the plugs to be separate plugs for the mic and external speaker.  I just need to get a couple of the appropriate size jacks.  Dang I wish Radio Shack still had a store in town.  As it is, I will need to mail order the plugs for the mic external speaker and key.  In the mean time I will spend some time surfing the bands and listening on it :-)

Attached is a picture of it in the shack.
Nelson
KG7GYS 

 I stay at the red roof inn across the intersection by the gas station.  I had stayed at the holiday inn but they wouldn't let my bengal stay there.  Maybe more of us are going and we could have a ubitx meet and greet . Would be nice to see some ubitxs in person and their owners.  I've been a Dayton attendee for 20+++ years.  Most that I know from dayton remember my bengal cat every year.  He's my best salesman and has lots of repeat customers for him. 
  Jay N3QPW

Attached is an idea that might work nicely for a drive control that can be varied in software by the NANO on a band by band basis.

The original drive control, RV1, is removed and a few parts added, along with a digital pot (I2C control) in place of R3 below  to form an attenuator in the RF path.

With some careful work it should be possible to design a small PCB that fits into the holes vacated by RV1, either vertically or horizontally.

(the schematic is from page 62 of the book by Randy L. Henerson on designing a Transveiver. Its avery old book (1997)   ISBN  0-07-028263-3)
glenn
vk3pe

Hello fellow hams:
I seem to have damaged my tuning encoder so that it can't work right(button push doesn't work).  Please can anyone 
recommend a suitable replacement from either Mouser, Digikey or ebay.  I searched all over in Calgary, and harder than hens teeth 
to source.
73 Thanks

HI John and the group.
I did the mod with the 100uH and 1nF cap on the MIC input fo the preamp board,
It did cut the interferance/feedback out completely. However, it has also cut the MIC gain dramatically (5W vs 20W CW)
Might play with the values, smaller inductor maybe?

Thanks.
Nick.

MIght try this as a 3 element:

Skip,

Thanks for the reply. I did as you said. I had to reload about four
times! Seems like a register value was not getting reset when I did the
reload or something. It finally took tho!

tim ab0wr

On Wed, 21 Mar 2018 14:29:23 -0400
"Skip Davis via Groups.Io" <skipnc9o=yahoo.com@groups.io> wrote:

Tim, I did the same thing and a reload of the firmware corrected the
problem.

Skip Davis, NC9O

On Mar 21, 2018, at 14:22, Tim Gorman <tgorman2@...> wrote:

In playing around with the menu's on the ubitx I seem to have
somehow gotten the LSB calibration so far out of whack I can't hear
anything.

With the dial set to 3.925Mhz I hear nothing. Moving the signal
generator to 3.938Mhz indicates a signal being received but no tone.

Do I just need to reload the firmware to start over? Or is there an
easier way to reset to default values?

tim ab0wr

I made the error of clicking the encoder instead of pushing PTT when trying to zerobeat WWV while having that high pitched tone come in, I found that the BFO got a saved shift point up +2kHz.

I ended up sitting down a few weeks ago and working out steps since it didn't always get saved.


Tune to WWV on the dial
Enter menu
Turn setup on
Reenter menu turn to and select calibrate
Zerobeat the WWV carrier. (May be difficult if BFO is too far off.)
Click PTT.
Click encoder, select set BFO.
Zero the sideband off WWV. (My BFO frequencies were 11.997.0 and 11.995.0 for each sideband it's been 3 weeks)
Click PTT to set.
Click encoder, turn setup off.
Wait more than 10 seconds to ensure setting are saved before removing power.


Due to local noise I made a few attempts to set it correctly on a local AM station. Usually I set the sideband side wrong, so I had to go in change the BFO again. Due to rushing myself, I'd click "Calibrate" instead of "Set BFO" screwing me up to start all over again.

I need to go look at the code to see if the calibrate function just adjusts the ppm of the Si5351 or does something else. Either way, I got put off working on my uBitx until I figured the calibration routine out.

