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OpenWebRX [using a transverter/down-converter with the Kiwi]

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  • Hi Lonecrow,

    I took a look at your KiWi but I'm not sure what you have connected at the moment.

    You have 2 very strong BC signals at an indicated frequency of 108.76 (which I assume is 760KHz) and 108.8 (which I assume is 800KHz).

    So I guess it's a wire antenna or similar, but the good news is that the KiWi itself seems OK.

    Can you feed your transvertor into another SW RX to test if it's functioning correctly ?

    Send me a private message if you wish to discuss off list.

    If get really stuck trying to sort out a problem with the transvertor, you can post it to me in the UK I'll take a look at it for you and then send it back.

    Regards,

    Martin - G8JNJ
  • @jks the downconverter is not plugged in right now its plugged into a whip I put it back to HF until I got some alligator clips. The solder job may not have been too good for the downconverter so I've been trying to get time to resolder it.

    I'm going to plug it back in shortly.
  • Thanks for the info - I'm positive the issue is the downconverter. Like I said it was working well except that one large area of noise and then over the weekend on its own it just died.
  • Nope nothing - could you guys take a quick look again you can move the config too if you'd like back to HF - I just have the antenna directly plugged into a discone antenna on our tower. I used to be able to pick up lots of HF with just that antenna before.

    The downconverter I took a look at it, its very well made very simple not a lot of parts on the board and nothing looks blown. I tried a completely different power supply and still nothing when I plug it in. No aircraft at all. So I'm thinking it has to be blown.

    I SHOULD pick up some HF tonight on this thing if I don't then I know the kiwi is having issues. It is picking up the nearby AM radio stations fine.
  • The nearby AM BCB is at -80 dBm (~S7) which is way too quiet. To rule out a fault in the discone/feed get a longish piece of wire, run in outside on the ground for a ways and hook it into the green terminal block on the Kiwi. Compare the spectrum from that to what you're getting from the discone.
  • There isn't anything wrong with the discone - I plugged it into my pi running a spyserver and I was able to pick up all the air band just fine. It seems to only be weak when I plug into the kiwi.
  • I think it may be the kiwi.. you are right. I can't pick up squat with it. You said it could have popped a diode? Any chance this is an easy repair?
  • Try knocking the Z401 TVS diode off the board with a soldering iron. It's on the top of the PCB near the HF SMA connector. There is a silkscreen "Z401" marking. If that doesn't help try knocking off Z402 next to the green header connector close by.

    If the problem persists after removing both diodes then measure DC resistance across the SMA. It should show open. See schematic: http://kiwisdr.com/docs/KiwiSDR/kiwi.schematic.pdf
  • If one of the protection diodes, z401 z402, has gone to a short, before you wipe them off it's dc coupled and an ohmmeter should show it...
  • jksjks
    edited April 2019
    Check the DC voltage used by your ohmmeter before doing that (use a second voltmeter to measure the first). The Vbr min of those parts (CDSOD323-T03C) is 4.0V. You don't want the ohmmeter operating voltage to be driving those TVSs into conduction. See: https://www.bourns.com/docs/Product-Datasheets/CDSOD323-TxxC.pdf
  • Thanks I'l pulling it out now.. been putting out a lot of fires and should have time today or next week
  • edited April 2019
    popped off 1 diode no joy.. popped the 2nd and....... still very weak even the local AM radio station comes in well but all the bands are dead. Going to check the voltage... probably should have read it all before removing the diodes

    What else could I check?
  • First, tell me what resistance you get across the antenna input now that the diodes are removed.
  • edited April 2019
    Any chance you could describe what you mean? From the antenna it has 2 leads and a middle solder point. Have to bare with me, I can follow instructions but have limited electronics experience. I mean do I check it with it powered up? I have a multimeter that is on a 12v battery. Been like literally 25 years since i've used one for anything other than testing voltage. Resistance I just look for a drop right? I just need to know where to put the 2 leads.
  • Any semi-modern multimeter on a resistance setting should do. Check with the Kiwi powered off. Measure between two screw heads on the top of the green terminal block. And to confirm, between the center pin solder pad and one of the outer one of the HF SMA. Put the multimeter +,red probe on the non-ground point in each case.
  • I checked between the middle and edge pin and there was no resistance nor from each inner.outer connection to the actual RF chips. I'll see which screw heads you are talking about. I have a brand new multimeter with a lot of features, just not the hands or vision to do this very well yet :) Getting old.
  • "to the actual RF chips". Not sure what you means exactly. Did you pop the top of the metal shield can and go checking around in there? Because if you're doing that then there is a whole different set of things you need to check for.

