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

I'm not a developer and never will be one. That being said I do want to run some a couple other openwebrx sites in the VHF Air Bands. But I want to be able to tag all the air traffic channels (there are A LOT here within 20Mhz). But there is nobody who has developed the labeling system yet except for Kiwi!

Is that part of the code ever going to be open sourced or was this taken from someone else who did it? Is there any way we can get a similar labeling system for the vanilla openwebrx?

I'd actually pay for another unit if it covered 20-30Mhz of UHF/VHF!


  • Hi Lonecrow,

    You could add a VHF down convertor ahead of the KiWi to shift a block of frequencies say 110 to 140MHz down to 0 to 30MHz. The KiWi has a function to re-label the frequency scale to match the original frequency.

    It's something I had thought of doing, but have not so far tried out. Maybe I'll have a look through my junk box to see if I could lash something up to see if it is feasible.


    Martin - G8JNJ
  • "Is that part of the code ever going to be open sourced ..."

    What do you mean? Both OpenWebRX and KiwiSDR are 100% open source. But back-porting features from Kiwi to OpenWebRX is not straightforward as the code bases have diverged greatly and are built on different backends.

    You can use a transverter / down converter ahead of the Kiwi and change parameters in the admin interface to offset the frequency scale appropriately. There used to be a couple of Kiwis listed on that tuned the 6m and 2m bands.
  • Oh really.... I may just pick up another one then! Thanks
  • Hi Lonecrow


    It's a very quick and nasty lashup which is lying on the floor of my workshop so there is a lot more unwanted noise and hash than there should be.

    VHF 144MHz band antenna, 100m of coax to workshop, 20dB low noise preamp, VHF BPF filter (6dB loss) , 10dB preamp, FM BC Band notch, 10dB preamp, Mini-Circuits Mixer, 115MHz LO injection from a signal generator, 40MHz LPF & into the KiWi.

    I've edited a few DX labels with local airports, but I've not done anything fancy with removing or editing the HF Band markers etc.

    Best performance is between about 120-130MHz as I had to quickly build a band pass filter to remove the FM Broadcast Band and it's not very good.

    I'll leave it running for a few days until I need it for something else.

    Have fun,

    Martin - G8JNJ
  • I have found that If you set the AGC threshold value to -80dB it sounds a lot nicer on the Airband :-)
  • yep thats pretty much what I want to see :) Except the top bar showing the wrong bands. Thats really cool the entire airband.
  • "Except the top bar showing the wrong bands"

    There are a few other anomalies associated with the way the URL's and other references link to the actual KiWI tuned frequency rather than the displayed frequency, but most could probably be fixed fairly easily if required.

    I just wanted to quickly try something to see how feasible it was.


    Martin - G8JNJ
  • Definitely pretty cool. I want one. Gotta go find another kiwi on sale and try to justify the purchase to the boss lol
  • Hi Lonecrow,

    The only problem is where to obtain a suitable VHF to HF downconvertor to put ahead of the KiWi.

    I'm not aware of anyone making a suitable device, although it may be possible to modify a HF to VHF Upconvertor as used to provide shortwave coverage with RTL dongles.

    Something like this with a 115MHz oscillator and the HF / VHF filters swapped over may possibly work.


    Martin - G8JNJ
  • Hi Jim,

    I think that model has got an internal SAW filter to define the 2m band, which would exclude the airband.

    What's really needed is a block down-convertor with approx 115-125MHz local oscillator (set the KiWi to tune 2-32MHz to avoid the LO blow through) then a 118-150MHz input BPF (to remove FM BC band II image) with pre-amp into the mixer and then an 0-35MHz output LPF into the KiWi.

    A Cross Country Wireless HF upconvertor may possibly work with the antenna and receiver ports swapped around but it would need an external pre-amp and BPF.


    Martin - G8JNJ
  • jksjks
    edited September 2018
    Gotta go find another kiwi on sale
    I think another Massdrop should be coming up soon (it's been 6 weeks since the last one). That's a source for $220 Kiwis with free US shipping if you're willing to wait a bit for delivery.

    Yes, there are a bunch of open bugs with transverter mode. Including "reverse tuning" for 23 cm converters using low-side (high-side?) LOs which is going to be tricky for me to implement.
  • Recommend a transverter?
  • Nevermind just caught up on the replies lol
  • "I think another Massdrop should be coming up soon (it's been 6 weeks since the last one). That's a source for $220 Kiwis with free US shipping if you're willing to wait a bit for delivery."

