Oh,

There's not much to do wrong, it's all up to the software!? But this program always seems to agree with the Elsie program by Tonne Software, so I think it's OK.? The values I am taking are from the v3 schematic -- I think the filters are still the same although arranged differently now.? I thought lots of people would have run these through a simulator program already; especially when investigating power variations it could be interesting to get some confirmation of the cutoffs and input impedances.

Cheers,


Mark.

Here is my posting from last year

The wire up drawing has an error regarding the volume control connections. It shows the orange wire as being Vol_high. And the yellow wire as being Vol_mid, going to the wiper.
The orange wire is in fact the Vol_mid, and should go to the wiper. And yellow to the hot end.
The pictures are correct.

Philip G7JUR

Mark,

That gives me confidence in how you are simulating these LPF's.
Could be that the 80m LPF really does have a corner at 7mhz.
Or could be that the boards are not being built exactly as described by the v5 schematic.

Jerry

That clever person could been me.
I see that the latest drawing is still wrong, This error has a long history.

Philip G7JUR

You folks might not have access to the flash drive on my chromebook.
Here's a better place to look for the v5 uBitx schematic:
? ??

Jerry

Hi Jerry,

Thank you for the information on the code.? Here is a simulation of the 750nH filter:



It looks like a good filter for 30m and 40m.? Input impedance showed 50 ohms on 30m and 40 ohms on 40m.

Sorry the image isn't bigger -- in linux the filter program only prints to either a printer or to "Microsoft XPS Document Printer" which I don't have going in linux so I have to do a screenshot.

Cheers,


Mark.

I use omnirig with com3 to communicate with WSJTx but I cannot get Hamlib to connect
--
John Faivre?WA9SGD

Hi,

I haven't had any luck on 160 meters so far due to a compromised antenna. But rest assured that I am using and external low pass filter that starts to rolloff a little above 2 MHz. The filters inside the radio are definitely *not* for 160 meters.

It hears pretty well on 160 for all I can tell:)

73,

Bill KU8H

Mark,

Interesting.? ?

You might be right that the filter with the 900nH inductors has an incorrectly implemented corner frequency.
Worth exploring further.
Your simulation shows a corner at around 7mhz, not the expected 5mhz.
That would let a 3.5mhz second harmonic leak by.
The second harmonic will be quite weak?due to the push-pull topology of the IRF510 finals,
this 7mhz corner may not matter.

However, the stock uBitx definitely does not have a low pass filter appropriate for 160m !!!!!
We've had a number of folks here who assumed it did, since the firmware allowed them to spin down and transmit on 1.8mhz.
The third harmonic of 1.8mhz at 5.4mhz will go out on the air almost as strong as the fundamental.

The filter with the 900nH inductors that you simulated is definitely the lowest LPF on the uBitx.
When I said it had a 5mhz corner, I was going by Farhan's circuit description notes.
I had assumed this had been gone over thoroughly, since lots of folks in the forum
were trying to figure out how to reduce the problematic v3 harmonics from leaking past the relays.

I don't think the apparent 7mhz corner you found has anything to do with lack of power on 40m as seen by some.
I think it is more likely that some of the uBitx boards have incorrectly wound 750nH inductors.
When operating on 40m, both the v3 and v5 versions of the uBitx are using the LPF with the 750nH inductors.
At least, when operating with Farhan's code as archived on github.
There are other firmware releases out there, but I suspect they mostly copied
the code to control the LPF relays from Farhan.



Here's the v3 schematic:
??

And here's the v3 code from
??
that switches the relays around to select an appropriate LPF:

void setTXFilters(unsigned long freq){

  if (freq > 21000000L){  // the default filter is with 35 MHz cut-off
    digitalWrite(TX_LPF_A, 0);
    digitalWrite(TX_LPF_B, 0);
    digitalWrite(TX_LPF_C, 0);
  }
  else if (freq >= 14000000L){ //thrown the KT1 relay on, the 30 MHz LPF is bypassed and the 14-18 MHz LPF is allowd to go through
    digitalWrite(TX_LPF_A, 1);
    digitalWrite(TX_LPF_B, 0);
    digitalWrite(TX_LPF_C, 0);
  }
  else if (freq > 7000000L){
    digitalWrite(TX_LPF_A, 1);
    digitalWrite(TX_LPF_B, 1);
    digitalWrite(TX_LPF_C, 0);
  }
  else {
    digitalWrite(TX_LPF_A, 1);
    digitalWrite(TX_LPF_B, 1);
    digitalWrite(TX_LPF_C, 1);
  }
}

So when operating on 40m (unless you are tuned to be exactly on the lower band edge, don't do that!),
the signals A,B,C? (driving the KT1,KT2,KT3 relays) are driven with 1,1,0 respectively.
KT1 and KT2 are in bypass mode (relay on), and KT3 (off) selects the 7mhz LPF (has 750nH inductors).
So no, on a v3 uBitx, the LPF with the 900nH inductors is only used when operating below (or exactly on) 7mhz.

