432/28 MHz transverter from transverters-store.com

  • Newcomer here. Sorry if my post is in the wrong subforum.

    My setup: Flex1500 (28 MHz) with ext. GPSDO --> 432/28 transverter from transverters-store.com --> SG-Lab 2400/432 transverter with ext.GPSDO --> Patch antenna in 1m dia. TV dish. (RX: 65cm dia. TV dish + modified LNB with ext. GPSDO --> AirSpy SDR with ext. GPSDO --> SDRConsole)

    The setup is basically working fine, but my TX frequency drifts several hundred Hz over the course of a QSO. Nothing serious for CW/SSB operation, just a bit annoying, but not the best for digimodes. The culprit seems to be the 432/28 transverter from transverters-store.com . I have contacted Serge UT5JCW and he wrote:

    "It is impossible to improve its stability because it is pll synthesizer and it is
    built in chip. Nothing could be done with it
    . "


    1. Does anybody have an idea how to improve the frequency stability of this transverter?

    2. Does anybody know of a 432/28 MHz transverter that is more stable and doesn't cost a fortune? (I know of DB6NT, Microwave East, Elecraft, MiniKits)

    3. Any idea? :)


    73 de Greg DF2IC

  • I had one of those transverters and in the end I threw it. You can improve it by putting a large metal block on the oscillator and then fill the case with cotton wool. It does stop the worst of the drift. I tried inserting a GPSDO local oscillator in instead, but it didnt seem to like it much.


    Sadly there aren't many good and cheap transverters. I have an Electraft 432 one and it isn't all that good either.

  • DF2IC , Greg, at first I tried a similar setup, also with the Ukrainian transverter from 28 to 432 MHz. In order to stabilize the oscillator I put in a small 12-Volt light bulb and placed it very close to the oscillator at the edge of the transverter board. At least that helped to speed up the warming-up process.


    In the meantime I totally changed my strategy and use the Taiwanese BU-500 up-converter with an IF of 50 MHz. However, in this case you should use a good filter, I use a specially-made interdigital filter made by ID-elektronik. It has a notch filter for the LO frequency of 2350 MHz that attenuates that signal by more than 90 dB!.



    Vy 73


    Holger 'Geri', DK8KW

  • my TX frequency drifts several hundred Hz over the course of a QSO. Nothing serious for CW/SSB operation, just a bit annoying, but not the best for digimodes. The culprit seems to be the 432/28 transverter from transverters-store.com .

    People who recently made QSO with me (Hi Remco!) have probably noticed the same behavior - there are some very polite people on QO100 who did not comment to me when they needed to adjust the RIT more than 500Hz over one QSO.


    I very much would like to use 10m in my setup because I need some really really long cables (to avoid trees) and 70cm doesn't work very well over more than 50m coax (unless the coax is expensive, and even then; I want to use RG58 for this).


    I've ordered some ADF4351 boards and I'm planning to replace the LO chip with a GPS-locked 404 MHz signal, so everything is GPS-locked.

    I'm now waiting for the boards to arrive from the East and will report if I get them to work (PLL should be clean because reference is divided by 5 and VCO would be divided by 202; so the PLL noise should be good, hopefully)


    The Ukrainian transverters aren't bad for the money, especially the ones for 6m and 4m, but you putting a 70cm antenna on one is probably not a good idea. As step-up for 13cm QO100 it doesn't matter much (For sat work, Dr Karl explained to me, many years back, that these signals "es versendet sich". which wonderful German I leave untranslated).
    But using it by itself on a 70cm antenna would put it next to Baofengs and similar kit you probably should not measure at.


    And unfortunately, Elecraft's 70cm transverter has issues too, you may want to read NT4RT's story at https://www.evernote.com/shard…r%2BUpgrades%2Bby%2BNT4RT


    GJ

  • Quote

    People who recently made QSO with me (Hi Remco!) have probably noticed the same behavior - there are some very polite people on QO100 who did not comment to me when they needed to adjust the RIT more than 500Hz over one QSO.


    From the QO-100 beginning I use my transceiver (FT-857) in 'split mode', which is more convenient than using the RIT.


    I consider it bad operating practice when a QSO partner 'discovers' he/she is drifting and aligns his/her frequency according to his/hers perception so that I've to retune into the signal and (sometimes) miss information as a result.


    My recommendation (which seems abject in the amateur satellite community) is, when one persistently wants to monitor him-/herself, tune the RX frequency while drifting and not the TX frequency.


    Bottom line: you're not in QSO with yourself but with somebody else,

    (although practice often proves people are in QSO with themselves: "Ooohhlaaa", "1, 2, 3 test", "Probaaa" ; -)

  • om0aao

    Viliam, that's interesting. Which type of this transverter do you use? Is it the one with the attenuator board or just the transverter board? My observation is that the less heat is produced in the transverter case the less the frequency drifts. If I reduce the output from the Flex1500 (28 MHz) to about 1 Watt the 432/28 transverter still gives full output but the frequency drift is considerably reduced.

  • pe1hzg

    I've ordered some ADF4351 boards and I'm planning to replace the LO chip with a GPS-locked 404 MHz signal, so everything is GPS-locked.

