Posts by DJ0VL

  • What TX amplifier do you plan to use?

    Quote from DD4YR

    You can describe how you did it.... ?


    73 de Robert

    Hello Robert,


    It's a small sketch running on an Arduino Nano (or Raspi Pi Pico with small adaption). The Arduino connects to the LMP92066 via testpads on the board. Some commands send to the Arduino by a terminal program read/write registers of the LMP92066. The main task was to read and understand the datasheet and to figure out the I2C wiring on the board :)


    In case of interest, I can publish the sketch and some instructions for use (in German).


    73 Jean

  • What TX amplifier do you plan to use?

    Hello Matthias,


    Ok, my assumption was wrong - sorry.


    Looking at the picture, your PA might use a LMP92066 for the bias voltage generation.

    I've written a tiny tool for the programming of those LMP92066, adjusting the bias voltage and the LUT of the peak transistor was no big deal (at least with my BLC9G22XS-400AVT PA).


    73 Jean

  • What TX amplifier do you plan to use?

    Hi Andrea,


    Good luck with the modification. Please email me if you need to reprogram the digital potentiometer.

    I'm not yet done with HF modifications. Without any changes to the signal path, the small signal gain at 2.4GHz is some 3dB lower compared to 2.6GHz.


    73 Jean

  • What TX amplifier do you plan to use?

    Hi,


    My DC bias modification for the BLF8G27LS-140V is quite simple. I removed two resistors in the bias path of the peak transistor (marked as ‘1’ and ‘2’ in the attached picture) and connected the bias by a wire (endpoints marked as ‘3’ and ‘4’). The wire connects the switched bias voltage to the peak transistor’s gate.


    I guess that it would be possible to change the potentiometer range to the desired value by reverse engineering of the bias circuit, however I’ve chosen the simple way. The transistors seem to be well matched, as their bias currents are nearly identical with their gates connected in parallel.


    73 Jean DJ0VL


  • What TX amplifier do you plan to use?

    Hello Matthias,


    I did some bias-adjustment tests on the PA that was sold as „ …4x BLF8G27LS-140V – STEREO ..:)“, assuming this is the PA we are talking about.


    This PA uses a programmable 8bit potentiometer for the bias adjustment of the main and the peak transistors (as part of an analogue temperature compensated bias network). Unfortunately, the programmable bias voltage range of the peak transistor is limited to 0.4-0.6V.


    As the PA uses the same transistor type for main and for peak channel, I simply connected the bias of the peak transistor in parallel to the main transistor and set the bias current to 1A per transistor.


    73 Jean DJ0VL



    PS: the other PA (2x BLC9G22XS-400AVT-2) that use the LMP92066 for the bias generation can be programmed to set the peak transistor to mode AB without any hardware modification.

  • Where can I buy a TCXO

    Hi,


    The main issue with the W3PM based design is the usage of fractional-N mode for the correction of the Si5351a output frequencies.


    There have been several discussions showing that a clean output cannot be realized when using an Si5351 in fractional-N mode (as required for the frequency corrections with this design).


    An Si5351running with integer mode is able to generate 25MHz and 40Mhz with a signal quality that is good enough for QO-100 operation.

    73 Jean DJ0VL

  • New DXpatrol "Groundstation" now Full-Duplex !

    Hi all,


    I do not own nor intend to buy a DX-Patrol groundstation. This said, I would be disappointed seing an offset of 200Hz between RX and TX with a setup claiming to be GPS locked.


    In principle, the ADF4351 can be programmed to output the exact frequency for generating the LNB LO of 10057,0 MHz as required for an IF of 432,5 MHz. The trick is to calculate using fractions and not trying to solve the fraction.


    According to the datasheet, the output frequency of the ADF4351 calculates to RFOUT = fPFD × (INT + (FRAC/MOD))

    Assuming fPDF as 10Mhz, 1650.379487xxx MHz can be generated exactly (meaning exactly 64 * 10057/390) with e.g. INT=165, FRAC = 37 and MOD = 975.


    73 Jean DJ0VL

  • Red Alert on the WB Transponder

    Hi Peter,


    On the NB-Transponder, the signal seemed to move in from lower frequencies, see the noise level shape. A few seconds after taking the screenshot, a huge signal (20 or more carriers spread around 100 kHz) swept in from the lower band end. Unfortunately, the signal was shut down before I could make another screenshot.


    73 Jean DJ0VL

  • reporting wspr bcn

    Hello Rene


    Thank you for the details on your nice setup with a Raspi for the beacon generation. For my test (I wanted to double-check the stability of a recently build homebrew GPSDO in addition to some ADEV measurements), I used my Pluto with just the SPF5189 driver into a 75cm dish with helix feed.

    The reports given by Edson nicely reflect the output level difference.


    73 Jean DJ0VL

  • reporting wspr bcn

    Hi all,


    My beacon transmission on Tuesday was just a short test for the stability of a new homebrew GPSDO. So far I do not intend to operate the beacon on a regular base.

    Nevertheless nice to read that he signal could be received with 1-2 db higher SNR levels as I experienced with my 75cm dish.


    73 Jean DJ0VL

  • Goonhilly WEB-SDR is not on Frequency ?!

    Quote from G0MJW

    I am sure he knows. I will ask next time. The reasons for these errors are probably interesting and subtle.


    See http://g4jnt.com/QO100_Stab.pdf

    Thank you for this highly interesting paper. Figure 4 confirms my observations regarding the short term stability. I commented on this as the observed stability may be normal behaviour for the type of GPDSO used, however it seems somewhat higher than the stated and measured stability data for this GPSDO.


    I'm fully aware that we are discussing deviations on a very high level, nevertheless I'm interested in knowing the reason for the errors. We do not know whether its all due to the stability of the GPSDO, but imho a decent GPSDO has a significantly higher stability.

  • Goonhilly WEB-SDR is not on Frequency ?!

    Quote from DH2VA

    Allan deviation is stability.. 130Hz in 10 GHz is accuracy. Check here for a good explanation of the subject.

    That said, there are numerous explanations for this offset including hw failures. Maybe telling the WebSDR team directly?

    Thanks for the link and of course you are right. I'm familiar with the difference between stability and accuracy, my comment referred to the noticeable jitter. Sorry for the unclear wording.


    73 Jean


    PS: I would like to tell the team directly, but finding a contact address on the webpage is not easy.

  • Goonhilly WEB-SDR is not on Frequency ?!

    Hi all,


    Half a year later, the issue remains unchanged. The Goonhilly WebSDR now seems to be off by around 130Hz. Apart from the offset, there is a visible jitter of quite a few Hz.


    The screenshot below shows the same audio signal as received simultaneously by the Brazil WebSDR (trace at the left side), the Goonhilly WebSDR (trace at the right side) and by my own receiver (trace at 762Hz).


    The Brazil WebSDR (http://appr.org.br:8902/) is shown just for comparison as Thomas mentioned it above and I guess it uses a simple TCXO as a reference. Both offset and drift are heavily dependent on the time of day.


    73 Jean DJ0VL


  • I think I broke my Pluto HELP!!

    Trevor,


    C123 and C124 form a capacitive voltage divider to adapt the ~1.8Vpp output level of the original Pluto oscillator to the 1.3Vpp required by the AD9363.

    The XTALN input of the AD9363 has an input resistance of about 10kOhm in parallel with 10pF, so that the capacitance of the input pin is sufficient to form the voltage divider with C123. Therefore C124 is not placed on the PCB.


    73 Jean