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

24

Comments

  • Managed to hack a way to get the fm bandstop inline and it helped a bit. Take a look for yourself though there is this HUGE area of noise I have no clue about.

    Shame there is no way of LIMITING the bandwidth. I really only need from about 119-136 but there are only option from 30-32Mhz

    The 125-134 noise is probably the last thing I need to kill.
  • is there a + conversion gain in the downconverter? How much? What unit did you buy?
  • edited April 2019
    http://www.hsmicrowave.com/

    He made it custom for me. Nothing but the input, output and 2 poles to attach + voltage and ground. I just soldered a raspberry pi power supply to the terminals.
  • if the RPi PSU is a switcher, that is the source of the noise
    Lonecrow
  • Hi Lonecrow,

    Looking at the spectrum and using the new peak hold function, the noise has a fairly well defined 'shape' that could possibly be a VHF Digital TV transmission using the ATSC standard.

    I have a theory about how this could be occurring, but a bit of testing is required to prove it.

    First - does the noise go away when you disconnect the Air Band antenna ?

    If it does then try.

    1. Adding an aircraft band Band Pass Filter to the input of the transvertor.

    Something like the "bandpass filter BPF 118-136MHz for Air band" that are sold on Ebay.


    2. Adding a 30MHz low pass filter between the transvertor and the KiWi.

    Something like the "ZETAGI F27 FILTER ANTI TVI FREQUENCY 0-30 MHZ 300W" or some other CB TVI filter as sold on Ebay


    Do either (or both) of these things appreciably reduce the level of the interference ?

    Regards,

    Martin - G8JNJ
    Lonecrow
  • edited April 2019
    I'll check. Not even sure how to determine whether its a switcher I just have a pile of 5v power supplies from various devices over the years. Do they usually designate on the supply with a sw or something (not at work can't check right now)

    I have an AM radio notch filter could that help between transverter and kiwi?

    Also you mean add an airband pass filter on top of the fm filter?
  • Hi Lonecrow,

    I think the problem could be a very strong out of band VHF Digital TV signal that is being down-converted to a frequency that is being aliased by the KiWi to the frequency range you are seeing.

    The reason for trying the Airband filter is to see if it reduces the unwanted signal that may not be suppressed sufficiently by the transvertor's built in filters.

    The 30MHz low pass filter will help test to see if the problem is the down-converted un-signal that is being aliased by the KiWi sampling frequency from somewhere around 70MHz to 18MHz.

    As I say, it is only a theory at the moment.

    Regards,

    Martin - G8JNJ
    Lonecrow
  • edited April 2019
    Ok I just followed the instructions and edited the band plan .. with a little effort I have got it working. So it does in fact display 118-137Mhz as the air band. It does say "Amateur" at the end though and I did'nt specify that. Any way to remove?

    Also is there a way of narrowing the bandwidth display to only display the airband and ignore below?

    What I was getting at is I didn't pick this up with sdrsharp but like I said its a 2mhz bandwidth. When I'm back at the office I will def unplug to see if the noise is from the antenna. We do have a lot of hot signals nearby.

    I'll see about getting the 30Mhz filter. In the meantime the question was can I use an airband filter and an FM filter together inline? Will that even help attenuate the signals?
  • edited April 2019
    One other issue I've found are that some of the actual signals are slightly offset to the true channel and the manual channel entry box has got small so you can't see the actual tuned frequency.

  • Also this will need to be fixed somehow

  • Hi Lonecrow,

    Yes you can use the airband and FM band filters together, if the airband filter is good enough you may not need the FM band notch.

    I think the reason you don't see it with the dongle and SDR Sharp may be an issue with the KiWi that you probably wouldn't otherwise notice, but this is what I'd hope to test.

    To get the frequency off-set correct you may need to either adjust the transvertor reference frequency and / or the KiWi Frequency scale offset (kHz) value.

    Regards,

    Martin - G8JNJ
    Lonecrow
  • Its funny because some of the channels and freqs are dead on.. others are offset. It isn't a progression one way or the other.
  • Here is another stupid question. My cable is 75 Ohms and I see a nice filter for sale but it says 50Ohms. What is the rule of thumb on impedance? I know you want to match it all the way through but since this is just RX would it make a difference if downstream the rest of the connectors were 50Ohm?
  • Hi Lonecrow,

    If they are fairly short patch cables it won't make much practical difference. Ideally you would use the correct impedance throughout, but it's less critical for receive only purposes.

    Note that frequencies on the airband commonly have off-sets to accommodate 8.66KHz channel spacing within 5KHz frequency steps supported by older aircraft radios and also to allow multicasting from several sites on the same frequency (typically for wide area stuff like Volmet).

    Aircraft and some ground based transmissions (typically at smaller or grass strip airfields) also have slight frequency errors that can often be observed on spot frequencies.

    Regards,

    Martin - G8JNJ
    Lonecrow
  • edited April 2019
    Good to know. I definitely still have some FM bleeding through so I've been trying to find a good bandstop on ebay that won't break the bank and is 75 ohms and comes with an enclosure (and doesnt ship from china)
  • edited April 2019
    https://www.amazon.com/Samsung-Micro-Charger-ATADU10JBE-i220/dp/B003KWNHJQ

    That is the power supply I'm using. It doesnt' mention anywhere on it that its 'switching'.

    Unless you were talking about the power supply of the kiwi itself?
  • With power supplies: If, by its heft, you can believe there to be an iron block inside, it's a transformer type. If it feels like it's (mostly) empty, it's a switching type. If its AC input voltage rating is something like "100-240 volts", it is definitely a switcher.