Henning,

I put the case together on the ubitx for now. I'll have to wait till I
open it up again to check on the filter bandwidth and the bfo frequency.

I tried pulling the windings on T7 away from the very bottom of the
core in order to minimize stray capacitive coupling. When I get a
chance I'll look at the carrier suppression again and let you know if
it changes.

The only asymmetry I can see in the balanced modulator is that perhaps
the diode pair is not loaded symmetrically by the stray capacitance of
the 50ohm, 4db pad. I haven't looked at the circuit board to see if
this might be an issue.

I wonder if the 50ohm, pi-network 4db pad is needed to control the level
into the filter or if a single 50ohm resistor would do?

I'm sure a double balanced mixer would provide better carrier
suppression but it's also more complicated.

When I get some spare time I might try putting together a single
balanced mixer like this and see what kind of suppression I can get.

tim ab0wr

On Wed, 21 Mar 2018 11:32:53 +0100
"Henning Weddig via Groups.Io" <hweddig=aol.com@groups.io> wrote:

Tim,

thanks for Your reply! For the overall carrier suppression two things
are to be considered:

1)  the balance of the single balanced modulator

2) the additional suppression done by the slope of the xtal filter

For 2) normally the so called -20 dB point of the filter attenaution
is chosen. This point is a function of the BFO frequency.

Regarding my unmodified BITX40 I noticed that I could hear the normal
tone but it seemed that I also get a response from the "upper
sideband". Further investigation showed that the BFO (measured to be
11.998 051 MHz) was within the passband of the xtal-filter. The 3 dB
points of the filter result in a bandwidth of 2 kHz, see the attached
plots.

The "resulting bandwidth" under these conditions is far too small,
resulting in a "muffled sound" already reported by other users. A
remedy of broadening the filter bandwidth is not the solution,
althogh a bandwidth of a bit larger than only 2 kHz is advisable.

The BFO frequency should be at the location of the marker. Replacing
the 47 pF cap with a 20 pF trimmer (as originally forseen) shifted
the  BFO frequency upwards.

For the uBITX the BFO is generated within the SI5351, so it should be
easy the adjust this frequency to the correct point. To do this the
filter center frequencxy, 3 dB points and 20 dB point must be known
or individually determined, not easy to be done without test
equipment.

For the balance of the modulator the following points have to be met:
    the exact symmetry of the windings including their center tap
    the exact balancing of capacitive (or inductive i.e. complex)
impedances
    the exact equal performance of the two diodes (switches) in
their on-resistance, off resistance and capacitances-- ok a double
diode on a single wafer may guarantee this requirement.

Please have a look back on the "old" discrete double balanced mixers
used as modualtors, they used:

    selected diode quads (even within a common housing e.g  offered
as a quad  for instance OA154 Q to match the thermal behavoiour)
    a potentiometer to individually balance resitive component and
exact symmetry fof the two center tapped windings of the modulator
     two caps (one fixed, one trimmer) to capacitively balance the
modulator

Of course the carrier suppression is also a function of the wanted
signal levels and IM performance of the modulator which is also a
function on how large the wanted signals can be made and how "good"
the IM performance has to be.

I have seen on other schematics using a single balanced mixer with a
potentiometer (as formerly used by Ashar) AND the capacitive
balancing has been implemented.

My guess is that a carrier suppression of at least 20 dB can be
reached. With the additional carrier suppression done by the fitler a
carreir suppresion of 40 dB should be possible.

I have built a double balanced mixer using two BN43-2402 cores with
trifilar windings and four non selected 1N4148 diodes. Without
further adjustments I got a carrier suppression of 26 dB, related to
a singel tone, but I did not measure the IM performance with a two
tone input.

I am not sure if the equal spacing of the trifilar winding alone
guarantees a perfect carrier suppresison.

