Sunday, June 5, 2016

Synthesizer with ADF4351

I have discovered interesting synthesizer modules on eBay:



I have also found an interesting project from Alain, F1CJN on the Internet.

This synthesizer can easily be controlled by Arduino Uno and a Shield with LCD Display:


Final result is here. A synthesizer that can be programmed for many stored frequencies. Following picture shows one of them:





I will upload more about this wonderful synthesizer shortly. Hoping to use it for a small local beacon for 23cm.

73 Herbert


UPDATE 2016-06-07:
------------------------------

Nothing is perfect. Not even synthesizers. There is a serious problem with spectrum purity when used for frequencies above ~ 1.1GHz. See following pictures.

We need 960MHz reference signal for a Microsource YIG that generates 23GHz. Spectrum around 960MHz seems to be OK:


However, 1296MHz seems to have a problem with spurious signal only 25MHz away and only 39dB suppressed:





Workable solution seems to be to generate the beacon signal on 1/2 frequency and double it. That would require 648MHz. Following picture shows reasonably clean spectrum for that. You can see the 2nd harmonic on the spectrum analyzer already:



Looks like I have to work on frequency locking in my lab - frequencies shown on my RIGOL analyzer are little off the frequencies shown on the Arduino. Luckily, this synthesizer allows (wonder of all wonders) locking to a 10MHz reference!

(to be continued)

73 Herbert
AF4JF


UPDATE 2016-06-10:
------------------------------

I have retrieved my old 23cm filter that I built long time ago with the idea of using Flex 1500 with IF between 28 and 50MHz in mind. This filter was made per W6PQL description and is described incl. pictures and frequency response in my other posting here.
Wonder of all wonders, it fixed the problem! The 1296MHz signal is a little weaker (6-7dBm) but all unwanted peaks seem to be suppressed more than 55dB:

In fact, I can't identify them in the noise floor anymore. Definitely good enough for a small local beacon! I will follow that idea soon ...

73 Herbert
AF4JF


8 comments:

  1. yes.. very interesting, look forward to learning more about it.

    Thanks

    ReplyDelete
  2. ALLo Mr AF4JF the french call is F1CJN, not F1CBF ...
    I have done an extention card to boost the outputs
    and have a 5 volts to 3,3v datas, this is available
    (ask me F1CHF@free.fr)

    ReplyDelete
  3. Cannot see from the photos, but are you powering the system (specifically the adf4351 board) off a usb port? F1CJN mentions this will produce spurious from the ad4351 board, and he is very correct from my measurements of the difference between powering the system from usb port and a 12v Battery

    Dave
    WW2R

    ReplyDelete
  4. Hi Dave,
    Yes I was powering it from USB port in this test. I have tried with separate power supply later, some of the spurious disappeared but these "needles" around 1296.23MHz were still present. I have ordered another board with ADF4351 with different design to test this, because I want to use it for a small local beacon on 23cm.

    Thanks for your reply,
    73 Herbert
    AF4JF

    ReplyDelete
  5. hello Herbert
    Also use the ADF4351A and found the spectrum is far from clean at 1296MHz. Question about the external REF.
    The ADF4351A needs a full TTL level at 10MHz. With external REF the spectrum does not improve. I heard that for the external REF some mods on the board exists but have not yet found more information about that
    good x-mas 73 Jaap PA0O

    ReplyDelete
  6. Hi Jaap

    I don't know about any changes on board. The only thing I heard and tried was to use clean DC power (tested with a battery) instead of USB. That helped a little, but the huge parasitics were still in the spectrum. I have finally fixed that by using metallic filter. REsults are on my blog too.

    Happy Holiday,

    73 Herbert

    AF4JF

    ReplyDelete
  7. Hello all. Help needed, I would like 1Khz step size!
    Had a play with the code and tied myself in serious knots. Can it be done ?
    73 Charles

    ReplyDelete
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