Changing the drive level of tune doesn't work.

[on3vna]

When setting the TUNE level in the transmit options to 10 we would assume that the output power would be 10% of the maximum output level.
There is no change at all in the output level it is always fulll transmit power.

[pavel-demin]

I don't think that I can do anything about this problem. It's a known limitation of the Red Pitaya board.

Red Pitaya does not have any hardware for the drive control. I suppose that some kind of variable or fixed amplifier or attenuator should be used to adjust the output level. I've seen a nice set of fixed value SMA attenuators at the FUNKAMATEUR online shop:
http://www.box73.de/advanced_search_result.php?keywords=Dampfungsglied+sma

Another idea discussed on the Red Pitaya forum was to use the OUT2 output to control an external amplifier:
http://forum.redpitaya.com/viewtopic.php?t=265&p=5292#p5292

[on3vna]

Maybe this could be used : AD8321 or a replacement for it. I have still 2 in the my junkbox.

[on3vna]

AD8324 could be used 3.3V supply or AD8325 5V supply.

[pavel-demin]

A discussion of a variable attenuator based on BAP70Q (quad PIN diode attenuator) can be found at this link.

[on3vna]

Advantage of the ADXXXX is that it is to be programmed by SPI.

[pavel-demin]

I've just found an interesting article about a variable attenuator based on HSMP-3816.

Looks like it works quite well between -4 and -20 dB.

[pavel-demin]

Advantage of the ADXXXX is that it is to be programmed by SPI.

I think that a pin diode attenuator could be combined with a small SPI or I2C DAC like AD5601 or AD5602.

[on3vna]

Both solutions could be tried out and see what is best. Always available for testing -;)

[on3vna]

Pavel,
I was looking around and found this:

PE4302 Digital RF step attenuator.

This could be used in the TX path and also in both receiver paths and is not so expensive.
you can find them on ebay .
http://www.aliexpress.com/store/product/PE4302-Digital-RF-Attenuator-Module-High-Linearity-0-5dB/1829717_32473840163.html

[on3vna]

Hello Pavel,

http://wiki.redpitaya.com/index.php?title=Command_line_utilities

Here i found that via the command line utility it is possible to set the amplitude of the generated signal:

redpitaya> generate
generate version 0.90-299-1278

Usage: generate   channel amplitude frequency <type>

       channel     Channel to generate signal on [1, 2].
       amplitude   Peak-to-peak signal amplitude in Vpp [0.0 - 2.0].
       frequency   Signal frequency in Hz [0.0 - 6.2e+07].
       type        Signal type [sine, sqr, tri].

Is that not something that can be implemented in the transceiver also for the output drive ?

Rgds
Johan

[pavel-demin]

The generate program scales the signal digitally before it's sent to the DAC.

In case of SDR applications, I don't think that scaling the input to the DAC is a good idea. It decreases the effective DAC resolution, SNR, etc.

Then it depends on what exactly you want to achieve.

If it's just for the test signals, then it's possible to generate digitally scaled test signals with via Setup/Tests. Level controls amplitude. Freq # 1 and Freq # 2 can be set to 0 to generate only one frequency.

If it's for the transmitted signals, then with Radio Model set to HPSDR the signals can be digitally scaled with the Drive slider.

[on3vna]

Well we had a discussion here at the QRL and indeed scaling the DAC, you will pay in resolution SNR etc.

So you say that with the type of radio set to HPSDR iso hermes the output level can be changed with the drive slider ?

[pavel-demin]

So you say that with the type of radio set to HPSDR iso hermes the output level can be changed with the drive slider ?

Here is what is written in HPSDR - USB Data Protocol :

When using Hermes or PennyLane the Transmitter output level is set by the drive level value (C0 = 0b0001001x, C1 = 0x00 to 0xFF) and not by the amplitude of the I&Q signals. These are held to a peak value of +/-1.0 by AGC action in the PC DSP code. When using Penelope the amplitude of the I&Q signals controls the output level. Set the drive level (C1) to 0x00 when Penelope is selected and whilst the transmitter is not active.

[on3vna]

Pavel,

The output of the DAC could be changed by putting in serie with the resistors used in AVIRES and BVIRES (R47 and R48 ) a FET like is done with some DDS chips. Hence it would be possible to drive the fet with a DC voltage and control the output voltage of the DAC and still keep the resolution etc.

Much simpler then using the AD chips or PIN diodes. Of course this needs some soldering on the red pitaya.

