G8JNJ

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  • Seeed Metal case and GPIO connector

    Hi All,

    I've had some issues with radiated noise from a KiWi that I installed on a shared site. The main issues were that it was interfering with of VHF satellite reception and degrading the GPS performance of another system in the same room.

    The KiWi was installed in the Seeed metal case, and I had fitted ferrites to the cables.



    As I'm currently building up a KiWi for installation at another site, I thought that it would be a good idea to see if I could further reduce the level of emissions from a KiWi fitted in the Seeed case.

    In order to do this I used an EMC H-Probe consisting of a 1"diameter screened loop connected to a spectrum analyser, in order to see what the level of emissions looked like and where they were escaping from the case.

    The majority of the noise was leaking out through the holes in the ends of the case and also via the additional interconnecting cables I had fitted to bring out the GPIO ports for antenna switching.

    This shows the general level of radiation from a KiWi without a case, with the Seeed metal case and with the Seeed case and additional modifications. Note that the measurements were made without the external GPIO cable connected.



    The next shot shows the difference between the Seeed metal case and with the Seeed case and additional modifications in more detail.



    As you can see the biggest difference is achieved by fitting the metal case, and I would definitely recommend doing this if you are still using the plastic frame supplied with the KiWi.

    However there is still a fairly significant amount of radiated noise throughout the whole spectrum, especially in the VHF / UHF / Microwave range, and the only way to cure this is to close up the holes in the box.

    As I didn't want to restrict airflow and ventilation I used some very fine woven brass mesh that I previously bought for antenna construction.

    I added a section of mesh at each end of the box and sandwiched it between the end plates and the box sides, having first cutout suitable holes for the connectors I still wished to use.



    Note that I had to solder short brass sheet straps between the Ethernet port metal socket surround and the mesh and also the -ve of the DC input connector where it enters the board (prior to the common mode choke on the board) in order to reduce the level of radiated noise from the external screened CAT5 Ethernet cable and DC power cable. There already was physical / electrical contact between the mesh and Ethernet connector, but I noticed that the screening effectiveness varied as I flexed the cable, and I didn't want to risk problems on-site at a later date if the mesh tarnished or developed an oxide layer.




    Here are a couple of external views, showing the wire mesh with the case closed.




    Once I had done this work I still had some noise from the GPIO port, so I added some 0.1uF decoupling capacitors and some 1/8th watt 1K Ohm resistors in series with the wires from the KiWI GPIO pins (not the 0v ground return) and the decoupled pins of the output connector. This also provided some short circuit protection, as previously suggested as best practice earlier in this thread.




    After doing all of this work, the level of emissions are now minimal, and the ambient level of noise in my workshop is higher than the majority of noise produced by the KiWi, even though the close field probe is right next to the case. There is still a bit of radiation along the seams between the top and bottom case halves, but this is very low level, and if necessary can be further reduced by running self adhesive aluminium (ducting) tape over the seams.

    One other interesting observation is that before fitting the mesh and additional earth bonding strap, I didn't find that using screened Ethernet cable made much difference to the level of noise radiated around 20MHz. However after performing the modification it's really noticeable that using screened cable makes a big difference.

    Overall I think the additional mods are worth doing, especially if you are bringing the GPIO pins out of the box. But if you are already housing your KiWi in a diecast box with suitable cable bonding, then you are probably already experiencing most of the benefits I have observed.

    Regards,

    Martin - G8JNJ
    PowernumptyHB9TMCG0LUJ
  • Seeed Metal case and GPIO connector

    Hi All,

    I've had some issues with radiated noise from a KiWi that I installed on a shared site. The main issues were that it was interfering with of VHF satellite reception and degrading the GPS performance of another system in the same room.

    The KiWi was installed in the Seeed metal case, and I had fitted ferrites to the cables.



    As I'm currently building up a KiWi for installation at another site, I thought that it would be a good idea to see if I could further reduce the level of emissions from a KiWi fitted in the Seeed case.

    In order to do this I used an EMC H-Probe consisting of a 1"diameter screened loop connected to a spectrum analyser, in order to see what the level of emissions looked like and where they were escaping from the case.

    The majority of the noise was leaking out through the holes in the ends of the case and also via the additional interconnecting cables I had fitted to bring out the GPIO ports for antenna switching.