    Definitely the way to go - I couldn't believe the price I got my last one for - it was about 1/3 the price of my original Kickstarter purchase.


    Martin - G8JNJ
  • Anyone have any luck finding someone who makes an upconverter? I'm really interested in covering the air bands with a kiwi.. I didn't see anything that was affordable and would work out of the box.
  • 'crow.... I think you mean downconverter.
  • edited March 2019
    I tried my old 144MHz-28MHz transverter and was OK on some parts of the airband, not very clean though.
    Perhaps you could send an enquiry to, they seem good value even though you would be using just the RX side.
    I looked for other downconverters and maybe due to RTL SDR @£10 world there is very little call for it so prices reflect the specialised nature.
  • JP1ODJ runs air band:
    On the stats tab is a link that has his email. Ask him what he uses.
  • I bought but have not yet deployed two of the $150 High Sierra Microwave downconverters Jim described, one for 6M and another for 70cm. They will customize the input frequency and include all the filtering, but you will need to supply a LO. For WSPR a high stability GPSDO LO like the $150 Leo Bodnar would be needed, but for other modes that would be over specced.
  • I use a Bodnar GPSDO as LO for a homebrew transverter . I just verified that it all works, though with a couple of significant issues.
    In the screen shot below, I'm using one of my switched antenna inputs for the 2m downconverter. I've told the Kiwi of my 118 MHz (exactly) offset and run the WSPR extension. WIth a completely separate local 2m WSPR GPS referenced signal it decodes properly but you'll see that the WSPR extension doesn't use that offset in displaying frequency, it gets it wrong. It gets it even more wrong too, I don't know where the WSPR extension is coming up with the frequency it does, since the actual IF is 26.490529 not 28.126129 as reported.

    This also means that the WSPRnet database gets a bogus entry:
    Timestamp Call MHz SNR Drift Grid Pwr Reporter RGrid km az
    2019-03-20 19:50 N6GN 28.126129 +39 0 DN70ll 5 N6GN/KIWI DN70ll 0 0

    Since the 118 MHz offset is global, the other antenna inputs read in the VHF range even though they aren't.

    For VHF-only use, it's probably OK as long as extensions aren't counted on to work properly.
  • Oh, just realized that the WSPR extension is using the 10m entry for band so assumes that means 28.1246 carrier. 28.1246+.001529 audio comes out as shown. At least it's correct at the 1 Hz level but not right about band or MHz ! There's apparently no way to run on other bands, such as VHF/UHF, or non-standard WSPR frequencies with the extension.
  • jksjks
    edited March 2019
    Correct. The WSPR extension ignores the tuned frequency. That's why it has WSPR band menu -- to allow the standard WSPR frequencies to be selected. It never even occurred to me to support non-standard frequencies. Why would I go to that considerable trouble when virtually no one would do that? (aside from maybe the transverter scenario) I don't even know how would handle an uploaded spot with an odd frequency. Probably just filter it out.
  • Until ~6 years ago when a few of us grew a significant base of VHF+ WSPRers, there weren't even 'standard' frequencies above 2m and virtually no activity. As more got on up there and discovered what a great tool WSPR was -contrary to what K1JT had expected since he had thought Doppler self-QRM would be prohibitive- and started discovering previously unrecognized propagation mechanisms such as aircraft scatter (ACS, good for 800-900 km day/night year-round) and wing-tip vortex (WTV)signals some worldwide frequencies for 70cm and 23 cm were adopted. I built a 70 cm multi-mode beacon that was placed at the KH6HME site on Maunba Loa which is now almost routinely copied on the mainland now 4100 km away on WSPR, JT9, JT65 and sometimes CW.
    But I think the WSPRnet database does keep track of 'non standard' frequencies, e.g. the dual 80m WSPR bandplan that has frequency reported correctly while both segments are lumped into '80 m'. If one runs WSPR on 10 GHz (yes, it's been done) I think it becomes available on the database and map though I can't remember what 'band' it calls it.
  • I built VHF/UHF band support into kiwiwspr and wsprdaemon and will add support for downconverters if there is an active user.
  • Thanks for the replies. I'm not interested in doing WSPR for the higher freqs. Mainly just need to label everything I can pick up where I am. I have a discone on our tower that is picking up aircraft hundred and hundreds of miles away. Its amazing and I literally have a database of all the tower freqs within the 200km area amounting to about 1000 freqs I'll need to add. I'd like to have the ability to scroll through and pick which one to listen to as I watch my adsb receiver.