    If you bought any power supply/wall wart in the past 10 years or so, and you didn't actually go our of your way to find one that is NOT a switching type, it will be a switcher: It is getting increasingly difficult to find linear power supplies at all these days, so if it says nothing at all about what type it is, it's likely a switcher - and almost universally, switchers - as they come from the manufacturer, without further modification - are anathema to LF-HF radio reception.

    73,
    Clint
    KA7OEI
    Lonecrow
  • jksjks
    edited April 2019
    @Lonecrow Please email your modified config.js file to support@kiwisdr.com and I'll have a look and see what the problems are.

    Also, those actual signals being offset: those are just frequency errors in the aircraft AM transmitters. I've seen that before. It's only off a few hundred Hz and with AM makes no difference. Look at the one below in your image. It's closer to being on-frequency.

    The frequency entry box being small is because you've made the "select band" menu too wide via the config.js modifications. Although even after fixing that it's going to be too small to display a complete VHF 8-digit frequency.
  • Interesting to know a bout the airband. I didn't know and hadn't seen it before on sdrsharp. It all still is received well enough I was just concerned while labeling everything.

    The other question was - I found my power supply for the kiwi itself IS a switching power supply. Could that be the source of noise? The power supply for the downconverter doesn't seem to be a switching or doesnt mention it but I'll look again.

    Does anyone have a good source on some 5v - 12 volt non switching types?
  • Fortunately the KiWi is a good diagnostic tool that can quickly help you find noise sources.

    Try the setup without an antenna connected - do you still see the noise on the waterfall / spectrum display ? If so the power supply is most likely to be the source of the problem.

    Next try a short length of wire (about 10cm or 4") on the input of the trasnvertor, Do you now see noise ?

    What happens if you move the short wire antenna closer to the power supplies or other items in and around the KiWi / transvertor setup. Do you see the noise increase ?

    Switching supplies don't necessarily need to be problematic. I use them and with a bit of care and some decent ferrites, most types can be tamed.

    Regards,

    Martin - G8JNJ
  • Actually I came back after the weekend and I was picking up nothing almost as if the antenna wasn't there. Its definitely there and its plugged in. I even bypassed and used the antenna with my laptop and its getting good signals.

    So I bypassed the downconverter and set it back to HF and still barely anything at all almost as if the built in amp isn't working. I checked the downconverter to be sure it was getting power it was getting 5v but now its like the kiwi doesnt work on hf or with the downconverter. It is picking up SOME signal but its like the antenna isn't plugged in. So I checked all the pins make sure nothing is bent (even though I didnt touch anything over the weekend) and it isn't.

    Its like its completely dead.. but everything runs.
  • I was going to email you the config but @jks but I ran into new problems. I can't get this thing to pick up any signals at this point of any significance.

    I'm thinking since I didn't touch it the latest update which was a day after it was working (14th) could have something to do with it?
  • Hi Lonecrow,

    That doesn't sound good.

    If you open up thew new Signal Generator extension and switch it on using the default settings you should see a carrier at 10MHz on the waterfall with a level of about -60dB.

    Regards,

    Martin - G8JNJ
    Lonecrow
  • Thanks sig gen is working and seeing the carrier -66.

    So reset the config to the .orig config and when I go back into the kiwi its still showing the wrong bands even after a cache flush and hard refresh. This is odd!
  • Hi Lonecrow,

    OK that's good so it doesn't look like anything major is broken.

    I'd suggest that as you are making a lot of changes to the config, it may be a good idea to buy a few decent quality SD cards so that you can backup an image of the whole KiWi and then you can recover, or at least quickly get back to a known good state without any hassle.

    I'd save the current config to a new card and then load up the original config from the SD that came with the KiWi and update it to the latest version and then do all the basic setup so that you have a working KiWi. Then save that version to another new SD card.

    You then have the original SD card supplied with the KiWi (get out of jail), a working basic recent config (gets you quickly to a good starting point for anything else on another card, and finally another with your most recent VHF config.

    Yet another card would allow you to backup your most recent working version, so you can very quickly get back to where you were, if you do accidentally mess something up. You can then rotate the two VHF SD cards so that you are only a few steps behind if things go wrong.

    I'm not a proficient coder, but I do mess around with my KiWi's from time to time and having a few backups on SD has saved me big time on more than one occasion when I thought I'd bricked the KiWi.

    Regards,

    Martin - G8JNJ
    Lonecrow
  • I've made backups of configs via scp but not the entire unit. Wouldn't the option (in admin tab) to rebuilt rebuild/recompile the code? Pretty sure I still have the card. It came in a plastic container with a micro adapter and the actual micro sd card right?
  • Hi Lonecrow,

    Yes that's correct.

    I'd suggest keeping the card as an emergency last ditch emergency backup, and buy some additional cards to write to and from.

    I've found it to be the easiest and most reliable method, even if you have other means of archiving the file system, as the network and USB ports can stop working correctly if you somehow corrupt the OS.

    Regards,

    Martin - G8JNJ
  • Can you open port 8073 on your router so I can get to it from the Internet?

    Otherwise, since the sig gen works but you're getting heavily attenuated signals (if I understood correctly), Occam's razor suggests that with the adding/removal of the transverter you may have damaged the SMA connector on the Kiwi or injected a static charge that has shorted the input protection diode.
  • port 8073 is opened but I can port forward for ssh as well if you need it. Just currently busy on something important and I'll email you the details.

    The shorting of the diode is completely possible. I've isolated it down to it possibly being just the downconverter itself. When I plug back into an HF antenna it looks to be working as its picking up some signals but it doesnt seem to be as hot as it used to be.
  • jksjks
    edited April 2019
    I looked at your Kiwi. The transverter was inline so I couldn't evaluate HF. But even that looked much worse than before. Lots of small carriers everywhere.

    I fixed the config.js file so it says "Air Band" now instead of "Amateur".

    Also the software update to v1.282 was perfectly fine.
    Lonecrow
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