    This shows the general level of radiation from a KiWi without a case, with the Seeed metal case and with the Seeed case and additional modifications. Note that the measurements were made without the external GPIO cable connected.



    The next shot shows the difference between the Seeed metal case and with the Seeed case and additional modifications in more detail.



    As you can see the biggest difference is achieved by fitting the metal case, and I would definitely recommend doing this if you are still using the plastic frame supplied with the KiWi.

    However there is still a fairly significant amount of radiated noise throughout the whole spectrum, especially in the VHF / UHF / Microwave range, and the only way to cure this is to close up the holes in the box.

    As I didn't want to restrict airflow and ventilation I used some very fine woven brass mesh that I previously bought for antenna construction.

    I added a section of mesh at each end of the box and sandwiched it between the end plates and the box sides, having first cutout suitable holes for the connectors I still wished to use.



    Note that I had to solder short brass sheet straps between the Ethernet port metal socket surround and the mesh and also the -ve of the DC input connector where it enters the board (prior to the common mode choke on the board) in order to reduce the level of radiated noise from the external screened CAT5 Ethernet cable and DC power cable. There already was physical / electrical contact between the mesh and Ethernet connector, but I noticed that the screening effectiveness varied as I flexed the cable, and I didn't want to risk problems on-site at a later date if the mesh tarnished or developed an oxide layer.




    Here are a couple of external views, showing the wire mesh with the case closed.




    Once I had done this work I still had some noise from the GPIO port, so I added some 0.1uF decoupling capacitors and some 1/8th watt 1K Ohm resistors in series with the wires from the KiWI GPIO pins (not the 0v ground return) and the decoupled pins of the output connector. This also provided some short circuit protection, as previously suggested as best practice earlier in this thread.




    After doing all of this work, the level of emissions are now minimal, and the ambient level of noise in my workshop is higher than the majority of noise produced by the KiWi, even though the close field probe is right next to the case. There is still a bit of radiation along the seams between the top and bottom case halves, but this is very low level, and if necessary can be further reduced by running self adhesive aluminium (ducting) tape over the seams.

    One other interesting observation is that before fitting the mesh and additional earth bonding strap, I didn't find that using screened Ethernet cable made much difference to the level of noise radiated around 20MHz. However after performing the modification it's really noticeable that using screened cable makes a big difference.

    Overall I think the additional mods are worth doing, especially if you are bringing the GPIO pins out of the box. But if you are already housing your KiWi in a diecast box with suitable cable bonding, then you are probably already experiencing most of the benefits I have observed.

    Regards,

    Martin - G8JNJ
    PowernumptyHB9TMCG0LUJ
  • Seeed Metal case and GPIO connector

    Hi All,

    Just some brief notes regarding the installation of a 15 way D connector on the Seeed metal case in order to bring out the GPIO port for use with an antenna switch.

    The ventilation slot cuts out very easily and only required a small amount of filing in order to make the connector shell fit.

    First the pinout I used



    End view of case



    Top view of connector



    Wiring to GPIO ports



    Side view



    Hope this is of some use to others.

    Regards,

    Martin - G8JNJ
    PowernumptyjksHB9TMC
  • Seeed Metal case and GPIO connector

    Hi All,

    I've had some issues with radiated noise from a KiWi that I installed on a shared site. The main issues were that it was interfering with of VHF satellite reception and degrading the GPS performance of another system in the same room.

    The KiWi was installed in the Seeed metal case, and I had fitted ferrites to the cables.



    As I'm currently building up a KiWi for installation at another site, I thought that it would be a good idea to see if I could further reduce the level of emissions from a KiWi fitted in the Seeed case.

    In order to do this I used an EMC H-Probe consisting of a 1"diameter screened loop connected to a spectrum analyser, in order to see what the level of emissions looked like and where they were escaping from the case.

    The majority of the noise was leaking out through the holes in the ends of the case and also via the additional interconnecting cables I had fitted to bring out the GPIO ports for antenna switching.

    This shows the general level of radiation from a KiWi without a case, with the Seeed metal case and with the Seeed case and additional modifications. Note that the measurements were made without the external GPIO cable connected.



    The next shot shows the difference between the Seeed metal case and with the Seeed case and additional modifications in more detail.