Rgds
Johan

[pavel-demin]

Yes, it's similar to how it's done on the Hermes board:

• PowerSDR sends drive level (0-255) to Hermes (see protocol description, C0 = 0001001x, C1 = Hermes/PennyLane Drive Level)
• then see the code in http://svn.tapr.org/repos_sdr_hpsdr/trunk/Hermes/Source/Hermes_v3.1/Hermes.v
• the value of the drive level is stored in the IF_Drive_Level register
• this value is used to generate a PWM signal that is output from FPGA as DAC_ALC
• then see page 9 of the schematics in http://openhpsdr.org/support/Hermes/Hermes_Final_Changes.pdf
• the DAC_ALC (PWM) signal is buffered, filtered and connected to the REFIO and FSADJ pins of the DAC chip

If I'm not mistake FSADJ is similar to AVIRES and BVIRES.

[on3vna]

I have given the info to RED PITAYA team concerning the implementation with the FET. I would love to try it out but the components on the pba are to small for my tools and eyes. I don't want to screw up my red pitaya.

Finally i did the hardware modification but with a DS1803-10.
So now I can change the drive level of the red pitaya.
The DS1803 has two 10K resistors that are I2C controlled, either separate of both the same value can be applied. This means that this mod also can be used in pure red pitaya applications in order to change the output levels independently .
I also added a screen shot from the spectrum analyser showing min and max output power from the RED
Some pictures of the HW change (Tnx Giovanni for the artwork)

[on3vna]

code changed for the HW modification.

[pavel-demin]

Great! I've added this code with a few minor changes to my repository: 384c6b0.

I've just replaced the 8-bit command 0xAF with the 16-bit command 0xA9.

[on3vna]

Pavel,
I think we can close this now as we have 3 ways of setting the drive level.
2 hardware solutions and 1 software solution

73 de ON3VNA
rgds
Johan

[ka6s]

Pavel,

You have us all very curious. I was wondering if you could publish a
future pin-out utilization possibly?

1. You have checked--in connecting the A/Ds recently - what are these going
   to source SWR F/R?? What is the pin assignment?
2. If you are going to bring in/out I2S channels for an external Codec -
   what is the pin assignment there?
3. What is the Software solution for the Drive?

Inquiring minds are REALLY curious!

Thanks,

Steve KA6S

On Thu, Sep 15, 2016 at 1:14 AM, on3vna notifications@github.com wrote:

Pavel,
I think we can close this now as we have 3 ways of setting the drive level.
2 hardware solutions and 1 software solution

73 de ON3VNA
rgds
Johan

—
You are receiving this because you are subscribed to this thread.
Reply to this email directly, view it on GitHub
#279 (comment),
or mute the thread
https://github.com/notifications/unsubscribe-auth/ABsJOCiINCnQu0KWJZ-52IaOUKpmajemks5qqP5rgaJpZM4Izkir
.

[pavel-demin]

1. You have checked--in connecting the A/Ds recently - what are these going to source SWR F/R?? What is the pin assignment?

Yes, the slow analog inputs are used for the Fwd and Rev power measurement. Fwd - Analog input 0, Rev - Analog input 1.

1. If you are going to bring in/out I2S channels for an external Codec - what is the pin assignment there?

The I2S interface is sharing pins with the ALEX interface. So, the two can't be used simultaneously.

1. What is the Software solution for the Drive?

It's what I didn't want to implement initially but after all I've added a multiplier just before the DAC interface. This way the DAC samples are scaled down digitally. The scale factor is controlled by the Drive slider in PowerSDR mRX PS.

[ka6s]

Thank you Pavel - that helps greatly!

Steve

On Sat, Sep 17, 2016 at 2:28 PM, Pavel Demin notifications@github.com
wrote:

1. You have checked--in connecting the A/Ds recently - what are these
   going to source SWR F/R?? What is the pin assignment?

Yes, the slow analog inputs are used for the Fwd and Rev power
measurement. Fwd - Analog input 0, Rev - Analog input 1.

1. If you are going to bring in/out I2S channels for an external Codec
2. what is the pin assignment there?

The I2S interface is sharing pins with the ALEX interface. So, the two
can't be used simultaneously.

1. What is the Software solution for the Drive?

It's what I didn't want to implement initially
#279 (comment)
but after all I've added a multiplier just before the DAC interface. This
way the DAC samples are scaled down digitally. The scale factor is
controlled by the Drive slider in PowerSDR mRX PS.

—
You are receiving this because you commented.
Reply to this email directly, view it on GitHub
#279 (comment),
or mute the thread
https://github.com/notifications/unsubscribe-auth/ABsJOK6QFLXPJXcyjt06dFV1To3lBcarks5qrFuHgaJpZM4Izkir
.