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G8JNJ

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  • 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
  • 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
  • Wellgood balanced loop amplifier, (Wellbrook clone).

    Hi John,

    Build the LZ1AQ instead.

    It's a better performer and easier to construct, plus I'm not 100% convinced about George's reverse engineered circuit, especially the transformer windings and specifically the configuration on the binocular core. Norton amplifiers bring about lots of other problems and after playing with a lot of different designs, I'm not sure they are worth the effort.

    My initial IMD measurements were constrained by my test setup, with my better test rig I measure

    LZ1AQ OIP2 +79dBm OIP3+36dBm

    Wellgood OIP2 +57dBm OIP3+37dBm (note that the Wellgood is based on an early Wellbrook design and the new ones are better)

    The overall performance of all loops, especially on the HF bands is determined by loop size and inductance and amplifier input impedance. This is why most loops 'run out of steam' above about 10MHz.

    I've found that contrary to most wisdom, if you can't build a nice 'fat' low inductance loop, it would seem to be better to use an amplifier with a higher value of input impedance (tens of Ohms), in order to improve performance on the HF bands (where the loop inductive reactance dominates the feed point impedance), and compromise a bit on the LF bands, where the natural noise floor tends to be a lot higher (particularly in urban areas) and the very strong Broadcast Stations tend to be problematic anyway.

    Some more info on my Active antennas web page

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

    Here's a link I found to a lot of Clifton Labs Norton amplifier circuits (grab them while you can) that may be of interest to you and others on here (use Google translate)

    https://www.okdxf.eu/index.php/technika/262-manualy-konstrukci-clifton-laboratories-k8zoa

    Interestingly for some reason they also produced a higher gain amplifier using four Gali-74's the Z10046A, but I still haven't been able to track down a circuit of the amplifier they produced for the Pixel Loop now sold by DX Engineering (they have withdrawn all Clifton Labs on-line circuit diagrams since they bought them) as the RF-PRO-1B

    https://www.dxengineering.com/parts/dxe-rf-pro-1b

    Send me a private message if you wish.

    Regards,

    Martin - G8JNJ
    KA7U
  • Aricebo - 5125KHz

    I just realised that I got the project reference incorrect, as I'd worked out the wrong time from the schedule.

    So the final session is now up and running until I estimate 18:00 UTC 14th June 2019

    I can now hear the carrier being swept on the Anasco, Puerto Rico WEB SDR http://kp4ca.ddns.net:8073/ but not on mine yet.





    They are using the dish.

    Simulation and modeling results show that both arrays have
    VSWRs less than 2:1 over a 100 kHz bandwidth no matter what the
    state of the other passive array’s feed is (shorted, open, or terminated).
    The gain at 5.1 MHz was 22.2 dBi. When fed with 600 kW of power,
    this corresponds to an ERP of 99.6 MW. At 8.175 MHz, the gain was
    25.5 dBi corresponding to an ERP of 212.9 MW. If the array is phased
    to achieve circular polarization of either RHC or LHC, the crosspolarization from the opposite mode was above 27 dB for both
    frequencies.

    http://www.naic.edu/~astro/ao50/Arecibo_50th_Paper_Breakall_revised_Oct_23_2013.pdf


    Here's the correct reference and summary of work.

    General Category: Astronomy
    Observation Category: Ionosphere
    Total Time Requested: 24 Hours
    Minimum Useful Time:
    Proposal Title: Natural Analogs Via Ionospheric Experimental Research (NAVIER)
    ABSTRACT:
    This proposal is in collaboration with the planned NRL Probing Regions via Ionospheric Modi?cation (PRIM)
    experiment, the goal is to study the physics of plasma irregularities created by the Arecibo HF Heater and their
    impact on HF communications waveforms. MITRE will be providing an advanced HF transmitter and receiver pair
    as well as standard HF radios to study the impact of arti?cial ?eld-aligned irregularities (AFRIs) on the HF signal
    propagation. The locations of transmit and receive sites will be the Dominican Republic and St. Thomas
    respectively. This a?ords a near-to-perpendicular signal propagation path with respect to the geomagnetic ?eld
    lines over Arecibo, as shown in Figure 1. The outcomes of this experiment will include investigation of the physics
    of the disturbed ionosphere, as well as a large-scale data collection and analysis on the impacts of heater AFRIs on
    HFnear vertical incidence skywave (NVIS) propagation.