    As you can see the biggest difference is achieved by fitting the metal case, and I would definitely recommend doing this if you are still using the plastic frame supplied with the KiWi.

    However there is still a fairly significant amount of radiated noise throughout the whole spectrum, especially in the VHF / UHF / Microwave range, and the only way to cure this is to close up the holes in the box.

    As I didn't want to restrict airflow and ventilation I used some very fine woven brass mesh that I previously bought for antenna construction.

    I added a section of mesh at each end of the box and sandwiched it between the end plates and the box sides, having first cutout suitable holes for the connectors I still wished to use.



    Note that I had to solder short brass sheet straps between the Ethernet port metal socket surround and the mesh and also the -ve of the DC input connector where it enters the board (prior to the common mode choke on the board) in order to reduce the level of radiated noise from the external screened CAT5 Ethernet cable and DC power cable. There already was physical / electrical contact between the mesh and Ethernet connector, but I noticed that the screening effectiveness varied as I flexed the cable, and I didn't want to risk problems on-site at a later date if the mesh tarnished or developed an oxide layer.




    Here are a couple of external views, showing the wire mesh with the case closed.




    Once I had done this work I still had some noise from the GPIO port, so I added some 0.1uF decoupling capacitors and some 1/8th watt 1K Ohm resistors in series with the wires from the KiWI GPIO pins (not the 0v ground return) and the decoupled pins of the output connector. This also provided some short circuit protection, as previously suggested as best practice earlier in this thread.




    After doing all of this work, the level of emissions are now minimal, and the ambient level of noise in my workshop is higher than the majority of noise produced by the KiWi, even though the close field probe is right next to the case. There is still a bit of radiation along the seams between the top and bottom case halves, but this is very low level, and if necessary can be further reduced by running self adhesive aluminium (ducting) tape over the seams.

    One other interesting observation is that before fitting the mesh and additional earth bonding strap, I didn't find that using screened Ethernet cable made much difference to the level of noise radiated around 20MHz. However after performing the modification it's really noticeable that using screened cable makes a big difference.

    Overall I think the additional mods are worth doing, especially if you are bringing the GPIO pins out of the box. But if you are already housing your KiWi in a diecast box with suitable cable bonding, then you are probably already experiencing most of the benefits I have observed.

    Regards,

    Martin - G8JNJ
    PowernumptyHB9TMCG0LUJ
  • More GPS Problems - Damaged hardware?

    Some further notes for anyone who may pick up this thread at a later date and wish to copy this information.

    If you wish to split the GPS signal from the antenna to feed multiple KiWI's.

    Do not attempt to simply use a tee adaptor or similar to split the feed, as this will introduce unpredictable impedance excursions on the coax cables, which is turn will result in very deep 'notches' in the signal amplitude at various frequencies.

    You can only use passive splitters if the antenna has sufficient gain to overcome the splitting losses and cable losses ahead of the KiWi.

    2 way split = approx 3.5dB additional loss
    3 way split = approx 5dB additional loss
    4 way split = approx 7dB additional loss

    Try to find passive splitters that only have a DC pass on one port. This will save having to fit additional external DC blocks in order to prevent one KiWi feeding DC back into another via the GPS connectors.

    Make sure they are rated up to 2GHz, like this model / style

    https://www.amazon.com/Ideal-85-332-2-Way-Digital-Splitter/dp/B003QM9UHS/ref=sr_1_2?keywords=ideal+2+way+splitter&qid=1563704237&s=gateway&sr=8-2

    https://www.amazon.com/Ideal-85-334-4-Way-Digital-Splitter/dp/B003V18KQ6/ref=sr_1_3?keywords=ideal+4+way+splitter&qid=1563704346&s=gateway&sr=8-3

    You can obtain 'F' type male to SMA male patch cables on Ebay at under $4 each. It's better to buy ones that are longer than you need, so that there is room to wrap them around ferrite rings if required. Make sure you choose the correct sex of connectors, as reverse SMA is quite common.

    https://www.ebay.com/itm/RG316-Cable-F-Type-male-plug-to-SMA-male-plug-RF-Pigtail-Coax-Jumper/273406498020?hash=item3fa84c14e4:m:mFvLi09dwBokRt1mcM3MNiQ

    Hope this helps anyone else following in these footsteps.

