Mounting of POTY on dish, SWR high, how to fix?

  • Hello,


    I have been listening to QO-100 for the past couple of weeks and today wanted to give transmitting a try. At the moment, I do not have a second dish or other means of doing TX and RX at the same time, so I removed the RX LNB from the dish mount and inserted a POTY in its place. When the PTT was engaged, the SWR LED on the transverter shined red, which means the SWR was too high.


    I experimented for awhile and the SWR LED turned green (low SWR) whenever the POTY was removed from the dish mount and pointed straight up into the year. But I could not get the LED to turn green with the POTY mounted on the dish. I tried moving the POTY in and out and side to side, also tried a different coax cable, no joy. I have two POTYs and tried the other one, same result.


    Any advice on what I need to do to get the POTY mounted properly on the dish with low SWR? I do not have an SWR meter that works at 2.4ghz or much else in the way of test equipment.


    Thanks for any thoughts and 73,

    Bill OM3BD

  • Bill - seems like you need to tune the antenna. You can't realistically do that without test equipment. How did you acquire it?


    Hopefully someone near you can help with test gear. You also, once tuned need to pay attention to the focus of the dish and where the antenna mounts. That might require mechanical work to the feed arm. Nothing difficult.


    Mike

  • Robert,


    Your idea worked, I moved the feed as shown in your diagram and now the SWR LED is green. I had to remove the SMA jack for 10ghz to enable the 2.4 ghz feed to be properly fitted.


    But now another problem, I'm not seeing my signal on the web SDR downlink. I have ample power and we know the dish is pointed correctly since I see the beacons and other stations. Am I possibly transmitting on the wrong frequency? My FT-817ND is on 432.2 mhz, the LO of the transverter is 1968 mhz, so I should be transmitting on 2400.2 mhz. An uplink of 2400.2 mhz should produce a downlink signal at 10489.7mhz, correct? Or am I miscalculating something?


    73, Bill

  • If the dish has not been moved since the LNB and the feed is in the same place - exactly the same, not higher or lower then you are probably pointing correctly but it is only a 60cm dish so you will need to run a few watts to see a reasonable signal. If the transverter is only the 2W one and if you are losing some power elsewhere it might not be enough. Also you have to really check you are on the right frequency which is hard to do with no test gear.

  • Thanks for the replies. I tuned my SDR receiver to 2.4ghz and could not hear myself, so I'm guessing that the problem is that the upconverter is not working. I can hear myself on 432mhz, so it seems the FT817 is OK.


    DD4YR - Robert, yes this is the SG Lab transverter V1.4 with the 20W PA V2. A photo of the dish and mount is attached, it's the same as it was in yesterday's photo, except that the feed is now further from the dish, with the reflector pushed flush against the mount, as shown in the diagram you posted.


    G0MJW - Mike, it is not a 60cm dish, it is 79x71cm. It is possible the dish moved when I took off the LNB and inserted the BamaTech feed, but I don't think so. I'll put the LNB back in to confirm.


    Assuming the problem is a bad upconverter, anyone have an extra for sale?


    73, Bill

  • Bill,


    the plastic LNB holder is on same position and not chanced the angle to the feed arm?

    If yes, than it is ok.



    If the angle has changed then the elevation of the dish has to be adjusted.


    I tuned my SDR receiver to 2.4ghz and could not hear myself, so I'm guessing that the problem is that the upconverter is not working.

    Are the jumper settings for LO 1968 MHz in the transverter correct? there are different possibilities.

    I dont think that the transverter has a problem. I have the same, is good quality and stable.


    the 20W SG-Lab PA has a DC output for HF power measuring. Is this voltage ok during HF power on?

    Is PTT correct jumped and PTT voltage for steering ok?

    And what is DC power consumption? Is drain rising up during transmission?


    73s de Robert

  • Robert, Bill,

    might be if it has not the better - wrote just to make shure !

    - i do not own the 13cm tansverter but

    my 23cm sg-lab has got that split (28mhz frq shift) option on both SMAs with a bridge inside (jumper 1)

    just have a look at sg-lab homepage "23cm transverter"


    Marcus

  • Bill


    I think the problem here is getting information out of you as to exactly what the set up is is quite difficult. If you need help tell us exactly what the end-end configuration is and then we will have a chance of understanding what might be wrong.


