Elecraft K4

Discussion in 'Ham Radio Discussions' started by W6RZ, May 16, 2019.

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  1. KM1H

    KM1H Ham Member QRZ Page

    Noise figure statements are only accurate when stated in particular bandwidths. While commercial/military users are typically using ISB and multi channel data the users I am referring to are measured in Hertz for data to a SSB bandwidth of ~2.3 kHz.

    I reference mine to cascaded 500 Hz CW filters altho 250 Hz can be switched in on the TS-950SD. The 75A4 started with 800 Hz mechanical filters but were changed to later 500 Hz Collins crystal filters when the antique mechanical filters deteriorated.

    A full size LP antenna can have superb F/S performance but only ~ -20dB F/B which is similar to a 3 el yagi. My smallest yagi when contesting was 4 el on 40 (42' boom) and 20 (40' boom) and currently 5 el on 15 and 6 el on 10 with 36' booms is ready to go up and were designed and optimized for high full 180 degree F/R. On 6M my 8 el on a 35' boom easily makes or exceeds -40dB worst case.
    Obviously I am very fussy about performance.

    While the tropics and places such as the Southern USA states can be noisy in the summer that can be mitigated by high end blankers and sense antennas that can be steered to specific noise sources.

    Since the discussion is actually about the K4 and other ham gear we can benefit quite often from very low noise conditions even on 160 where my preamp has a 1.5dB NF in 500 Hz.

    I have a 9 Band DXCC with a QRP 5W to prove it isnt all that rare as some would force us to believe.

    It is more of a fixed mindset than cost these days as improved front ends are dirt cheap as seen by the TS-890 review in the June 2019 QST. Some commercial and most all military contracts are written to a specific spec by the user and are only tested/accepted to that spec even if far better.

    Many users can most likely get sufficient performance from off the shelf Icom, Kenwood, and Yaesu products at far less cost than those you mentioned. The TS-890 can have the TX disabled for RX only sites:D

    I know my antennas are working when I can peak noise from EU cities, swing off a bit and hear weaker signals; this includes 6M which easily makes or exceeds -40dB worst case.
    Obviously I am very fussy about performance.

    I was never impressed by Collins receivers especially the 75A4 I rebuilt in several areas ...in 1965 mind you....and early S Line plus the 51S1 which set new records for IM problems when a perfectly matched antenna was not used. As the old story went: If you want a frequency meter buy a Collins, if you want to hear the weak ones buy a National. Later added: If you want to hear the whole band without tuning buy Hammarlund or Hallicrafters aka Hallidrifters.

    Carl
     
  2. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Fortunately, manufacturers have begun to clean up their transmitted signals despite the contesters, and I believe Elecraft was among the first to do so.
     
  3. W3WN

    W3WN Ham Member QRZ Page

    You do realize that this statement is factually inaccurate.

    There is a long gap in time between Riley’s retirement from the FCC and his being appointed to head up the new Volunteer Monitor program. He did not retire to immediately take on the program.

    And what does this have to do with the subject at hand, anyway?
     
    N2SR and N2EY like this.
  4. KM1H

    KM1H Ham Member QRZ Page

    Over a period of about 10 years after continuous user complaints including from DXpeditions. I give them credit or actually doing something unlike other companies......but they didnt flog an old design for over 10 years either and came out with a new one that was often a slight improvement.
     
  5. SM0AOM

    SM0AOM Ham Member QRZ Page

    Noise figure is bandwidth independent, it lies in the formal definition of noise figure as (S/N out)/(S/N in).

    Noise power N, expressed as kTB has a bandwidth dependence, which cancels out in the above expression.

    Bandwidth only enters the picture when power readings are normalised and converted to noise figure.

    A difficulty appears when the shape factor for the information filter and the detector characteristics have to be factored in, but it can be circumvented by actually measuring the noise figure of the measuring receiver or spectrum analyser using the ENR method, and then use this figure for comparisons.
    However, reasonably modern EMI test receivers and spectrum analysers have these functions in firmware.

    When the antenna noise figure exceeds the receiver noise with at least 6 dB, the total S/N starts to be determined by the antenna noise. The directional patterns of HF antennas do in some extent influence the noise performance, but only if strong local noise sources exist, or if the natural noise is highly variable in the azimuthal plane. In the days of HF point-to-point radio, this was investigated by the CCIR Study Group 3.
    Their findings were that in temperate climates, atmospheric noise has a quite limited directional behaviour. My own observations are in line with this.

    73/
    Karl-Arne
    SM0AOM
     
    N2EY likes this.
  6. K8JD

    K8JD Ham Member QRZ Page

    WOW !
    Whole radio room in a box ?
    I would have no earthly use for the ;
    Ethernet
    USB
    HDMI
    & RS232 Connectiors seen on the back panel !
    I will save that money to take the XYL on another Caribbean cruise for a few weeks. :D
     
  7. KM1H

    KM1H Ham Member QRZ Page

    You are absolutely correct; I was trying to quickly relate it to bandwidth for the less informed and stay away from the math which is easily found online.

    I have used NF meters at work since the 60's and have owned a HP 8970A since 2000 which I bought at a local equipment auction complete with HP noise head, and manual with all installed updates and cal records.

    Those conditions are quite common in ham radio where point to point comms is not the object and the azimuth remains fixed or set in only a few directions. That is a completely different world.

    I have no interest in that and it confuses the discussion to what WE HAMS experience. Please lets stick to those parameters.

     
  8. SM0AOM

    SM0AOM Ham Member QRZ Page

    Maritime or Ground/Air HF is certainly not point-to-point, and is actually very similar to amateur radio, as it usually operates using quite modest S/N ratios.
    In contrast to amateur radio however, all readability and signal reports are not '59'.

    However, I do not think that this discussion is going any further.

    You are the obvious expert regarding everything HF, and my mere 35 years of professional activities doing system design and evaluation of civilian and military HF systems together with participation in ITU, ICAO, CEPT and AEEC work in related matters is not relevant.

    73/
    Karl-Arne
    SM0AOM
     
    KY7K, KJ4VTH, AD5HR and 1 other person like this.
  9. WN1MB

    WN1MB Ham Member QRZ Page

    Let me fix that for you:

    "You are the obvious expert regarding anything and everything."

    There. That's more betterer...
     
    N2EY likes this.
  10. K1VSK

    K1VSK Ham Member QRZ Page

    You might want to add the words “trivial and largely irrelevant” at the end
     
    N2EY likes this.
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