    Regards,

    Martin - G8JNJ
    WA2ZKD
  • More GPS Problems - Damaged hardware?

    Hi Chris,

    I use passive satellite TV splitters with an inbuilt DC block (or steering diodes) on all but one port.

    This sort of thing with suitable adaptors.



    I use a two way to feed two more two ways, so that I can feed the office and workshop (Trimble) with a mid point split, This gives about about 7-8dB loss in total on each leg, which is fine with an antenna with 40dB of amplification.

    Regards,

    Martin - G8JNJ
    ChrisSmolinski
  • TDoA background maps not loading

    >
    >John, is it possible to have the basic (landmass boundaries) maps that TDoA used when I first got my Kiwi last summer?
    >Presumably the multiple TDoAs I do when I TDoA in order to see the results "group" requires the same map tiles be loaded that many >times. I'm only interested in the coordinates. Landmass boundary maps I'm guessing might not have that problem... but then what do I >know?
    >

    Brett's suggestion is a good one.

    I use the TDoA function a lot, and I'm concerned about the costs to John associated with the provision of maps.

    Maybe have the option for no map, just the co-ordinates overlay, then once you have got a good plot you can re-run it with the required map turned on. This would save downloading tiles and additional cost.

    Regards,

    Martin - G8JNJ
    Powernumpty
  • Advice on sharing RX antennas with 3 SDRs in the most effective way

    Be careful regarding some of the commercial active splitters. Their IMD performance is not that good as they often use MMIC chips that can only achieve modest performance.

    For example the Elad unit specifies an output IP3 of >24dBm, which is not particularly good, and would be typical of something using a PGA-103+ or similar as the active device which will provide an IMD performance of around an IOP2 of +50dBm and IOP3 of +30dBm.

    My suggestion would be to use something like the DX Engineering RPA-1 followed by a Mini-Circuits splitter.

    I've built a copy of the RPA-1 and it works well from about 10KHz to 40MHz and I have measured the IMD performance as an IOP2 of +92dBm and IOP3 of +45dBm.

    Details are on my Active antennas web page.

    https://www.g8jnj.net/activeantennas.htm

    For GPS splitting you can use active L-Band splitters that were originally designed for distributing satellite TV services.

    https://cpc.farnell.com/global-communications/split4af/4-way-active-splitter/dp/SE00009

    I used this one but modified by cutting some tracks and adding an internal regulator so that it provided +5v out to feed the GPS antenna



    Regards,

    Martin - G8JNJ
    PowernumptyHB9TMC
  • SAQ 17.2KHz - 30th June 2019

    Good signals into the UK this morning from SAQ on 17.2KHz using an historic alternator transmitter

    https://alexander.n.se/?lang=en

    15dB above the noise floor into Farnham WEB SDR http://farnham-sdr.com/ in SE UK

    12dB above the noise floor into Kernow KiWI WEB SDR http://kernow.hopto.org:8073/ at Goonhilly Earth Station in Cornwall SW tip of UK (despite a very high noise floor)

    Unfortunately too much switched mode power supply noise on my SWUK KiWi SDR http://southwest.ddns.net:8073/ which masked the SAQ signal.

    Another transmission due later today at 13.30 (11.30 UTC) the alternator starts and at 14.00 (12.00 UTC) will be broadcasting a message

    Martin – G8JNJ (Admin for Farnham / Kernow and SWUKSDR)
    PowernumptyKA7USWLJO43
  • SAQ 17.2KHz - 30th June 2019

    Good signals into the UK this morning from SAQ on 17.2KHz using an historic alternator transmitter

    https://alexander.n.se/?lang=en

    15dB above the noise floor into Farnham WEB SDR http://farnham-sdr.com/ in SE UK

    12dB above the noise floor into Kernow KiWI WEB SDR http://kernow.hopto.org:8073/ at Goonhilly Earth Station in Cornwall SW tip of UK (despite a very high noise floor)

    Unfortunately too much switched mode power supply noise on my SWUK KiWi SDR http://southwest.ddns.net:8073/ which masked the SAQ signal.

    Another transmission due later today at 13.30 (11.30 UTC) the alternator starts and at 14.00 (12.00 UTC) will be broadcasting a message

    Martin – G8JNJ (Admin for Farnham / Kernow and SWUKSDR)
    PowernumptyKA7USWLJO43