Posts by DF1QE

    I don't think the lowpassfilter is a matter if the LNB sychronises or not.

    As DH2VA already wrote, the PLL synchronizes best with a high (but not to high) slew rate.

    But the signallevel matters in some LNBs a lot.

    Usually the x-tal oscillates with a level of around 0.5-1.0 Vss.

    If you drive it externally with more than 1.0 Vss, some LNBs don't like it.

    Then the DC-Level on the OSC out pin drops very low and the AC curve gets limited at ground or a frequency doubeling occurs.

    You can easyly test that by inserting a potmeter (around 100 Ohm) as a voltage divider in the REF line.



    I also recommend a low- or bandpassfilter. Else you "spread" your whole shack with a ladder of 25 MHz harmonics if your cables are not well screened. And your neighbour will like it :-)

    (In our region there is a loved radio broadcast on 100 MHz)

    But another question :

    Does not all Oktagon LNBs use 27 MHz reference ?


    Armin DF1QE

    Hello Sat Friends !

    After modification of lots of Single- and Twin-LNBs for external LO input and the use of them I found it uncomfortable to have only one IF output.

    So I decided to modify a Diavolo Quad LNB for external LO, which gives me 3 simultaneous IF outputs now.

    I use one for the NB-Transponder converter, one for the WB-Transponder converter, and one for a SDR-Stick.

    I wrote a complete modificationreport in my Forum for you.

    You find it at :…lnb-f%C3%BCr-externen-lo/

    Hope you find it interesting.


    Armin DF1QE

    Hello Sat-Fans !

    Based on a discussion, after I described my 739 to 144 MHz converters, whether it is possible to make a converter to 28 MHz, I did some experiments, and found out that it IS possible.

    So came out a converter 739 to 28 MHz that really works fine.

    I called it the "NB-Konverter tiny28 V1.0"

    You can find the description at :…-0-739-mhz-auf-28-27-mhz/

    I build up two versions, one for 28,5 MHz for use with regular shortwave receivers, and one for 27 MHz for use with CB-radios. The CB-version is nice for monitoring the beacons and for outdoor use for alignment of dishes and LNBs.

    Sorry, the description is german language only, but there are many pictures, shematics and layouts so anyone might find it interesting. In other case "deepl" helps.

    For me it was a very nice experiance to tune over the OSCAR100 with the old analog "flyheel" of my Trio JR599 and to tune the SSB-Signals with no digital steps.

    If there is a lot of interest in this project I can offer some smiprofessional PCBs and a package of the "uncommon" components.

    best 73 and stay healthy

    Armin DF1QE

    Hello George !

    and the 25 MHz is clean

    Yes I agree .... IF it's clean and not any kind of digital signal ....

    But why always work with minimum components ?

    Are we chinese ?

    Shouldn't we as technicians not better try to optimize components ?

    1 or 2 chokes and 2 or 3 capacitors should not burst our ham budged.

    If I would build such an amplifier for myself it would have a high level MMIC, a regulated power supply with EMV components, a double Pi low pass filter at the output, and may be a damping regulator at the in- and/or output, and sure a tight metal case with good sockets.

    Is that to much for ham radio ?


    Armin DF1QE

    But keep in mind to add a lo-pass filter after the last Amplifier to keep the signal sine form and not to "send out" harmonics.

    25 MHz x 3 = 75 MHz (security Band) and 25 MHz x 4 = 100 MHz (Public radio Band).

    Also you may disturb yourself in the SAT IF.


    Armin DF1QE

    Hello Sat Fans !

    Meanwhile several types of Diavolo Twin LNBs appeared in the market.

    I named them V1, V2 and V3 in order of the appearance in my Workplace.

    For V1 and V2 I already wrote modification reports and posted them here earlier.

    Meanwhile I found out that V3 is the oldest one, then came V1 and V2 seems to be the "up to date" one.

    I got several requests about V3, which I thought it was out of the market, but they were still sold, especially on Amazon.

    So I wrote a modification report for V3 too.

    BTW: V3 is completely different to V1 and V2.

    Here is a list for all Diavolo modification reports I wrote :

    V1 :

    V2 :

    V3 :

    All Pages are german language but there are lots of photos and shematics so it will help all.

    In other case "deepl" helps.

    Hope this was an interesting information for you.


    Armin DF1QE

    Somehow my entry from September disapeared, so I post it again :

    After my Oldschool Converter project I developed and build an other tiny converter 739 MHz to 144 MHz based on some earlier publications I found in the net.

    It works excellent for receiving Oscar100 NB transponder with a 2m RX.

    I wrote a complete report and building instruction for it.

    You can find it at :

    Sorry, german language only.

    But there are lots of pictures an shematics also for download so everyone should it find interesting.

    In other case "deepl" helps :-)


    Armin DF1QE

    PA3FYM : Hi Remco !

    That's why I wrote "new (?)"

    But ok, let's say : you won :-)

    Anyhow, there is some difference.

