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Default [KD8CEC] How to connect SDR (RTL-SDR) to uBITX and uBITX Firmware CEC Version V1.071 (Beta) Release

KD8CEC Amateur Radio

How to connect SDR (RTL-SDR) to uBITX and uBITX Firmware CEC Version V1.071
(Beta) Release

Posted: 13 Apr 2018 08:58 AM PDT

How to connect SDR (RTL-SDR) to uBITX

(uBITX Firmware CEC Version V1.071 Beta Release,
At the end of the beta test, we will release to 1.08.)

uBITX and SDR usage will be divided into several and will be posted.
Some users have attempted to connect SDR to uBITX.
I also supported SDR connections from uBITX since CEC Firmware 1.070 (Beta).

In addition to CEC Firmware, any firmware can connect SDR in the following
way.If you are not using CEC Firmware version 1.070 or later, you need to
modify the source code a little bit because RTL-SDR can only receive more
than 24Mhz.

Also, there are a lot of better ways than I explain. I think that hardware
experts will find ways to improve even more.
For example, using Latch Relay to control SDR connections, RTL-SDR to
connect impedance, etc.

The current source structure is constantly changing to support various LCDs.
After the LCD type to support is selected, we will organize the source file
structure and distribute it.
It will not take long. Please upload the Hex file using XLoader or avrdude
for the time being. (I sometimes push source code to github but do not use
it. It will continue to change for the time being)


uBITX CEC Firmware V1.071 Beta

1. Cable preparation
If you are going to connect SDR directly to uBITX, this is not necessary.

2. Connecting the cables
The schematic of ubitx can be downloaded below.

I connected the SDR to the bottom.

As you can see in the picture, that part is convenient to connect.
I will write about why I chose that part (the front of the 12Mhz filter) at
the end of this document.

In particular, do you see a blank space next to it? I will put a relay on
that space later.
But SDR performance is better than I thought. So maybe I can continue to
use it as it is now.

If you SDR built in uBITX or connected the SDR antenna directly to the
uBITX, the following operation is not necessary.

It's a really simple work.

3.uBITX Manager Settings
Click th 'Connect'

Click the 'Read from uBITX'

Click the 'Deocde ='

4.Configuration for SDR
You will see the following screen.

4-1 SDR Offset Frequency
This is where you enter the base frequency to transmit to SDR.

(Again, SDR connections do not necessarily have to use my firmware.
In most firmware you can change the IF frequency very simply by simple
modified source code.)

Since I can receive more than 24Mhz for RTL-SDR, I entered 30Mhz here.
This depends on your radio condition and the type of SDR you have.

Enter 30000000

4-2 AutoSave - Enabled SDR Mode
In CEC firmware, uBITX should either send sound to the speaker, send it to
SDR, or choose either one.

In SDR mode, no sound is output from the speakers.
In order to prevent misunderstandings, uBITX always operates in speaker
mode when it is bootup.

However, if you have a very good SDR mode like me, you may want to keep in
SDR mode until you switch to speaker mode through the menu. If you check
this menu, SDR Mode will not be automatically released even if uBITX is

I checked this option because SDR Mode and Speaker Mode can be switched at
any time by menu.

4-3 SDR Frequency Mode
This part is too complicated.I had to make a few options for most SDR
software on Windows and Linux.I will post an optimal connection with SDR
Sharp, Linux, and Raspberry based SDR.

0 is transmitted at a fixed frequency.

1.The frequency entered above + uBITX is connected to SDR at the frequency
shown on the LCD window.
For example, if the offset frequency is 30.000000 Mhz and the frequency
displayed on the uBITX LCD window is 7.074000, it will be received at SDR
of 37.074000.

2.SDR Offset Frequency + Mhz unit.
If Offset frequency is 30.000000Mhz and uBITX LCD display 7.074000Mhz, SDR
will be received at 37.074000Mhz.
If Offset frequency is 30.000000Mhz and uBITX LCD display 14.074000Mhz,
SDR will be received at 34.074000Mhz.

If Offset frequency is 30.000000Mhz and uBITX LCD display 21.074000Mhz,
SDR will be received at 31.074000Mhz.
That is, We can read the frequency from SDR even if it does not support
Cat and IF.

3.SDR Offset Frequency + Mhz unit.
If Offset frequency is 30.000000Mhz and uBITX LCD display 7.074000Mhz, SDR
will be received at 30.074000Mhz.
If Offset frequency is 30.000000Mhz and uBITX LCD display 14.074000Mhz,
SDR will be received at 30.074000Mhz.

If Offset frequency is 30.000000Mhz and uBITX LCD display 21.074000Mhz,
SDR will be received at 30.074000Mhz.
Now select 0 because the example uses SDR-Radio to support CAT
communication and IF input.

5.Press the '= Encode'

Write to uBITX

6. Omni-Rig Setting (Option)
It is not necessary.
However, I used the Omni-Rig because I wanted to be able to communicate
uBITX simultaneously with SDR software and Wsjt-X.

You only need to set Rig Type, Port and Baudrate.
Rig type : FT-817
Port : COM 13
Baud rate : 38400

Do not press 'OK'. You must leave it alone.

7.Launch the SDR Console.

SDR-Console can be downloaded from SDR-Radio. Please refer to the SDR-Radio
homepage for details.

Run your own SDR.

The reason I chose SDR-Radio is below.
This is because it supports IF output.
This is a great way to connect your HF device to your computer.
But do not worry. With the above options, other SDR software can be used
without difficulty. Including Linux.

Press the Select button on the View toolbar.

Select External Radio.

Then an External Radio button will be created on the toolbar as shown below.

Click the External Radio button. The program will be restarted and the
following screen will appear.

Press the '?' Button.

If Omni-Rig is running, it will automatically be selected as below.(if
unselected, select '1 : FT-817:On Line')

Click the Frequency button on the left.
Select IF output as shown below and enter 30.000.000.
30.000.000 is the value entered in uBITX Manager.

Press OK to close the window and press the 'Track' button.

SDR and uBITX are fully connected.

8.Switch to SDR Mode
Menu - SDR Mode On? - Press the Button

9.Enjoy playing uBITX with SDR

The reason I chose SDR-Radio for my first posting on uBITX and SDR
connections is that it is easy to apply to most firmware that supports CAT
communication as well as my firmware.

I used the $ 8 low-cost RTL-SDR. Digital communication as well as general
communication is possible. Using the IF to connect to the SDR for computers
was limited to most expensive HF radios.

In particular, SDR-Radio can receive multiple frequencies at the same time.
Wsjt-X receives FT8 and I can receive CW.

The following post is an application of SDR-Radio.
I will post SDR #, Linux, or Raspberry based SDRs in order.

11.Why did I put the SDR connection point there?
I looked for a way to connect SDR to uBITX.
Most people used the SDR connection point following a 45Mhz filter.
It is a great way and is the only way to connect SDR.

The purpose of connecting the SDR was probably to see the spectrum.
But the test result was too weak. If the purpose of connecting the SDR to
the uBITX is to see the spectrum, it could be used, but the SDR could not
be used as the main receiver.

So I chose the front of the 12Mhz filter, which is amplified once more.
But the signal here is around 12Mhz, which is not available with RTL-SDR.

I decided to put 12Mhz at a good frequency to connect to the SDR and
instead use the speakers instead. Of course, when SDR Mode is off, you will
hear the sound from the speaker again.

The second reason I chose this place is to make it a little more convenient
for most SDRs that do not support IF and Linux-based SDRs.
It is to change the frequency connected to the SDR so that the frequency
can be easily read in the SDR software.
The other candidates were Sound Out, 12Mhz after the filter passed.

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