So pelase determine the 12 MH x-tal filter bandwidth and -20 dB
point(s) and then adjust the BFO frequency to this -20 dB point. But
make sure that the lowest audio frequency to be passed through is
still in the range of 300 Hz or so.

One problem exists: the xtal filter skirts are not equal (due to the
ladder filter topology).  If the other sideband is to be used (for
the BITX 40 in USB mode) by not shifting the VFO  the -20 dB point
can result in a higher "lowest audio frequency".

Henning Weddig
DK5LV

Am 21.03.2018 um 02:54 schrieb Tim Gorman:

I forgot the attachments!



On Tue, 20 Mar 2018 20:40:15 -0500
"Tim Gorman" <tgorman2@...> wrote:

Henning,

I've looked at the balanced modulator in the ubitx. It is set up
differently than what I am used to but it should work.

The arrangement I am used to is shown in the first attachment. The
ubitx is in the 2nd attachment.

In looking at T7 the windings are not very well spaced on the core.
They are crammed together at the bottom near the circuit board. I
don't know if this could cause some stray capacitance that would
upset the balance of the circuit.

I might see if I can take a probe and separate the windings and
get a little better spacing and see if that helps to balance the
carrier out.

I have to say that I am a little surprised that no one else has any
suggestions on how to better balance the carrier.

tim ab0wr

Tue, 20 Mar 2018 05:29:59 -0400 "Henning Weddig
via Groups.Io" <hweddig=aol.com@groups.io> wrote:

Tim, this is a nice measurement-
At which output power did You take the measurement? What is the
attenauation of the power attenuator between the output of the
uBITX and the Input of the spectrum analysser? Your measaurement
shows a thrid intermodulation of 34 dB/ related to a tone, in
relation to PEP please add 6 dB results in 40 dB of d3! BUT:
marker 1 shows the supressed carrier is only 20 dB below the
carrier, or 26 dB to PEP. Commercial rigs suppress by at least 40
dB or better. This result is a"proof" of my worries concerning
the unsuffiecient carrier Suppression of the balanced modulator
and xtal-filter..

Henning Weddig
DK5LV.

-----Ursprüngliche Mitteilung-----
Von: Tim Gorman <tgorman2@...>
An: BITX20 <BITX20@groups.io>
Verschickt: Mo, 19. Mrz 2018 22:46
Betreff: [BITX20] two-tone test on ubitx

Attached is a screen save from my spectrum analyzer for a two-one
test of my new ubitx.

The tones were driving the finals to about 10watts output (not
quite, but close). I had a 30db external pad and a 10db internal
pad in the SA.

The carrier was only down about 20db (marker 1). That's not as
good as I expected. I'll have to look at that and see what can be
done to improve it.

The 3rd order IMD (marker 4) was down about 34.5db which is
adequate.

The heat sinks get *hot* while running a key down measurement like
this. If you are going to use the rig for a digital mode it
probably needs to be set for about half-power out of the rig.
That or a significant increase in heat-sink capability should be
installed.

tim ab0wr

Jacob,

This sounds like what I probably did!

I'm not sure what you mean by "zero the sideband off WWV".

Do you mean set it so it sounds the best?

tim ab0wr

On Wed, 21 Mar 2018 19:37:25 -0700
"Jacob Farnes via Groups.Io" <kk6jtl=yahoo.com@groups.io> wrote:

I made the error of clicking the encoder instead of pushing PTT when
trying to zerobeat WWV while having that high pitched tone come in, I
found that the BFO got a saved shift point up +2kHz.

I ended up sitting down a few weeks ago and working out steps since
it didn't always get saved.

Tune to WWV on the dial
Enter menu
Turn setup on
Reenter menu turn to and select calibrate
Zerobeat the WWV carrier. (May be difficult if BFO is too far off.)
Click PTT.
Click encoder, select set BFO.
Zero the sideband off WWV. (My BFO frequencies were 11.997.0 and
11.995.0 for each sideband it's been 3 weeks) Click PTT to set.
Click encoder, turn setup off.
Wait more than 10 seconds to ensure setting are saved before removing
power.