    As I saw in your Twitter picture, you just disconnected one side of the x-tal and directly connected it to the F-socket.

    I don't think the x-tal works optimal this way.

    I did some experiments until the x-tal was in optimal resonance.

    In the Diavolo quad I modified, I even mounted a variable C to "tune" the x-tal.

    But to all of you who did that before : Why did noone post it here ?


    Armin DF1QE

    DL5MGD Hi Andreas !

    Uhhh, not a good idea ...

    The x-tal needs this capacitive load to work on the right frequency.

    And actually the coax input needs a termination, at least a nearby one ...

    Ok, if you didn't implement the resistors, you have the high capacity of the coax on one side of x-tal,

    but then you need at least half the capacity (6p) on the in pin to get the x-tal in a good resonance.


    Armin DF1QE

    Sorry Remco, I cound not resist this wordgame in the subject :)

    So Folks, here's a new (?) idea for injecting an external TCXO, which I successfully tested.

    Just leave the x-tal where it ist, disconnect the LO out pin of the PLL-Chip, and inject the external LO at the x-tal.

    I tested succsessfully this method with 2 Diavolo Twin V2 and one Diavolo Quad V2.

    This method has some advantages :

    you don't have to remove the x-tal

    you can easily go back to internal LO (original)

    the external LO signal will be filtered by the x-tal

    easy to implement

    so many advantages :)

    The value of R1 in my shematic determins the sensivity and optimal level of the external LO.

    With 820 Ohm at a RT320M chip it is optimized for 1Vss LO input.

    For other levels you should make your own experiments.

    The value of R2 in my shematic depends on which impedance and coax cable you use.

    68 - 82 Ohm is fine for 75 Ohm systems.

    47 to 56 Ohm is fine for 50 Ohm systems.

    But this value is actually less important.


    This method is not useful for (older) NXP chipsets.

    Therefor you better take a look at Remco's Subject : other-method-to-inject-external-ref-into-lnb


    Armin DF1QE

    @pe1hzg : I won :-)

    Take a look at : New ATV Converter for Oscar 100 WB Transponder



    I have been considering prototype-ing something like this with a few changes:

    To be fed from the IF output, not external power supply;
    Allow it to be fed from 18V;
    18V DC power from the IF output passed-through to the input;
    144 MHz filter removed, or changed for 1335 MHz (1335 = 740 + 595 MHz)

    This way, one would have an in-line converter that I can put in-line between LNB and sat receiver, and which will convert the WB passband to a frequency range the sat receiver accepts. Because the sat receiver supplies 18V, the LNB would switch polarity.

    PA3FYM : Hi Remco !

    Yesterday I modified an older Divavolo Twin LNB.

    It was what I call in my reports the V3. (not found often)

    I did that as help for another OM.

    It has a complete different design compared to modern LNBs.

    For each channel works a seperate PLL & Mixer chip, but with a common 25 MHz X-tal.

    The chips are TFF1014HN from NXP.

    In an NXP short form application catalog I found exact this design.

    So I started my usual methode to find the in and out pins.

    25 MHz injected to one pin and monitored the other pin if they come out.

    And right the first test was fine.

    For some reason, I don't know, may be it was the RF sense of my body :-) , I twistet the pins and what wonder : The 25 MHz were also transfered, with the same quality and level.

    Another wonder was, that one pin had a few volts DC-Level, the other not.

    It was not possible to follow the PCB tracks, so I assume one pin is capacitive coupled.

    So what type of Oscillator ist that ?

    The answer is simple : It must be a push-pull oszillator.

    This oscillators are fully symmetrical an were frequently used for high frequency x-tal oscillators.

    Now it makes sense, why there is no specific in- and outpin.

    They remind me to my old pirate radio transmitters I build 45 years ago :-) 2xCV6 or ECC85 :-)

    But the thing why I write this to you is : Now your whole thread about symmetrial feeding the LO makes sense.

    If inside the chip, the design continues to be symmerical, it's sure that symmtrical feeding improves the singnal quality.

    I tested both feedings asymetric and symetric, and the signals at the x-tal pin were extreme better with symetrical feeding with a transformer.

    So again I must say thanks to you for this great idea !

    But for all others : Keep in mind, the symetrical feeding is important for this type of oscillator only, othes work better asymetric.

    I documented all with photos and will write a report about the modification as soon as find the time.

    And BTW, I found a perfect FXC for a trafo : the inductivity found in an old GEDU2411 Antenna wall plug from Hirschmann.

    With windings it has exact the size of the HC49 x-tal and it has a big inner hole to take enough windings with good isolation.


    Armin DF1QE

    Hi Leonid !

    Thanks for your comment.

    Hmmm, interesting idea ....

    I never checked that out.

    I'm sure it depends on the type of modulator.

    Older versions had free running oscillators, but I saw newer ones with a x-tal based PLL.

    The newer ones should be stable enough to act as LO for ATV converting.

    But to be honest, why doing that if one can have it in a single 5x7 mm SMD case ?


    Armin DF1QE