    But I feel we're starting to go down a rabbit hole here. Was there any chance of an induced static charge while you were handling the unit since the last time it worked? (e.g. do you live in a low-humidity environment this time of year?) Also, has there been any close-by thunderstorm activity since it was last working? What about high winds + low humidity? (I've been bit by this combination before)
  • nonono didn't pop the shield. There was the final terminal from the diode that went into the rf chip. I just checked to that.

    Nope none of that. Was a nice weekend. It was running fine when I left Friday, just had the noise to deal with and I ordered an airband filter. Came back Monday signal was dead.

    I guess I could try reloading the entire software?
  • Reloading the software isn't going to change a problem like that. I think the ADC preamp (inside the metal shield can) is somehow blown. But I've never heard of a problem like that before.

    You should really try my original suggestion of getting a longish length of wire, hook it to the green terminal block (non-ground pin), and run it outside a little ways. See how the signal strength of AM BCB stations compare.
  • Will do. I'll let you know.
  • edited May 2019
    Yeah there is a difference between signals when I switch antennae but not much. Interestingly I plugged into the discone bypassing the splitter that is grounded (so I have no ground) and I'm picking up everything quite a bit stronger including much more noise as expected. However this is nothing like I had at home where I was getting all sorts of 40 and 80 meter traffic even at home. At least now I'm getting some broadcast shortwave channels. But considering this is 100Ft on the tower makes me wonder.

  • It would be much better to push the "auto scale" button and show spectrum plots ("Spec" button) in addition to the waterfall. That image has WF max/min settings that mask the true sensitivity. The bottom one actually looks pretty good. I couldn't tell from your description what case it corresponds to.
  • I do that to clarify the signals. I can assure you this is too clean for this area even with the auto scale on you don't see squat.
  • Log into the unit to see for yourself.
  • Whatever antenna is on there now is about the same as I saw before (signals much too attenuated). Could you hookup whatever produced the bottom part of the screenshot above?
  • Bottom signal was the discone with no amp directly plugged in. Before when I was at my house I was able to pick up HF off a regular dongle and he hamit up and able to pick people up 1500miles away and sats etc..

    So I switched back to the mini whip with the amp plugged in. Its very poorly installed with a lot of noise. No am filters are on it. But you can see the signals are stronger. Even picked up a fax. But if i plug in a regular dongle to the discone I get all sorts of air traffic, or hamit up I get good reception. Kiwi just doesnt like it.
  • Currently the noise situation is terrible on that Kiwi. You've got a very bad case of Ethernet noise every 60 kHz in certain places (e.g. especially 20m). Also, there is a very loud carrier every 200+ kHz. Then there is a terrible switcher starting at 40 kHz with each harmonic getting successively wider in bandwidth. This is probably responsible for a lot of the broadband noise at HF.

    All of this makes it difficult to judge what's going on.
    Lonecrow
  • Yeah well it is run up a tower with a lot of cables. Its a really poor installation just to get something up while I had the guys climbing. I'm going to move it to its own pole with a g5rv or magnetic loop on the roof. No more mini whips for me. (for my 2nd unit).

    But plugging into the discone you don't see noise this bad and the same cables run right next to it so I should see just as much ethernet noise. Also keep in mind that a lot of the cables that are run up the tower are POE.

    I'm stuck with switching power supplies for now though unfortunatly until I can find some affordable power supplies. I've been looking around but I've had much better reception


    I'm going to give the downconverter one more shot.. I have a feeling maybe that is it.
  • edited May 2019
    I stuck a whip up becasue I thought the Mag Loop noise level was a little better than I remembered, turns out the loop is still covering an horendous level of switchmode noise that I just can't handle with the whips.
    I tried double copper shielded coax, Cat5 with baluns (worked before but this run is longer), lots of ferrite and earthing but everything I did pushed the noise around, reduced in parts but nothing made it useable.

    I've got a portable spot I want to try a whip but in my short garden or close to other kit just waste of time and effort (for me).

    On the power supply why not try one of the DC-DC step-down's mentioned on the forum, linear on the input side, surprisingly good.
    That said here the general switch mode junk is so bad with a whip and and Kiwi on linear supplies it still picks up every switcher to the next county.
    I'll stick a second kiwi online to compare "Loop to Whip" if anyone wants to see a real-time comparison.
    Lonecrow
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