    I'm now waiting for the boards to arrive from the East and will report if I get them to work (PLL should be clean because reference is divided by 5 and VCO would be divided by 202; so the PLL noise should be good, hopefully)

    Please keep me updated on the proceedings of your project. Doing something like that is exactly what I was thinking about

  • DF2IC : I agree with Remco:


    "Place a PTC on the LO, or a glued PNP transistor with a resistor to GND so that it heats up the LO-chip and therefore the relative T-change is less."

    Did the same 20 ago with a 10 GHz transverter. There had been X-tal PTC-clips available, so you could pull it over the xtal in the LO. That worked quite well for CW and SSB.


    75, 55 Mike

  • Please keep me updated on the proceedings of your project. Doing something like that is exactly what I was thinking about

    Status update, as requested. To recap, I wanted to add a 432-28 MHz transverter to my setup so I can drive the PE1CMO transverter kit QO100 station over a looooong coax cable, on 28 MHz, using non-critical RG58 coax.
    (I'm using a separate cat5 cable for remote control and monitoring).


    Unfortunately, the Ukrainian transverter's LO drifts, expecially when it is warmed up using the groundplane of the transverterboard. My solution was to replace the 404MHz LO with a LO from an ADF4351 board (Ebay), whose reference is the same 10MHz GPS lock as used by the PE1CMO kit.


    This posting is not a "how-to" but perhaps gives inspiration to others. Many of the info is copied from others, the least I can do is make my stuff available too.




    The ADF4351 board came with a 25 MHz TCXO, but it is possible to use an external (GPS-locked) reference by lifting a few SMD's, see the 2nd picture.


    I completely lifted the 404MHz TXCO off the transverterboard to have solderpads to solder a sort coax to the output of the ADF4351. The transverterboard provides termination; the ADF4351 board has two outputs, as recommended I terminated the other output with 50E.


    The ADF4351 board requires 5V so I needed to add a 7805. This stabilizer is noisy but it is only used to power the 3V3 stabilizer on board.


    To make the ADF4351 work you need to program it using the values from the ADF4351 designer program. While there are solutions with arduino I thought this was way too big, I rather like the approach of OK1CDJ, see https://www.hamshop.cz/pll-adf…d-with-attiny13-kit-i351/

    With apologies to the seller I made the same thing on breadboard with an ATtiny85 (leftover from another project). See the link on the website to the github data. I did find that for the ATtiny85 I needed a 4k7 pullup to the reset signal (pin1 - pin8) to keep the AVR programmer happy.


    I made some effort to minimize the PLL noise of the ADF4351 and used the parameters below (suggestions appreciated)!


    To program, I used the AVR programmer and programmed the ATtiny85 to use the lowest clock speed to minimize noise - all it needs to do is to clock 5 32-bits words and then halts until power is removed. I modified OK1CDJ's code to make it work on Atmel Studio 7, my code is below.


    adf4351-transverter.c.zip


    I also used the CPU board to add a Lock Detect LED using the LD pin of the eval kit and a 1K resistor.


    What else is there to say - when you case the Ukrainian transverters, make sure the case is big enough to have this addition.

  • pe1hzg THe GCD (Greatest Common Denominator) of 10 and 404 MHz is 2 (MHz), so that'll be your PFD. No REF doubler or halver. R counter is 5 (10/5 = 2), channel spacing is 2 MHz and then you don't have a FRAC.


    Although I am not sure what loopfilter is on the standard board, this should give the lowest phase noise for this REF and RF combination. Also try to put the ADF into INT mode (LDF is now in FRAC mode) and experiment with the charge pump current.

  • pe1hzg R counter is 5 (10/5 = 2), channel spacing is 2 MHz and then you don't have a FRAC.

    ...

    Although I am not sure what loopfilter is on the standard board, this should give the lowest phase noise for this REF and RF combination. Also try to put the ADF into INT mode (LDF is now in FRAC mode) and experiment with the charge pump current.

    Thanks for reviewing my programming, it is what I was hoping to get.

    The setting of R was what I could not find (it was staring at me all the time!) and now I think it would look like this:



    I found the schematic of the board (at least, all the parts on the board I can recognize do match:

    ADF4351board.pdf


    How would I optimize the charge pump current? I have an aged Hameg analyzer but it can't look that deep.

  • Interesting, in the circuit diagram a 54 MHz ref is depicted (instead of more commonly 25 MHz)


    Concerning charge pump current, use different settings and check on the analyser the shape/purity of the generated signal and if changing the CP current has an effect at all.

  • Finally the PTC heating elements from China arrived, they are labelled as 12V 50°C

    I made a quick setup to see if there is any improvement on stability. After 15 minutes of warmup and a few CQ calls the system seems to have reached a temperature equilibrium that is quite stable. Frequency drift now is reduced to less than 50 Hz during a QSO and the TX is still on spot after long periods of not transmitting. What bothers me now is the accuracy, the TX frequency is 3-4 KHz higher than the RX frequency, so I'm back to sending dots or dashes or a carrier to tune in on frequency. Well, a AD4351 board is ordered and I will try to reproduce what pe1hzg has done