    JKS - thats exactly what I'd like to do but remove the bands on the top. He has however that is interestingly quiet connection for air traffic in an area like that. He also is showing a lot of noise in some bands. Makes me wonder.

    I'll check out those sites thanks for the leads. I hadn't seen those sites yet. ALso power numpty that guy in japan's site is pretty noisy too by the looks of it. I'm wondering if the kiwi will be able to handle it. In SDRSharp the air band with this antenna has a few noisy spots but mainly a lot of long range clear signals coming in.
  • "I'm wondering if the kiwi will be able to handle it" I'm pretty sure downconverting that range has a lot of other VHF (+FM broadcast) mixing stuff to reject so filtering is important before and after the conversion, The Kiwi is just excellent test kit showing up any failings and mixing products.
    Admittedly I was using one set up for 2m so birdies in the airband may have been intentional to keep them out of the required band.

    Does make me yearn for a version that does 32MHz of VHF/UHF or even a modular one, lots of rf boards are being sold for self assembly RF chains.
  • jksjks
    edited March 2019
    It seems I already made (and forgot about) a fix for the "band scale" and "select band" menu not being correct when the Kiwi is configured for transverter/downconverter mode. It's a little complex to configure. You must know how to login to the Beagle via ssh/PuTTY and use a few Linux commands including editing a text file with the "nano" program (or a similar editor package). This fix will work even if you're not running the very latest software version. It's been present for a long time.

    You'll be editing a Javascript file. You don't necessarily need to know Javascript because you can follow the pattern of code that is already there (i.e. "read between the lines"). Because this file is in the kiwi.config directory changes will survive a software update. The "mi" (make install) used below only creates the file with the latest version if the file doesn't already exists. It does this to preserve any changes you may have made. That's why below we have to remove it (by renaming) before doing an "mi".

    Login to the Beagle and type:
    mv config.js config.js.orig        saves old file
    mst       stop server
    mi        reinstall, which updates to new version of config.js
    nano config.js        assuming you know how to use the nano text editor
    ku        server up, test your changes
    config.js defines, in a programatic way, what appears in the band scale and select band menu. You'll note a little ways down in the file a couple of variables called down_converter_2m and down_converter_6m both defined as false. There is corresponding code below those that selectively disables the numerous definitions for HF and instead uses a single "band.push(...)" via if/else statements.

    If you are using a 6m or 2m downconverter you can simply change the appropriate variable from false to true. However the "min:" and "max:" values in the band.push() may have to be adjusted to account for where the band segment actually appears in the Kiwi 0 - 30(32) MHz reception range. By default 28 and 32 MHz are specified because the downconverter LO is 116 MHz, so 144-148 MHz - 116 MHz = 28-32 MHz (Kiwi assumed set in 32 MHz mode). And of course the 116 MHz LO value needs to be specified in the config tab on the admin page ("frequency scale offset")

    If you're down converting, say, air band you can add another variable e.g. down_converter_airband and the associated code or just overwrite one of existing entries. There can be multiple band scale/menu definitions if you decide it's appropriate, just like for HF. A band.push() entry can be used to define a band scale, band select menu entry or both. Read the comments in the file for details and do some experimenting. Yes, this could be done in the admin interface. But that would take a fair amount of time. Time I don't have.
  • Thanks for the instructions. I'm experienced with linux so not a problem. Just figuring out which bands will be the issue :)
  • edited April 2019
    I purchased a 118-137Mhz to 10-29Mhz down converter. Ok so I've installed the down converter and soldered on a 5v power supply. It seems to work however I need to set the offset. Just plugging it in I'm picking up all sorts of aircraft very nicely however the entire band is completely populated with noise... in large quantities. I have an FM bandstop but not the right connectors (I need bnc to sma to coax) to put it in before the downconverter.

    Question is what would be the offset? 108Mhz? Once I get the right bands in there I can try to ID some of this noise and then work on the band plan.

    Yep 108 seems to be it

    Take a look for yourself

    I did have this exact antenna plugged into a pi running a spyserver and it didn't have anywhere near this sort of noise in the band and I didn't even have the bandstop installed (mainly because the rtlsdr only has 2Mhz bandwidth)
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