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Re: Sbitx bandpass filter

 

Juan,
There is lurking danger with the t/r circuitry.
As the entire receiver is bidirectional, when you go from transmit back to receive, there can a millisecond or less of time when the rx power line capacitors still hold power and the tx circuitry is powered up.
This can cause the entire power amp and the if aml to go into self oscillations. These can be very large oscillations that can blow up the finals.
Be careful to time the T to R transitions carefully. When starting tx, the rx line should go down, you wait a millisecond or so and then the tx line powers up.
The transition from T to R should be similar. Power donw the T line, wait for a millsec or so for everything to discharge power, then turn on the R line.


On Mon, Oct 28, 2024, 5:45 AM WP3DN via <3voltios=[email protected]> wrote:
I meant to say from 30m to 6m
Re: Why is sbitx spectrum limited to 25k?

 

The ideal place to tap would be between the crystal filter and the mixer.
This can be a very interesting and powerful second receiver.
Here is how it will work.
1. Consider that an rtl sdr is connected to the point between the if filter and the mixer.
2. Let us assume that the main radio is tuned to 7 mhz. The local oscillator is now at 47 mhz.
3. If the rtl sdr's own sdr, running seperately is now? tuned to 68 mhz.
4. The rtl sdr can now listen to 21 mhz band (68-47 = 21 mhz). It can also display a spectrum of upto 2 mhz wide.


On Mon, Oct 28, 2024, 12:37 AM William Hemmingsen via <lee.hemmingsen=[email protected]> wrote:
thanks
Re: Sbitx bandpass filter

 

I meant to say from 30m to 6m
Re: Sbitx bandpass filter

 

Hi everyone,?
?
Today to test the amp, did setup the lpf bits manually from 10m to 6m. Had to add 20db amp between the 2nd if output and the bandpass filter board. Power output is 14-15w up to 10m and 11-12w at 6m and 8m. Too bad we dont have the 8m band yet.
?
Have to work on the tx rx switch and the lpf band controll.
?
Need to sit down and learn about the i2c. If I can send the frequency to an arduino, then control the bpf and lpf bits.?
The amp board also have the swr bridge. So replacing the attiny with an arduino and also control the filter is the way to go.
Still lots to learn.
?
Juan WP3DN
Re: sBITX out of band transmit

 

On the hardware side of things you have to consider band pass filters which are band specific.
Re: Why is sbitx spectrum limited to 25k?

 

thanks
Re: Why is sbitx spectrum limited to 25k?

 

The IF frequency is approximately 40 MHz. ?I am not sure of the actual frequency. ?It would be the center of the 40 MHz crystal filter which should be a few KHz less that 40 MHz.?

73
Evan
AC9TU
Re: Why is sbitx spectrum limited to 25k?

 

Another question.? If I wanted to tap in an external SDR for more spectrum bandwidth.? I'm assuming J7 before the crystal filter would be the place to connect.? What is the IF frequency?
sBITX out of band transmit

 

A good buddy of mine got an sBITX V3 and I upgraded his and mine with V4.1.
Now he is really wanting me to set his up to transmit outside our frequency privileges. I'm pretty sure that is something beyond my skill set but I said that I would at least look into it. So just wondering, if that would be software or hardware.?
--
'72
Aaron?
Re: Why is sbitx spectrum limited to 25k?

 

Thanks!? I knew there was an answer.
Re: Why is sbitx spectrum limited to 25k?

 

Hi William,
The limiting factor is the 40MHz crystal filter, not the audio codec.? Farhan used the higher-frequency 40MHz crystals to accommodate the 25 MHz bandwidth.? The original uBiTx used 12 MHz crystals that were limited to 3 KHz bandwidth, then tried 25 MHz, and ultimately went with the 40 MHz crystals to get the maximum bandwidth on the waterfall.
?
73
Evan
AC9TU
Re: Why is sbitx spectrum limited to 25k?

 

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Processing power of the RPi in the radio? That would be my initial thought...

Ken, N2VIP

On Oct 27, 2024, at 12:09, William Hemmingsen <lee.hemmingsen@...> wrote:

?
The audio codec supports up to 96k, so wondering why the sbitx is limited to 25k?
Why is sbitx spectrum limited to 25k?

 

The audio codec supports up to 96k, so wondering why the sbitx is limited to 25k?
Re: Sbitx bandpass filter

 

Raj,?
?
The amplifier I plan to use is from and old sdr kit and it has that chip.?
?
So I bave to modify the software to generate the three outputs.
?
Will keep looking for ideas how to implement.
?
Thanks,
Juan
Re: FT8 sBitx v3 v4.01 Power Output

 

Hey Kevin,
I noticed that the drive icon is set for 25. That icon is a percentage of the output. Try bringing it up to 75 or 100 percent and see if the watts increase while using FT8. This is the way I increase my power output to 25 watts on FT8. I was even able to make a contact with an Australian ham 9274 miles from my QTH with 100 percent power and an
Elecraft AX1 antenna sitting on my kitchen counter. These radios are great.
Daryl
N4NVS
Re: CAT control crashing when transmit on FT8

 

It is worth checking that it is grounded at one point, i.e. there is no ground loop. Lead the grounding of the devices separately to the grounding point. It is worth winding as much of the power cable (the positive and negative) as will fit on the ferrite ring in parallel. I have 6 turns of an FT140-43 ferrite from 2x 2.5mm2 wires, so that no RF signal goes out on the power supply wire.
--
Gyula HA3HZ
Re: WM8731 alternative?

 

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Wow! Absolutely amazing. I had no idea the stuff was going on. I need to get with the times.

Gordon kx4z



On Oct 27, 2024, at 00:11, WP3DN via groups.io <3voltios@...> wrote:

?
Gordon,?
?
That is the chip used in the adalm pluto.
?
If you want a nice project look for the langstone project.
?
Juan
Re: CAT control crashing when transmit on FT8

 

I suspect common mode RF from the antenna especially if you are using an end fed even with low SWR. Try adding a counterpoise of 10-12 ft of wire connected to the shield of the antenna connector or adding an RF choke by winding 6-8 turns of the coax in a coil.
?
=Vic=
CAT control crashing when transmit on FT8

 

Hi all,
?
My uBitx v6 cat control crash when transmit on FT8. Problem happens in 10m band, when the radio is transmitting, almost half way through 15 second tx interval, error msg pops up that "a usb device connected to computer has malfunctioned". I have wrapped the usb cable in a FT240-43 toroid, 8turns. But this also did not help. Kindly suggest an solution.
?
Regards
Ashok
Re: Sbitx bandpass filter

 

The processor has to generate the BCD depending on your dial frequency.

With 3 lines from processor you can get 7 bands or with this chip 4 lines and 9 bands.

In the older rigs of the 80s this was a standard approach. You run 3 lines all over the PCB

and decode 7 bands for input and final filters and any PLL or such.

On 27/10/2024 9:33 AM, WP3DN via groups.io wrote:
Raj,
How did you generate the bcd inputs?
Juan
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