The v5 uBitx wires up the relays much differently to avoid having harmonics leak around the relays.
? ??file:///home/chronos/u-ba688dba5e13d507cb8c8d472169a2b5e212d72b/MyFiles/Downloads/ubitx_v5.pdf
The code for v5
? ??
drives the LPF relays with A,B,C == 0,1,0? when operating in the 40m band:

  else if (freq > 7000000L){
    digitalWrite(TX_LPF_A, 0);
    digitalWrite(TX_LPF_B, 1);
    digitalWrite(TX_LPF_C, 0);
  }

This powers the middle relay on the v5 to select the filter with the 750nH inductors,
the other two relays are left unpowered in bypass mode.
Note that the highest freq LPF with the 330nH inductors (for 15m,12m,10m) is always inline on the v5.

Jerry, KE7ER

I have just installed a nextion 2.8 screen to my ubitx v5 and I noticed when I tap the screen to select, the s meter shoots up to s8 and sticks there until I either reboot or speak loudly into the mike. I have tried both TFT files with and without s meter but still the same fault. No problems with the old 2 line display screen. I have the kit projects ALC board fitted which works fine with the 2 line display.
Any ideas folks?
Maurice
Vk6hly

开云体育

开云体育

So, what has two thumbs and is a huge doomarse? <- this guy.

I was on LSB but adjusting the USB setting. 95% of the display noise is gone now.

Hi,

I used the AADE filter simulation/design program.? I posted because I had seem some comments on the power outputs and was curious to simulate the low filter to see if that might impact some of the power levels.? I simulated the lowest filter I saw on the ubitx v3 schematic.? Did I miss a lower one?? This one seems to be the lowest and used for both 40m and 80m with a cutoff very close to 7MHz (actually showed -2dB at 7.3MHz).

Yes the design environment is 50 ohms.? That does not mean the filter will show that for all frequencies.? At the design frequency, they should show that (as this one does for 40m).? At other frequencies they can present higher or lower impedances which will affect power output.? This one does also show around 50 ohms at 80m.? However at 60m it shows to be about 20 ohms and at 160m about 10 ohms.? Even using another filter on the output, with this filter inline it may cause trouble.? So it would be best to have a designed 160m filter linked directly to the output of the PA if one wants to use that band.? My thoughts anyway.

Of course it would be good to see an actual measurement of the filter with a VNA etc.? My equipment is packed away from a move at the moment so I have to rely on software at the moment.

I just thought people may be interested in what I had found.?? I can work on my own no problem.




Cheero,


Mark.

I have a v5 uBITX in Sunil's 5" case with audio amp kit. Audio sounds just fine until I power the Nextion display. It's got a terrible buzz, and you can hear digital noises when the display changes, or when you turn the encoder.?

I've run separate power for the display and the noise remains. I Also tried powering the display with a battery pack, the noise is just as bad. How do you get this noise out??

Also, my audio (when not influenced by the display) sounds very tinny and a bit high pitch, and it doesn't seem to change when adjusting the BFO much at all.. any ideas?

Mark,

I assume you posted to this old thread because
you wanted to tell us about your simulation results.

Yes, the uBitx should not be used on 160m without a suitable LPF
inline with the antenna.? Without that LPF the third harmonic will be
nearly as strong as the fundamental.

Not sure exactly how you went about simulating the filter
or exactly what corner frequency you saw.
Regardless of what your filter program thinks, the 80m LPF
is being used in a more or less 50 ohm environment.
Changing the impedances will change the frequency response.

Attenuating some harmonic by 13dB may or may not be sufficient.
If that particular harmonic coming out of the final amp is already 30dB down
from the fundamental, then the extra 13dB of attenuation from the filter
will be sufficient to meet FCC regs.? Due to the push-pull configuration
of the IRF510 final, it is mostly the 3rd harmonic that gives us grief.

Would be interesting to measure (not simulate) the response of the 80m LPF
using something like the Antuino, driving the filter from a 50 ohm source
and terminating it into 50 ohms.

I believe the 3dB corner frequency of the 80m LPF is around 5mhz,
so if you tried to use it on 40m you would not be putting out much of a signal.
?
Here's the post you quoted? ??/g/BITX20/message/68292
It happens to be in the same thread as our current conversation,
though this thread hasn't been active for over 6 months.,

Jerry, KE7ER

Thanks guys.?

I ran into the front panel board problem - after I’d soldered the board (I built it first since it was “simplest”j. ?The front of the jacks are set back from the edge of the board. ?Thankfully, I have a Dremmel and the trace was far enough from the edge that I could ground the board back so things would fit.?

Looking at the pictures for powering the audio amp, agc board and fan (and expecting to add a CW filter later), I’m not crazy about having all those wires soldered to the small contacts below the relay on the bottom of the ubitx board. ?I’m thinking about pulling gnd, 12v xmit and 12v rcv to a terminal strip so I can add only one wire each below the board and connect the 3-4 others on the strip.?