Hi Don,
I pulled the board and tested with sig gen on input and only the scope on the output.? Same huge crossover distortion.? The
(simple) circuit looked OK and the + input bias was 1/2 Vcc.? That chip is going to the waste bin!

Have hundreds of 741 devices in the junque box.? Used one - Works great.
The output is terminated into the high side of a 1K pot.? The wiper feeds an old TBA-810 circuit for several watts (if I want it ;) of output audio.

Woody ?? KZ4AK

No, left open.? Had not experienced a problem before this.?? But then, there is this ;)
A new board using a 741 is working great.
Woody? KZ4AK

On 11/29/2018 4:35, Skip Davis via Groups.Io wrote:

Woody the LM358 is a dual op-amp so did you terminate the unused op-amp? If not then it could be the cause of your distorted output.

Skip Davis, NC9O

--

Try a 1458 instead. It has the same pin-out and is drop-in compatible with a much higher output capacity. I mention this since it appears that you are feeding a lower impedance than what it is capable of driving since that is the waveform that one would expect if doing so. What are you driving? I substituted an LM380 as an output AF amp in the V4 and it does very well. No pre-amp needed.
73, Don

--

Raj and group,

Farhan was also suggesting a filter to remove the 12mhz spur in the transmitted output
that resulted from crosstalk from clk0 into clk2 at the si5351.
Should that be included in this recommended cure-all?
I still feel the best way to deal with the 12mhz spur might be a high pass filter on clk2
rather than a tuned (and finicky) notch filter.

Do the new inductors for the 45/90mhz LPF have to be a specific kind of shielded inductor?
Or can we get by with any old 1206 surface mount inductor?

How much better are the results when L5,L7 are replaced with shielded
surface mount inductors?? Are we legal without that change?

At one point, Raj saw better results with the torroids at L1,2,3,4 replaced with?
shielded surface mount inductors.? Is that still the case?

There was some discussion about different coils in the various Axicom relays,
has it been determined that the higher current coils are required
to reduce coupling sufficiently?

Ideally we would have web references to specific easily obtained
parts for the relays, caps, and inductors needed to clean up the uBitx.
Even better, perhaps somebody could provide a kit of appropriate parts.
But I think this should wait till a specific list of recommended mods is nailed down,
and we know that the results are repeatable.?

Would be very cool if there was a cheap way to see this trouble in a stock rig,
and to verify that it works better after the fixes have been applied.?
For example, use a second receiver (a second uBitx?) to check uBitx transmissions
for the 12mhz spur and the?45mhz-DialFreq spur?
I assume the transmitted signal would have to be attenuated by 40dB or so
to prevent damage to the receiver, attenuate by an additional 43dB when
listening for spurs.? And put rig under test plus dummy load in a Faraday cage.
Can the procedure include checks for harmonics, at least on the lower bands?

The previous method of adding a second 45mhz crystal filter is no longer recommended.?
This new 330uH-51pf-330uH low pass filter to knock out the 90mhz harmonic of the 45mhz IF
goes into the same position as that 45mhz crystal filter did, but works better.
It does not attenuate the desired signal so much as the 45mhz crystal filter did.


Sarma asked:
> will the smd inductors in post PA lpf mode, take that power?

Answer: NO

Raj said:
> This has nothing to do with the spurs issues.??
I believe that should read:
? ?This has nothing to do with the harmonic issues.

Leave the post PA LPF's with the stock torroids, the new smd inductors will not take the power.
The harmonics thru the post PA LPF's at L11 through L22 are fixed by just swapping out
the relays at KT1,2,3 with Axicom relays, the stock relays are not very suitable for RF.
There are other methods of fixing the post PA LPF's, these involve adding extra relays,
or?adding a band specific low pass filter external to the rig in line with the antenna coax.

We need to finish this up with a detailed and complete list of recommended mods
so folks can use their uBitx with confidence.? Very few have a spectrum analyzer.

Jerry, KE7ER

开云体育

Well I’ve used them several times successfully. The audio band width is not quite as large as one would like. ?You can change some capacitors in the Crystal filter to fix that if you wish; I haven’t yet?

@ Ashok Khachar: Screen Saver mode was disabled.

Uploaded the default .tft program, which is flashed in factory before shipping from =>
The "white screen issue poped up after 3min again!!

Guys,

This has nothing to do with the spurs issues. Just a test to see if the SMDs are as good as the
toroids. I am pleased that smd is a good alternative at signal stages.

For a cure all I stand by - change KT1/2/3 to Axicom relays, change L5/7 for good measure and
ad Farhans LPF filter for another good measure.

Raj

At 29-11-18, you wrote:

Sharmaji, this is on a test jig.

At 29-11-18, you wrote:

I’m new to the group and to BTX kits so please excuse me if this has already been covered.

I’m involved with emcomm wonder if anyone uses these small hf rigs with Winlink?

If so would you please let me know if any mods are required to the basic kit.

73, thanks, WU0G

Raj, is - 0.65 the total loss on a 50 ohm load for this filter on SSB? What is the CW loss on various bands?

Sarma, that is the LPF to remove spurs between the IF, so it will

Almost identical results! very encouraging.

SMD Yellow shielded 331 x 2 + 51pf to ground



Toroids 330nf x 2 + 51 pf

--
Raj, vu2zap
Bengaluru, South India.

Thank you

Hi Ricardo,

I re-installed .tft file few times. But no luck.