    For example your earlier comment about SWR getting better after you moved the feed back does not make sense. Moving the feed should not significantly impact VSWR. We later find out there is a 20W PA in line, but I recall the LED is on the transverter - so where is this VSWR being measured? Is there also an LED on the amplifier? I don't think there is. Therefore you have now a good match from transverter to amplifier which is useful but does not relate to the feed. That amplifier does have forward and reverse power monitoring. This should tell you if you are getting the correct power out and what the reflected power is. Measure these voltages. Compare with the manual. Tell us the result.


    Mike

  • @DD4YR

    G0MJW

    @DG8ABG


    Thanks to all for the replies. My setup for TX is an FT-817NB to the SG Lab transverter (using TX side only) to a 6db attenuator to the SG Lab amp to the BamaTech duo feed on a 79x71cm dish. My setup for RX is a Raspberry 3B with RTL-SDR to a GoSat LNB modified with TCXO. I got all of this equipment from another local ham who says it was working for him and he was making QSOs via QO-100. I put the LNB back on the dish this morning to verify it is still pointed correctly and it is, I'm getting good reception from QO-100. But TX is still an issue.


    First, I may have been wrong yesterday when I guessed the transverter was not working. I thought so because I put another SDR on my laptop, loaded SDR Sharp, tuned to 2400.2 mhz, and did not see my own signal. But even though I was able to tune to 2400.2mhz on SDR Sharp, I later discovered that, according to rtl-sdr.com, the upper limit of this hardware is 1.75 ghz, which would explain why I heard nothing. Also, following your advices, I removed the covers off the transverter and the PA and measured all voltages. They seem a bit low but largely in accord with what is said in the manual. The jumpers appear to be set correctly for LO 1968 mhz (jumpers 1 and 2 on, photo attached if you would like to double check me). So at this moment I don't really have any good clues as to what is wrong, maybe the angle of the BamaTech feed is off, as suggested by Robert.


    Transverter voltage readings:

    B+ 12.1v

    SWR voltage Forward 0.8v Reverse 0.04v


    PA voltage readings:

    B+ 24.2v

    DRV 0.35v

    SWR voltage Forward 3.1v Reverse 0.1v


    There are some anomalies that I don't understand. Perhaps most importantly, Mike says moving the feed should not affect the SWR. In my case, moving the feed (both when it is on and off the mount) does cause the LED to change from red to green. I tried connecting the feed directly to the transverter output (bypassing the PA) and it became much more difficult to get a green LED. To check if perhaps there was a bad coax connection, I tried a different coax cable to connect the feed, same result. The PA has no LEDs, but the voltage readings indicate the SWR is OK.


    I'm also having trouble getting a green LED for transverter input. The manual says orange for low, green for normal, red too high. I'm always seeing the LED with a yellow/green color, and it never changes regardless of the output setting on the FT-817 and regardless of the position of the TX POWER trimmer. I don't know what to make of this.


    Any further thoughts? I can send a video, more photos, or any other details that might help.

    73, Bill

  • SWR voltage Forward 3.1v

    What says the documentation from the SG-Lab PA? I believe 3,1V is near the 20W power.


    If so, your tx power and SWR seems to be ok.


    In next step you have to check are you on the correct TX frequency.

    If OK, you have to check the elevation of the dish, maybe a different angle from the BaMaTech dual feed must be corrected.


    Robert

  • @OM3BD

    Hi Bill,

    forgive me but your photos are too small and do not show the whole. Really, it's hard to give you good advice.

    Is the PTT connected correctly? Are you using the VOX-RF / PTT?

    It is really impossible not to listen to yourself on the satellite with that configuration which is the same as I have. To reduce the power, which is definitely excessive, I have to power the PA at 12 Volts otherwise they ban me from the satellite. ;)


  • I would go with the wrong frequency. If there is 20W going out and not a lot back it's got to be going somewhere. The coax is short I assume, not 50m of RG213! Dish should be brad enough at 2.4 GHz to be aligned. Why don't you check the LO is correct with the SDR ?


    Mike

  • With the SG-LAB transverter there is a very simple way to check the correct frequency set in the local oscillator.

    How to understand what is the current LO frequency:

    After switching power ON, input LED lights up in Red for 3 sec.

    If you switch ON and hold PTT during this time, you can hear on CW, on 432.000 MHZ what are current LO frequencies - RX and TX.