    Name Institution E-mail Phone Student
    Edlyn V. Levine MITRECorporation evlevine@... 412-7265480 no
    Remote Observing Request
    X Observer will travel to AO
    Remote Observing
    In Absentia (instructions to oper-
    ator)
    Instrument Setup
    430 Xmit
    Atmospheric Observation Instruments:
    Tilt-Photometer Spectrophotometer Fabry-Perot Ionosonde Lidar
    Description of Observer Equipment: MITRE will provide a Digisonde ionospheric sounder for 1
    deployment near to the Arecibo facility. MITRE will appreciate the AO support to deploy the instrument
    Special Equipment or setup: The ISR will be the primary instrument as well as our own
    diagnostics. The other instruments are a backup.
    RFI Considerations
    Frequency Ranges Planned
    2

    Sweep rate is 100mS occupying 26KHz.

    Scope and Spectrum plots attached but I was only able to sample in a 10KHz BW.





    Regards,

    Martin - G8JNJ
    HB9TMC
  • RF Pro-1B Issue Developing

    >
    >I think half the worlds supply of silicone was used to seal every seam and screw.
    >

    So the magic smoke is probably still contained within :-)

    At least you can unpick silicone, go on you know you want to do it, and we all want to see what's inside :-)

    Regards,

    Martin - G8JNJ
    Powernumpty
  • Aricebo - 5125KHz

    Aricebo was operating again last night, putting a very strong carrier (but with weak 120Hz sidebands) into the UK on 5125KHz.



    It was a LOTstronger into KP4CA http://kp4ca.ddns.net:8073/ in Anasco, Puerto Rico ?as you would expect :-)



    No sweeps were observed this time, however it looks like there may be more opportunities over the next week or so.

    It's a pity that there is so little up to date information about this on the web, but I have found an operational schedule.

    Look up reference T1193 running up to and on the 15th of June and again commencing Sat 29th of June

    http://naic.edu/vscience/schedule/scedfra2.htm

    Note that AST is equal to UTC -4

    LST (Local Sidereal Time) could be anything :-)

    Regards,

    Martin - G8JNJ
    Powernumpty
  • QRM: Radio China International - From Albania - OV +++

    Hi Giulio,

    Adding a series tuned notch filter across the KiWi RF input will help reduce the problems on 7345KHz.



    These values give the bets compromise between notch depth and attenuation on the adjacent 40m amateur band.

    For this simulation I have used an inductor with a Q of 50. But if you can use a better inductor, it will provide a deeper and narrower notch.

    31 turns wound on a T50-2 iron powder core would be a good starting point, but you would have to add or remove turns in order to tune the notch to the exact frequency.

    It will attenuate signals on 40m to a certain extent, so the signal levels will drop slightly, however as the natural noise floor is usually the limiting factor on the lower frequency bands, I don't think it will harm the Signal to Noise ratio.

    As a test you could run the WSPR decoder with and without the notch in circuit, and compare the average S/N before and after, but always compare reports of the same transmitting stations, don't compare different stations with each other.

    The other interference is something local to you, but sort out the 7MHz overload before investigating the other problems.

    Regards,

    Martin - G8JNJ
    WA2ZKDIZ3EAWG0LUJ
  • QRM: Radio China International - From Albania - OV +++

    No, you need to either notch out the strong signal which has a minimal reduction in overall performance across the whole frequency range, or put an attenuator in line which will reduce the performance on the higher frequency bands where the natural noise floor is lower and you need the additional gain.

    If you read the many posts on this forum regarding 0V indication, the notch is the best solution for this particular problem.

    I have notches for all the SW broadcast bands ahead of all my KiWi's.

    Regards,

    Martin - G8JNJ
    WA2ZKD