Due to local noise I made a few attempts to set it correctly on a
local AM station. Usually I set the sideband side wrong, so I had to
go in change the BFO again. Due to rushing myself, I'd click
"Calibrate" instead of "Set BFO" screwing me up to start all over
again.

I need to go look at the code to see if the calibrate function just
adjusts the ppm of the Si5351 or does something else. Either way, I
got put off working on my uBitx until I figured the calibration
routine out.

Nice! I like your boat anchor gear. Is that an old S-38 I see?

tim ab0wr

On Wed, 21 Mar 2018 16:53:46 -0700
"Nelson" <ngtdlt@...> wrote:

I got my uBITx wired up today and powered it up this afternoon.  Not
much on the air but I did go out to my jeep and fired up my Yaesu
FT-817ND on 10 meter and had my wife listen down in the shack.  She
said it hurt her ears it was so loud (I had the AF Gain up all the
way) but other than that it worked fine.

Now I just need to get the microphone wired up and/or a key wired up
so I can test the transmitter portion.  For the key I think I will
just make an adapter from the 1/4" mono plug I use on my other rigs.
The mic I will use is a mic that I use with my Baofeng UV-5.  I will
modify the plugs to be separate plugs for the mic and external
speaker.  I just need to get a couple of the appropriate size jacks.
Dang I wish Radio Shack still had a store in town.  As it is, I will
need to mail order the plugs for the mic external speaker and key.
In the mean time I will spend some time surfing the bands and
listening on it :-)

Attached is a picture of it in the shack.
Nelson
KG7GYS

Dana,

Does the encoder actually work? Can you change frequency?

You might be better off add a small normally open pushbutton switch
near the encoder and paralleling it onto the two encoder
switch terminals.

It would be a lot cheaper and easier to do and is actually something
several people have done. Trying to push the encoder switch without
turning the dial is, quite frankly, a pain. I plan to do this to mine
the next time I open the case!

tim ab0wr

On Wed, 21 Mar 2018 18:40:41 -0700
"Dana Marcy" <ve6kbi@...> wrote:

Hello fellow hams:
I seem to have damaged my tuning encoder so that it can't work
right(button push doesn't work).  Please can anyone recommend a
suitable replacement from either Mouser, Digikey or ebay.  I searched
all over in Calgary, and harder than hens teeth to source. 73 Thanks

Yes, tune the carrier to 0Hz (tone  goes quiet/away). In mine a high-pitched tone appeared and confused me, so take your time and try to ignore the birdy signal.

The problem with doing it to an AM station is that you can reverse USB and LSB, so having something to check immediately after calibrating is a good idea. FT8 tends to be busy enough even when the ragchew nets have gone to sleep.

If you can't hear them on 7.074 LSB (except for the one guy in low tones), but booming in on 7.074 USB you've got it right.

When I got my uBitx, the sidebands were reversed from the factory in the Raduino. Which was fine until the auto-sideband switch flipped it back on me. That's where I started to check the tuning and calibration.

I kept seeming to make it worse each time I tried to make the calibration. Took a week off to clear my head and come back to looking at it.

I hope I've been helpful despite seeing a few details I could be more explicit about.

73 de Jacob AG7CT

Hello Nik,

I am confused. A 100uH and 1nF filter has a cutoff frequency of 503KHz, so am not sure how it can affect your audio.

You also mentioned CW, and CW works directly on the unbalance of the mixer and does not come near the audio circuit, therefore I can't understand how it affect you power out.

Are you sure there is not something else?

Also I placed the low pass filter on the input of the SSM2167 module (if you still have it in-line).

But either way it should not affect your power out.

All the best,

73, John (VK2ETA)

HI John.

Sorry, I was a bit unclear.
CW power is normal, no effect there, I get the full 20+w output.

But the SSB is low now... I will check it over tonight, try it with and without again, and post up a few pics.

Cheers.