开云体育

Thanks for the report.
Very informative!

I think the consensus is that replacing L5,L7 should reduce coupling from the power amp?
back into the 45mhz IF amp where it takes another trip through the D1,D2 mixer.
Raj had a specific manufacturer in mind:??/g/BITX20/message/61261
They have to be well shielded, commonly available surface mount inductors did not help at all.



Here's a brief recap regarding what other changes and why between v3 and v5,
as best I recall:

As mike gain is increased, Allison has noted that spurs increase disproportionately
due to distortion, especially in the 45mhz IF amp.? The mmbt3904's there are being
asked to work well beyond their gain-bandwidth spec.? So we have other stuff besides 45mhz
going into the first mixer.
On v5, Farhan added a low pass filter with L31,L32,C205, I'd assume it's there mostly to?
remove the 90mhz 2'd harmonic due to distortion in the 45mhz IF, which mixes
with the VFO to produce a very strong spur at? 2*45mhz - (VFO=DialFreq+45mhz) == 45mhz - DialFreq
where DialFreq is the desired transmit frequency.

He went to higher frequency transistors in the 45mhz IF amps to reduce distortion
and give more gain.

He also changed R26 from 470 ohms to 220 ohms, at the output of the 45mhz IF amp for tx.
I believe the reason for this was to give a higher level 45mhz signal into the first mixer,
helping swamp out the 12mhz crosstalk from CLK0 into CLK2.

R100, R106, R110 where CLK2, CLK1, CLK0 go into the mixers have changed to larger values,
probably to reduce loading on the si5351, and thus crosstalk between the three channels.

The routing for the three relays that switch between the four transmit LPF's has changed to
reduce the transmitted harmonics.?
The 2'd IF has been moved from 12mhz to 11.059mhz to avoid the possibility of nasty audio tones
due to beat notes of the BFO with clocks on the Nano.
These two changes both require minor adjustments to the firmware.

?I see these changes between v3 and v5 down in the PA:??
? ? c81=470pf r83=2.2 R97=R98=220 C261=C262=0
which I assume is mostly to get more power out on the high bands.

Stuff from the M2 relay contact on through the volume control and audio power amp, out to the speaker
has changed considerably across v3,v4,v5.
v3 had the TDA2822 which worked fine, except that parts from one particular clone manufacturer were exploding,
so v4 when to a discrete push-pull audio amp.
But v4 had issues with crossover distortion and low max volume, so v5 punts with the tried and true LM386.
v4 and v5 have a 2n7000 (perhaps its a 2n7002?)? at Q74 added to reduce PTT pops to the speaker.

I've undoubtedly missed a few changes, but that should be most of it..

Jerry

I agree.
A good check for something not working
But maybe not a check for something being a bit out of spec.

In addition to good balance in the diodes, you also need good balance in those two windings of T7 that drive the diodes.

Note how close R113 (CLK0 into the modulator) is to the trace between C30 and R47 (feeding the middle D3,D4 mixer).
Rather surprising that most of these rigs have as good of carrier suppression as they do.

Jerry, KE7ER

That is the 7805 ?

I put six 1n400x diodes in series with the 7812 regulator that cut down on some heat.

Hi, is there a pic of this work??

Thanks
Joe
KD2NFC

Jerry, as always, thank-you for your information.

One point, the Clock#0 Vpp is 760mV as I measured it with the Siglent 100 mHz scope that I have.? As you stated, I cannot find the signal on pin 3 of D5 matched diodes.? To me that is at least a gross test that the diodes are working, as I would have expected a signal if one or the other side was bad.? That is with the rig able to receive signals.? I believe that it would still be able to decode a signal if only one diode is working, as the receive section would filter the 12 mHz rf.

73
Evan
AC9TU

That 1mV figure for the main signal is too small.
Should have around 0dBm max coming out of the modulator, or roughly 200mV RMS

Though using the usual scope probe alligator ground clips,
you may still have trouble seeing much given all the 12mhz energy coursing through T7.

Sounds like you're mostly on the right track.

However, the normal signal level at the junction between diodes is quite small, perhaps down around 1mV RMS.
The residual carrier should have less than a thousandth of that power, so less than 1/30'th of an mV.
I doubt you'll see the desired signal when using a typical scope probe, let alone the residual carrier.
You may need something like a well shielded/grounded/decoupled AD8307 to see it.?

In addition to any imbalance in those modulator diodes, we also have unshielded 12mhz from CLK0?
crawling around the rig, adding to the residual carrier.?

A good introduction to how hard it is to get the single board uBitx to work properly with no shielding.
How can such a small signal coexist with 10 Watts out of the final?

Jerry, KE7ER
?

Phil

Welcome to the worldwide community. Let's see you need some kind of microphone,? a suitable power supply, and a good 40m antenna.

Put it on the air once? Glad you have it so it can be used many times. We can debate a good 40m antenna, but something like a half wave dipole can bring many contacts.

Use the rig before you decide if it needs anything more. Yes they can be modified to use on other bands. I will relate that its easier to make low power ssb contacts on 40m rather than 80m.

Curt

Apparently, I was a lot smarter two years ago.
Here's a brief description of how that modulator "multiplies" to get sum and difference frequencies:
? ??/g/BITX20/message/22530
The rest of that old thread might be worth reviewing as well.

Jerry, KE7ER

When I read this thread with the comments about the diodes being open, shorted, or improper bias, and having had an issue with the D5 diode(s) prior, I got to thinking I should test D5 to verify that that was not the cause of my BFO needing adjustment (post #66111).? The most accurate test would be to remove it from the circuit and test.? As my SMD skills are still under development, I did not want to go that route.? I then came up with using a scope to measure the 12MHz signal into the diodes, and then the result at the output.

What I believe you should see (as I did) is the square wave (with ringing) on pins 1 and 2 of D5, and no (or very minimal) signal on pin 3.? That would be testing the diodes and T7 for proper operation.? I did this on both transmit and receive, seeing the same results when connected to a dummy load and no audio in on transmit.

The above process may be obvious to most, however it was not to me, so I am sharing in case someone else questions their BFO mixer prior to adjusting the frequency to reduce the carrier and is unaware of how to test in circuit.

If the process is not accurate, please comment back so that I can better understand.

73
Evan
AC9TU

Mike,

That's what you get when the display is powered up but it receives no commands from the Nano.

Take a hard look at page 7 of the datasheet for your LCD that you posted previously in this thread.
Pin numbering on that 16 pin connector is very very strange!
Pin 14 is at the corner of the LCD board, and counts down from there to the square pin 1.
After pin 1, we have pins 16 and 15, in that order.

Pin 15 is on the outside edge of the connector, and would normally get grounded by the Raduino,
pin 16 is one pin in and the Raduino gives it 5v for the backlight.??
By default, this would mean your backlight should not turn on, but the jumpers on page 8
show how those two pins can be swapped.

Wow!

I have never seen such a screwed up connector pin-out.
Smells like somebody laid the board out without a hard look at what everybody else was doing,
then adjusted the documentation as inconspicuously as possible to agree with common pin numbering.
But that sort of crap should be in big red letters at the top of page one of the documentation,
not hidden away in a barely understandable mechanical drawing..

You have probably also given pin 14 a ground, and pin 13 +5v.
Those are both data lines into the LCD, and happen to be two of the four bits that need to work.
I'm guessing that the LCD controller chip survived this, but I could be wrong.

Be sure to complain mightily to the vendor.
Give a review that warns others of this major botch if you can.

Jerry, KE7ER

I purchased an assembled Bitx40 from another local ham.? He stated that he had assembled the kit, put it on the air once and then bought a uBitx.
I have seen numerous discussions here about modifications and operating the radio.?

I'm looking for any suggestions to use this radio on the air.? I would like to use it as a portable rig and possibly operating on 80M.

Thanks in? advance,
Phil KC2YLM?

Hi,

Maybe you've got it backwards -- I think the backlight will work even when hooked up in reverse because of the way the power is wired on pins 1 & 2 and on 15 & 16?

73,


Mark.

Same.? It seems wise to always have a fallback point at the ready, maybe even stored in a spare Uno board for quick change or diagnostic type stuff (or the zombie apocalypse, whatever).?

Ted
K3RTA

edit:? TO-220